Long Yagi for VHF (Ch 8-11)
 

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.p...1&d=1374168088

http://forum.tvfool.com/attachment.p...2&d=1374168094

http://forum.tvfool.com/attachment.p...3&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.

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Re: Long Yagi for VHF (Ch 8-11)
 

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?

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...

Research Communications Preamp and Balun
 

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.p...4&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.

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4NEC2 Analysis: YA-1713 & Homebrew Long Yagi
 

Analysis with 4NEC2 software 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 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.p...6&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 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 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.p...7&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.p...8&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.

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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!

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.

Thank you Pete for your kind remarks.

Long-Yagi Gain Assessment
 

Previously shown were computer simulations of antennas; 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.p...5&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 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. 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. 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.p...1&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.

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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.

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?

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.

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

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.

Single Long Yagi on Main Tower
 

In October 2010, a single long-Yagi 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.p...6&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.p...4&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.p...5&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.

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tripelo,

Another interesting read.

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} if you want to take a look. Last night, I ordered a second one to try with my tower array.

Two Long Yagis on Main Tower
 

The signals from a single long-Yagi 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.p...0&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,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.p...1&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.

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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.

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.

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.

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.

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.

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.

NTE/ECG U-106 Rotor
 

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.

Yes, I'm not sure either.

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.

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.

Multipath: Antenna Stack & Diversity Gain?
 

Following up on a partial response to Pete’s thought provoking question as to whether space diversity gain could be a mechanism for alleviating frequency selective fading, presumably originating as a result of multipath.

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.

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.

.

Antenna or Spatial Diversity
 

tripelo,
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.

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.

Multipath: Antenna Elevation Pattern Discrimination
 

Elevation angle discrimination is a possible mechanism allowing this vertical stack to reduce frequency dependent nulls, 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 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; overlaid is a stack at 89 inches.

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.p...2&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.p...3&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.p...4&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.p...5&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.

.

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.

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, 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).

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

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

Thanks for your comments about the elevation beamwidth and multipath.

No charge.

.

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?

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

Stacked Antennas: Multipath & Diversity Gain?
 

Continuing with a previous topic: Multipath: Antenna Stack & Diversity Gain?

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), 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.p...4&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, 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.

.

Multipath: STB-Converter Performance
 

The reception of WHAS-11 using the stack of long-Yagis 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/NABSTVDig...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://forum.tvfool.com/attachment.p...0&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. 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.p...9&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.

.

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

Post 3688

Thanks Pete. Glad you like.

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.

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?

Tripelo,

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.

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)

Quote:

Could you take some detailed photos of the innards?

Will try to take & post. Probably next week.

LNA-200 findings
 

tripelo,

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

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

Televes DAT-75 vs. Antennas Direct 91XG
 

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.p...6&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.p...7&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.p...8&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.

.

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).

Satellite dish mount on tower leg
 

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.p...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.

Hi Pete,


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

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.

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

Thanks Gil, for your kind remarks.

UHF Signal Strength vs Antenna Height (AGL)
 

In May 2012, Bob Nelson (forum member re_nelson) 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 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, 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.p...5&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.p...6&d=1410720896


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


http://forum.tvfool.com/attachment.p...8&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.

.

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.

[IMG]http://forum.tvfool.com/attachment.php?attachmentid=799&d=1410727208[/IMG]

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)