Some Antenna Photos and Tests

[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]

Originally Posted by Pete Higgins

... 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 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, 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.




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 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.

[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]

Originally Posted by Pete Higgins

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 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. 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.



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.



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.

Originally Posted by Pete Higgins

... 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, 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 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.



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]

Originally Posted by Pete Higgins

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]

Originally Posted by 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.

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.



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]

Originally Posted by Pete Higgins

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. 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).



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 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 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.



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.

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