Some Antenna Photos and Tests

[tripelo]

Tests were conducted in 2011 to evaluate performance of some TV antennas.

The tests involved a signal source feeding a CM-4228 at ~45 ft AGL radiating to antenna under test located ~150 feet distant at ~level height to source antenna.

The signal source was a homebrew signal synthesizer, remotely controlled at the receiving location by a notebook PC.

Received signals from the test antenna were measured using a homebrew wideband power meter with digital readout and logged into an Excel spreadsheet.

The test frequencies were chosen to represent channels that might be of personal interest.

This location is rural, the only UHF strong signal is at Channel 14; the frequency band was omitted from the tests.

The last image below shows results from comparing four antennas:

- Channel Master 4228 (the most common of the older versions)
- Channel Master 4251
- Antennacraft P7
- Antennacraft SuperG 1483 (the stacked Hooverman version)

http://forum.tvfool.com/attachment.php?attachmentid=495&d=1364921502

http://forum.tvfool.com/attachment.php?attachmentid=497&d=1364923084

http://forum.tvfool.com/attachment.php?attachmentid=494&d=1364921475

The decibel scale is relative for a comparison between the units.

Caveats:

Each antenna was installed at the test mast for a few days while several preamps were individually tested with that particular antenna. So, each antenna was measured days apart from others.

There may be some SWR effects in the antenna gain patterns, affecting each antenna differently.

Comments:

In general, testing against distant weak TV signals was consistent with the measured results. CM-4251 was best on upper UHF. P7 performed well on mid UHF channels. SuperG 1483 was comparably good on mid-20 range channels.

496

[GroundUrMast]

Are the signal source and/or power meter proprietary works? Or can you share details of those with us also?

Thanks for the work, and willingness to share it with us.


Oh, nice towers. :)

[tripelo]

Thank you GroundUrMast, for your kind words.

Are the signal source and/or power meter proprietary works? Or can you share details of those with us also?

No, not proprietary. Yes, can provide some details.

The synthesizer is based on IC Silicon Devices SI570. PDF available here:

http://www.silabs.com/support%20documents/technicaldocs/si570.pdf

The version (BBB) that covers range from about 10 MHz up to about 950 MHz was used.

Some kits containing major parts of the circuitry and components are available from SDR hobbyist groups. SDR=Software Defined Radio

http://en.wikipedia.org/wiki/Software-defined_radio

SDR-Kits were used in this particular synthesizer.

http://sdr-kits.net/QRP2000_Description.html

The components are not complicated to assemble, nearly all were thru-hole. The synthesizer IC is SMD (surface mount).

One should have output attenuators, power supply, metal housing, and filters. Other modifications and items are useful, but with these become quite useful. USB power can be used when near such, otherwise wall wart with additional filtering can be used.

The controller for the synthesizer chip is USB based.

Software to control the synthesizer from PC can be obtained on the web.

For remote control one can use USB to LAN adapters at each end of the circuit, then use whatever LAN devices one desires in between.

In this case, for remote control, ~165 feet of Ethernet LAN CAT5e cable was used, probably beyond specifications without repeaters, but worked fine. To reach greater distances, one could probably use wireless game bridges, or something similar.

The wideband power meter is based on Linear Technology LT5534 integrated circuit.

http://www.linear.com/product/LT5534

Haven't seen a kit of parts for such.

Manufacturer provides a good reference design. Found a PCB made for another similar part and adapted it. It is all SMD.

For accurate results, one should provide for a matching circuit on the input. Resistive pad matching at input combined with ~ 10-20DB fixed attenuation provides a reasonably low SWR. Can use ordinary DMM for digital readout.

Need: power supply, metal housing, and external attenuators.

Below is an image taken in 2011 around the time of the preceding test. The workbench is behind that window, inside the building next to the receiving antenna mast.

http://forum.tvfool.com/attachment.php?attachmentid=498&d=1365093205

Shown on part of the workbench, among cables, planks, and bricks; from top to bottom, left to right:

- Some version of Research Communication preamp (loose)
- Blonder Tongue FSM-11 signal strength meter with brick
- Antennacraft preamp power supply (loose)
- Signal synthesizer (in aluminum case)
- Half Wave Loop balun
- DMM (Red)
- HP notebook computer
- Holland Splitter
- Various fixed attenuators (in-line)
- Another Research Communications preamp (in-line)
- Power Inserter (in-line)
- Winegard Power Inserter (loose)
- Fixed attenuator (Red, in-line)
- Wideband power detector (blue aluminum case)
- Some version Winegard preamp
- Channel Master preamp (loose)


Oh, nice towers. :)

Thank you.

The near tower has the transmitting CM-4228. Hard to see, it is mounted directly behind the CM-4251. The tower and that particular CM4251 have stood for more than 40 years.

.

[Pete Higgins]

tripelo,

I finally got cleared to post. As I mentioned last week, I’ve contacted Antenna Craft to see if they will sell me a Super G and what it will cost with shipping. Still haven’t heard back from them yet so I'll probably try to give them a call.

Again, thanks for pointing me to this most interesting information. You do have an envious test setup.

[tripelo]

...

I’ve contacted Antenna Craft to see if they will sell me a Super G and what it will cost with shipping...

Very interesting.

That was a good idea to contact Antennacraft. Maybe we can learn something from it. Curious as to what Antennacraft's response will be.

-----------------------

Pete, thank you for the compliments.

[Atis]

Just chatted with a rep at www.summitsource.com she said both the sigle and stacked version are in stock there.

[Pete Higgins]

The problem isn't availability, its paying for the excessive shipping weight.

When I went to the Summit Source web site to order it, in addition to the $109.95 for the antenna, they want $76.88 for ground shipping. That brings the total to $186.83!

They list two different weights, one for the United States Postal Service @ “37 lbs, 11.62 oz”, and a second for UPS / FedEx @ “(2 x 37.72575 lbs)”.

I contacted Antennacraft to ask about the weight and they said "We pack the Super G1483's 2 per box when they leave our facility. The weight for a 2 pack is 8.5#'s. So each antenna would weigh approximately 4.3#'s each.”

I then talked to Erick @ Summit Source and he confirmed that even though the AntennaCraft shipping weight for a box of two Super G1483's was only 8.5 lbs the Summit Source computer takes into account dimensional weight and ground shipping would cost me $76.88.

I think before I shell out $186.83 to try one of the commercially available Hoverman designs it might be prudent to cost out building one of the more versatile Grey-Hoverman designs.

[tripelo]

No intention to divert from other antennas and tests, or other related.

Took down an antenna this morning and thought it (or the story) may be interesting to someone.

It's a Log-V antenna, VHF (low and high), maybe FM.

It was located at an apartment complex and appeared to be a potential hazard to those who lived there. From the ground, the antenna looked to be in good shape (see photo). Realizing that the antenna might soon be lost to wind, an inquiry was made and the responsible people were glad to have it removed.

http://forum.tvfool.com/attachment.php?attachmentid=505&d=1365875492

The antenna originally had four guy wires that had long since broken. The guy wire remnants were so degraded that flexing a couple of times, they crumbled.

http://forum.tvfool.com/attachment.php?attachmentid=506&d=1365875520

.

Turned out, the antenna is in good shape. Whoever designed and built it, made it to last. Element-to-boom support is very sturdy. All the elements folded back to the boom perfectly, no insulator was cracked. On the ground, the gold anodizing is still visible.

The antenna could be vintage mid-1960s. Certain features in the construction point to early times. Mid 60's is about the earliest date that Log-V antennas were available, and was probably about the time the apartment complex was constructed. Could be a Radio Shack antenna. Seems that during the 60s, Radio Shack marketed several major brands; Finco, Channel Master, JFD, and others.

If anyone has clues to it's origin, please post.

Anyhow, back to regular program.

.

[Pete Higgins]

tripelo,

Great find. Wish I could find an old Channel Master 4251 that someone wanted removed.

I got started last summer playing with a 40+ year old Channel Master 4228. If it had received CBS on channel 43 (2.1) as well as it received NBC channel 36 (4.1) I probably wouldn’t have built my new system using a 91XG and an AntennaCraft Y10-7-13. Now, the 91XG always gets CBS but rarely gets NBC and the CM-4228 always gets NBC but rarely gets CBS. Go figure! I have them connected through a coax switch in the garage so I can switch between them when needed.

It would be interesting if you could compare this old LPA to some of the current crop of VHF High antennas like the Winegard YA-1713 or the AntennaCraft Y10-7-13 Yagi Antennas.

Enjoy.

[tripelo]

... Wish I could find an old Channel Master 4251 that someone wanted removed.

Yes, hope you can find such. Was the CM-4251 popular in California?

I got started last summer playing with a 40+ year old Channel Master 4228. If it had received CBS on channel 43 (2.1) as well as it received NBC channel 36 (4.1) I probably wouldn’t have built my new system using a 91XG and an AntennaCraft Y10-7-13.

You have some nice antennas.

Interesting that you have found such a difference between the antennas. As you probably know, for the 91XG, its directivity (gain) increases with frequency, whereas the 4228 has relatively flat gain characteristic from around channel 20 or so, through channel 51. Unless there is some other factor, the 42 MHz difference between the two channels means quite a lot for the 91XG.

Would be interesting to see the TVfool predictions for your antenna locations, can you post them?

I have them connected through a coax switch in the garage so I can switch between them when needed.

Seem like a workable solution.

It would be interesting if you could compare this old LPA to some of the current crop of VHF High antennas like the Winegard YA-1713 or the AntennaCraft Y10-7-13 Yagi Antennas.

Yes, good thinking. That would be quite interesting.

Maybe that could be feasible. Right now, the Log Periodic is here in suburb Dallas, and the good antenna range is in KY. The LP is too long to ship by conventional means. And, probably the most interesting antennas (that I have) to compare against the LP are also located in KY.

Although, have done antenna comparisons at both locations (KY and here).

Such a test would be interesting and worth some thought and effort.

[tripelo]

The vintage antenna (previous post) (http://forum.tvfool.com/showpost.php?p=36192&postcount=8) is a Finco CS-V10.

http://forum.tvfool.com/attachment.php?attachmentid=510&d=1366051673

The image is from: Popular Science 1967 (http://books.google.com/books?id=1SoDAAAAMBAJ&pg=PA29&lpg=PA29&dq=Finco+CS-V10&source=bl&ots=pzBZcOz_Za&sig=ZYwbLpB4Slsn18vxtmaPNqiEhyw&hl=en&sa=X&ei=rktsUcSkDqjv2QW0noC4BQ&ved=0CDYQ6AEwBA#v=onepage&q=Finco%20CS-V10&f=false)

It is covered by Finco patent No.3,427,659. (http://www.google.com/patents/US3427659?dq=3427659&hl=en&sa=X&ei=7SpsUcadJKHL2QXmi4H4CA&ved=0CDQQ6AEwAA)

FISHBONE TYPE ARRAY WITH DIPOLE SPACING INCREASING TOWARDS THE SMALLER END

The patent describes Finco’s discovery that log periodic dipole antennas could achieve greater gain for TV frequencies if the element spacing was tapered somewhat wider towards the front. Previous thought was either; logramithic spacing which tapered smaller spacing towards the front, or uniform spacing.

In the patent, an example antenna lists dimensions and increased gain values. The dimensions given in the example match those measured on this CS-V10 antenna.

The patent was originated in 1964 and issued in 1968.

Interesting in this same time period , The University of Illinois (holder of the log periodic patent) was in litigation with several TV antenna manufacturers, of which Finco (Finney) was one.

[Pete Higgins]

tripelo,

here you go:
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d1dda169109ca5c

FM Fool shows 99.9 MHz @ -13.4 & 91.9 @ -26.9

I've got to run to the Dentist

[tripelo]

...If it had received CBS on channel 43 (2.1) as well as it received NBC channel 36 (4.1)...

Initial thought:

You cannot receive Channel 43 very well because it isn’t there (that is; in the TVfool table)! :)

Then, after eliminating analog channels from the table, channel 43 shows.

That’s a difficult situation to receive such a weak signal in the presence of very strong signals.

--------------------
2nd thought:

When applied to your area, TVfool signal prediction algorithms (presumably based on Longley-Rice model) must not be as accurate as they usually seem to be.

1. It’s unlikely that an ordinary TV receiver can simultaneously process signals having a dynamic range of 106.5 dB (difference between KVCR, -15.6 and KCBS, 122.1).

Then, recalling that you used a notch filter to essentially remove KVCR, obviously improving the dynamic range situation, tho still very challenging for an ordinary TV receiver.

That’s not to mention the complications of two FM stations at –13.4 and –26.9 dBm, plus some more moderately strong TV stations.

2. The available antenna gain is insufficient to compensate for a noise margin of -22 dB.

-------------------
For many, receiving KNBC, at predicted noise margin =-16.8 dB, would be a challenge.

Do you receive both KNBC channel 36 (-107.7 dBm) and KCBS Channel 43 (-112.9 dBm) on their assigned antennas throughout the day (say most of 24 hours)?

-------------------

Regardless the accuracy of TVfool predictions for your particular location, you undoubtedly have a situation that challenges the dynamic range of amplifiers and tuners.

Pete, you have an interesting situation. From reading in other forums, you have worked out a good approach toward solving the problem (filters, high dynamic range drop amplifiers, and such).

[Pete Higgins]

tripelo,

We’ve had the Time Warner’s “Everything” package for years (my wife even got me the Playboy channel) so OTA is mostly a hobby. I originally started just trying to see what I could get with a 40 year old Channel Master CM-4228 8-Bay Bow Tie. After receiving both VHF & UHF channels from LA & San Diego I decided to see how much I could improve my reception. Things just kind of grew from there.

I am not currently using the Channel Plus NF-471 notch filter.

My original plan was to use a Winegard AP-2870 pre-amp. with separate VHF & UHF inputs. I tried the Channel Plus NF-471 55 dB channel 26 (KVCR) notch filter in-line with the UHF input to the 2870 but the amp. overloaded so badly that I almost didn’t get anything. I also tried both antennas into a UVSJ, through the notch filter and into my Winegard HDP-269 with basically the same result. The PCT MA2-M’s don’t seem to overload, even without the notch filter.

A pictorial of my new antenna array setup can be found @:
http://www.digitalhome.ca/forum/showthread.php?t=42426&page=7
(Post # 3348).

The CM-4228 is on a push-up mast with a rotor and is using the HDP-269. I have the coax from the tower array and the HDP-269 going into a coax switch in the garage, the output of which feeds my PCT MA2-4P distribution amp.

Channel 2 seems quite reliable on the new array, but the array rarely gets channel 4. By the same token, the old 8-Bay always gets channel 4 but almost never can hold channel 2. A lot of the one hour shows my wife & I like are on CBS (Ch. 2.1) so when the 8-Bay couldn’t pull it in I was motivated to come up with a better solution. To that end my new setup does what I wanted. I’m just not sure what the mechanism is that prevents the new array from getting NBC (channel 4.1). For the most part, the SNR between the two antennas is within 2-3 pts. with the 91XG higher in a little over half the cases. It could be as simple as it has better response on RF 43 (2.1) than the 4228 and the 4228 has better response on RF 36 (4.1).

[tripelo]

Pete, have been out of town for a while. Was actually in KY at the main antenna test location, and climbed above the top of the tower a few times. Above the top, to be explained later. :)

Please, feel free to update on your antenna work.

----------------------

In the meantime, this is an image taken in 2009 of the main tower (lower part shown in Post #1 (http://forum.tvfool.com/showpost.php?p=35950&postcount=1)) as it has stood since I personally erected/installed in the early 1970's. The tower and antennas were largely ignored all those years, (meaning almost no maintenance), although they reliably provided TV reception for my parents.

The large VHF antenna is a Channel Master Quantum CM-1110.

The plastic bucket lodged in the tower was there temporarily for convenience to hold tools and such. The photo was taken just before the CM-1100 was lowered to the ground.

Since that time in 2009, there have been several different antennas residing above the tower top, or near the top of the tower. Maybe later can show some of the other antenna arrangements.
.

http://forum.tvfool.com/attachment.php?attachmentid=517&d=1369333651

[Pete Higgins]

tripelo,

Good to hear from you.

As I said in my last post, the CM-4228 was on a push-up mast with a rotor and was using the HDP-269. I ordered a Winegard YA-1713 Prostar 1000 10 El. Hi-Band VHF Antenna to go with it.

I thought I would use that combination to test the Winegard pre-amplifiers that overloaded with my tower array.

I installed the YA 1713 above the CM-4228 and ran two new 17’ pieces of RG-6 down the mast, one from the CM-4228 (white) and the other from the YA-1713 (black), so I could experiment with UVSJ's, my HDP-269 and AP-2870, and several cable drop amps I’ve collected without having to lower the mast for each change. In anticipation of testing the pre-amps, I ordered three Antennas Direct FM Band 20 dB traps and two 3 dB & two 6 dB in-line attenuators to go with my Channel Plus 55 dB channel 26 notch filter.

When I got everything hooked-up, the new Winegard YA-1713 wouldn’t receive channels 7 or 13. It is mounted about 30’ south and 6’ lower than my Antenna Craft Y10-7-13.

When it wouldn’t work with my amps., I hooked it directly to the cable that runs to my PCT-MA2-4P distribution amp. and was able to receive 8 (8.1) & 10 (10.1) out of San Diego and 9 (9.1) & 11 (11.1) from LA. I then disconnected the YA-1713 and hooked up my Channel Master CM-4228 to the cable that runs to the PCT-MA2-4P distribution amp. and got a very pixelated channel 7, a fairly solid 9, intermittent 11 and a pretty good 13. All 4 LA stations measured high “Green” on my SNR meter with the Antenna Craft Y10-7-13 switched in (of course it has a +15 dB MA2-M mounted right behind it). Adding an amplifier to the Winegard 1713, at the base of the push-up didn’t improve/add the missing LA stations. It did considerably improve VHF reception from the CM-4228.

Since I only had one 50’ run of RG-6 going from the base of the push-up mast into the garage, I had to get up on the roof to switch antennas. I added a second run (white) so I could route the UHF and VHF signals to a garage coax switch separately. After I got tired of running out to the garage to switch between antennas I added a 4th RG-6 run into my office so I could monitor both push-up antenna signals from the office. That’s kind of where I’m at right now. With no amplifiers in-line, the 4228 actually does better getting channels 7 & 13 than the YA-1713. Mid-band, the YA-1713 does better.

I sent Winegard an email on May 13th to see if they could think of any reason performance would roll off that dramatically at the top & bottom of the YA-1713’s band. So far I haven’t heard back from them. They probably got the email and thought I was nuts!

Solid Signal sent me an email flyer for an 8-Bay “Solid Signal Xtreme Signal HDB8X High Definition Blade 8 Bay Xtreme Antenna (HDB8X)” for $59.99 with $0.05 shipping. It looks to be 2 4-Bays on a swivel with 2-BALUM’s hooked to a combiner. It has the multi-directional feature like the new Antennas Direct DB8e and blade elements similar to the 91XG. For $60.04 delivered I couldn’t resist. They claim a maximum gain of 25 dB when both sides of antenna are parallel, which I believe defies the laws of physics, but if their matching harness arrangement is any good at all, I expect it will perform about as good as any other 8-Bay. They don’t expect to ship them until after 1 June.

Next, I want to pull down the push-up, inspect the YA-1713 and swap the 17’ cables. I’ll probably also try it on my tower and try the Antenna Craft Y10-7-13 on the push-up.

I can’t drop or raise the push-up mast by myself. I have to set a ladder in front of it so I can reach the U-bolt through the upper stand-off bracket. Once I get the U-Bolt off I need somebody to hold it while I move the ladder out of the way so it can be laid horizontal. Going back up, I need somebody to hold it so I can position the ladder and re-install the U-Bolt. There’s a real shortage of people in my neighborhood lining up to climb on a roof to raise & lower antennas! Since I’ll want to try the new 8-Bay anyhow, I’ll probably wait until the HDB8X gets here to do any more YA-1713 testing.

The tower got too heavy to lift, even with help, so now I can lower and raise it by myself with help from a 110 VAC winch. When I have the new patio roof put on I’ll try to figure a way to get winch’s working for the push-up and my other tower.

Take care.

[tripelo]

Pete, looked back at your tower array, mentioned in your earlier post.

Direct link to post #3348 here:

http://www.digitalhome.ca/forum/showpost.php?p=1541530&postcount=3348

As to why the poor reception of the YA-1713 for VHF compared to the 4228:

Not a lot of suggestions, there are several variables.

The YA-1713 and most antennas have a bit less gain at the band edges (in this case; channel 7 and 13). If there were extra attenuation in the YA-1713 path, then the normal roll-off of the gain vs frequency pattern for the YA-1713 could become more obvious.

As you mentioned, reversing the cables between the CM4228 and the YA-1713 seems a good step.

If you have cables with pre-installed factory connectors, they sometimes cause problems.

The YA-1713 has a snap on balun that could have a problem.

-----------------------

Your thoughts on the new 8-bay (Solid Signal HDB8X) will be interesting. Since it has separate reflectors (not-continuous like the 4228) then it will probably have less response for your VHF signals.

[Pete Higgins]

tripelo,

I made up both of the 17’ cables going to the antennas just to simplify testing. Since I still had both white & black rolls of coax, I arbitrarily used white for the UHF run & black for the VHF run. I installed the boot that came with the YA-1713 on the black cable & new Channel Master (PCT) compression connectors on both. I doubt that I have a bad connection on the black cable but that’s why I want to swap them.

The original black cable that runs into the garage is probably 30 years old with crimp on connectors. It is the one I originally used to compare both antennas so I’m pretty sure it is still Ok. The “new” cable I pulled is a 50’ “factory” Magnavox M61210 roll of white RG-6 with molded ends that my son gave me. I have swapped the antenna feeds between both of the garage runs and can’t tell any difference so I’m pretty sure both of those are Ok.

The 4 cables from the garage to my office are new RG-6 runs with compression connectors that are routed between the downstairs ceiling and the upstairs flooring through PVC conduit, then down through the office wall to a metal plate with 4 F-81 barrels.

The YA-1713 balum looked like it could install either of two ways so I checked online with Winegard and found that it didn’t make any difference. I didn’t pay a lot of attention to it but as near as I remember it just looked like a clip-on microstrip line matching transformer. It should have been foolproof. If I can get it apart without destroying the plastic housing I’ll inspect it for any signs of damage or missing parts.

I think the most informative test will be dropping the tower and swapping the VHF antenna locations. That will put the YA-1713 in a known good signal location with plenty of amplifier gain and all new end-to-end proven cables.

Of course I want to compare the HDB8X to my 40 year old Channel Master CM-4228. That may not sound fair, but last summer I compared the 4228 to a brand new 91XG and in the same location both antennas provided about the same SNR +/- ~1 dB on most channels. I also want to see how it does on channel 36 (4.1 NBC) & channel 43 (2.1 CBS) since the 91XG has trouble with NBC & the 4228 has trouble with CBS (from the same location).

My San Diego UHF stations arrive from ~169 deg. and seem pretty strong. One of the things I also want to try with the HDB8X is pointing one panel towards San Diego and the other towards LA (292 deg.) and see how the 4-Bays do through the combiner and/or individually. That’s assuming that they will swivel through 123 deg. Fortunately, I have the rotors so if I don’t get the angle set to exactly 123 deg. I can “bump” align each panel for best signal.

I’ll be waiting to hear how you climbed “above the top of the tower”.

[tripelo]

Pete, you have an extensive cabling arrangement.

Your idea of swapping antenna positions is a good one. Vertical signal layering can cause a substantial signal strength variation over relatively short distance when antennas are relatively close to ground (in terms of wavelength).

About the Winegard balun. It can be installed either way, phase relationship flips with balun reversal, matters not much on single antennas. For stacking, to maintain phase relationship, one must take this into consideration.

Antenna rotators can be very useful tools in troubleshooting.

--------------------------------

'Above the top' will be easier explained after a few more photos.

--------------------------------

This is a photo of the antennas that replaced the CM-1110.

.

http://forum.tvfool.com/attachment.php?attachmentid=518&d=1369571323

.


The only objective of the VHF antennas was to better receive WKYT (at that time RF channel 13), 74 miles distant, 2-edge diffraction according to TVfool.

The configuration:

- Two Winegard YA-1713, stacked
- Combiner; Winegard CC-7870
- Spacing; 43 inches (was varied +/- 18 inches while watching Signal Meter)
- Mast length; 10.5 feet, ~ 7.5 feet above tower.
(Made from heavy duty top fence rail (SS-20, ~1 & 3/8 inch outer diameter)

- Channel Master antenna rotator moved inside tower for stability.
- Final Preamp, Channel Master CM-7777 (original), a WG-3700 was tested
- All cables RG-6, custom installed connectors.

In 2010, WKYT changed RF channels from VHF 13 to UHF 36, so the YA-1713s were not of much use after that.

The configuration stayed in place for approximately a year, until ~mid 2010.

.

[tripelo]

The following image shows an 8-bay antenna that was purchased in 1970. Pretty sure it is Channel Master, probably a precedent to the popular ’original’ CM-4228. The physical dimensions and construction are different. Note the differing transmission line feeding the right and left 4-bays, it extends downward. The antenna demonstrated about 0.5 dB better gain on low to mid UHF channels than the popular ‘original’ CM-4228. No comparison was made for upper channels.

That antenna was hit by a tornado in 1971, breaking a whisker (upper right). The tornado destroyed surrounding buildings, along with the tower and other antennas on it.

Note: People lost their lives and many homes were destroyed in that tornado.

The 8-bay whisker was repaired and it was placed in storage until 2010.

http://forum.tvfool.com/attachment.php?attachmentid=519&d=1370105543

Mid 2010, the antenna was installed to receive channel 22 WCTE at 65 miles distant. At that time WCTE was transmitting 57 kW ERP. TVfool showed the path diffraction as 2edge.

http://forum.tvfool.com/attachment.php?attachmentid=520&d=1370105556

For convenience and shorter preamp feed length, the 8-bay was mounted upside down.

The preamp was the UHF section of the CM-7777 (VHF portion in use for Yagis), using an 'inside' balun (with silicone waterproofing).

The Yagis and the CM-4251 already had their separate cables and were combined with UVSJ behind the TV. So, behind the TV, the 8-bay channel 22 signal was separated from CM-7777 coax with another UVSJ, then added back to CM-4251 UHF signals via a Channel Master Jointenna.

Although the reception was very good for WCTE, channel 22, this antenna configuration lasted only a few months.

.

[Pete Higgins]

tripelo,

Until you pointed out the feed line configuration, I thought it looked just like my "original" CM-4228. It appears that the "original" CM-4228 is a design evolution of this model?

Solid Signal notified me that my HDB8X shipped on the 30th. It was originally scheduled for delivery on Wednesday, but now FedEx tracking is saying it could be delayed because of the storms and tornados. It’s been sitting in PERRYSBURG, OH since 4:37 AM Friday morning.

[tripelo]

... It appears that the "original" CM-4228 is a design evolution of this model?...

Yes Pete, it appears so.

Since your comment, I looked at a 1973 Channel Master catalog, it shows the 4228 as is commonly known. So, guess the design change occurred before 1973.

Some of the story behind it:

When the antenna was purchased, I was working as a technician at a regional TV repair & Motorola 2-Way radio service center. That business only handled Channel Master TV antennas. And, I thought it was a Channel Master antenna.

Last year, a long-time retired TV antenna installer was at my shop (garage in the earlier photo). Inside on one wall, were six 8-bays hanging side-by-side.

Without providing any information, I asked the experienced TV antenna man to identify the antennas.

He identified all the 8-bays.

He pointed out:

- Four of the 'original' CM-4228s,
- One 8-bay was copy of a 4228 made at a regional factory, and
- This particular 8-bay antenna as an old Channel Master antenna.

So, if it looks like a ..., quacks like a ... it must be...

...Solid Signal notified me that my HDB8X shipped on the 30th...

Yes, saw your comments in a neighboring thread:

http://forum.tvfool.com/showthread.php?t=2288

You may have the earliest reports on it.

Will be quite interested in your assessment of the antenna.

[tripelo]

Previously mentioned was that the stacked YA-1713’s on the main tower (http://forum.tvfool.com/showpost.php?p=36658&postcount=19) were not much use after WKYT moved from Channel 13 to Channel 36. Then, it was realized that for part of the time, a Louisville KY VHF station could be received and was occasionally watchable. The station:

WBNA (ION) Channel 8, 24.5 kW, at ~80 miles, TVfool Noise Margin -7.0 dB

And also interesting, for short periods of times, Louisville’s WHAS channel 11 (16.4 kW, at 101 miles) could be received, but was not actually watchable.

The signal goodness indication on a CM-7000 DTV converter was calibrated using a Signal Level Meter (~1.5 dB per each 10% indication for channel 11). This calibration of CM-7000 was used to help evaluate the two stations’ signals, hoping to make antenna changes for potentially better reception. For several weeks, reception of these two stations was checked daily.

An additional two YA-1713’s were purchased for possibility of a installing a quad stacked arrangement of YA-1713’s.

Analysis of signal data suggested:

An additional gain of 7 dB, above that provided by the stacked YA-1713’s, may be required for reliable reception of WHAS-11.

This required amount of increased gain (7 dB) essentially ruled out a quad stack of YA-1713’s.

A quad stack of YA-1713s (2 horizontal, vertically stacked above 2 horizontal, or even a diamond stacked quad) would at best provide ~3dB gain above a dual stack.

At the time, the highest gain for commercially available VHF antenna was Jerrold/Wade VIP-306 (specified gain of 12 dB on Channel 11). The VIP-307 version had a bit more gain but was no longer available.

That VIP-306 gain listing was dBd. In the late 1960's when the VIP series were designed (http://www.google.com/patents/US3534369), computer simulation (dBi) was virtually non-existant. So dB values were commonly provided in dB, as actually measured, with respect to a dipole (dBd).

A pair of VIP-306’s was purchased for evaluation and potentially for stacking.

Below, is an image of a single VIP-306 installed at the test location, aimed towards the main tower.

http://forum.tvfool.com/attachment.php?attachmentid=524&d=1370511504


Over the next few weeks, other VHF antenna configurations were mounted on the test mast and reception observed.

.

[tripelo]

If higher gain antennas were to occupy the top position on the tower, then a taller mast may be required. For maximum stacking gain, individual antennas with higher gain require increased stack spacing. At that time, the existing mast (http://forum.tvfool.com/showpost.php?p=36658&postcount=19) was 10.5 feet of SS-20 (heavy duty), 1 & 3/8 inch outer diameter top fence rail.

Realizing that if a longer mast was ever bent by wind force, with unreachable antennas installed, it might be difficult to remove.

To maintain highest rigidity and minimize weight, a mast was configured of three parts:

· Full-length Outer – 15.5 feet of SS-20, 1 & 3/8 inch outer diameter
· Inner – 10 feet of Schedule 40, 1.064 inch outer diameter
· Lower-Outer - 6.5 feet EMT, 1.5 inch outer diameter.

The mast thickness were:

· Bottom portion was 3 pipes thick (EMT, SS-20, & Sch 40)
· Mid-section was 2 pipes thick (SS-20 & Sch 40)
· Top portion consisted of one pipe (SS-20)

The Inner was positioned inside the Full-length Outer, such that it did not reach the top ~ 4.5 feet. In other words, the top 4.5 feet consisted of only the SS-20 pipe. Also, the Inner pipe did not extend all the way to the mast bottom, but there was pipe overlap inside the tower.

The Lower Outer (EMT) was positioned to reinforce the lower part of the mast, up to ~ 4 feet above the tower top.

The Full-length and the Inner mast were assembled with stainless steel screws. The Lower-outer was to be added after the assembly was in place. The assembled mast (without antennas) weighed 35 pounds.

A sort of a ‘gin pole’ (lightweight pipe with upper loop) was temporarily fastened to the tower top as an aid during installation. The top end of mast was fed up through the loop to help balance and stabilize it during installation (especially with air movement). This additional stability was probably most critical when inserting the lower end of mast into the tower top.

Below is an image of the mast on the tower without the Lower-Outer portion. Later when antennas and the Lower-Outer mast portion were installed, the mast was raised a bit higher. The install support ‘gin pole’, is also shown but was later removed.

http://forum.tvfool.com/attachment.php?attachmentid=528&d=1371132108

[Pete Higgins]

tripelo,

Very interesting account. I especially enjoy seeing all the earlier antenna designs. It’s a shame that the superior ones like the Channel Master 4251 are no longer available. It is even more of a shame that proven designs like the CM-4228 have been cheapened and redesigned for shipping cost rather than performance. You’ve obviously been doing this a long time and have a wealth of practical experience. Are you still working in the field?

I got the Condo turned over to my property manager on Tuesday so I was able to try your panel isolation suggestions yesterday. I’ll talk to that in the other thread.

[tripelo]

tripelo,
... I especially enjoy seeing all the earlier antenna designs.

You probably can appreciate the innovations exhibited in those antennas.

It’s a shame that the superior ones like the Channel Master 4251 are no longer available... designs like the CM-4228 ...

Yes.

You’ve obviously been doing this a long time and have a wealth of practical experience. Are you still working in the field?

Thanks Pete, not working in TV related field, you might call it an avocation.

Very early – Interest in TV antennas led to electronics, then amateur radio (call WB4LXU).

Career years - Hardware design and systems engineer for two corporations (Texas Instruments and Raytheon).

Recent years - Main interest is in molecular biology and aging research.

-------------------

Pete, seems you have quite a lot of practical knowledge, maybe you worked in a related field?


I got the Condo turned over to my property manager on Tuesday...

OK, seems like your condo could have been some work, but having such in California seems good.

...so I was able to try your panel isolation suggestions yesterday. I’ll talk to that in the other thread.

Yes, the other thread: http://forum.tvfool.com/showthread.php?t=2288&page=1

[tripelo]

The Channel Master 8-bay (http://forum.tvfool.com/showpost.php?p=36689&postcount=20) coupled through a CM-7777 and a Join-tenna provided reliable reception of WCTE-22 (~ 65 miles distant in Tennessee).

It was noticed that Channel 23 WPXK, also in Tennessee, might also be receivable. WPXK-23 is separated by about 54 degrees in azimuth from WCTE-22. If both stations were receivable, they could probably be accommodated by the single existing Join-tenna.

In addition, a third station Tennessee station, WBXX-20 located in azimuth between WCTE-22 and WPXK-23. If channels 22 and 23 were receivable, then due to higher signal strength of WBXX-20, it might be pushed through the same Join-tenna.

At distances of 65-75 miles, the TVfool noise margin levels and azimuth angles were:

Noise Margin Azimuth (Deg.)

WPXK-23 -0.4 dB 145
WBXX-20 +13.2 dB 152
WCTE-22 -2.0 dB 199

Note: WBXX-20, in azimuth, lies between the weaker stations & closer in angle to WPXK-23.

A wide-beamwidth antenna with moderate gain could be a solution. Some candidates:

· Channel Master CM-4221
· Antennas Direct ClearStream C2
· Custom corner reflector (CR)

Another option could have been something like an Antennas Direct ClearStream C4 or Winegard HD-8800 with:

· Relative phase of right–left (RL) feed lines reversed
· RL Bay spacing optimized for split-beam lobes at 54 degrees separation

Some features of a custom CR antenna were appealing, one of which was it could be optimized for narrow range of channels around channel 22.

First, a CR backbone was retrieved from a scrap Antennacraft all-channel antenna. Then reflector elements were scrounged. Shorter reflector elements can yield wide beamwidth, but compromise some gain. For a few reasons, a moderately short reflector length of 16” was selected. The driven element was made from longer trimmed-to-length elements and supported by recycled insulators.

When the prototype was assembled, it was simulated in a computer model using Arie Voor’s 4NEC2 software (http://www.qsl.net/4nec2/). One objective was to get every tenth of dB gain while maintaining a good match to 300 Ohms. Since wide-beamwidth antennas usually have only moderate gain, then in this case it was important to have a good impedance match to optimize efficiency.

The prototype was tested with three preamps:

· CM-7777 with low loss balun
· CM-0264 (internal balun)
· Blonder Tongue Vaulter III (internal balun)

The image below shows the prototype and a couple of preamps on the test mast.

http://forum.tvfool.com/attachment.php?attachmentid=542&d=1371920415

The main variables in optimization with 4NEC2 software were:

· Driven element length,
· Position of driven element relative to apex
· Position of reflector elements near apex

After a few rounds of optimization; computer simulations, trimming, and on-the-mast testing, the CM-0264 was chosen as the preamplifier. The final tweak on the main tower was trimming the transmission line between the CR and the preamplifier for maximum signal.

The image below shows the installed corner reflector on the main tower. Most obvious change in the two photos is the position of the two reflector elements near the apex.

http://forum.tvfool.com/attachment.php?attachmentid=543&d=1371920423

With antenna direction at a compromise between the two weaker signals, the signal strength was not high on either of them. Fortunately, for all three signals being 1-Edge diffraction, their signal strengths were relatively stable, especially considering the distance of 65-75 miles. In normal viewing, no TV image dropouts have been seen or reported. Image dropouts have been seen when severe thunderstorms were between the stations and the receiving location.

A CM-0264 preamplifier was modified to replace its internal balun with an internal half-wave coaxial loop balun. In tests, the modified CM-0264 yielded ~1dB more S/N margin for all three stations. It has not been installed.

Early in 2011, WCTE-22 increased power to 200 kW (from 57 kW). This power increase allowed a re-positioning of the antenna in azimuth, with improved signal strength levels for all three stations.

.

[Pete Higgins]

tripelo

You outline an interesting design scenario. Did you ever implement the coax balun? From what I’ve read, coax balun’s have a very narrow bandwidth so I would have thought even 24 MHz (ch. 20 -23) might be too wide? Or, did you wind one on a toroid core?

I scavenged a VHF/UHF combo antenna from a rental house I own when one set of tenants moved out. It has a CR in front of the VHF portion so who knows what that might turn into one day.

I assume you weren’t in Dallas when you did this?

[tripelo]

Thanks Pete.

... Did you ever implement the coax balun?...

Yes, a CM-0264 was physically modified to remove the internal balun and replace it with an internal coaxial half-wave loop balun.

Two types of lab tests were performed:

1. Gain vs. frequency response (dB)- Results before and after the modifications were compared.
2. Post-detection S/N (dB)- Using off-the-air DTV signals, both the modified and an unmodified CM-0264 were measured and compared.

No, the modified preamp has not been installed on the main tower.

From what I’ve read, coax balun’s have a very narrow bandwidth so I would have thought even 24 MHz (ch. 20 -23) might be too wide?

Depending on how one defines bandwidth, a half wave loop could be considered to have narrow bandwidth relative to ferrite core baluns. However, for use in TV reception the half wave loop balun has a fairly wide usable frequency range. The losses of a half wave balun depend, as does a ferrite core balun, on design and construction. If one considers usable bandwidth to be when signal loss of a half wave balun is comparable to that of a conventional balun, then it probably has a usable bandwidth approximately equal to the current UHF band (Channels 14 –51).

It may be instinctive to think of functions that require specific wavelengths of coax to be narrow in bandwidth. This thinking could arise because such coaxial items can be a specific length (in terms of wavelength) at only one frequency. Only one frequency, that does seem narrow :)

The above is true if the objective depends on signal cancellation (e.g. notch or trap filters). For signals to nearly cancel, the amplitudes must be near exact and the phase relationship (wavelength-related) must be nearly exact.

But, the function of a half wave loop balun depends not on signal cancellation (subtraction, or out-of-phase condition) but instead utilizes in-phase signal addition. The half-wave delay (180 degrees) of a loop balun attempts to align (in phase) the normally out-of-phase signals of the left and right halves of a dipole antenna.

Even if their phase and amplitudes are not perfectly aligned, signals (vectors) can add with relatively small loss. When adding misaligned signals there is loss, but over a usable range the losses increase somewhat gradually as the misalignments worsen.

The main losses (in no particular order) associated with half-wave loop baluns:

1. Phase alignment Loss (Imperfect 180 degree delay)
2. Amplitude Loss (Normal coaxial attenuation for the half-wave section)
3. Impedance mismatch (Resulting from impedance transformation of non half-wave section)

Bottom line: Over much the UHF band (470-698 MHz), a well designed half wave loop balun can have lower signal losses than a ferrite-core balun and can at worst (near band edges) be comparable to good commercial ferrite core baluns.

Or, did you wind one on a toroid core?

Not in this particular case. It is essentially open-air loop, in close proximity to PCB plane and plastic housing.

Having wound many ferrite core baluns for VHF and UHF, winding twisted-pair on a 2-hole ferrite core could be an alternative, especially if coverage of channels at both both band-edges (near channels 14 and 51) is required.

I scavenged a VHF/UHF combo antenna …who knows what that might turn into one day.

Yes. you may find a good use for it.

I assume you weren’t in Dallas when you did this?

All the antenna work, discussed so far, was done in KY.

The preamp modification (balun related) and testing was done in Dallas.

The modified preamp is now stored in KY.
.

[tripelo]

Returning to VHF antenna tests (http://forum.tvfool.com/showpost.php?p=36728&postcount=23), recall that an objective was to receive WBNA-8 and WHAS-11 from Louisville KY at distances of 70 and 101 miles. A project was initiated to determine if an antenna arrangement could make such reception possible.

TVfool report (both stations listed as 2-Edge):

Noise Margin Distance (miles)

WBNA-8 -7.2 dB 79.3
WHAS-11 -14.9 dB 101.1


A few antennas were compared at the test mast location (garage); Jerrold/Wade VIP-306, Channel Master Crossfire CM-3610, stacked pair of Winegard YA-1713, and a channel-cut Wade antenna.

Other high gain antennas were available, but only single units. It became fairly clear that no single antenna would suffice.

WHAS was listed as 2-edge and at the test site the signal was almost continuously variable. The actual signal strength, on an analog meter, fluctuated ~15 dB within something like 30 to 45 seconds. Portions of the WHAS 6 MHz spectrum varied independently.

The signal variation was such that antenna gain differences of maybe 1 or 2 dB were not visible.

It became apparent that, at this location, there were no commercial VHF signals strong enough or stable enough for definitive signal evaluation. Actually, there were no closer or stronger VHF signals at all. A local signal source was needed.

At the time in 2010, the signal synthesizer discussed in earlier post (http://forum.tvfool.com/showpost.php?p=35987&postcount=3) had not been constructed. So, a 20 MHz crystal oscillator was built to use as a VHF transmitter. The 9th and 10th harmonic of the crystal frequency provided test signals for channel 8 (180-186 MHz) and Channel 11 (198-204 MHz). The signals from the crystal oscillator were fed to a transmitting antenna at the main tower.

The transmitting antenna was a portion of a YA-1713 mounted on reverse side of CM-4251 on the main tower. It was fed by coax from the crystal oscillator located on the ground. The transmit antenna was aimed toward the test mast (at the garage). The signal was then received by the antenna-under-test mounted at the test mast location. Height of receiving test antenna was adjusted to be ~ level with the transmit antenna (~45 ft. AGL).

The above arrangement provided stable signals for use in gain comparisons between candidate VHF antennas.

The image below shows the upper-VHF transmit test antenna.

http://forum.tvfool.com/attachment.php?attachmentid=552&d=1372886021

Later, a crystal oscillator was built that could have provided UHF signals, but it was determined that a synthesizer was a better solution.

The crystal oscillator was used as a reference transmitter in tests throughout 2010, until the synthesizer was constructed in early 2011.

.

[Pete Higgins]

tripelo,

Do you remember how far apart you mounted the Winegard YA-1713’s in post 20?

I made a Home Depot run this afternoon & bought a 10½’ chain link fence top rail. I’ll try it in the Radio Shack rotor & see if I can spread out the Cushcraft A147-20T and the Winegard YA-1713. It’s been 97 deg. here all afternoon so trying to stay off the roof & out of the hot sun. Maybe tomorrow or Friday?

You just have to keep showing me pictures of those beautiful CM-4251’s don’t you.

Looking forward to the rest of the VHF High story

[Stereocraig]

Tripelo.

Do you make your own clamps for the tower verticals, or is there something commercially available.
I have used clamps from my drum rack, but don't trust them for durability.
A picture would be nice, if you're able to provide one.

[tripelo]

Do you remember how far apart you mounted the Winegard YA-1713’s in post 20?

The YA-1713 were mounted 43 inches apart.

This particular stack spacing provided highest signal strength for Channel 13, it will probably different for other channels. Best spacing will be different for other types of antennas.

Signal strength varies slowly vs stack spacing so stack spacing for gain is not very critical (within a few inches at upper VHF).

...bought a 10½’ chain link fence top rail. I’ll try it in the Radio Shack rotor...

The rotor may need a bearing to take side stress of it.

Don't know, maybe something like a NTE TB-105?

Maybe you have something like this already. From the YA-1713 photo, can't be sure how your rotor is mounted.

You just have to keep showing me pictures of those beautiful CM-4251’s don’t you.

Guess so, those antennas are a bit different.

Saw someone, located in California, posted a photo of a CM-4251. So guess Channel Master did some marketing there. Maybe you can locate one some day.

[tripelo]

Tripelo.

Do you make your own clamps for the tower verticals, or is there something commercially available.
I have used clamps from my drum rack, but don't trust them for durability.
A picture would be nice, if you're able to provide one.

Sorry, don't have any photos that I know of. Presently, I am not at the main tower site to take any photos.

Mostly use recycled antenna manufacturer clamps (the ones that come with antennas).

However, a pair of conduit clamps back-to-back makes a pretty good mast-to-mast or mast-to-tower leg clamp for light masts with light antennas. For mast sizes up to about 1 & 3/8 inches, the clamp size, not sure but think, is labeled 1 inch.

This labeling results from pipes being dimensioned according to inside diameter whereas mostly antenna installations are involving outer diameters (tubing convention).

This photo, a generic conduit clamp from the web, represents the type of clamp discussed.

http://forum.tvfool.com/attachment.php?attachmentid=553&d=1372962330

Look for heavy duty clamps, Lowes and Home Depot here don't seem to have the heavier grades. Probably electrical supply or old fashioned hardware store might be good places to find heavy clamps.

Bolt two clamps together, through the hole shown in the left of the image above. A 1/2 inch long, 5/16 inch bolt with two thick washers and a nut works well to hold two clamps back-to-back. If the bolt is much longer than 1/2 inch it will interfere with the masts.

This arrangement has an advantage in that it allows two pipes to be connected regardless or their orientation (horizontal or vertical or some angle).

Almost any mounting using these clamps requires four clamps (two pair). But maybe in a heavier installation more clamps could suffice.

[Pete Higgins]

tripelo,

That’s interesting, I assume you derived your measurement through empirical testing for channel 13? Winegard recommends optimum vertical stacking @ .94 wavelengths spacing and minimum @ .6 wavelengths for the lowest receive frequency of a broadband antenna. They published a chart for single channel antennas showing channel 7 @ 48”, 8 @ 46”, 9 @ 44.5”, 10 @ 43.5”, 11 @ 42.25, 12 @ 41” and 13 @ 40” or all at approximately .6 wavelengths.

Right now, it’s just the bare Radio Shack rotor & mast. So far that thing has taken everything I’ve thrown at it, including the big Wilson Shooting Star for several years. My TV tower rotor is an NTE ECG U106 with a TB-105 thrust bearing ~ 2.5’ above it. I had just ordered another TB-105 before I got your post. Great minds?

Boy, those things sure have gone up in price since I bought the first one a few years ago. I think I paid $17.50 + shipping and this one cost me $24.49, so with tax & shipping was $36.48.

Channel Master was one of the premier brands here from the mid 1950’s through the late 70’s or mid 80’s, when it seemed like their antenna quality and customer service really declined. I think I bought my CM-4228 in 72 or 73 when I was stationed in Sacramento, CA. I also still have one of their 300 ohm dual input VHF/UHF antenna amps. with a 75 ohm output. The power supply has a 110 VAC cord and sends AC up the coax to the mast mounted pre-amp. I used its VHF input (through a 300/75 balun) with my FM Yagi up until last year. No idea what the model number is or its specs.

[Stereocraig]

Thanks, Tripelo.
Probably could sweat them together, too.

[tripelo]

That’s interesting, I assume you derived your measurement through empirical testing for channel 13?

Yes.

The signal strength of the combined stack was observed on a signal level meter while the lower antenna was moved up and down by approximately +/- 18 inches.

Interesting about Winegard recommendations, in that they list two recommended stacking heights.

In general, the wider spacing (around 1 wavelength) yields higher gain for a given channel.

---------------------------------------

On the stacking gain topic:

In recent years, read several accounts of unsatisfactory experiences with vertical stacking.

Stacking two antennas for gain (horizontally or vertically) requires near equal illumination of both antennas (equal signals). If the two antennas do not receive equal signals, then the situation tends towards the two-antenna situation discussed earlier (http://forum.tvfool.com/showthread.php?t=2288&page=2). The antenna receiving the weak signal tends to load the strong one and either loses signal in the combiner or re-radiates signal.

The above scenario more likely occurs with vertical stacking as compared to horizontal stacking. The sub-optimal effect on vertical stacking is mainly due to layering (signal reflection from ground, or diffraction from an elevated edge). To equalize the received signal in each antenna, it is usually necessary to have them mounted high above ground, so high that layering affects both antennas about the same.

How high is high enough for effective vertical stacking? Don't know, depends.

In many cases, probably high enough that the spacing between the antennas represents only a small fraction of the height above ground (could be 10 wavelengths or more).

Unequal illumination is related to another factor that has a role in producing less than expected gain from vertical stacks. That factor is vertical angle-of-arrival of received signal.

Stacking antennas may have some advantage (space diversity) other than increasing gain.

---------------------------------------

My TV tower rotor is an NTE ECG U106 with a TB-105 thrust bearing ~ 2.5’ above it.

What are your impressions regarding the NTE rotator, compared to the Radio shack rotator?

...Channel Master was one of the premier brands here from the mid 1950’s through the late 70’s or mid 80’s...

Interesting that Channel Master was into California that early. Many of the antenna manufacturing companies in those days were sort of regional. Seems as if Channel Master must have had the best (Quality x Performance)/Price ratio of all manufacturers.

...when it seemed like their antenna quality and customer service really declined...

Probably about the time when satellite-fed cable was coming on strong.

[Pete Higgins]

tripelo,

What are your impressions regarding the NTE rotator, compared to the Radio shack rotator?

No comparison. The Radio Shack 15-1220 is a 5-wire rotor that uses a balanced bridge for exact positioning. In the 50 years I’ve used it; it has never gone out of alignment. It also seems to produce more turning torque. The accompanying control box displays ‘N’ at the top & ‘S’ – ‘S’ at either end of rotation. Being an old flyer, that fits the way I think.

I also have an RCA 10W707S that is almost identical. Motor unit is exactly the same and control box looks identical except it displays ‘S’ at the top and ‘N’ – ‘N’ at either end of rotation. The one drawback is the directional calibration. Tic marks on both rotors are 4.5 deg. apart. When aiming towards a “True” heading, I can visualize the heading with respect to true north and align the knob pretty close. Degrees with respect to true south –not so much. (If I put the RCA in service, I’ll make stick-on labels for the cardinal headings (S-S, W, N, E) to cover the ones silkscreened on the control panel. Other than control panel screening & branding, they really are identical.)

The U-106 is a three wire rotor that uses a timing circuit for calibration. 3-wire rotors use AC synchronous motors that run at a predictable speed, and the control box simply runs the motor for the amount of time needed to turn the antenna from where the controller thinks it is to where the controller wants it to be. Over time, the position error grows.

After moving it to “home” or 00 deg., basically, you rotate it full clockwise (360 deg.), hit a button labeled “Initial” and it memorizes the time it takes to return to 00 or “home”. Unfortunately, it frequently requires recalibration. Since my signals come from four directions, it’s fairly easy to detect when it needs calibration because when I turn the array there is either nothing there or the signals are barely watchable. I probably have as much calibration mileage on the rotor as actual array turning mileage. Sometimes, when the calibration goes off, it won’t fully turn to a true 360 so to get it full clockwise you have to power off, power on with a “reset” turn some more and repeat the process until it visually has the array pointing north. I’ve since read that other folks are experiencing the same calibration issues with other brands of 3-wire rotors. I think AntennaCraft, Centronics, Channel Master, Magnavox, Philips, RCA, Stern and probably others sell this same design under their own labels.

I bought the U-106 because the literature said “Digital display indicates antenna position during operation” & “Pre-set to 12 TV/FM station directions for automatic antenna positioning”. What I didn’t pick up on was that the bearing readout was a 2-digit display. North is 00 or 36, east is 09, south is 18 and west is 27. My street is aligned with True North and my house sits squarely on the lot facing east so visually it’s easy to determine array alignment. Even after a fresh calibration, manually turning the rotor to display “18” can have me pointing somewhere between ~175 & ~185. Fortunately, if you “bump align” for max SNR and memorize the location to a pushbutton it seems to return to that location –at least until it goes out of calibration.

I’ve been tempted to put the RCA on the tower, but then I’d have the new U-106 just sitting in the garage gathering dust. It’s useable, but I couldn’t in good conscience sell it to anybody.

Hello Pete,
The TB-105 support bearing that you ordered is currently out of stock. The vendor will not have anything available until mid September.
Please let me know if you wish to keep your order open or cancel.
Thank You
Tom

Kept order open, so it looks like I don't have to go out in the 100 deg. heat (at least until September).

http://forum.tvfool.com/attachment.php?attachmentid=555&stc=1&d=1373129246

Found this ad in the Pitsburg Post-Gazette for Friday August 24th 1973. I think I bought mine about 10 years earlier for $29 or $39.

[tripelo]

Thanks Pete, for your interesting writeup on the antenna rotators.

Looks like your Radio Shack and RCA rotators are good ones.

Couple of thoughts:

Rotators currently available may be suitable for a single small antenna, but not much more than that.

At present, seems like if one wants a heavy-duty antenna rotator with some accuracy in pointing, one may have to look at rotators marketed to amateur (ham) radio. Likely, the ham radio rotators will cost more than the typical TV rotator.

[tripelo]

Recalling the VHF antenna project objective:

To receive WHAS-11 and WBNA-8 located in Louisville KY.

TVfool report (both stations listed as 2-Edge):

Noise Margin Distance (miles)

WBNA-8 -7.2 dB 79.3
WHAS-11 -14.9 dB 101.1

Observations over several weeks with the stacked YA-1713 antennas (http://forum.tvfool.com/showpost.php?p=36658&postcount=19) on the main tower, it was determined that an additional gain of 7 dB may be required for reliable reception of WHAS-11.

After testing for a few weeks at the test location (garage) with some high-gain antennas, it seemed like there were few options that could provide 7 dB gain above that obtained with a pair of YA-1713 antennas. A stack-of-two large, either Wade/Jerrold (http://forum.tvfool.com/showpost.php?p=36728&postcount=23)or Channel Master antennas seemed likely to be insufficient, and a quantity of four of such antennas was unavailable.

At about half the length and 1/3 the width, the gain of the channel-cut antenna tested to be within about 2 dB of a single large antenna.

Since it was desired to receive two stations separated in frequency, WHAS-11 and WBNA-8, then using channel-cut antennas for a single channel could be problematic

Fortunately, in this case, a characteristic of Yagi antennas is that gain decreases less rapidly on the low side of the design frequency. Since the design frequency would be weak signal channel (channel 11) and the lower in frequency, channel 8 signal was considerably stronger (not requiring as much gain), then a channel-cut antenna might suffice.

Considering the above information, it seemed a pair of long channel-cut Yagis designed for channel 11 might meet requirements. Since a channel-cut Yagi of about 85 inches in length delivered a gain within ~2dB of a VIP-306 or a CM-3610, then a channel-cut Yagi of 170 inches probably could exceed the performance of either of the larger antennas.

Location: Dallas

In an attempt to maximize signal from such antennas, half-wave coaxial loop baluns were designed.

A small channel-cut Yagi for channel (Wade 5y10s) 10 was purchased for balun design and testing.

http://forum.tvfool.com/attachment.php?attachmentid=556&d=1373568437

At that time, there were 3 VHF stations (Channels 8,9, and 11) in Dallas. The signal paths were line-of-sight and the signals were strong and steady at the Dallas test location. The broadcast DTV signals provided signals for gain comparisons between antenna modifications and balun types.

Several loop baluns were constructed and reception compared to each other, and to commercial baluns (using the small Yagi and broadcast DTV signals).

After suitable half-wave loop balun designs had been constructed. The input impedances of several balun and antenna combinations were quantified. Knowing complex input impedance allows SWR to be calculated. The impedance measurements were performed using a vintage Boonton/HP RX250A The RX250A is capable of accurately measuring complex impedance from 500 kHz to 250 MHz. Measurements confirmed that the three-bar folded dipole had sufficient bandwidth and that a half-wave coaxial balun provided a low SWR match to 75 Ohms.

Half wave baluns were constructed using both RG6 and RG-62 (93 Ohms). In agreement with theory, the RG-62 cable provided the widest bandwidth and best match over channel 8-11 and thus the lowest overall signal loss.

Note: At, or near, the loop half wavelength frequency, loss was less with RG-6 cable. Away from that frequency, losses were less with RG-62.

.

[tripelo]

Time: Summer/Fall 2010
Location: KY

Yagis (channel-cut for 10, Wade 10y10s) were used as raw material and a starting point in the design. Channel 10 was selected because it seemed a good compromise for the driven element between Ch. 8 and Ch 11. Wade Yagis used a 3-bar folded dipole for the driven element. Such a folded dipole is probably broadband enough to cover channels 8 through channel 11 with good impedance match. Also, since channel 10 antennas generally have longer elements than channel 11 antennas, this allowed flexibility in trimming elements (longer than desired elements can be trimmed).

The front three elements from a YA-1713 were added to the channel 10 antenna. Repeated testing and 4NEC2 analysis were performed. Eventually, an extra length of tubing was added containing two more elements, repeat analysis and testing. Then, all elements were analyzed in 4NEC2 for length and location. Gradually the element positions and lengths were changed toward the 4NEC2 specified parameters, with testing in between small steps to confirm the direction of the change.

When it was thought the antenna was near optimized for channel 11, then searches were performed in 4NEC2 to determine if channel 8 could be improved without adversely affecting channel 11 performance. Few changes were available. A change was made, lengthening the reflector improved gain by more than one dB on channel 8 and reduced gain for channel 11 by maybe 0.1 dB. Measurements confirmed these differences.

Final element progression illustrated in images below:

- 13 elements
- 14 elements
- 15 elements

http://forum.tvfool.com/attachment.php?attachmentid=561&d=1374168088

http://forum.tvfool.com/attachment.php?attachmentid=562&d=1374168094

http://forum.tvfool.com/attachment.php?attachmentid=563&d=1374168099

The antennas were made from parts of:

1. Wade Channel-cut Yagi (trimmed directors, less reflector)
2. Winegard YA-1713 (reflector)
3. Winegard YA-1713 (front three elements trimmed)
4. Portion of Channel Master boom (portion extending out front)
5. Channel Master elements (front directors, trimmed)
6. Portion of Antennacraft boom (support boom)
7. Homemade support boom brackets

The final 15 element Yagi had total length ~170 inches.

Two identical antennas were constructed.

Later, a pair of these long-Yagis were stacked and performance compared to stack of Winegard YA-1713 Yagis.

.

[Pete Higgins]

Later, a pair of these long-Yagis were stacked and performance compared to stack of Winegard YA-1713 Yagis.

tripelo,

When do we get the rest of the story? Anxiously awaiting comparison results. How close were you able to come to 7 dB gain above that obtained with a pair of YA-1713 antennas with coaxial balun's and the additional 5 elements?

[tripelo]

tripelo,

When do we get the rest of the story? ...

Thanks Pete.

Glad you find the story interesting.

For the most part, kept handwritten logs, Excel files, and photos. Takes a bit of time to go back and put a 'hopefully' coherent story together.

Once upon a time...

[tripelo]

Earlier, it had become apparent that sufficient gain (predicted 7dB above pair of YA-1713) to enable reception of WHAS-11 would be difficult to achieve.

To make most use of the available gain, a pair of Research Communications Preamplifiers (Models RC-9267) were ordered. The primary rationale for this approach was noise figure related.

The advertised VHF noise figure of major manufacturers of preamps ranged from a low of 2.6 dB to around 3.0 dB. The RC preamps were advertised to have a noise figure of 0.4 dB. Signal-to-noise ratio is closely related to noise figure. As an example, at UHF frequencies, a real improvement in noise figure of say; one dB, can result in a signal-to-noise improvement of about one dB. It is more complicated than this example, and also less likely at VHF, but this can be a close approximation for TV reception purposes.

This begs the question of whether advertised noise figures are accurate. With measurements, using normally expensive equipment, the question can be directly answered. Indirect measurements at the lab bench have indicated that the major manufacturer noise figures are overly optimistic. In any event, field tests here demonstrate the RC preamp provides improved S/N ratios.

Testing with the RC preamp encountered a hitch. One day a thunderstorm arose quickly. The test station was abandoned with antennas in place and the RC preamp powered on. As the scene was observed from the back porch of the house about 100 feet away, lightning struck the earth or a tree, about 600-1,000 feet distant. After the storm passed, the RC preamplifier was no longer functioning. On the main tower, two Channel Master preamplifiers survived.

There are several complication factors in the above scenario, but it is clear that:

- The RC preamplifier can be susceptible* to atmospheric discharge.
- The coaxial half-wave loop balun contributed to the demise of the RC preamp.

*More susceptible than the Channel Master preamplifiers.

The outcome was that testing with the coaxial loop baluns combined with RC preamps was terminated for a time.

http://forum.tvfool.com/attachment.php?attachmentid=564&d=1374516336

Some different brands of commercial baluns were compared to half-wave coaxial baluns on both the test bench and also installed at the long Yagis. A selected pair of Philmore MT-74 baluns provided the lowest loss at Upper VHF. The signal loss of the MT-74 baluns was ~ 0.4 dB worse on channel 11, than the half wave loop baluns. The Philmore MT-74 baluns were used with an RC-9267 preamplifier throughout the remaining tests.

* Recent purchases and testing of Philmore MT-74 baluns indicate quality of construction, materials, and performance at VHF, have significantly changed (negatively) compared to the units tested in 2010.

.

[tripelo]

Analysis with 4NEC2 software (http://www.qsl.net/4nec2/) can often help provide insight into antenna modifications and resulting performance.

A computer simulation of an antenna is an approximation that is no better than the models represented in the software. The software model is based on numerical parameters that represent an antennas physical dimensions and electrical specifications. Often the dimensions are measured on a physical model. Electrical specifications may have to be determined by experiment. It is rare that measurements and specifications allow software to fairly completely describe an antennas performance, but is often close enough for practical purposes.

The performance of Winegard YA-1713 (http://forum.tvfool.com/showpost.php?p=36658&postcount=19) without balun, was simulated, both as a single antenna and stacked at 43 inches. The plot below shows gain (dBi) and Standing Wave Ratio* (SWR) over the upper VHF band. For a single antenna, the maximum gain is about 12 dBi, which would be close to Winegard specifications of ~10 dBd.

http://forum.tvfool.com/attachment.php?attachmentid=566&d=1374967617

Interesting that stacking at 43 inches shows higher gain (~2.9 dB) at the low end of the band. Recall that a stack distance of 43 inches (http://forum.tvfool.com/showpost.php?p=36658&postcount=19) was empirically determined as best (within +/- 18 inches) for reception of channel 13. The real world includes ground effects (mainly reflections) that were not included in the simulations. Variations in height above ground can dramatically affect antenna patterns, thus affecting perceived gain. The change in SWR from single unit to 2 units stacked, could be a result of mutual impedance or coupling between the two antennas. A stack distance of 43 inches is relatively close, and some mutual coupling could be expected.

The performance of the long Yagi (http://forum.tvfool.com/showpost.php?p=37156&postcount=41) without balun was simulated, both as a single antenna and stacked at 89 inches. The plot below shows gain (dBi) and SWR (relative to 300 Ohms) over the upper VHF band. For a single antenna, the maximum gain is ~>14 dBi, about 2 dB greater than the YA-1713. Stacking at 89 inches shows additional gain improvement approaching 3 dB over most of the band.

http://forum.tvfool.com/attachment.php?attachmentid=567&d=1374967644

The following plot shows the mismatched gain for both the stacked pair of YA-1713 and the stacked pair of long Yagis.

http://forum.tvfool.com/attachment.php?attachmentid=568&d=1374967653

Mismatched gain is the normal gain (shown earlier) that has been reduced by the effects of SWR (normalized to 75 Ohms). The numerical value of SWR represents the mismatch to the characteristic impedance of the system. In this case, the characteristic impedance is 75 Ohms. Any impedance presented by the antenna other than 75 Ohms reduces the amount of power that can be transferred from the antenna to the transmission line or to a system (preamplifier, receiver etc). The amount of power rejected due to mismatched impedance is the mismatch loss. Mismatched gain is the full gain minus the mismatch loss. Mismatch loss is present to some degree in all systems with SWR greater than 1. It appears this final gain figure is the equivalent of what has been called ‘Net Gain’ by Ken Nist, at HDTVprimer.

The mismatched gain shown in the graph is probably realistic for a system with good SWR with respect to the transmission line and tuner, or preamp (if one is used). If the transmission line and tuner, or preamp, have poor SWR with respect to each other, then the overall mismatch is statistically likely to be worse with greater mismatch losses causing gain for the system to be less than that shown.

* Standing Wave Ratio (SWR): A measured or calculated number that mainly represents an impedance mismatch. SWR=1 represents a perfect impedance match, numbers greater than 1 represent progressively worse impedance match. SWR is an indirect way to describe ‘Return Loss’. To have a ‘Return Loss’, there does not have to be a transmission line physically long enough to support an actual standing wave length.

.

[Pete Higgins]

tripelo,

Clear, concise & very interesting. Your installments keep me anticipating and coming back for more. At my age, I hope you make some miraculous breakthroughs on aging but I’m not sure your talents wouldn’t be better served back in Engineering!

[tripelo]

...Clear, concise & very interesting. Your installments keep me anticipating and coming back for more.

At my age, I hope you make some miraculous breakthroughs on aging...

Soon, I will be your age. Relatively soon, all now alive will be your age.

Human aging is a scientific and engineering problem, it will be solved.

... but I’m not sure your talents wouldn’t be better served back in Engineering!

Thank you Pete for your kind remarks.

[tripelo]

Previously shown were computer simulations of antennas (http://forum.tvfool.com/showpost.php?p=37314&postcount=45); Winegard YA-1713 and homebrew long Yagi. For the channels of interest (Channel 8 and 11), the analysis data showed gain for a pair of long Yagis compared to the stacked pair of YA-1713 to be as listed in table below:

http://forum.tvfool.com/attachment.php?attachmentid=575&d=1375546854

Having finalized construction of the long-Yagi, several comparison tests at the test range were conducted.

A test involved an antenna-under-test (AUT) mounted on the test mast, receiving signals from the transmit antenna. The transmit antenna (http://forum.tvfool.com/showpost.php?p=36949&postcount=30) was a portion of a YA-1713 mounted on the main tower (aimed towards the test mast) fed with a crystal oscillator as a transmitter. The frequencies available were the 9th and 10th harmonic of a 20 MHz crystal (180 MHz and 200 MHz). The AUT signal was amplified by RC-9267* preamplifier then received on a Blonder Tongue FSM-11 (signal level meter). Signal levels at 180 MHz and 200 MHz were recorded.

*RC-9267 – Particular interest due to specified low noise figure. This model has band pass filtering to attenuate frequencies outside upper VHF (174-216 MHz).

As with previous testing over several weeks, the test started with the homebrew long Yagis stacked at 89 inches (http://forum.tvfool.com/showpost.php?p=37199&postcount=44). The two antennas with MT-74 baluns fed an Antronix CMC2002U splitter (used as a combiner). The combiner output was coupled to the preamp/FSM-11 receiver system as listed above. FSM-11 readings were recorded.

Then, the long yagis were changed to the YA-1713s stacked at 43 inches, using the exact cables and Winegard CC-7870 combiner that was used on the main tower (http://forum.tvfool.com/showpost.php?p=36658&postcount=19). The preamplifier was a RC-9267 instead of the original CM-7777. The FSM-11 meter readings were recorded.

Measured Results:

Freq. Delta
(MHz) (dB)
180 . 3.3
200 . 4.8

That these results generally agree with the computer simulations was bit of luck.

In this test, there were some confounding variables, examples (no particular order):

- Antronix combiner on long Yagis had less loss (maybe ~0.2 dB) than Winegard 7870
- MT-74 balun on long Yagis may have had more loss than YA-1713 balun.
- Preamp SWR; briefly explored near the end of these tests.
- There are others

Suppose the gain improvement was ~4.8 dB, this falls short of the predicted needed value of 7 dB gain above that of the pair of YA-1713s, as previously discussed.

A somewhat compensating factor was that the noise figure of the RC-9267 was considerably better than of a CM-7777.

Later in 2012, lab comparisons in thermal noise background, using a Sencore 1456CM, indicated ~3dB better post-detection S/N with the RC-9267 compared to the older version of CM-7777.

There are probably few locations (certainly not this location) in the USA where the background noise at Upper VHF is as low as thermal noise. So, one would not expect an approximately 1 for 1 improvement in S/N with improvements in noise figure. But, there was some reason to think that the combinations of antenna gain and noise figure improvement might suffice for adequate reception of WHAS-11.

Over-The-Air reception at the test site with long Yagis, RC preamp, and a Channel Master CM-7000 DTV converter was observed for a few weeks. WBNA-8 reception was very solid with an occasional pixelated image, and WHAS-11 was watchable. But, signal dropouts were present on WHAS-11, especially during hours between about 10 AM and 5 PM or so. This viewing experience seemed to indicate a lack of sufficient antenna gain, or possibly some other deficiency in reception of WHAS-11.

http://forum.tvfool.com/attachment.php?attachmentid=571&d=1375532939

Previously collected antennas and materials were available, so building two more long Yagis for a quad stack was feasible.

Decided to observe performance of these antennas on the main tower for a period of time.

.

[Pete Higgins]

tripelo,

This is starting to remind me of a time when we listened to the radio every Saturday night for the next installment of Boston Blackie or the Shadow –great stuff.

Yesterday, Time Warner dropped KCBS {RF 43}(channel 2.1 which carries a lot of the shows my wife & I watch, especially the evening news @5,6 & 11) KCAL RF 9 channel 9.1, plus all of our Showtime & Movie channels.


A somewhat compensating factor was that the noise figure of the RC-9267 was considerably better than of a CM-7777.

OTA, I get 9 pretty reliably but CBS {RF 43, 2- Edge with a Noise Margin of -22.1 dB @ -112.90 dBm} comes & goes especially during late afternoon early evening hours. Do you think I would see any improvement swapping out my 91XG’s PCT MA2-M 2.7 dB NF amplifier with one of the new Winegard LNA-200’s that they claim has a 1 dB NF on UHF? Or would the improvement be “in-the-noise” –so to speak?

[tripelo]

...This is starting to remind me of a time when we listened to the radio every Saturday night for the next installment of Boston Blackie or the Shadow –great stuff.

Yep. “…return with us now to those thrilling days of yesteryear!…” .

Listened to radio shows such as: Dragnet, Suspense Theater, Gunsmoke, and the Lone Ranger.

Yesterday, Time Warner dropped KCBS {RF 43}...

They dropped KTVT (CBS) here in Dallas. Such as this, may in long run be good for all broadcasters.

OTA, I get 9 pretty reliably but CBS {RF 43, 2- Edge with a Noise Margin of -22.1 dB @ -112.90 dBm} comes & goes especially during late afternoon early evening hours. Do you think I would see any improvement swapping out my 91XG’s PCT MA2-M 2.7 dB NF amplifier with one of the new Winegard LNA-200’s that they claim has a 1 dB NF on UHF? Or would the improvement be “in-the-noise” –so to speak?

Hard to say.

Seems as any improvement could help with such a low signal level.

Based on my measurements of industrial/commercial drop amplifiers, of which your PCT MA2-M is one, the specified noise figure of the PCT MA2-M is probably realistic. So, if Winegard LNA-200 specifications are accurate, you could see approximately 1.7 dB improvement in S/N ratio. That is worthwhile, especially in a low signal situation as you describe.

Small improvements, even if they do not entirely eliminate dropouts, can reduce dropout time duration. On the other hand, if the dropouts are a result of severe multipath, signal level increases often have less noticeable effect.

-----------------------------

On Winegard LNA-100 and LNA-200 specifications: It is plausible that all the specifications are accurate. The information provided by Winegard suggest a design using pHEMT transistor or IC. With such GaAs FET devices available these days, all Winegard’s specifications are within reason, and preamplifiers using such devices could be manufactured at low enough cost to enable mass marketing.

The thing to watch for in pHEMT based preamplifiers is susceptibility to atmospheric discharge. To a large degree this problem is solvable, hopefully Winegard has done so.

Of course if Winegard's specifications are not accurate, as seems sometimes, then the above speculations are meaningless.

Couple of ways to help answer such questions:

- Test the preamplifier to see if it meets specifications.
- View the layout of the circuit to identify the class of active devices.

------------------------------

Pete, in your situation, I would probably give it a try, and be prepared to add it to my collection of interesting but maybe not very useful preamplifiers.

Note: Based on ADtech's comment in another forum, the LNA-200 may be more like Winegard's previous preamplifiers. In such a case, it is unlikely the preamplifier would help your reception.

[tripelo]

In October 2010, a single long-Yagi (http://forum.tvfool.com/showpost.php?p=37156&postcount=41) was installed at the top of the main tower mast along with an RC-9267 preamplifier. A Blonder Tongue FSM-11 signal level meter was used at the tower top to observe signal strength of both WHAS-11 and WBNA-8.

The sensitivity of the Yagi height above ground was investigated. The Yagi, with RC-9267 and FSM-11 connected, was raised from near the tower top to the upper end of the mast. The FSM-11 was observed as the Yagi was raised, and about every foot or so, the Yagi was fastened in a fixed position for longer observation of the signal level. This process was repeated until the Yagi was at the top position. While raising the Yagi (~11 feet variation in height) there were no obvious signal strength differences from one position to the next. But, signal fluctuation could easily have masked differences in average signal strength at some particular location.

Often, at any position, the signal would fluctuate rapidly, changing as much as 15-20 dB in a time period of 20 –60 seconds. In the depth of the fades, the signal would be at or below the required threshold of detection for 8VSB DTV (at around 15 dB above the noise floor). The fades were frequency selective. For example, the signal level in lower portion of the 6 MHz wide channel might be fairly strong while in the upper portion of the channel the signal could be critically weak, or vice versa.

The image below shows the long-Yagi at the main tower mast.

http://forum.tvfool.com/attachment.php?attachmentid=586&d=1376060047

For several days the single Yagi was left alone while reception quality was observed at the house (using a CM-7000 DTV converter). Reception was fine for WBNA-8 (with occasional image pixelation). Reception for WHAS-11 was good for several hours of the day, but signal loss and breakup was common through midday hours until early evening.

Comment: Rapid Fluctuations and Frequency Selective Fading

The signal observations at the top of the tower with the Blonder Tongue FSM-11 were similar to those seen at the test mast location. Those rapid fluctuations and frequency selective fading were indicative of multipath. The terrain in central KY is hilly with trees, no mountains. This is the path that a 2-Edge signal (according to TVfool) from Louisville must traverse. At first thought, such a path with abundant vegetation as RF absorbers might not seem to support severe multipath. It could be that for a significant part of the time the attenuation of the path was large enough that the propagation mode was tropospheric scatter (Tropo) or a combination of Tropo and 2-Edge. The propagation mode of Tropospheric scatter is always present, but ordinarily the path is so attenuated that such signals are not seen. If this is the case, 2-Edge propagation combined with Tropo scatter may provide multiple paths that combine to cause rapid frequency-selective signal fading. Tropospheric scatter alone often supports multiple varying paths, and even without 2-Edge propagation could be sufficient to cause such fading.

The image below is an excerpt from a recent TVfool report for this location with stations of interest WBNA-8 and WHAS-11 marked.

http://forum.tvfool.com/attachment.php?attachmentid=584&d=1376059588

In 2013, an opportunity arose to replicate the above antenna configuration and observe some of the signal spectrum characteristics with a Sencore SLM1456CM. The graph below illustrates the signal fluctuation.

Notes for graph, below:

- Mid-morning, sunny day, May 9, 2013
- Measurements taken at tower top
- Long-Yagi mounted at top of main tower mast
- Homebrew ferrite balun
- Homebrew pHEMT preamp with power inserter.

http://forum.tvfool.com/attachment.php?attachmentid=585&d=1376059603

The frequency selective signal fading is evident at the upper portion of the 6 MHz spectrum, at about 203 MHz. Relative to Sample 1, the signal level of sample 2 shows a fade of approximately 25 dB.

.

[Pete Higgins]

tripelo,

Another interesting read.


Listened to radio shows such as: Dragnet, Suspense Theater, Gunsmoke, and the Lone Ranger.

You may have listened to the Lone Ranger but I bet you don’t still have a Hopalong Cassidy wristwatch!

I was discouraged by ADTech’s findings with his LNA-200. He’s very up-front about his test equipment and the constraints of his test environment, so even if they are contributors to his absolute measurements, his relative findings are invaluable. He had previously mentioned testing an RCA TVPRAMP1R amplifier and posted his findings for me. Like most others, it didn’t quite meet advertised but was many dB’s closer than some designs that I already own. I ordered one last week (for $22.80 delivered!) and in my environment it didn’t show any signs of overload. Subjectively, my SNR’s seem better with the RCA than with either of my Winegards. I posted his information and my results in a new thread titled “RCA TVPRAMP1R Amplifier” @ {http://forum.tvfool.com/showthread.php?t=13530 (http://forum.tvfool.com/showthread.php?t=13530)} if you want to take a look. Last night, I ordered a second one to try with my tower array.

[tripelo]

The signals from a single long-Yagi (http://forum.tvfool.com/showpost.php?p=37565&postcount=51) were observed for a few days. Then, in October 2010, a second long-Yagi was installed on the main tower mast.

The second Yagi was installed 89 inches below the top Yagi. Before the antennas were combined, signal levels were observed on a Blonder Tongue FSM-11 signal level meter. Snap-on connectors were temporarily installed to allow quick switching of the preamplifier (RC-9267) between antennas. There was some indication that the signal level from the top Yagi was stronger than the Yagi at the lowest position. Again, as with the single Yagi, signal variation could have masked any real differences in the average signal levels.

Satisfied the antennas were performing normally, both antennas were connected to an Antronix CMC-2002U splitter (reversed, as a combiner). Signal indications on the FSM-11 showed an increase above that obtained separately from either antenna.

The antennas and connections were secured in their final positions. The configuration:

- Two long-Yagis stacked 89 inches apart.
- Two selected Philmore MT-74 baluns
- Antronix CMC-2002U combiner &
- Research Communications Preamp (RC-9267) mounted between antennas
- Suitable lengths RG-6 cable with custom connectors.

Below is an image of the antennas at the main tower.

http://forum.tvfool.com/attachment.php?attachmentid=590&d=1376667264

Reception was monitored inside the house using a Channel Master CM-7000 converter. Reception of WBNA-8 was good with occasional pixellation. WHAS-11 reception seemed to be improved with the antenna stack compared to the single antenna. WHAS-11 reception was good except there were some dropouts in the troublesome daytime hours. The dropouts were less frequent than seen either at the test location with both antennas stacked, or with the single Yagi at the tower top.

Interesting: The depths of frequency selective fading (http://forum.tvfool.com/showpost.php?p=37565&postcount=51),seen with the single Yagi, imply that gains in signal strength alone would not be sufficient to overcome the effects of the deep fades. Clearly, a 25 dB selective fade could not be mitigated by a 3 dB increase in signal strength (in reality, stack gain is likely less than 3 dB). Those fades shown in the spectrum (earlier) were not difficult to capture, meaning they were fairly frequent during daylight hours. With the stack of two antennas, the fades were less noticeable. The fades continued to exist but were more difficult to capture via the FSM-11. The equalizer in the tuner demodulator can mitigate the effects of some fades, but equalizers have a limited range. One limit being that the signal level at the depth of the fade must remain above the minimum required for DTV detection (~15 dB S/N) --there are other limits. It seems likely the stack of antennas provided something more than merely an increase in signal strength (theoretical ~ 3 dB).

In 2013, an opportunity arose to nearly replicate the above antenna configuration and observe some of the signal spectrum characteristics with a Sencore SLM1456CM. The graph below illustrates the signal fluctuation.

Notes for graph, below:

- Mid-morning; sunny day; May 10, 2013
- Two Long-Yagi, stacked @ 89 inches, mounted at top of main tower mast
- Homebrew ferrite balun
- Homebrew combiner (transmission line type)
- Homebrew pHEMT preamp with power inserter.
- Measurements taken in house, at converter input
- Signal conditioned: attenuator, filters, UVSJ, industrial drop amplifier, attenuator

http://forum.tvfool.com/attachment.php?attachmentid=591&d=1376667713

Frequency selective signal fading is evident at the mid- portion of the spectrum, at about 200 MHz. Relative to Sample 1, the signal level of Sample 2 shows a fade of approximately 10 dB. The fading depth of ~25 dB (as shown earlier) has not yet been observed with the two antenna stack.

Reception Summary (At end of year 2010):

WBNA-8: Acceptable at all hours of the day.

WHAS-11: Near flawless during evening hours through early morning hours. During daylight hours; could be considered acceptable, but occasional loss-of-lock remains.

.

[Pete Higgins]

tripelo,

That’s a lot of separation between your long Yagi’s. Do you think that ~1.5 wavelengths of spatial diversity is mitigating your frequency selective fading? It would certainly help explain improvements in excess of simple combining gain.

I received my second RCA preamplifier on Monday. I dropped my tower and removed the PCT MA2-M’s from my 91XG and from my Antennacraft Y10 7-13. I made up new antenna cables w/boots and installed the RCA TVPRAMP1R amplifier on the mast midway between the two TV antennas. I configured it for separate inputs with the FM trap selected.

I decided to use the supplied power supply/inserter. The run from the garage to the amplifier is ~125’ through copper coated steel RG-6 so I was expecting I might encounter too much voltage drop. Turns out, it works just fine. The RCA draws <80 ma and my 3 PCT MA2-M’s were drawing almost ten times as much.

My Winegard AP-2870 overloaded with my 8-Bays on my push-up mast, but it overloaded a lot worse on the tower with the 91XG /Y10 7-13, so I was half way expecting the RCA might overload on the tower as well. No such luck. Since I installed it, it’s been rock stable with no signs of overload what so ever. When I was first setting up my system, because of the big price difference, I never would have considered buying the much cheaper RCA amplifiers. Just goes to show ya!

Subjectively, I think the RCA is outperforming the PCT drop amps. especially on VHF. Rescanning I’m picking up 1 low VHF channel, 1 high VHF channel and several UHF channels that I haven’t received in the past. Of course I’ll have to learn new languages to understand some of them. The RCA is specified to have 1 dB more gain on VHF & 7-8 dB more on UHF so that could be the reason with my long cable runs. The PCT’s are specified to have a Noise Figure of 2.7 dB (avg.) & 4.0 dB (max) with no distinction between VHF & UHF so it could be that I’m seeing a NF advantage. My main concern was with overload from my two strong local stations. So far, neither RCA amp. has exhibited any signs of overload. In the same situation, both of my Winegard’s (AP-2870 dual input & HDP-269 single input) displayed debilitating overload. I would sure like to know where the 1 dB compression point is reached with this design.

Looking forward to your next post.

Edit:

I calibrated my NTE/ECG U-106 rotor mid July. When I turned it to 090 deg. to drop the tower I noticed the array was pointing ~110 deg. I parked it so the antennas would be pointing straight up, lowered the tower and made my changes. After I raised the tower I had to recalibrate the rotor again. I’m not impressed with the accuracy of these 3-wire rotors. My 40-50 year old 5-wire rotors always point where they say they are pointing.

[tripelo]

...The RCA draws <80 ma and my 3 PCT MA2-M’s were drawing almost ten times as much...

Yes, the drop amplifiers use more current. The regulators are more conservatively designed. And, all things being equal (which they seldom are), high dynamic range amplifiers consume more power.

My Winegard AP-2870 overloaded ...expecting the RCA might overload on the tower as well. No such luck. ... no signs of overload

That is a bit puzzling. The Winegard preamplifiers that I have scrutinized are, in principle, not much different than the RCA design appears to be. Both use BJT, bipolar junction transistors. Might expect a few dB difference in overload characteristics but not many dB.

Subjectively, I think the RCA is outperforming the PCT drop amps. ... I would sure like to know where the 1 dB compression point is reached with this design.

It appears to be similar to the original CM-7778, and by extension it would be similar to the CM-7777. Both CM's are about as good as one could expect for single-ended BJT designs. But, neither would be considered outstanding in terms of high dynamic range.

...I calibrated my NTE/ECG U-106 ... I’m not impressed with the accuracy of these 3-wire rotors. My 40-50 year old 5-wire rotors always point where they say they are pointing.

Yes. The more mass the three wire rotors have to rotate, the more frequently they become uncalibrated. As you know, the principle involves two synchronous motors (one in the control and one on the mast) that rotate at about the same speed, no feedback loop for correction. Problem is that the mast motor runs slower.

Do you think that ~1.5 wavelengths of spatial diversity is mitigating your frequency selective fading? It would certainly help explain improvements in excess of simple combining gain.

That is good thinking.

The antenna spacing of 1.5 wavelengths is sufficient to provide a signal path that is at least partially independent (not completely correlated with the other antenna). Independent, or at least partially independent paths are necessary for diversity gain.

It seems, with this configuration, there are some difficulties with realizing true space diversity, because of the method of combining the two antennas.

Maybe more thoughts on this later.

[Pete Higgins]

tripelo,

I’m not sure that the programmable “digital display” 3-wire rotors employ two synchronous motors (one in the control and one on the mast).

From what I’ve been able to gather, the control unit has a counting or “timing ckt.” that calibrates itself to the time of travel from 360 deg. to 0 deg. My calibration procedure involves running the antenna motor full CW until it is at the end of its travel and the display reads 36 (360 deg.) and then pressing the “INITIAL” button.

When it gets really badly out of sync, I have to reset the control box several times to just get the array to point north. I’ve had the digital display read over 40 before reaching the CW end of the rotors travel. The control unit then returns the rotor CCW to 0 deg. to complete its calibration. If I run it back around CW the display shows 36 and the rotor is back to the end of its CW travel.

I do hear a slight hum whether the rotor is running or not and a relay click when the rotor starts or stops turning. I haven’t tried to take the control box apart to look for a separate motor but that sounds like a good indoor project on these 100 deg. days.

[tripelo]

I’m not sure that the programmable “digital display” 3-wire rotors employ two synchronous motors (one in the control and one on the mast).

Yes, I'm not sure either.

From what I’ve been able to gather, the control unit has a counting or “timing ckt.” that calibrates itself to the time of travel from 360 deg. to 0 deg...

The well-known Channel Master rotator and clones essentially use the synchronous motor in the control as a timer. So, it could be in newer units that a timing function is implemented in a smaller or less costly circuit.

When it gets really badly out of sync,...I’ve had the digital display read over 40 before reaching the CW end of the rotors travel. ...

I do hear a slight hum ...that sounds like a good indoor project on these 100 deg. days.

Yes, for the curious mind there is always a project.

Seems unlikely that a timing motor would be used with a digital indicator, when a timing circuit could be smaller and probably less expensive.

I haven't used, or looked at circuits of, any of the newer digital indicator rotators, so my comments are speculation.

[tripelo]

Following up on a partial response (http://forum.tvfool.com/showpost.php?p=37726&postcount=55) to Pete’s thought provoking question as to whether space diversity gain could be a mechanism for alleviating frequency selective fading (http://forum.tvfool.com/showpost.php?p=37565&postcount=51), presumably originating as a result of multipath.

That’s a lot of separation between your long Yagi’s. Do you think that ~1.5 wavelengths of spatial diversity is mitigating your frequency selective fading?

The writing below is an opinion, subject to revision.

There are several methods of combining two or more independent signals to achieve diversity gain. The list below represents some techniques, but is not a complete list.

Wikipedia was consulted for some of the diversity combining names (http://en.wikipedia.org/wiki/Diversity_combining).

1. Maximal Ratio or Ratio Squared
2. Equal Gain
3. Switched
4. Selection or Scanning
5. Other

Maximal Ratio or Ratio Squared: The gain applied to each signal is determined by the S/N ratio of each signal. Higher S/N signals are increased in gain relative to low S/N signals, then combined.

Equal Gain: The signals are phase shifted into alignment and added without altering gain of either signal

Switched: The receiver uses only one signal until the signal becomes essentially unusable or drops below a fixed threshold, then switches to the other signal.

Selection: Signal strength of each separate path is evaluated; only the strongest signal is used.

Other: Other methods have been devised, depending on field of application. An example for TV might include post-detection combination of the video from each separate antenna or path. This method requires separate tuners with timing and delay hardware suitable to align two independent video streams; then combining based on some of the principles suggested by the above techniques.

Combining in a summation/additive device such as a splitter (reversed), hybrid combiner, or transmission line combiner, does not fit into any of the above categories. These directly additive combinations make no allowances for either phase or amplitude adjustment before combination. Having no means of modifying the signals before addition permits potential destructive interference between signals to continue. The main reason multipath is a problem in reception is destructive interference.

Destructive interference arises when signals add in such a way as to reduce signal strength. Electromagnetic (RF) signals are characterized by magnitude (amplitude) and phase; they add according to principles of vector addition.

Examples:

1. Two signals of near equal amplitude and nearly 180 degrees phase shifted relative each other, add to nearly zero amplitude.

2. Equal strength signals with less than 180 degrees relative phase shift can interfere with each other (depending on amount of phase shift) , but not complete cancellation.

3. Signals that are 180 degrees out of phase with unequal amplitudes interfere with each other, but do not completely null to zero.

There are many possibilities in between those of the preceding examples where two or more signals add to a sum (amplitude) that is lesser than the amplitude of either signal alone.

The summation of two antennas (in a stack arrangement) essentially increases the antenna aperture. Antenna aperture is the effective area in space over which signals are intercepted. In special cases such aperture increases could alleviate mutlipath effects by intercepting better quality signals. If so, this is a matter of aperture placement rather than diversity gain. If the multipath effects are random and equally distributed in space, then a larger aperture will not produce diversity gain.

An increase in aperture usually means a decrease in antenna beam width. Decreases in beam width may eliminate or reduce some potential multipath signals. (More on this later)

It appears, the additive combination of two antennas does not eliminate (through the mechanisms of diversity) the potential for the destructive signal combinations resulting from multipath signals.

.

[Pete Higgins]

tripelo,

Interesting: The depths of frequency selective fading, seen with the single Yagi, imply that gains in signal strength alone would not be sufficient to overcome the effects of the deep fades. Clearly, a 25 dB selective fade could not be mitigated by a 3 dB increase in signal strength (in reality, stack gain is likely less than 3 dB).

From the little bit of reading I’ve done on the subject, VHF is more prone to rapidly-changing multipath conditions than UHF although the new demodulators with long equalization spans have dramatically reduced multipath effect, both static and dynamic for 8-VSB reception.

None the less, your early sample 2 data showed ~25 dB of what appears to be frequency selective fading evident at the upper portion of the 6 MHz channel 11 spectrum. Assuming your test setup was undisturbed between samples, I think the apparent loss of signal has to be attributed to some mechanism external to your test setup. In my experience frequency selective fading (when neither the transmitter nor the receiver is moving) is generally due to destructive interference from multi-path causing cancellation of certain frequencies at the antenna. For high VHF & UHF, which are usually received via a LOS mechanism, this is typically from reflections off the ground and nearby objects.

For WHAS-11, using 984’ (300m) Tx antenna height and guessing your tower @ ~65’ I get a line-of-sight path of roughly <50 miles. I reasoned that when there isn't a line-of-sight path between transmitter and receiver the signal has to be both diffracted and reflected along multiple paths before finally reaching your array. I expect some signal arrives via tropospheric scattering due to changes in temperature, humidity and barometric pressure causing slight changes in the refractive index although I’m not sure that would in and of itself explain short term selective fading.

In any case, each of these arrival mechanisms introduces signal anomalies that can destructively interfere with one another at the aperture of a receiving antenna. With a single antenna or two closely spaced antennas, I would expect little difference in coherence of the arriving signal(s) yielding a theoretical overall 3dB stronger signal, but, exhibiting the same overall characteristics (frequency response). By coherently combining two separate apertures spaced ~1.5 wavelengths apart, however, I would expect slightly lower overall gain reflecting a summation of all the different paths coherently combining at the antennas. The phase differences causing frequency selective fading at one antenna would in effect be mitigated by the arrival phase at the other antenna.

From WikipediA:
Antenna diversity, also known as space diversity, is any one of several wireless diversity schemes that uses two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and indoor environments, there is no clear line-of-sight (LOS) between transmitter and receiver. Instead the signal is reflected along multiple paths before finally being received. Each of these bounces can introduce phase shifts, time delays, attenuations, and distortions that can destructively interfere with one another at the aperture of the receiving antenna.

Spatial diversity employs multiple antennas, usually with the same characteristics, that are physically separated from one another. Depending upon the expected incidence of the incoming signal, sometimes a space on the order of a wavelength is sufficient. Other times much larger distances are needed…

I guess my thinking is that if your frequency selective fading data is the result of multipath signals arriving out of phase at a single antennas aperture, combining two antennas narrows the aperture (beam width) eliminating some portion of the fade contributor. Additionally, with 1.5 wavelengths spacing, you have signal arrival from different paths at each antenna. As one antenna receives frequency selective out of phase signals (a fade) there is a good probability that the other antenna will receive in-phase signals, mitigating the depth of the fade. If that mitigation is sufficient to keep you above the detection threshold the equalizer can do its job, further minimizing the fade effect on reception.

It will be interesting to see what you postulate in your next installment.

[tripelo]

Thanks Pete, for your thoughts and comments.

Probably soon, more can be written about space diversity.

Would like to explore antenna elevation pattern discrimination as it applies to long distance multipath.

[tripelo]

Elevation angle discrimination is a possible mechanism allowing this vertical stack (http://forum.tvfool.com/showpost.php?p=37723&postcount=53) to reduce frequency dependent nulls (http://forum.tvfool.com/showpost.php?p=37565&postcount=51), presumably a result of multipath. Elevation angle discrimination depends on the elevation beam width of the combined antennas. The antenna’s elevation pattern also depends on height above ground.

Elevation angles of reception have importance in that signals from distances beyond the horizon can arrive at different angles with respect to the horizon. Communications research indicates, in general, lower angles near the horizon are favored for long distance reception. This may particularly apply to long distance TV reception because broadcast transmit antennas are designed to ensure maximum radiation is below the horizon (negative elevation angles). In general, full-power broadcast antennas have a narrow vertical beam width and also incorporate downward beam-tilt. With narrow vertical beam patterns and beam-tilt, the transmitted signal strength decreases rapidly for angles above the horizon.

At the receiving antenna, the effects of the ground reflections cause great attenuation at an angle of zero elevation degrees. This is due to the reflected signal being 180 out-of-phase with respect to the direct signal, and cancellation occurs.

Two conditions are necessary for a vertical stack of receiving antennas to achieve both a low angle and narrow elevation beam width:

A. Height above ground of several wavelengths
B. Large stacking separation

Computer simulations with 4NEC2 software (http://www.qsl.net/4nec2/)provides for graphing the vertical beam pattern of antennas. The horizon is shown on the 4NEC2 graphs as 90 degrees. The image below shows on the left, the upper half-pattern in free space of a single long-Yagi (http://forum.tvfool.com/showpost.php?p=37565&postcount=51); overlaid is a stack at 89 inches (http://forum.tvfool.com/showpost.php?p=37723&postcount=53).

The second pattern, on the right side, shows the response of one long-Yagi at 64 feet that is overlaid with a stack at 60.5 feet (60.5 feet is the average height of the stack). This pattern shows multiple nulls or minimas, these arise from ground reflections being out of phase with the direct signals. The presence of ground also produces additional ~6dB antenna gain at vertical angles where the reflection adds in phase with the direct signal.


http://forum.tvfool.com/attachment.php?attachmentid=602&d=1377293565

It can be seen that the antenna stack has increased gain at lower angles. This could help the problem of frequency selective fade. The rationale is; for both tropospheric scatter (tropo) signals as well as 2-Edge signals (if the nearest edge is relatively far away), the major signals arrive at lower angles. Since the troposphere reaches to ~6 miles in height, tropo can have many paths, with some signals arriving at higher angles. For higher angles, the signal must travel greater distances and may be out of phase with the low-angle & earlier signals. The stacked antennas provide some angle-of-arrival discrimination for elevation angles greater than about 1.2 degrees (88.8 degrees on the graph).

To estimate how much rejection may be required to improve a deep signal fade (null). The sum of two signals can be calculated using vector addition. It can be visualized that the sum two equal vectors at, or near, 180 degrees out of phase with respect to each other, add to near zero.

Suppose the desired, or direct, signal had amplitude of +1 Volt, and a multipath signal had equal or lesser value of amplitude, but was 180 degrees out of phase (-1) with the desired signal.

As examples, to the direct signal add decreasing magnitudes of a multipath signal:

+1 added to –1 = 0
+1 added to –0.95 = 0.05 (26 dB below a Voltage of 1 Volt)
+1 added to –0.90 = 0.10 (20 dB below a Voltage of 1 Volt)

In above, dB=20 x [Log10(Volts)]

Changing the multipath signal magnitude from 0.95 to 0.90 results in a ~6 dB improvement in the combination. In terms of dB rejection relative to desired:

Magnitudes of Multipath and dB Rejection

0.95 = 0.45 dB (relative to desired),
0.90 = 0.92 dB (relative to desired)

Difference = -0.47 dB

A multipath reduction of 0.47 dB, relative to desired signal, improved combined signal ~6 dB (26 dB to 20 dB).

As the amplitude of one of the vectors becomes smaller than the other, then the magnitude of their combination rapidly increases. The image below graphically shows the result of combining two signals arriving; one of them 180 degrees out-of-phase with respect to the other.


http://forum.tvfool.com/attachment.php?attachmentid=603&d=1377293703

In the graph, as an example observe the curve at 25 dB. A 25 dB null can occur if the reflected signal has amplitude that is only ~0.5 dB lower than the direct signal. The greater the difference in amplitudes of the two signals, then the shallower the null will be. For example if the multipath signal is about ~10 dB weaker than the direct signal, then the combination may be reduced about 3 dB.

It can be seen that the deep nulls (say 25 dB) are sensitive to small changes in amplitude of the direct and multipath signals. The image below shows sensitivity to multipath signal changes of 0.25 dB relative to the direct signal.


http://forum.tvfool.com/attachment.php?attachmentid=604&d=1377293764


In the chart immediately above, for an initial ~ 25 dB combined cancellation or null, if one could decrease the multipath signal by 0.25 dB, there could be an improvement in the combined signal of ~3 dB. If the initial combined null depth is ~10 dB, this improvement diminishes to ~0.5 dB improvement for a 0.25 dB multipath amplitude reduction. That is more than a 2 for 1 reduction in destructive interference for every 0.25 dB rejection of the out-of phase (multipath) signals. So, it appears that relatively modest amounts of signal discrimination can result is appreciable improvement for the combined (desired) signal.

In this case, the low angles are of most interest. The image below shows an expanded view of the elevation patterns shown in the first image above. The stacked antennas have increased gain, but in order to compare vertical patterns responses, the single antenna and the stacked antennas are shown with both patterns normalized. For convenience, the vertical angle is shown as degrees above the horizon.


http://forum.tvfool.com/attachment.php?attachmentid=605&d=1377293773

It can be seen that for angles above about 2 degrees, the stack has at least 0.5 dB discrimination compared to the single antenna. On average, higher angle-of-arrival signals above 2 degrees are rapidly decreased due to the narrow elevation response of the stack.

Summary

If an appreciable fraction of multipath signals arrive at higher angles than the desired (often most direct path) then a relatively small rejection of multipath can yield an appreciable improvement in multipath null depth. It follows that vertically stacked antennas at sufficient height (AGL) and relatively wide spacing could be advantageous for rejection of multipath signals.

.

[Pete Higgins]

tripelo,

WOW! I don’t even want to know how long it took you to pull all this all together! I just hope you’re not going to bill me for it later?

This is great work and way beyond my ability to provide for the community; essential information for anybody considering multiple, same band, antennas. In addition to the expected <3 dB combining gain you’ve illustrated the importance antenna spacing can play. Again, clear concise and to the point.

I have a pretty good handle on LOS propagation and refraction extending the range to the “radio horizon”, multipath and even the “wavelet” concept that explains why we can receive diffracted signals that simple insight would suggest should be completely blocked. I even have a handle on how differences in the troposphere (temperature, water vapor, barometric pressure etc.) can cause tropospheric scattering. What I have trouble rapping my head around is which mechanism is responsible for what I see as channels fade both short term (multi-path?) & for hours at a time (tropospheric absorption?). I’m sure it has to be the “vector sum” of all these simultaneous mechanisms. I’m tempted to get a decent rotor and weld a plate into the top of my tower to support a “long mast“ and another 91XG. Other than it should work better though, I’m not really sure what to expect without trying it.

Those two RCA pre-amps. that I reported on worked out so well that my wife got after me to order two more. Ordered on Monday and received today. Since Time Warner blacked out CBS & CBS blocked Time Warner customers from downloading content (series episodes) from their website, my wife & I’ve been able to watch them from either San Diego or LA. I have also been able to let her watch the LA CBS evening news which she really prefers. Since I turned 70 last month, I had to go to the CA DMV and retake my driver’s license and motorcycle operator’s tests this afternoon so still need to bench check them tonight or tomorrow. I must have ordered two of the last ones because when I went back to the site they no longer list them.

Looking forward to your next post.

[tripelo]

...What I have trouble rapping my head around is which mechanism is responsible for what I see as channels fade both short term (multi-path?) & for hours at a time (tropospheric absorption?)...

Multipath is difficult to counter because of the variety of sources that can cause it. Multipath is the main reason that mobile TV is not very practical for 8VSB (the US DTV standard).

It can be difficult to distinguish between multipath and direct signal fade.

There can be two classes of multipath:

1. Static Multipath (resulting from fixed objects)
2. Dynamic Multipath (resulting from moving objects)

Static or long term signal attenuation can result from multipath, when the multipath sources are stable (fixed). Examples could be reflections off a building or a fixed object that partially cancel the direct or desired signal. One prominent contributor is the surface the earth. As can be seen in the previous vertical antenna patterns (http://forum.tvfool.com/showpost.php?p=37864&postcount=61), for specific angles-of-arrival, a ground reflection can cause a static fade.

Dynamic of fast fading (in minutes or seconds) is usually the result of multipath (Doppler effects). For Doppler to occur, something has to be moving such as antenna moving (Mobile TV).

For fixed antennas the something could be;

- Traffic in a city,
- An airplane flying over,
- Trees moving in the wind,
- Atmospheric motion (tropo scatter), or
- Something else.

For long distance reception, the atmosphere is the most likely ‘something’ that causes Doppler.

---------------------------------------------
Daytime Signal Fade (Independent of Multipath)

Gradual bending allows radio signals to somewhat follow the earth’s curvature for some distance beyond normal line-of-sight. This gradual bending is somewhat independent of phenomenon like ‘tropo scatter’. As you know, long distance TV signals can fade (reduce in strength) in daylight hours. This can be due to smaller temperature gradients that result when the sun uniformly heats the air in the lower atmosphere during much of daytime hours. Smaller temperature gradients result in less bending of the signals back towards the surface, thus the daytime fade.

Note: Temperature is not the end cause of the bending of RF signals. Temperature is a measure of one particular driving factor (thermal energy) that can decrease atmospheric density, thus affecting the density of everything contained in the atmosphere (water vapor, etc).

---------------------------------------------

… RCA pre-amps...have ordered two of the last ones because when I went back to the site they no longer list them.

Maybe your good reports caused a run on the RCA preamplifiers. Well, it was/is petty good deal.

... I just hope you’re not going to bill me for it later?

Thanks for your comments about the elevation beamwidth and multipath.

No charge.

.

[Pete Higgins]

tripelo,

I liked your explanation of how uniform daytime heating can produce smaller temperature gradients, limiting how far out a refracted signal travels. I know it happens because I frequently see it but I hadn’t thought it through to that point. Thanks.

Well, I configured my two new amps. for separate inputs & FM trap IN (default) and got outside before it got too hot (only 82 deg. when I finished) to check them. The first one I tried, I lost all the of VHF signals but UHF was fine. I thought I might be experiencing a temporary fade. I pulled it down and tried the second one. VHF & UHF worked great.

Back to the roof to swap them out again & high VHF was gone. I left it in –line and went back up and switched it to “combined”. To my surprise high VHF was restored. Unfortunately, the UHF antenna is my CM-4228 which has been shown to have a fairly good high VHF response. In any case, signal to noise ratio was restored to the same level as with the other two amps. so if I were to guess it was seeing the signal from my Winegard YA1713. Need to explore further to determine if the VHF port is left connected when the amp. is switched to the combined position. Finally, I tried switching back to “separate” and left the switch ~1/16” from the end of its travel. VHF & UHF signals were both restored to the SNR levels I saw with the other two amps. Presumably, this amp has a bad switch. It has enough friction that I think it will hold where I need to set it so I left it there. If it doesn’t hold I think it would be easier to replace the switch with jumpers than to try and send it back. I have a soldering station with a vacuum pump so pulling the switch is easy. I guess I should be happy that only one out of four had a minor problem?

[Stereocraig]

Pete,
I would also opt for jumpers.
Not sure I'd bother w/ removal of the switch, though.

[tripelo]

Continuing with a previous topic: Multipath: Antenna Stack & Diversity Gain? (http://forum.tvfool.com/showpost.php?p=37734&postcount=58)

The following is a thought experiment.

Consider multipath effects to be the sum of only two signals, the desired or direct signal (D) and the multipath signal (M).

For a sum (combination) signal to experience a deep null (say 25 dB (http://forum.tvfool.com/showpost.php?p=37565&postcount=51)), the two signals must arrive at the antenna aperture nearly 180 degrees out of phase and nearly equal in amplitude.

Let D and M represent the frontal area of signals propagating through space.

Constraints on D and M:

1. Equal Frontal Area: Size is less than, or equal, that of a single antenna aperture.

2. M = - D, or Integrated Field Strength of Multipath = negative Direct


http://forum.tvfool.com/attachment.php?attachmentid=614&d=1377880087


In the image above, for a single antenna there is one combination that yields a null. That is; Both signals arrive at the antenna. For the stack there are 3 distinct combinations adding to a null. These 3 combinations are; both signals arrive at the center of the stack, or one signal arrives at the upper antenna and the other signal arrives at the lower antenna (2 ways).

Consider larger frontal areas, with larger integrated field strength:

1. One frontal area larger than stack aperture.

A. Direct signal frontal area greater than the stack aperture.

Nulls could not occur at the stack aperture because the Multipath would not be sufficient to cancel the larger Direct signal.

If frontal area of direct signal could be larger than the stack aperture, then the inverse could occur.

B. Multipath signal frontal area greater than the stack aperture.

Nulls could not occur at the stack aperture because the Direct would not be sufficient to cancel the larger Multipath. Multipath would dominate.

2. Both Direct and Multipath frontal areas larger in area than the stack aperture.

In this latter case, the larger stack aperture could be considered as a single antenna and would have no multipath advantage over the smaller antenna aperture.

There are uncountable combinations of direct and multipath signals, large and small frontal areas with varying amplitudes and phases. Most combinations would not result in large cancellations or deep nulls. When deep nulls result from combinations, mostly they could be analyzed as described above.

In the image, the stack has twice the aperture of the single antenna. This increased aperture allows more signal combinations. If the number of signal combinations were directly proportional to the aperture size, then a stack could have twice as many combinations as a single antenna. For the stack; 2 times possible combinations there could be 3 times as many null-generating combinations. Statistically, this represents an increase in proportion of null-generating events.

Very wide spacing, with a large gap between apertures could eliminate the possibility of both Direct and Multipath combining at the center of apertures. That could reduce the possible number of null-generating combinations at the stack from 3 to 2. Thus, very wide spacing could allow stack performance to be similar to that of a single antenna.

Unless the statistics of the Direct or Multipath signals changed, then wider, or different spacing of the stack would not greatly improve the above scenario. If widely spaced locations were found for one antenna where the Direct signal had better statistics relative to Mutipath, then positioning both antennas in those regions could provide even better results. But, that would appear to be a matter of optimal antenna positioning instead of diversity gain.

Note:

With normally stacked antennas a combiner cannot take advantage, or mitigate the effects, of the differing phases of separate antenna signals. To mitigate multipath or to take full advantage of signals arriving with differing phase, a combining system must provide a means to either; synchronize the phase of separate antenna signals if combined pre-detection, or neglect phase if combined post-detection.


Summary

Considering information in the earlier post (http://forum.tvfool.com/showpost.php?p=37734&postcount=58), it seems difficult to rationalize that an antenna stack provides diversity gain against multipath.

Absent a plausible mechanism, one could conclude:

Against Multipath: Stacking antennas does not provide diversity gain.

.

[tripelo]

The reception of WHAS-11 using the stack of long-Yagis (http://forum.tvfool.com/showpost.php?p=37723&postcount=53) was evaluated through the end of 2010 and into 2011.

Most of the time the signal strength seemed sufficient. It appeared that multipath was the main cause of occasional loss-of-lock in the daytime hours. Since multipath seemed likely as the cause, there was a possibility that differences in a DTV receiver’s equalizer could affect the situation.

Previous testing and TV viewing utilized a Channel Master CM-7000 set-top box. A comparison between two available converter boxes was made. The two other converters were Apex DT-250A and Magnavox TB110MWG. Each converter was connected to the antenna/TV combination and WHAS-11 was viewed for several minutes, then the CM-7000 was installed. This process was repeated multiple times over a period of two days. The visual display of loss-of-lock and picture pixelation was different, but there was no clear difference in overall performance.

Later in 2011, two other converters were tested. These were Digital Stream DTX-9900 and Zentih/Insignia NS/DXA-1. This time the tests were conducted in parallel, using a Holland GHS-2 splitter, both converters feeding separate monitors were operated from the same antenna. There was very little difference in visual performance. When a dropout occurred with one converter, nearly simultaneous a dropout appeared on the other converter. If there was any advantage, it went to the CM-7000. With the CM-7000, there seemed to be a very slight audio advantage, providing maybe a syllable more, either before dropout, or recovering early sometimes.

A search of literature, as to whether different converter boxes had appreciably different approaches to equalization, yielded the following report:

NAB/MSTV Digital Converter Box Evaluation – December 2008

http://www.nabfastroad.org/NABSTVDigitalConverterBoxEvaluation/Converter_Box_report.doc.pdf

In the above report, the performance of some set top boxes were evaluated. The Sansonic FT-300A appeared better able to handle both the longest delayed echos and the most advanced echos (+50 uS & - 50 uS).

Also, the “Pilot-nulled multipath threshold of visible (TOV)” test showed the Sansonic FT-300A to be 0.5 dB better than any of the other 6 converters tested.

The following image was drawn from data available in the above referenced report (http://www.nabfastroad.org/NABSTVDigitalConverterBoxEvaluation/Converter_Box_report.doc.pdf).


http://forum.tvfool.com/attachment.php?attachmentid=620&d=1378475348

That 0.5 dB differential (left portion of above image, W Acq) for pilot nulling might not seem like much improvement. But if the pilot signal is lost, the system will lose lock. The pilot is located at the low frequency end of the 6 MHz DTV spectrum and is a fundamental synchronizing signal. A multipath signal could cause a frequency dependent null to severely attenuate the pilot. Recall, that 0.5 dB rejection of multipath can improve null depth up to about 6 dB (http://forum.tvfool.com/showpost.php?p=37864&postcount=61). This means that the Sansonic unit was probably handling a worse pilot degradation than indicated by the 0.5 dB difference in applied signal.

A Sansonic FT-300A unit was purchased.

A simultaneous parallel comparison to the CM-7000 was arranged as described above. The CM-7000 lost lock a few times over the test period covering parts of several days, but the Sansonic unit provided solid reception.

The report above provided the identification of tuners and demodulators in the converters used in the test. Sansonic used a Microtune MT2131F tuner and an Auvitek AU8515AA demodulator. These components are different than any of the other test converters, they are also different than those used in the CM-7000.

Other testing confirmed that when a low noise moderate-to-high gain preamplifier is used, the tuner sensitivity is not a crucial factor in reception. So, the Sansonic tuner was probably not the critical part that contributed to better handling of multipath. The equalizer function is the likely reason for good performance and it is undoubtedly associated with the AU8515AA demodulator.

A search for more a commonly available converter that included the AU8515AA demodulator turned up Zinwell. Several Zinwell units were purchased including: ZAT-950A, ZAT-970A, newer versions labeled ZAT-970A on outside with ZAT-950 components inside. A visual inspection revealed all Zinwell units (made at that time) had the AU8515AA demodulator. Of the Zinwell units, some had can tuners (Sanyo) and some with silicon tuners (Microtune).

Simultaneous parallel tests of the Zinwell’s against the CM-7000 and the Sansonic were arranged as described above. The CM-7000 lost lock several times over the test period (covering parts of several days). The Sansonic unit and all the Zinwell units provided solid reception. Then, the Sansonic was compared against the Zinwell units, performance was identical.


http://forum.tvfool.com/attachment.php?attachmentid=619&d=1378474486

A Zinwell unit was placed in service with the stack of 2 long Yagis.

Reception of WHAS-11 and WBNA-8 has been very satisfactory.

.

[Pete Higgins]

tripelo,

Two thought provoking posts in a row. Today’s almost sounds like a conclusion. I’ve been looking forward to these every Friday.

I bought one of Winegards new LNA-200’s. It didn’t work out nearly as well as I had hoped. You can check out my findings @:

http://www.digitalhome.ca/forum/showthread.php?p=1782361#post1782361 (http://www.digitalhome.ca/forum/showthread.php?p=1782361#post1782361)

Post 3688

[tripelo]

Two thought provoking posts in a row... I’ve been looking forward to these every Friday.

Thanks Pete. Glad you like.

...Today’s almost sounds like a conclusion...

Maybe close to a conclusion for the long Yagis. Additional work was done for reliability reasons and reduction of losses. Earlier briefly mentioned homebrew: ferrite core baluns, combiner, and preamp.

Probably change topics to some UHF related.

Will soon take a break for a few weeks to go to KY.

I bought one of Winegards new LNA-200’s. It didn’t work out nearly as well as I had hoped.

Thanks for your testing the Winegard LNA-200.

Sometimes there are many variables at a particular test location, then combined with equipment variables it takes some time to sort it out.

Have you opened the case of the LNA-200?

Could you take some detailed photos of the innards?

[Pete Higgins]

Tripelo,


Sometimes there are many variables at a particular test location, then combined with equipment variables it takes some time to sort it out.

For my first test, I substituted the LNA-200’s power inserter in the garage for the RCA’s and pulled two cables off the HDB8X RCA amp and connected them to the LNA-200 to minimize variables. Of course, with a single input, for the array test I had to add a UVSJ and an additional cable at the amp but used the original array lead-in RG-6.


Have you opened the case of the LNA-200?

No, but I will. The overnight low here was 78 deg. & it’s expected to climb to 103 deg. by mid-day. I start to get dizzy if I do a lot of climbing and spend too much time out in that kind of heat. It’s safer for me to wait for this heat wave to break. (I’d probably be OK but my wife would kill me)

Could you take some detailed photos of the innards? Will try to take & post. Probably next week.

[Pete Higgins]

tripelo,

Here is a link to my LNA-200 findings -with pictures.

http://forum.tvfool.com/showthread.php?t=13636

[tripelo]

A pair of UHF antennas were compared:

Antennas Direct 91XG and Televes DAT-75

Both antennas have built-in baluns.

Equipment used in the tests:

- Push-up sectioned mast with two ~5 ft. extensions
- Fifty feet RG6 quad shield coaxial cable (CATV grade)
- Sencore SLM1456CM (Digital signal level meter)

The Sencore 1456 can scan channels, after each channel is locked-on and signal strength and quality measured, it tunes to the next channel and repeats until all channels have been analyzed. The 1456 saves the results as normal computer files, they can be downloaded for later analysis.

Signal sources: Multiple DTV stations in the Dallas/Fort Worth area. All stations generally located at the same bearing with LOS at ~29 miles.

The center boom of each antenna was raised to a height of 25 feet above ground (AGL).

The following is an image of the antennas in the test positions:

http://forum.tvfool.com/attachment.php?attachmentid=626&d=1379075827

Test Sequence:

The tests were performed in mid-morning during a 2-day period. For each antenna test, the Sencore 1456 was allowed to scan available UHF stations three times. The first day there were 3 scans for each antenna for a total of 6 scans. On the 2nd day, the tests were repeated for 12 more scans.

A recording (run) consists of the SLM1456CM scanning the UHF band and recording the average signal strength (dBmV) for each channel.

Day 1: 3 consecutive runs with 91XG followed by 3 runs of DAT-75
Day 2: 3 consecutive runs with 91XG followed by 3 runs of DAT-75, then 3 consecutive runs with DAT-75 followed by 3 runs of xg-91.

In all, there were 3 sets of 3 scans for each antenna. Each scan took ~2-3 minutes. So the measurements were no more than 2-3 minutes apart

The results were downloaded and graphed in Excel. All 9 runs for each antenna were averaged together to yield a composite, shown here:

http://forum.tvfool.com/attachment.php?attachmentid=627&d=1379075841


Observing that the 91XG provided the overall highest received signal power, the difference was computed and graphed in the image below:


http://forum.tvfool.com/attachment.php?attachmentid=628&d=1379075849

The 91XG had about 1 dB more gain for the mid portion of the UHF band.
The two antennas were nearly equal at the lower channels.

These results can be rationalized as follows:

The DAT-75

- Large reflector & essentially a stacked pair of driven elements provide lower frequency gain.

- The 3-stack spacing becomes wider (in terms of wavelength) at upper frequencies, increasing gain.

The 91XG

- Colinear directors (X directors) and long boom length provide high gain thru the band.

.

[Pete Higgins]

tripelo,

I have never heard of the DAT-75 although if the 91XG held its own or performed better I guess it doesn’t matter. I compared my new 91XG to my ~40 year old CM-4228 last year and with two exceptions couldn’t tell any real difference. The 91XG did real well with CBS channel 43 (2.1) which TV Fool lists @ -112.4 dBm but had trouble with NBC channel 36 (4.1) which TV Fool lists @ -107.4 dBm. My CM-4228, and now my HDB-8X as well, almost always get channel 36 (4.1) but very rarely can get channel 43 (2.1). I even tried swapping the 91XG from the tower to the pushup mast and putting the CM-4228 on the tower with the same result. One of the reasons I tried the HDB-8X was to see if the differences in design would improve reception of channel 43. Other than the two channels mentioned I haven’t been able to find any significant difference between the three UHF antennas in terms of SNR’s delivered to my tuners. I don’t have a way to measure and graph signal strengths. My Samsung TV has a signal strength indicating bar graph, but sometimes one bar can give me a solid signal lock to watch and at others 3-4 bars can result in a picture that pixelates and freezes (i.e. one bar with a moderate SNR works better than 4 bars with a poor SNR).

[Pete Higgins]

tripelo,

I finally modified the satellite dish mount that I removed from one of my rentals and attached it to the west facing leg of my aluminum tower. Attached my one remaining RCA 5-wire rotor and with a short piece of schedule 80 PVC, my HDB8X 8-Bay Bow Tie. I angled it so that I can rotate the antenna between 169 deg. (the San Diego UHF stations) and 292 deg. (the LA UHF stations). Moving it ~15 feet north and being able to rotate it for maximum SNR gave me a 2-3 dB improvement in signal strength even though its physically 6-10 feet closer to the ground.

http://forum.tvfool.com/attachment.php?attachmentid=640&stc=1&d=1381102988

The HDB8X still won’t get channel 43 (CBS 2.1) but has channel 36 (NBC 4.1 & .2) as well as channel 31 (CW 5.1, .2 & .3) booming in (SNR’s ~ 28.5-.7). My 91XG on the tower is getting channel 43 with an SNR of 19.9 – 20 .5 but has channel 36 dropping in & out and jumping between 0 and 17.1 with lots of correctable errors. It does a little better with channel 31, holding a steady 21.1 with no errors. TV Fool lists channel 31 @ 2-Edge -103.8, channel 36 @ 1-Edge -107.7 and channel 43 @ 2-Edge -112.9.

The LNA-200 is wedged in place, mid-way between the horizontal cross braces, by the right panel's reflector end cap. Seems much more secure than using the supplied black tie-wrap! Mounted this way I'm not seeing the overload I saw when it was mounted on the mast, below the antenna.

[GroundUrMast]

Hi Pete,


Have you considered mounting the LNA-200 inside the tower leg? (Hoping/testing for some shielding effect.)

[Pete Higgins]

GroundUrMast,

No, I haven’t. Wedging it between the PVC mast and the plastic end cap was a convenience to keep me from climbing off the patio roof and running to the garage to get another tie-wrap. Success was accidental!

I have thought about mounting it in a metal box to see if that would help but the RCA amps I bought seem to work as good (maybe even better), support dual inputs and cost a lot less, so I’m not sure it would be worth the effort. I can’t fathom how sticking it in front of a piece of PVC and partially behind a reflector rod could provide much shielding. Other than relocating the antenna & the amp., everything else stayed the same (panel cables, combiner, combiner to amp. cable and cable to garage).

I’m trying to get all the window screens vacuumed this morning. We have a whole house fan that draws a lot of dust through them and I want to get that off before it starts to rain tomorrow & Thursday. If I don’t wear myself out on that project I plan to replace the PVC mast with a metal one this afternoon. It got pretty windy yesterday and the HDB8X was bouncing all over the place. Too much flex in the PVC mast.

********************************

The TV Fool website went down while I was typing this. Finished the screens washed the windows & swapped out the mast. I still had two real heavy Channel Master 5½‘ sections circa 1962.

[Gil]

Hi Tripelo,

Congratulations for the nice publication usefull for guideline and advise for good tv reception.

The conclusions that you posted involved a lot of work and spertise.

Regards

Gil

[tripelo]

Thanks Gil, for your kind remarks.

[tripelo]

In May 2012, Bob Nelson (forum member re_nelson (http://forum.tvfool.com/member.php?u=1759)) and I performed some experiments to observe the effects (in a suburban area) of UHF signal strength versus height of an antenna.

Signal strength measurements of 27 DTV stations versus receiver antenna height were recorded. On average, signal strength increased with height increase. Individual stations showed variability of signal strength (in a repeating pattern), this could indicate the presence of signal layering. Signal layering can result from reflections (ground or other) that either reinforce or reduce signal strength at various receiver antenna heights.

Location: Garland, TX

Signal Path: Line-of-Sight, about 28 miles from TV stations located at Cedar Hill, TX.

Local Clutter: Single story residential homes with some trees (approximately 30 –45 feet tall). The LOS path was essentially between any tall trees.

Signal Sources:

At that time there were 27 DTV stations in the same general azimuth direction that could be received at this location. These 27 stations served as stable signal sources to compare strengths at various antenna heights.

Equipment:

Antenna: Terk HDTVi (http://www.terk.com/indoor-tv-antennas/?sku=HDTVI) mounted to a push-up mast. The HDTVi was chosen because of it’s small aperture (allowing better height resolution), small size, and relatively flat response across the band. The HDTVi is shown in image below.

Mast: A push-up mast capable of being quickly lowered or elevated up to about 45 feet. The mast had numerical marks on it every foot for quick determination of height.

Signal Analyzer: Sencore 1456 (http://www.testequipmentdepot.com/sencore/signal-level-meter/slm-1456.htm), capable of scanning the UHF TV band for signals and measuring and recording the amplitude and MER (quality).

Coaxial Cable: Fifty feet of commercial quad shield RG-6 with custom connectors.


http://forum.tvfool.com/attachment.php?attachmentid=795&d=1410720596


Methodology:

Beginning at 15 feet AGL, measurements of all measurable* signals were taken at close intervals up to a height of 33 feet AGL. Most measurements were made at 1 foot intervals, between 18 and 24 feet, the measurements were made at 2 feet intervals.

* All stations had adequate signal strength, but some were low power (LP). For a few reasons, LP stations among several full power stations are difficult for an analyzer (tuner) to reliably decode. However signal strength measurements were feasible. The entire UHF TV band (Channel 14-51) is well represented by measurable signals.


http://forum.tvfool.com/attachment.php?attachmentid=796&d=1410720896


Below is a chart showing the average signal level of 27 UHF channels versus height.


http://forum.tvfool.com/attachment.php?attachmentid=798&d=1411221833


Each point in the graph represents that average signal strength of 27 DTV stations (RF channels) at that particular height (AGL). The averaging process takes out a lot of information, but does help provide an overall view.

The graph shows there is a signal strength plateau around 24 feet. But, increases resume at heights greater than 30 feet. Interestingly, the FCC uses 30 feet AGL for outside antenna in many propagation/contour analyses.

Much appreciation to re_nelson for his assistance, equipment, and support.

Later, the data illustrating signal strength versus height for individual stations can be graphed and posted, in a few weeks maybe sooner.

.

[Pete Higgins]

tripelo,

Interesting exercise.

I experienced a similar phenomenon when I moved my single HDB8-X from my aluminum HAM tower leg (@ ~19’ AGL) to my TV tower mast (@ ~40’ AGL). Most stations got stronger (marginally), some stayed about the same, I lost one and picked up a couple of others. When I added a second HDB8-X to my TV tower array most channels signal strength improved 1-2 dB but at least one actually appeared to get weaker? The two HDB8-X’s are vertically stacked.

http://forum.tvfool.com/attachment.php?attachmentid=799&d=1410727208 (http://forum.tvfool.com/attachment.php?attachmentid=799&d=1410727208)

The HDB8-X I ordered to form my 16 bay array arrived pretty damaged (kinked reflector rods & 3 of the 4 bow-ties on one panel loose). Solid Signal replaced it for me and I installed the replacement on the TV tower. I straightened the bunged up antenna as best I could and hung it from the aluminum tower leg. Once again I started to receive the channel lost by moving to the TV tower. (If only I spoke Spanish it would do me some good)

[tripelo]

Pete, that's a nice image of your vertically stacked HDB8-X antennas.

... When I added a second HDB8-X to my TV tower array most channels signal strength improved 1-2 dB...

... but at least one actually appeared to get weaker?

Interesting.

There can be certain locations in elevation (height) where an antenna with an aperture that is small in the vertical dimension provides more signal strength than a larger antenna.

Could be that two (not-in-phase) signal fronts simultaneously arrive at different heights within the vertically spaced array (upper and lower portions of the antennas).

Maybe, analogous to the diagram posted earlier under the heading:

Stacked Antennas: Multipath & Diversity Gain?
(http://forum.tvfool.com/showpost.php?p=38045&postcount=66)
The post, linked above, contains a drawing of stacked antennas and shows a direct wavefront (D) arriving at the lower antenna with a multipath wavefront (M=-D) arriving at the upper antenna. The signal summation would be less than the direct (D) alone.

A following post will show some measured signal variation versus height, likely the result of multipath.

.

[tripelo]

This post is a continuation of:

UHF Signal Strength vs Antenna Height (AGL) (http://forum.tvfool.com/showpost.php?p=46528&postcount=79)

In the previous post linked above; the signal strength of 27 DTV channels was measured as a small antenna (Terk HDTVi) was raised in height.

The signal strength of the individual 27 measured DFW stations varied considerably, from ~-35dBm to about -90 dBm. Due to the wide range of strength, it might not be very instructive to plot all signals on the same graph.

The following graph shows three of the weaker signals strength plotted versus antenna height.


http://forum.tvfool.com/attachment.php?attachmentid=802&d=1411227205

This graph illustrates what can be seen throughout all the measured signals (strong and weak).

That is:

1. Some channels show maxima and minima in signal strength as antenna elevation is changed.
2. The general trend is increasing signal strength with increases in antenna height.

Channel 50 shows the most distinct pattern of maxima and minima. This is evidence of signal layering; the constructive and destructive summation of two or more wavefronts.

Channel 51, although close in frequency, shows increasing signal strength with small perturbations. The two stations (channels 50 and 51), yield different responses at the receiving antenna, this could be related to differences in path geometry.

The transmitting antennas of these two stations are located on different towers and at different tower heights*. Incidentally, both are low power=15kW.

*Such transmitter/antenna info can be found at the FCC site, or more conveniently at Rabbitears.info.
(http://www.rabbitears.info/market.php?request=station_search&callsign=kata)
Channel frequency does matter. The signal wavelength is inversely related to frequency and constructive/destructive combinations are a matter of signal phase (which is wavelength related). Signal strength differences at the receiving antenna are a result of the combination of frequency and path geometry.

In a different environment, it is likely that the above trends continue, but a specific frequency (channel) may or may not respond with observable maxima and minima.

The response of channel 27 is somewhat typical of the measured channels (total number=27).

.

[Pete Higgins]

tripelo,

As always, very interesting information. I am guessing that the channel I lost by moving my UHF antenna up to 40’ is a phenomena similar to your channel 50 between 18’ & 22’. The ~ 6 dB weaker signal probably didn’t stop demodulation at your location but with my already weak 1 & 2 edge signals 6 dB is a real killer.

You are much better equipped to perform meaningful analysis with your Sencore SLM 1456 than I am using my software defined radios. My SDR’s have ~50 dB dynamic range and I believe the Sencore has ~114 dB (-98 to +16 dBm) range. It also appears to support direct readout in dBm and all I can do is compare relative signal strength differences in dB. But then I expect your Sencore cost you slightly more than the $8 to $9 that each of my SDR tuners cost me. These little devils plug into a USB port on a computer and tune from 24 MHz to 1.7+ GHz with good sensitivity. In addition to their limited Spectrum Analyzer capabilities I use a free program called SDR Sharp, under XP & Windows 7, to listen to commercial FM, tune the Ham bands (including all the local repeaters), VHF & UHF air and NOAA weather broadcasts. I even downloaded a plugin that allows me to start them scanning and stops on an active channel. I posted some information about them here:

http://www.highdefforum.com/local-hdtv-info-reception/143795-inexpensive-software-defined-radio-spectrum-analyzer-10-00-a.html

When I posted my dual HDB8-X picture I couldn’t remember how you told me to make it show up on this site. If you have time, can you post that information again?

[rabbit73]

Pete:
The clue is in the text box. Just read the text box in a post as if you were going to quote it. You used the link icon for a URL instead of just adding the BB code to the attachment URL:

http://forum.tvfool.com/attachment.php?attachmentid=805&d=1411269035

[Pete Higgins]

rabbit73

Hi rabbit –long time again!

I put the image tags ( ) on the link to my picture in post 80, expecting them to cause the picture to display in the post.

http://forum.tvfool.com/attachment.php?attachmentid=799&d=1410727208What I ended up with was the link displayed with IMG tags (see midway in post 80).

Since we can’t store pictures on this site in a photo album and use the bb code to display them I need to relearn how to get them to display. tripelo told me how some time ago, and it worked, but I lost the recipe. It looks like the example you posted worked so I’m not sure what I’m missing?

OK,
1. Add the graphic as an attachment to the post
2. Paste the graphic's link into the post
3. Add the image tags ( & to each end of the link
4. Highlight the complete link including the image tags and click on the "Wrap [quote] tags around selected text" icon. See above, it works!

Intuitively obvious to even a casual observer?

Thanks rabbit.

[rabbit73]

You're welcome.

You don't need to wrap quotes in step 4. Just leave the attachment showing at the end of the post and add BB code to attachment URL in text box. However, your way does eliminate the duplication of image in post and image in attachment. I never thought of that option. The quote box around the image does look nice.

In some forums, if the attachment isn't used at the end of the post, the link to the attachment is no longer active. So, it's best to do it like tripelo does, using just the BB code for the URL and leaving the attachment in place. As a bonus, you get an image counter by the attachment link that tells you how many times the image was shown, and anyone can download your image just by clicking on the attachment link.

The only reason I mentioned quote is to see what another person has done in his text box so that his attachment would show in post. Just click on the Quote button at the lower right corner of his post. This is what tripelo's text box would look like:

http://forum.tvfool.com/attachment.php?attachmentid=807&stc=1&d=1411424172
Intuitively obvious to even a casual observer? It wasn't obvious to me until I learned how to do it. HA!:)

[tripelo]

Signal measurements from several preamplifiers were compared, while receiving selected UHF channels and one VHF channel in the Dallas Fort Worth area.

Preamps Compared (shown in image below):

- Channel Master 7777 (new version)
- Channel Master 7778 (new version)
- Channel Master 7777 (old version)
- Channel Master 7778 (old version)
- RCA TVPRAMP1R
- Winegard LNA-200
- Antennas Direct PA-18


http://forum.tvfool.com/attachment.php?attachmentid=911&d=1422111119


All 7 preamps performed overall within ~0.5 dB of each other when comparing the measured MER* (modulation error ratio). The RCA TVPRAMP1R showed best UHF MER performance at 30.2 dB. MER is essentially the post-detection S/N ratio in dB. (MER performance graph below)


http://forum.tvfool.com/attachment.php?attachmentid=915&d=1422121160


As expected, there was considerable difference in UHF output signal strength (approximately 9 dB variation). Both the CM7777 versions (old and new) had highest UHF output signal strength. (Output signal strength graph below)


http://forum.tvfool.com/attachment.php?attachmentid=914&d=1422121174


Note: Previous measurements, made a day earlier, with these preamplifiers indicate that the results are somewhat repeatable. As the data in the graphs indicate, the precision of measurements can be made to within 0.1 dB, but mainly due to the propagation path, the accuracy is somewhat less. The rank order of the preamp’s measured performance was unchanged from one day to next.

*Modulation Error Ratio (MER)

Measured MER can be a good relative indicator of the overall system noise figure. Within limits, a system with a lower noise figure will have a higher MER. There is nearly 1:1 correspondence between noise figure and MER; a 1dB improvement in noise figure will provide about 1dB improvement in MER.

Other factors affect system MER, for example if two preamps had the same noise figure and one had higher gain, then likely the system MER would be highest for the preamp with highest gain. With typical preamps and system losses, there could be about 0.1 dB MER increase for about 1-2 dB of additional gain.

More to be posted, some tomorrow:

- Test Procedure & Configuration
- MER Performance per Channel
- Signal Output Level per Channel
- VHF Channel 8 Performance (MER & Signal Strength)
- Other Preamps
.

[ADTech]

Since all the MER readings were with 0.5 dB, it's pretty much a statistical dead heat. No one would ever notice any difference under typical customer reception conditions. If you use a wider scale on your bar graph say from 15 to 35, you'd have a very gradually sloped line, almost flat, around the 30 dB line.

[Pete Higgins]

tripelo,

Based on manufactures specs. & cost my mind tells me that my $70.00 LNA-200 should perform better than my $23.00 RCA’s but when I swap them back & forth I can’t tell any difference (signal strength & SNR). The one difference I’ve repeatedly noticed is that the RCA’s seem more immune to overload from my strong FM & TV stations when the array is pointed at them.

I’ve only found two amplifier designs that don’t show this overload issue, the RCA’s and my various PCT drop amplifiers (MA-B1015-1A, PCT-MA2-4P & PCT MA2-M). The drop amps don’t have as much gain but my SNR’s hardly change when I trade between the RCA’s & the PCT’s.

It would be really interesting to compare the dynamic ranges & strong signal handling characteristics of the various offerings.

As always, great work!

[tripelo]

Thank you ADtech and Pete. Your comments are appreciated.

Since all the MER readings were with 0.5 dB, it's pretty much a statistical dead heat…

That is a possibility.

…No one would ever notice any difference under typical customer reception conditions…

Most would probably agree.

…If you use a wider scale on your bar graph say from 15 to 35, you'd have a very gradually sloped line, almost flat, around the 30 dB line.

Yes

---------------------------

...found two amplifier designs that don’t show this overload issue, the RCA’s and my various PCT drop amplifiers (MA-B1015-1A, PCT-MA2-4P & PCT MA2-M)...

Interesting experience with preamps and drop amplifiers.

As both you and ADtech seem to understand and appreciate, in many cases, the dynamic range of a preamp is a strong factor contributing to overall satisfactory performance.

…interesting to compare the dynamic ranges & strong signal handling characteristics of the various offerings…

Yes

[tripelo]

Referring to Preamp Comparison data posted earlier.
(http://forum.tvfool.com/showpost.php?p=48946&postcount=87)

Comparison method; signals and path from antenna to measurement receiver:

1. Received on Radio Shack all-band antenna (similar to VU-90) at approximately 29 feet AGL, thru 50 feet commercial grade RG-6 cable

2. Attenuated by 40 dB; two JFW serial step-attenuators total 37 dB followed by 12” RG6, then one Holland 3 dB FAM attenuator.

3. Amplified by preamp-under-test with its power inserter and power supply

(If available, preamp FM trap set to ‘In’, If dual inputs, set to ‘Combined’)

4. Attenuated 3 dB; Output thru 4” RG-59 and Holland 3dB FAM attenuator

5. Received from preamp and 3dB attenuation, measured on Sencore SLM1456CM

Image depicting Test configuration shown below:


http://forum.tvfool.com/attachment.php?attachmentid=916&d=1422202514


The Sencore 1456CM executed a channel scan program wherein Modulation Error Ratio (MER) and Signal Level were measured and recorded while receiving DFW stations. Each test consisted of SML1456CM channel scan that measured signal MER and Strength for each of the following channels: 8, 9, 14, 23, 29, 36, 41, and 48. The scan was repeated three times (total three scan test time ~ 5 minutes). Then, the next preamplifier was tested, and sequence repeated until all 7 preamps had been examined.

Channel 9 data not planned to be included in the posted data. This is mainly because channel 9 is weaker than channel 8, to reliably receive it with all preamps would have required input attenuator adjustment during the tests.

The time from beginning-to-end for the complete test operation was about 75 minutes. This total time included, as a data integrity check, some replication of the first two scans at the end. Also included some other tests not reported.

The test data was downloaded from the Sencore 1456CM to a desktop computer for analysis and formatting.

The distance to the stations is ~28-30 miles, the path line-of-sight. Prior and post measurements indicated the signals were relatively steady during the test time. A clear stable-weather day was chosen to perform the tests. The signals are strong at this location, thus the need for 40 dB attenuation prior to the preamps. The objective was to lower signal strength such that the stations had only moderate S/N ratios within measurement range. (High signal strength can cause maximum S/N indication (max MER=36 dB) on the SLM1456CM.

The RF environment in DFW consists of dense signals. Virtually every usable UHF channel is occupied, only 2 VHF stations (Channels 8 & 9). The FM band has nearly every available channel occupied (many with full-power). Other strong signals include NOAA weather radio ~ 4 miles away.

The Radio Shack antenna responds to most of the above listed signals.

The test setup somewhat emulates conventional TV reception. The 40 dB of attenuation to preamp input reduces all signals, including FM and other potential interference sources. This reduction in signal strength could correspond to fringe area reception. The receiver is represented by the SLM1456CM and a transmission line loss between preamp and receiver being represented by a 3dB attenuator (similar to ~50’ RG-6 at UHF).

----------------------------------

Reference charts below: TVfool & FMfool charts for the preamp compare test location.

http://forum.tvfool.com/attachment.php?attachmentid=918&d=1422238547


http://forum.tvfool.com/attachment.php?attachmentid=919&d=1422203105


More preamp test data to be posted later.

.

[Pete Higgins]

tripelo,

It’s obvious that you put a lot of work into this professional caliber test report. I wish more people would take the time to pictorially depict their test setups like you do. Clear, concise & helps answer questions generated while reading your reports.

I’d be really pleased if I had your signal environment. My strongest signal of interest is ABC, channel 7 @-87.0 & 2-edge to boot. Box Springs Mtn. 3.5 miles out my back door and in-line with my LA stations is home to numerous communication towers, a channel 26 PBS TV station, several FM broadcast stations, a 2-Meter repeater that just booms in on my TV antennas plus I also pickup four NOAA weather channels with my LA array.

One of the items I found to eliminate some of the unknowns in my testing was the inline Channel Plus LPF-750 Low-Pass Filter. It’s basically a 0 to 750 MHz band pass filter I use to remove the cellular signals emanating off Box Springs Mtn.
http://www.solidsignal.com/pview.asp?p=LPF-750&utm_campaign=base&utm_medium=organic&utm_source=google_base

The only amplifier that I’m aware of that filters that portion of the spectrum is the new Antennas Direct Juice. ADTech did an excellent write-up on that amp here:
http://www.digitalhome.ca/forum/showthread.php?p=2406201#post2406201

More preamp test data to be posted later.

Looking forward to your follow-on.

[tripelo]

Pete, thank you for your comments.

…I’d be really pleased if I had your signal environment…

Your signal situation does seem particularly tough.

Guess most people have a more difficult TVfool chart than this one in DFW.

This DFW location is good for UHF test purposes.

…One of the items I found to eliminate some of the unknowns in my testing was the inline Channel Plus LPF-750 Low-Pass Filter…

That's a good idea.

Filters are almost a must for detailed testing, and sometimes necessary for ordinary TV reception. Although, often it is difficult to purchase filters with desired frequency and attenuation characteristics.

On one occasion for the KY setup, built a custom band pass filter.

The only amplifier that I’m aware of that filters that portion of the spectrum is the new Antennas Direct Juice.

Thanks for the info, looks interesting.

[tripelo]

Referring to previous posts:

- Compare Several Preamplifiers OTA-DFW (http://forum.tvfool.com/showpost.php?p=48946&postcount=87)
- Compare Preamplifiers - Test Procedure & Configuration (http://forum.tvfool.com/showpost.php?p=48961&postcount=91)

As mentioned earlier, the two VHF channels in the DFW area are channels 8 and 9. Measurements of both channels were attempted during the channel scans. Because channel 9 signal strength is weaker than other channels in the scanned list, it could not be reliably decoded by some of the preamps without attenuator adjustment during the tests.

Below is a graph showing the averaged MER value for each of the 7 preamplifiers receiving channel 8. The values shown represent the average of 3 individual measurements. The range of MER for the preamps is nearly 3 dB. The AD PA-18 provided the highest MER (26.7 dB), with the new CM7778 second (26.6 dB).


http://forum.tvfool.com/attachment.php?attachmentid=921&d=1422653098


The image below shows the output power level for each of the preamplifiers.

The highest output power is shown for the CM7777 versions:

- CM 7777 new (-54.6 dBm) and,
- CM 7777 old (-57.7 dBm)


http://forum.tvfool.com/attachment.php?attachmentid=923&d=1422653259


Notably, the lower MER values for channel 8 originated in the preamplifiers with separate amplifier sections for VHF and UHF.

- TVPRAMP1R
- CM7778 old
- CM7777 old
- WG LNA200*

*The WG LNA-200 has separate amplifiers even though it doesn’t have dual inputs.

A plausible explanation for lower channel 8 MER values could be;

The VHF-only sections have higher noise figures & generally lower gain than the VHF-UHF combination or UHF-only sections (single or dual amplifier versions). Investigations into the hardware design tend support this. Some factors specific to VHF could make this design choice seem logical to a manufacturer.

.

[Acme]

Hello Pete,
Do you still have the RCA 10W707 user manual and hopefully some schematic too ? I have this rotor but do not have a rotor control box. I would like to make it computer controllable, so the schematic would come in hand. Thank you for any info you might get me.

Acme

tripelo,



No comparison. The Radio Shack 15-1220 is a 5-wire rotor that uses a balanced bridge for exact positioning. In the 50 years I’ve used it; it has never gone out of alignment. It also seems to produce more turning torque. The accompanying control box displays ‘N’ at the top & ‘S’ – ‘S’ at either end of rotation. Being an old flyer, that fits the way I think.

I also have an RCA 10W707S that is almost identical. Motor unit is exactly the same and control box looks identical except it displays ‘S’ at the top and ‘N’ – ‘N’ at either end of rotation. The one drawback is the directional calibration. Tic marks on both rotors are 4.5 deg. apart. When aiming towards a “True” heading, I can visualize the heading with respect to true north and align the knob pretty close. Degrees with respect to true south –not so much. (If I put the RCA in service, I’ll make stick-on labels for the cardinal headings (S-S, W, N, E) to cover the ones silkscreened on the control panel. Other than control panel screening & branding, they really are identical.)

The U-106 is a three wire rotor that uses a timing circuit for calibration. 3-wire rotors use AC synchronous motors that run at a predictable speed, and the control box simply runs the motor for the amount of time needed to turn the antenna from where the controller thinks it is to where the controller wants it to be. Over time, the position error grows.

After moving it to “home” or 00 deg., basically, you rotate it full clockwise (360 deg.), hit a button labeled “Initial” and it memorizes the time it takes to return to 00 or “home”. Unfortunately, it frequently requires recalibration. Since my signals come from four directions, it’s fairly easy to detect when it needs calibration because when I turn the array there is either nothing there or the signals are barely watchable. I probably have as much calibration mileage on the rotor as actual array turning mileage. Sometimes, when the calibration goes off, it won’t fully turn to a true 360 so to get it full clockwise you have to power off, power on with a “reset” turn some more and repeat the process until it visually has the array pointing north. I’ve since read that other folks are experiencing the same calibration issues with other brands of 3-wire rotors. I think AntennaCraft, Centronics, Channel Master, Magnavox, Philips, RCA, Stern and probably others sell this same design under their own labels.

I bought the U-106 because the literature said “Digital display indicates antenna position during operation” & “Pre-set to 12 TV/FM station directions for automatic antenna positioning”. What I didn’t pick up on was that the bearing readout was a 2-digit display. North is 00 or 36, east is 09, south is 18 and west is 27. My street is aligned with True North and my house sits squarely on the lot facing east so visually it’s easy to determine array alignment. Even after a fresh calibration, manually turning the rotor to display “18” can have me pointing somewhere between ~175 & ~185. Fortunately, if you “bump align” for max SNR and memorize the location to a pushbutton it seems to return to that location –at least until it goes out of calibration.

I’ve been tempted to put the RCA on the tower, but then I’d have the new U-106 just sitting in the garage gathering dust. It’s useable, but I couldn’t in good conscience sell it to anybody.

Hello Pete,
The TB-105 support bearing that you ordered is currently out of stock. The vendor will not have anything available until mid September.
Please let me know if you wish to keep your order open or cancel.
Thank You
Tom

Kept order open, so it looks like I don't have to go out in the 100 deg. heat (at least until September).

http://forum.tvfool.com/attachment.php?attachmentid=555&stc=1&d=1373129246

Found this ad in the Pitsburg Post-Gazette for Friday August 24th 1973. I think I bought mine about 10 years earlier for $29 or $39.

[Pete Higgins]

Acme,

I have a service manual that covers the Alliance C225 & C225A rotor’s. As near as I can tell, the Radio Shack 15-1220 and RCA 10W707S circuitry is almost identical to these Alliance models.

Send me a PM with your email address and I’ll be happy to email you a copy.

[MrMotivations]

Since I mounted this on the eaves, around 40 + miles from Nashville signal sources, this design I targeted for 183 Mhz on the Vhf frequency. To my astonishment, it picks up all the available channels as well as my commercial Antennas Direct 91XG. We are happy with the Antennas Direct unidirectional, however. My little jobbie is not very robust. But it works surprisingly.

[tripelo]

A series of antenna tests were conducted on April 14, 2016.

Objective: Compare performance of selected UHF antennas while receiving DFW TV channels

Antennas:

1. Antennas Direct 91xg
2. Solid Signal HDB91x
3. Channel Master CM-4228 (old version)
4. Antennas direct DB8 (non-e version)
5. Terk HDTVi (as reference)

Images of antennas at test location in a following post.

Test Location:

Garland, TX, ~30 miles line-of-sight to 27 DFW stations, located within +/-3 degrees azimuth.

Test location TVfool info posted earlier:

Compare Preamplifiers - Test Procedure & Configuration (http://forum.tvfool.com/showpost.php?p=48961&postcount=91)

Test Equipment:

1. Sencore SLM1456 – Signal Level and MER measurements
(Scans channels one-by-one, dwells a few seconds per channel to lock and obtain a signal average, total scan time for 27 channels ~6-7 minutes)
2. DG8SAQ Vector Network analyzer -VNWA
(Measure scattering parameter S11 (complex input impedance->return loss/SWR)
3. Belden Coaxial Cable 1694A (40 feet)
4. Ferrite Cores at Coax to balun/antenna connection (Qty=4)
5. Balun for CM4228 (homebrew, hand-wound ferrite core, measured loss <1 dB)
6. Push-Up Telescopic Mast, 25+ ft.

Test Procedure

1. Calibrate VNWA, with the 40’coax cable (refers measurements to antenna/balun connection).

Starting with Terk HDTVi antenna:

2. Mount antenna w/coax and ferrites to mast, raise center of antenna to 25 feet
3. Align antenna for peak signal on Channel 29 (~central angle to DFW stations)
4. With 1456 scan all DFW UHF stations for signal strength and MER (record times)
(repeat scan, while in this configuration)
5. Take at least 2 Photos
6. Turn antenna ~90 degrees, disconnect coax from 1456, connect to VNWA
7. Measure S11 (input impedance, SWR/Return Loss) for the band
8. Lower Mast remove antenna
9. For each antenna repeat steps 2 through 8, finishing with a repeat of HDTVi antenna.

The test location and setup was similar to that described in previous posts:

Televes DAT-75 vs. Antennas Direct 91XG (http://forum.tvfool.com/showpost.php?p=38316&postcount=72)

UHF Signal Strength vs Antenna Height (AGL) (http://forum.tvfool.com/showpost.php?p=46528&postcount=79)

Compare Preamplifiers - Test Procedure & Configuration
(http://forum.tvfool.com/showpost.php?p=48961&postcount=91)

Compared to previous tests, some differences in equipment, this test:

- No attenuator was used,
- Sencore SLM1456 instead of SLM1456CM
- Others, VNWA, etc.


Credit:

Forum member re_nelson provided much appreciated assistance throughout test planning, test, and follow-up.

RE_nelson also:

- Provided most of the antennas
- Provided the Sencore SLM1456
- Aligned antenna, operated the SLM1456, performed scans, & collected data.

Image below: RE_Nelson at the antenna test station with his Sencore SLM1456.


http://forum.tvfool.com/attachment.php?attachmentid=1980&d=1461943453


The antenna mast is at far left behind the ladder and porch post. To aim the antenna, re_nelson observes SLM1456 and hand rotates antenna mast to maximize the signal strength indication.

(To be continued)

.

[tripelo]

(continued from previous post)

Part 2. Images of 5 Antennas at Test site

The following are images of the five antennas at the test site (antenna center height=25 feet).

Image below shows Terk HDTVi and CM4228 (old version)


http://forum.tvfool.com/attachment.php?attachmentid=1981&d=1461943811



Image below shows Solid Signal HDB91x and Antennas Direct 91XG.


http://forum.tvfool.com/attachment.php?attachmentid=1982&d=1461943818


Image below shows Antennas Direct DB8 (non-e).


http://forum.tvfool.com/attachment.php?attachmentid=1983&d=1461943957


(To be continued)

.

[tripelo]

(continued from previous post)

Part 3. Received Signal Strength Data Analysis, Five UHF Antennas

Attached are four Graphs depicting a summary of data analysis.

1. Average Relative Gain, (Image below):


An average 2 scans of all channels for each antenna, relative to the HDTVi antenna.

http://forum.tvfool.com/attachment.php?attachmentid=1984&d=1461944561


2.Average Relative Gain per Channel (image below)


A two-scan average of all antennas except HDTVi relative to HDTVi
(included four scans, two at beginning and two at end).

http://forum.tvfool.com/attachment.php?attachmentid=1985&d=1461944568


3. Average SWR 5 Antennas (image below)


SWR was derived from measured S11 (Return Loss). The curves represent the
smoothed scan averages for each antenna.

http://forum.tvfool.com/attachment.php?attachmentid=1986&d=1461944576


4. Mismatch Loss vs. SWR* (image below, see Note at end)


Table showing mismatch loss as a function of SWR.

http://forum.tvfool.com/attachment.php?attachmentid=1987&d=1461944583



========== Comments ====================

The CM4228 had overall slightly higher signal levels, this was mainly due to better gain at lower channels.

The HDB91x delivered highest signal strength at mid and higher channels, and with exception at channel 20, 2nd highest at lower channels.

The 91xg pretty much tied with the HDB91x at very highest channels, with average levels at lower channels.

The DB8 was about average at lower channels similar to the two Yagis. At midband signal levels dropped and stayed lower thru upper band. The signal level loss at midband might be related to the SWR (approaching SWR=4, with nearly 2 dB mismatch loss).


Notes: SWR* & Mismatch Loss

SWR is a positive number representing how well the antenna impedance matches a transmission line. For Example: SWR=1 represents a perfect match, Antenna impedance transformed by balun or other means to 75 Ohms perfectly matches a 75 Ohm coaxial line. Greatly simplified a SWR of 2 could be that the antenna impedance is either 150 Ohms or 37.5 Ohms, either of which is mismatched by a factor of 2.

When there is an impedance mismatch at intersection of antenna and transmission line, there is a certain amount of signal that is rejected (cannot be transferred from the antenna into the transmission line). This loss is called 'mismatch loss'.

When modeling antennas in software (i.e. 4NEC2), to obtain the true gain (sometimes called 'net gain') the mismatch loss must be subtracted from the calculated gain.

When measuring antennas in field test or at an antenna range, the effect of SWR is incorporated in measured signal levels. So, no subtraction is required. One could add back in the mismatch loss and derive a gain-like number, this number would be the 'directivity' of an antenna.

In the case of the antennas above, if the mismatch losses were added back to the measured responses, then one would see that the 'directivity' of the DB8 might be nearer to the 'directivity' of the other antennas.


Derivation of SWR & Mismatch Loss

Scattering parameter S11 was measured with reference at antenna/balun terminals. S11 represents a complex (real and imaginary) reflection coefficient, which includes ‘return loss’.

From return loss (RL), both SWR and ‘Mismatch Loss’ (ML) can be can be calculated:

http://forum.tvfool.com/attachment.php?attachmentid=1988&d=1461944589


(To be continued)

.

[tripelo]

(continued from previous post)

Part 4. The HDTVi Antenna as a Reference

Another way of comparing gain of the antennas is to directly compare received signal levels to that of the HDTVi antenna. The HDTVi antenna was selected as a reference antenna mainly because it was thought that it’s gain would be relatively flat across the UHF band. Also it was thought that the SWR of the HDTVi would be relatively good (close to 1). Part of the reason for the above assumptions is that Log Periodic antennas can be designed to meet the criterion: flat gain and favorable SWR. The physical appearance of the HDTVI suggest as much.

A 4NEC2 analysis of the HDTVi tends to support the assumptions of flat gain and favorable SWR.

Below are images of the results of 4NEC2 analysis

http://forum.tvfool.com/attachment.php?attachmentid=1989&d=1461945188


Top Image shows Gain in dBi (recall dBi=dBd+2.15), Lower image shows SWR


The above simulation SWR results agree favorably with the actual measurements. If the HDTVi gain were to be measured, likely it would also agree. If that were the case, than a direct comparison of the higher gain antennas with the HDTVi might provide insight.

Below is an image that shows the other four antennas compared directly with the HDTVi antenna:


http://forum.tvfool.com/attachment.php?attachmentid=1990&d=1461945198



The above image illustrates the tendency of increasing gain of the four higher-gain antennas with increasingly higher frequencies.

As can be seen in this image and a preceding image, there is a discontinuity at channel 20 and channel 31. These two channels have lower signal strength than most of the others and also have been observed to exhibit multipath effects. The effects that were related to multipath were observed as part of a previous field test performed in May 2012, some results shown in a previous post (Ch 20 & 31 data were not presented).

UHF Signal Strength vs Antenna Height (AGL) (http://forum.tvfool.com/showpost.php?p=46709&postcount=82)

Omitting those points (Ch 20 & 31), the overall data might look smoother, but they were included for completeness.

The following image represents a best-fit linear approximation to the measured data and could illustrate some trends. Caution when interpreting this linear approximation; for a specific channel, it might be better to refer back to the raw data averages (shown earlier).

http://forum.tvfool.com/attachment.php?attachmentid=1991&d=1461945205


Both Yagis show increasing gain with increasing frequency (channel number). The 8-bay bow tie, or panel array, antennas show a flatter response with some increased gain with increasing frequency.

CM4228 and DB8

Notable is the approximately 2 dB difference in gain between the CM4228 and the DB8. This difference could partially be explained by the increased SWR of the DB8 (about SWR=4 at mid band), an SWR of 4 could cause approximately 2 dB loss. Some of the signal strength difference and transmission line matching could be attributed to baluns. The DB8 balun was supplied by the manufacturer (Antennas Direct). The CM4228 balun was a homebrew hand-wound ferrite-core balun with a measured loss of less than one dB.

91XG and HDB91x

The measured signal level difference between the gains of the two Yagi style antennas is less pronounced. The HDB91x shows a clear advantage at the top end of the band, however this indication is partially an artifact of the linear approximation. Note the raw data average show signal levels from the two antennas to be fairly close near the upper end of the band. The reason for the overall differences is unknown, but could partially be related to a better impedance match to the transmission line. The S11 measurement of the HDB91x reveals a better impedance match starting at ~500 MHz (Ch 19) and upwards. It is known that the 91XG has an ~microstrip balun that in some ways resembles a usual half-wave loop (but is markedly different). The factory-supplied balun of the HDB91x has not been inspected.

After a first set of data on the 91XG was collected, it was thought something might be amiss. The 91XG balun housing was opened and inspected; a nut that holds the driven element to the balun seemed to not be tight. The nut was tightened and a second set of data was collected. The results of the second 91XG data set were close to that of the first set.

Overall, the appearance of the 91XG and the HDB91x seems similar. But, close inspection shows most component parts of the HDB91x are in some way different than the 91XG. There are measurable physical and electrical differences that may account for some of the difference in performance.

Test Location and Data Variability

Even though the test site is LOS to the DFW stations, some multipath has been observed with received signal on some channels. This is probably a result of the first Fresnel zone (https://en.wikipedia.org/wiki/Fresnel_zone) not being clear.

A repeat of each measurement probably helped reduce effects of brief transitory multipath effects. The individual data sets were fairly consistent. Measurements using the HDTVi at both beginning-of-test and end-of-test somewhat verified data consistency. The HDTVi final-measurements were about 0.2 dB lower in signal strength than the beginning-measurements. A scaled correction factor could have been incorporated into the data but was deemed unnecessary.

.

[tripelo]

A series of antenna tests conducted on July 1, 2016.

Objective: Compare performance of selected VHF antennas while receiving DFW TV channels

Antennas:

1. Antennas Direct C5
2. Televes Band III Yagi

Antennas Direct C5: Driven element is a loop design (contains two loops, inner and outer) with reflector screen. The balun is ferrite core design.

Televes Band III Yagi: Folded-dipole driven element with reflector and five directors. The balun is sealed in metal can.

Images of antennas shown below:

Antennas Direct ClearStream 5 (C5)

http://forum.tvfool.com/attachment.php?attachmentid=2089&d=1467817306


Televes Yagi B-III

http://forum.tvfool.com/attachment.php?attachmentid=2090&d=1467817317



Test Location:

Garland, TX, ~30 miles line-of-sight to DFW stations, both VHF channels (8 and 9) located on same transmitting tower.

Test location TVfool info posted earlier:

Compare Preamplifiers - Test Procedure & Configuration (http://forum.tvfool.com/showpost.php?p=48961&postcount=91)

Test Equipment:

Same as previous*, except:

1. Sencore SLM1456CM instead of Sencore SLM1456
2. 3dB attenuator at input of Sencore SLM1456CM
(From antenna perspective, improves coax cable match to 75 Ohms)


*Previous similar test: Compare Received Signal Strength of 5 UHF Antennas (http://forum.tvfool.com/showpost.php?p=55091&postcount=98)

Test Procedure

1. Calibrate VNWA, with the 40’coax cable (refers measurements to antenna/balun connection).

Starting with Antennas Direct ClearStream 5 antenna:

2. Mount antenna w/coax and ferrites to mast, raise center of antenna to 25 feet
3. Align antenna for peak signal on Channel 8
4. With 1456CM scan DFW VHF stations (Channels 8 & 9) for signal strength and MER.
(repeat scan 9 times while in this configuration, record times).
5. Take at least 2 Photos
6. Turn antenna ~90 degrees, disconnect coax from 1456, connect to VNWA
7. Measure S11 (input impedance, SWR/Return Loss) for the band
8. Lower Mast remove antenna
9. Mount Televes Yagi B-III, repeat steps 2-8
10. Then again, for each antenna, repeat steps 2-9


The test location and setup was similar to that described in previous posts:

Televes DAT-75 vs. Antennas Direct 91XG (http://forum.tvfool.com/showpost.php?p=38316&postcount=72)


Credit:

Thanks to Stuart Sweet of Solid signal for providing the Televes Yagi B-III.

(To be continued)

.

[tripelo]

Part 2. Images of the Two Antennas at Test site

The following are images of the two antennas at the test site (antenna center height=25 feet).

Image below shows Antennas Direct ClearStream 5 and Televes Yagi B-III.


http://forum.tvfool.com/attachment.php?attachmentid=2091&d=1467817525


(To be continued).

.

[tripelo]

Part 3 (continued from previous post)

Attached are Graphs depicting a summary of data analysis.

1. Average received power levels, (Image below):

An average 9 measurements of each channel (8 & 9) for each antenna (ClearStream 5 and Televes Yagi BIII).


http://forum.tvfool.com/attachment.php?attachmentid=2093&d=1467817772


2. Average Relative Gain per Channel (image below)

A nine-scan average of both antennas.


http://forum.tvfool.com/attachment.php?attachmentid=2094&d=1467817778


3. Average SWR 5 Antennas (image below)

SWR was derived from measured S11 (Return Loss). The curves represent the
smoothed scan averages for each antenna.

http://forum.tvfool.com/attachment.php?attachmentid=2095&d=1467818016



For mismatch Loss vs. SWR, see previous post*.

*Received Signal Strength and Data Analysis (http://forum.tvfool.com/showpost.php?p=55093&postcount=100)


No mismatch loss for SWR equal to 1, a SWR of 2 results in a mismatch loss of about 0.5 dB.


========== Comments ====================

The Antennas Direct ClearStream 5 (C5) and Televes Yagi BIII provided nearly the same average signal strength for Channel 8 and 9, with an approximately 0.1 dB advantage for the Televes antenna. Since 0.1 dB is near the measurement accuracy limits of the test configuration, the difference may not be very significant.

The per channel data shows that the Televes antenna provides a higher signal on channel 9 (by about 0.2 dB) relative to the Antennas Direct antenna. This could be a result normally expected of Yagi type antennas, that is the gain increasing with increasing frequencies, up to the design limit.

Test Location and Data Variability

Even though the test site is LOS to the DFW stations, some multipath has been observed at UHF with received signal on some channels. However, effects of multipath have not been explored at VHF frequencies, and there have been no symptoms to suggest it might be prevalent.

Several repeats of each measurement probably helped reduce any effects of brief transitory signal variability. The individual data sets were fairly consistent. Measurements using the Antennas Direct ClearStream 5 at both beginning-of-test and end-of-test somewhat verified data consistency. The Antennas Direct ClearStream 5 final-measurements averages were within a few hundredths of a dB of the signal strength of the beginning-measurements average.



(To be continued)

.

[tripelo]

Part 4 (continued from previous post)

4NEC2 Analysis and Discussion

Antenna simulation software (4NEC2) could be useful in comparing antennas. Generally, software analysis is not a substitute for field tests. Choices must be made of available approximations that are necessarily incorporated in software models. Without some field measurement data to guide the design of a simulation model, rarely does a simulation model account for all factors in an antenna design.

In cases where field data is limited, but available enough to help confirm the models and if one can be fairly sure the software model something close to reality, then software analysis can provide insight.

The physical dimensions of both antennas; the ClearStream 5 and the Televes Yagi B-III were measured and software models created in 4NEC2.

The gain values shown in the following 4NEC2 results do not include balun loss or mismatch loss.

Below are images of the results of 4NEC2 analysis

Top Image, Gain in dBi, Lower image SWR

(Recall dBi=dBd+2.15)


http://forum.tvfool.com/attachment.php?attachmentid=2096&d=1467818232


The above simulation SWR results agree favorably with the actual measurements.

If the Antennas Direct ClearStream 5 gain were to be measured, likely it would also agree.

Below is an image that shows the Televes Yagi B-III antenna gain and SWR:


http://forum.tvfool.com/attachment.php?attachmentid=2097&d=1467818239




The shape of the Televes SWR pattern above above is in reasonable agreement with actual measurements (see previous post). Overall, the SWR is lower than measured. No explanation has been found. It could be that the software model does not account for some factor that could alter the SWR values. Another possibility is that the balun (not modeled) could contribute to the SWR difference. For example; In some cases LC components are added to a balun to improve response at band edges at the expense of impedance match at center band.

The above image illustrates the tendency of increasing gain for higher frequencies, often seen in Yagi-type antennas.

These simulation results are also in fair agreement with data present at the two manufacturers websites:


Antennas Direct ClearStream 5

Gain and SWR (simulations of both, plus measured values of SWR at 10 ft AGL),

Located in this document:

https://www.antennasdirect.com/cmss_files/attachmentlibrary/C5%20technical%20data%20with%20uhf.pdf


Televes Yagi B-III (Gain),

Located in this document:

https://www.televes.com/sites/default/files/catalogos/1._terrestrial_antennas_en_0.pdf


Azimuth Beam Width

The following images show the computed azimuth (horizontal) antenna patterns of the two antennas at three frequencies representing lower end of the band (174 MHz), mid band (194 MHz), and upper end of the band (216 MHz).


http://forum.tvfool.com/attachment.php?attachmentid=2098&d=1467818461



Note the C5 has a somewhat broader beamwidth, especially evident at the upper end of the band, than the Televes antenna.


http://forum.tvfool.com/attachment.php?attachmentid=2099&d=1467818471

http://forum.tvfool.com/attachment.php?attachmentid=2100&d=1467818478



The difference in gain at 216MHz is mainly related to increasing gain from the Televes B-III. The Televes B-III is advertised to cover up to 230MHz, so it is expected the gain would be higher at the upper end of the band.


(To be continued)

.

[tripelo]

Part 5 (continued from previous post)

Specifications, Measurement, Analysis and Discussion

In an effort to reconcile the various gain and SWR numbers available for these two antennas, the following chart was composed.

For each of the two antennas and each channel (8 and 9), the gain and SWR are presented. The sources for the gain and SWR are listed in the left column.

The manufacturers numbers are derived from the technical documents found in the links provided in a previous post. Antennas Direct lists gain figures as dBi, very likely the Televes numbers are also in dBi.

The 4NEC2 results are from simulations described in the immediately previous post. The gain numbers (dBi) listed here are calculated to include mismatch loss due to SWR.

The DFW Measure numbers are a summary of actual measurements at 25 ft from a location in Garland TX (described in a previous post). The units of values listed as gain are dB, either positive or negative relative to that averages of the two antennas (per channel).


http://forum.tvfool.com/attachment.php?attachmentid=2101&d=1467818654


Summary and Discussion

These two antennas are of different design, but for the channels tested yielded relatively close gain and SWR numbers.

The Antennas Direct antenna consists of driven element loops (inner and outer) with a screen reflector. The loop is made of relatively thick conductor that helps to broaden frequency response (flattens SWR). This design is in some ways similar to two stacked dipoles (top element fed at ends instead of center fed). This stacking effect tends to compress vertical beam width, thus for a given amount of total gain, allows for a slightly wider horizontal beam width. This C5 antenna being a relatively broadband design tends to have a flat gain and SWR response across the entire VHF high band.

The Televes antenna is a conventional Yagi design with folded dipole driven element. This design tends to have increasing gain with increasing frequency, up to the design limit. According to Televes literature the design limit is 230 MHz (the upper channel in the European band). Conventional Yagi designs tend to have a flattened oval shaped aperture (area over which signal is gathered). This flattened oval-shaped aperture shape means more of the antenna gain is a result of horizontal beam becoming narrow. So, one would expect the beam width of the Televes antenna to become more narrow at higher frequencies (where the gain is highest).

Since much of the data presented in the above preceding chart is in agreement.

The above chart for these two antennas tends to indicate:

1. Antennas Direct and Televes gain figures are consistent with each other.

2. Manufacturers gain numbers are consistent with 4NEC2 simulation results.

3. Antennas Direct SWR values are consistent with actual measurements (at 25 ft. AGL).

4. Computer simulations combined with field measurements can be used to characterize antenna performance, in some cases.

.

[tripelo]

Antenna tests conducted on June 15, 2017.

Objective: Compare performance of selected VHF antennas while receiving DFW TV channels.

Antennas:

1. Terk HDTVi (as reference)
2. Antennas Direct DB8e
2. Channel Master 4228HD

Terk HDTVi antenna measured as reference (see previous posts (http://forum.tvfool.com/showpost.php?p=55094&postcount=101)).

Both Antennas Direct DB8e and Channel Master 4228HD are panel type antennas, also known as 8-bay antennas.

Main differences between the two panel antennas are feed system design and reflector backplane.

Images of antennas shown below:

Antennas Direct DB8e

http://forum.tvfool.com/attachment.php?attachmentid=2746&d=1498307192

Channel Master 4228HD (below)

http://forum.tvfool.com/attachment.php?attachmentid=2747&d=1498307234


Test Location:

Garland, TX, ~30 miles line-of-sight to DFW stations.

Test location TVfool info posted earlier:

Compare Preamplifiers - Test Procedure & Configuration (http://forum.tvfool.com/showpost.php?p=48961&postcount=91)

Test Equipment and Test Procedure:

For details of test equipment & procedure, see previous similar tests:

Compare Received Signal Strength of 5 UHF Antennas (http://forum.tvfool.com/showpost.php?p=55091&postcount=98)

Compare: Antennas Direct C5 & Televes Yagi B-III (http://forum.tvfool.com/showpost.php?p=55491&postcount=102)


Credit:

Thanks to forum members ADtech and re_nelson for providing the Antennas Direct DB8e antenna.


(To be continued)

.

[tripelo]

(Continued from previous post)

Part 2. Images of Three Antennas at Test site

The following are images of the two antennas at the test site (antenna center height=25 feet).

Image below shows the reference antenna: Terk HDTVi


http://forum.tvfool.com/attachment.php?attachmentid=2748&d=1498307949


The image below shows both the Antennas Direct DB8e (left) and the Channel Master 4228HD (right).

http://forum.tvfool.com/attachment.php?attachmentid=2749&d=1498307986

(To be continued).

.

[tripelo]

(continued from previous post)

Part 3. Data Collection & Analysis

The amount of data collected represents:

Number of UHF channels: 23
Measurements per channel
DB8e4 and 4228HD: 9
HDTVi: 12

Total (individual channel measurements): 23 x 9 x 2 + 23 x 12 x1= 690

Attached are Graphs depicting a summary of data analyses.

1. Average received power levels, (Image below):

The image below represents an average of 23 UHF channels, nine measurements per UHF channel for each antenna (4228HD and DB8e), 12 measurements per channel for the HDTVi.


http://forum.tvfool.com/attachment.php?attachmentid=2750&d=1498308360


The image below shows the received signal strength per UHF channel for the three antennas. Note signal strength is shown in dBmV (dB referenced to milliVolts in a 75 Ohms system. To convert to dBm (milliWatts) subtract 48.75. from the dBmV numbers.


http://forum.tvfool.com/attachment.php?attachmentid=2751&


The image below shows the received signal strength of the DB8e and 4228HD antennas in dB, relative to the HDTVi antenna. The HDTVi signal strength is referenced to zero on the vertical dB scale.


http://forum.tvfool.com/attachment.php?attachmentid=2752&d=1498308424


The image below shows a linear best-fit approximation of the received signal strength of the DB8e and 4228HD antennas in dB, relative to the HDTVi antenna.


http://forum.tvfool.com/attachment.php?attachmentid=2753&d=1498308449


The following image shows SWR for the three antennas, it was derived from S11 (Return Loss), measured at 25 feet AGL.

The fuzziness of the lines in the SWR graph results from simultaneously receiving the broadcast stations in DFW with the Vector Network Analyzer. The reception of these strong signals caused some interference with the live impedance measurements. The antennas were not turned away from the stations as was done in previous measurements


http://forum.tvfool.com/attachment.php?attachmentid=2754&d=1498308464


All three antennas have respectively good values of SWR. No mismatch loss for SWR equal to 1, a SWR of 2 results in a mismatch loss of about 0.5 dB.

Antennas Direct Technical data sheet indicates the SWR is less than 2 from 470 to 698 MHZ. The SWR measurement shown above for the DB8e is fairly well in agreement with Antenna Direct published specifications (https://www.antennasdirect.com/cmss_files/attachmentlibrary/Technical%20Data%20PDF%27s/DB8E-TDS.pdf). Published SWR specifications for the 4228HD are not available.


For mismatch Loss vs. SWR, see previous post*.

*Received Signal Strength and Data Analysis (http://forum.tvfool.com/showpost.php?p=55093&postcount=100)


========== Comments ====================

The Antennas Direct DB8 provides highest overall signal strength, with an advantage over the 4228HD at high channels approaching 4-5 dB. TheCM4228HD performs well for channels below about channel 23, with an advantage of more than 1 dB at the lowest end of the band.

The 4228HD appears to have reduced gain as the frequency increases. The reason for this phenomenon was not investigated in this effort. However, it may be related to the transmission line feed for individual driven elements in the 8-element array, and particularly the feed between the two 4-bay segments.

Others have explored this 4228HD gain effect:

HDTV primer: Designed an improved antenna transmission line feed. (http://www.hdtvprimer.com/ANTENNAS/TemporaryPage.html)

Antennahacks: Implemented an improved transmission line feed system. (http://www.antennahacks.com/Hacks/NistHarness.htm)


Test Location and Data Variability

The test site is LOS to the DFW stations, however effects of multipath have been observed at UHF with received signal on some channels

Several repeats of each measurement probably helped reduce any effects of brief transitory signal variability. The individual data sets were fairly consistent. Measurements with the HDTVi, at both beginning-of-test and end-of-test, somewhat verified data consistency.

(to be continued)

.

[tripelo]

(continued from previous post)

Part 4. Compare 6 antennas (DB8, DB8e, 4228, 4228HD, 91xg, HDB91x)

Having earlier measured four other high-gain UHF antennas relative to the HDTVi antenna, this could suggest that all six could be compared.

http://forum.tvfool.com/showpost.php?p=55092&postcount=99

The main link between the two data sets is the measurements of the HDTVi antenna. The HDTVi was used as a reference antenna in both experiments. Realizing that errors can accumulate, a direct comparison of the two data sets might be somewhat useful.

Below is an image that shows the other four antennas compared directly with the HDTVi antenna:


http://forum.tvfool.com/attachment.php?attachmentid=2755&d=1498309317


The Yagi antennas (91xg and HDB91x) stand out as having higher gain as the channel number increase. The two Yagis appear to have the highest gain available at the top of the UHF band.

It appears that the older CM4228 (non-HD) is a fairly good match to the newer DB8e, both show a wideband response with relatively high gain at the lower channels.

If the above graph were accurate for every channel (which is doubtful), one could add the gain of the HDTVi to every antenna, to obtain a total gain figures. Previous calculations (http://forum.tvfool.com/showpost.php?p=55094&postcount=101) show the gain of the HDTVi to be about 6.5-7 dBi.

Caveat: Keep in mind that real antenna gain patterns are rarely (if ever) linear, and the above chart (although based on measured data) is an approximation.

.

[tripelo]

The tower shown in previous posts has been in use since 1971. It is located in Russell County, KY. The earlier posts showed some antennas that have been resident on the tower. Hopefully, a series of posts could show nearly all that antennas that have been on the tower and some rationale as to the purpose of those antennas.

In 1971, with the help of my younger brother, tower sections were individually lifted & assembled, then two antennas installed with a Channel Master rotator.

- Channel Master Crossfire CM-3600 VHF antenna
- Predecessor to CM-4228 UHF antenna (shown previously)

The image below shows the almost completed project of installing antennas just after the final tower section was placed. The 2nd image shows an excerpt from Channel Master literature describing the new 'Crossfire' antennas.

http://forum.tvfool.com/attachment.php?attachmentid=3007&d=1514911861

http://forum.tvfool.com/attachment.php?attachmentid=3008&d=1514911873


The next image shows the predecessor to what is now know as the old CM-4228 UHF antenna (previously posted (http://forum.tvfool.com/showpost.php?p=36689&postcount=20)).

http://forum.tvfool.com/attachment.php?attachmentid=519&d=1370105543


The objective was to receive stations from 3 cities:

- WAVE-3 Louisville (~101 miles, across typical hill & forested areas)
- WHAS-11 Louisville (~101 miles, across typical hill & forested areas)

- WLEX-18 Lexington (~77 miles, across typical hill & forested areas)
- WKYT-27 Lexington (~74 miles, across typical hill & forested areas)

By rotating antenna, receive:

- WATE-6 Knoxville TN (~93 miles, mountains in between)
- WBIR-10 Knoxville TN (~93 miles, mountains in between)

For most of the stations above, allowing for a bit of 'snow', reception was satisfactory mornings and night. Reception could be unreliable during day.

With the antenna rotator, this might have been a good setup for DX’ing. Stations could almost regularly be seen from various cities in Indiana, Ohio, Tennessee, Virginia, and West Virginia.

Maybe later, more details of subsequent antennas.

.

[Pete Higgins]

tripelo,

Really interesting material. I always look forward to your posts. Hope the New Year finds you & yours in good health.

[davodavo]

Situation: 70-120 miles away from some very big signals (1 MW), but almost nothing less than 30 miles away. Everything is UHF except VHF 7 and 11.

Goal: Grab every signal I can; currently at about 75 virtual channels (but up to 100 are possible)

Baseline: Stacked AntennaCraft Yagis with WG7870 combiner CM7777 preamp. Due to wife's objections, these are at about 15' AGL (although we're near at the top of a hill, the signal has to pass through some treetops).

Hypothesis: Hotter antenna (think CM4251) would do the trick. But...why not go even bigger with the parabolic reflector? Acquired 10' C-band satellite dish, repurposed with bow-tie element.

Photos, measurements, and lessons learned: when it stops raining.

[Stereocraig]

I've been working on a similar project, w/ a couple of 8 footers for the last couple of years.
I have the bowties and reflectors built, but will need to reconfigure the suspension conduits higher, or lower for focal point due to the bowtie placement conflicting w/ the same distance as where the old horn mount is.

Oh well, eventually.

[davodavo]

So, the first thing you have to realize is that the 10' C-band antennas are pretty solid, heavy and with a fair degree of wind resistance. As the reflecting surface is typically expanded metal with 2 mm perforations, this thing is going to present quite a wind load. Even after removing all the C-band electronics and unnecessary aiming motor, the parabolic and its mounting structure is probably 150 lbs...so this is not going up on a mast.

http://www.saleslogistix.com/IMG1.jpg

What it does get mounted on is 3" galvanized steel, and for obvious reasons that pipe needs to be at least 5' out of the ground. In my case, I went for 7 feet out of the ground...but that means 5' in the ground, surrounded by at least 300 lbs of concrete. Unless you have a really big augur, it's hard to do much more than that. Luckily, the ground drops off significantly from where the pole is, so it's effectively maybe 12' AGL.

Once the dish is mounted, configuring the antenna element is pretty straightforward. I live in an area with almost no signals in any direction, so I don't need a reflector behind the antenna element: it's just a matter of making the element (bow-tie) the right size and in the focus of the dish.

http://www.saleslogistix.com/IMG2.jpg

According to theory, the bow-tie is of infinite size...and I'd like to get down to to channel 7 so the wavelength is almost 2 meters. But the focus of the dish is probably less than a meter across, so there's not going to be any advantage to an bow-tie even that big. My first pass is with bow-tie wires 16" long. (I will experiment with solid bow tie and other variations in a week or so.) Through experimentation and measurement, I find the best distance for the bow-tie element and we're off to the races.

http://saleslogistix.com/IMG3.jpg

My main signal challenges are about 100 miles away, and my baseline for comparison metrics is a pair of yagis, with the bottom one about 12' AGL actual...but due to drop off of ground level effectively 17' AGL. According to the models, I shouldn't be getting much of anything...but with the stacked yagis and a nice preamp most of the time I get about 75 virtual channels (from about 20 transmitters). The new dish with a preamp gets nearly all the channels the same way, and the first pass of spectrum analysis (using the Nuts about Nets USB-based system on a PC) shows nearly identical signal strength. The dish is more directional than the Yagis (no surprise) but not as super-directional as I was worried about.

So now: how do I make the bow-tie outperform the Yagis? They are signficantly farther off the ground, which gives them a big gain advantage (I'm guessing 6 dB)...but the "collecting surface" of the dish should give the bow-tie even more than that.

The answers come next time I have time to mess with it.

[Stereocraig]

So, the first thing you have to realize is that the 10' C-band antennas are pretty solid, heavy and with a fair degree of wind resistance. As the reflecting surface is typically expanded metal with 2 mm perforations, this thing is going to present quite a wind load. Even after removing all the C-band electronics and unnecessary aiming motor, the parabolic and its mounting structure is probably 150 lbs...so this is not going up on a mast.

I have a pair of 45' towers each sunk in 35 60# bags of ready mix and various engine blocks and bicycle frames, so I'm confident I can go up at least 2 sections. I just need to fabricate clamps.

[davodavo]

I have a pair of 45' towers each sunk in 35 60# bags of ready mix and various engine blocks and bicycle frames, so I'm confident I can go up at least 2 sections. I just need to fabricate clamps.
Wow, well if you've got a 3000 lb+ foundation that's cool.
I'm not sure how you're going to get the dish very far up in the air--you'll need to set up some sort of winch system or use a very tall bucket. Just don't try it on a windy day--the dish becomes quite an unwieldy sail.

[rabbit73]

So now: how do I make the bow-tie outperform the Yagis?

Thanks for the interesting photos of your dish.

Bowties are full wave dipoles. Since they are a collinear pair of dipoles spaced very close together, they don't have a lot of gain over a halfwave dipole. I suggest you use a stacked pair of halfwave dipoles, one above the other, fed in phase, for smaller size and greater efficiency at the focal point. A vertical spacing of 5/8 wave at the design frequency would give max gain. Adding a reflector behind the dipoles would give additional gain.

http://www.w1ghz.org/antbook/chap6-2.pdf

[davodavo]

Thanks for the interesting photos of your dish.

Bowties are full wave dipoles. Since they are a collinear pair of dipoles spaced very close together, they don't have a lot of gain over a halfwave dipole. I suggest you use a stacked pair of halfwave dipoles, one above the other, fed in phase, for smaller size and greater efficiency at the focal point. A vertical spacing of 5/8 wave at the design frequency would give max gain. Adding a reflector behind the dipoles would give additional gain.

http://www.w1ghz.org/antbook/chap6-2.pdf

Thanks for the tips, and the reference to the antenna book! Seems like all of its characterizations are for transmission...but they should apply reflexively to reception.

I'll give the stacked dipoles a shot. In the "duh" department: won't I have an impedance mismatch when using stacked dipoles (I'm feeding a 300 ohm balun)?

Bowties are actually "supposed" to be solid (rather than "whiskers") for maximum gain...I'm going to be giving that a shot and will tell you the results.

However, given the special case of bowtie in the focus of a parabolic reflector I doubt that a reflector behind the bowtie (or dipoles) would help much: at that point, the waves are out of focus and bouncing off at a range of angles from 0 to about 120 degrees, causing a bunch of phase cancellations. Given I'm trying to use this from 170 to 700 MHz, I'm doubtful there's an optimum at all ;-) I don't have any issues with front/back ratio as there are no signal sources within 30 miles of me, and the landscape around me shields unwanted strays.

I'll give it a try and report back here.

[davodavo]

So with COVID-19 I have time on my hands at home and did a bunch of comparative measurements. Used Nuts About Nets spectrum analyzer to compare--the only variation in the configuration was the final antenna.

Note that the dish is mounted on a short pole (due to wind loading issues, couldn't go higher) but the ground level slopes off and the dish is effectively maybe 10 feet above ground level.

Also note that this would have to be called deep-fringe conditions--the nearest real station is 75 miles away and some of the stuff I'm shooting for is 125 miles away. Due to atmospherics, signal strength varies significantly during the day, so I always did my measurements within the same hour and comparable weather conditions.

Baseline was as shown in the photos above--very thin copper "whiskers". They are long because (1) I'm trying to get some VHF channels and (2) from what I read, making them longer doesn't significantly hurt the UHF.

Modified the whiskers to make solid triangular pieces. Within the variability of the signal/atmospheric effects, no measurable difference.

Put a reflector screen behind the active elements. No appreciable difference

Modified the whiskers and made "stacked" dipoles. Maybe 1 dB difference.

Took a Channel Master 4228 HD antenna and used that as the active antenna (facing in toward the dish). Depending on its location in the dish focal plane, got up to 5 dB of gain. The 4228 HD can be modded to improve its gain by another 3 dB (there are a couple of sites that describe how to do this)--I didn't make those mods, but I'll believe the claims.

But---the advantage of the parabolic, collecting a huge amount of signal, is fighting the disadvantage of "no altitude". And the measurements showed that it's a losing battle.

I took the Channel Master and raised it about 15 feed higher than the parabolic--and got more signal at every channel from the naked 8-bay bowtie at that altitude. Sigh.

Then I did a comparison of the Channel Master versus a pair of stacked broadband Yagis (AntennaCraft) and got surprising news: at almost every frequency, the Yagis beat the Channel Master. Obviously in VHF (actual channels 7, 8, and 11) there was no contest...but even in high UHF the Yagis were providing more signal, or were within a dB or two of the Channel Master.

So in this deep-fringe reception area, the lessons are pretty clear (even if somewhat counter-intuitive):

Altitude trumps everything else (duh)
If you need VHF channels, a Yagi or two is in your future
The 10-foot parabolics don't offer that much of a gain advantage at terrestrial TV frequencies (this was a surprise to me)
Modifying the active elements of the antenna didn't make as much of a difference as I'd expect
I'm glad I ordered the Channel Master via Amazon, as they allowed me to return it


Although this has turned out to be a wild-goose chase (I'm back with the Yagis I started with), hopefully my experience will persuade some of you to not go down this path unless you have a really strong tower to put your 10-foot, 100 pound parabolic on.

[bobsgarage]

Thanks for your follow up report, interesting results, indeed!

[davodavo]

Did some further research, analysis, and testing.

One of the things that surprised me was the breadth of the beamwidth, which on a dish you'd expect to be pretty narrow. At these frequencies and in my circumstances, it was about +/- 10 degrees. Hmmmm, perhaps the antenna elements weren't in the focal point of the dish. Did some physical measurements and calculations, found that my empirical "focus" of the elements was about 3 inches off from the theoretical. Moved to the theoretical, not much help--in fact, spectrum analyzer says it's 5 dB lower. Grrrr. Here's my theory: the parabolic is designed to focus the beam for a C-band antenna...a dipole a couple of centimeters across. For my much larger UHF elements, I have to move them in toward the dish so I get the signal before it's focused too tightly. Following my theory further, that's why the back-reflector didn't help: it was bouncing the signal off at an odd angle that didn't hit my antenna elements, rather than reinforcing the beam (to really work, the reflector would also need to be a small parabolic).

After reading several articles on real-world bow-ties for reception (rather than transmission), I determined that the length of the "whiskers" was too long (16") and could be safely reduced to 12" or even 8" (particularly given the small area of focus for the dish). My first change was to cut the whiskers down to 12" and was surprised that the performance might have actually improved a bit (even down at channel 2, 56 MHz!). Next up: reshape the bow tie to form dual dipoles (phased, stacked vertically). This isn't really optimal for the C-band dish, which has an f/D ratio of about .35 -- but we'll see.

I spent time researching antenna feeds using AARL and other sources, and found that virtually every article emphasized the importance of careful tuning of the antenna elements and feed, with a focus (so to speak) on transmitting. This would make a lot of sense: when transmitting, it's relatively easy to send out a continuous power signal and then have a friend with a receiving antenna more than a mile away to take measurements-- over the course of a phone call, all kinds of quick optimizations could be made and compared against the received signal strength. Once you've optimized the transmit, the receive is already done. But in my situation -- terrestrial DTV, broadband reception, deep fringe -- you don't get the luxury of easily-compared tweaks. As a corollary to this, all the articles are focused on single-frequency optimization (unless, of course, there are two feeds...) -- none of the articles mention anything about bow-tie antennas or broadband reception. So with a DIY dish receiving antenna, YOYO....and it seems that a broadband dish is inherently sub-optimal (because a lot of its gain comes from the tuning).

As I live in a deep-fringe area with essentially no local interference, the spectrum analyzer numbers don't really tell the story on marginal channels (i.e., pixelation)--the signal strengths vary over the duration of the spectrum-analyzer sweep, so they're hard to compare. Further, the issue isn't raw signal strength: it's singal-to-noise at the demodulator that is trying to fish the digital streams out of the signal. If there's any multipath (likely in a refracted signal from way-over-the-horizon source) or competing transmitters on the same wavelength (definitely a problem on one of my frequencies), the signal analyzer may show that I've got 5 or even 10 db of "signal" yet nothing on screen. The final arbiter of "better" has to be the TV itself.

Because the transmitters are waaaaay over the horizon (under, actually...), one effect I hadn't anticipated is spacial diversity. Moving the antenna up or down just 10 feet can make a big difference -- particularly in the early morning and evening when temperature gradients are causing changeable patterns in the propagation. Which height is better depends on temporary conditions: of course, normally higher will be better -- but refraction can be tricky.

So the end of the story is "the wife wins" -- the dish goes, because it offers no advantage in my situation and it has been a butt-ugly novelty.

Sigh.

More updates after I get some more performance data.