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

Interesting.

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

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

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

Stacked Antennas: Multipath & Diversity Gain?

The post, linked above, contains a drawing of stacked antennas and shows a direct wavefront (D) arriving at the lower antenna with a multipath wavefront (M=-D) arriving at the upper antenna. The signal summation would be less than the direct (D) alone.

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

.

UHF Signal Strength vs Antenna Height (AGL)
 

This post is a continuation of:

UHF Signal Strength vs Antenna Height (AGL)

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

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

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


http://forum.tvfool.com/attachment.p...2&d=1411227205

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

That is:

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

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

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

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

*Such transmitter/antenna info can be found at the FCC site, or more conveniently at Rabbitears.info.

Channel frequency does matter. The signal wavelength is inversely related to frequency and constructive/destructive combinations are a matter of signal phase (which is wavelength related). Signal strength differences at the receiving antenna are a result of the combination of frequency and path geometry.

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

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

.

tripelo,

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

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

http://www.highdefforum.com/local-hd...r-10-00-a.html

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

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

http://forum.tvfool.com/attachment.p...5&d=1411269035

rabbit73

Hi rabbit –long time again!

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

What I ended up with was the link displayed with IMG tags (see midway in post 80).

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

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

Intuitively obvious to even a casual observer?

Thanks rabbit.

You're welcome.

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

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

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

http://forum.tvfool.com/attachment.p...1&d=1411424172
It wasn't obvious to me until I learned how to do it. HA!:)

Compare Several Preamplifiers OTA-DFW
 

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

Preamps Compared (shown in image below):

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


http://forum.tvfool.com/attachment.p...1&d=1422111119


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


http://forum.tvfool.com/attachment.p...5&d=1422121160


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


http://forum.tvfool.com/attachment.p...4&d=1422121174


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

*Modulation Error Ratio (MER)

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

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

More to be posted, some tomorrow:

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

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

tripelo,

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

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

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

As always, great work!

Thank you ADtech and Pete. Your comments are appreciated.

That is a possibility.

Most would probably agree.

Yes

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

Interesting experience with preamps and drop amplifiers.

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

Yes

Compare Preamplifiers - Test Procedure & Configuration
 

Referring to Preamp Comparison data posted earlier.


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

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

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

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

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

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

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

Image depicting Test configuration shown below:


http://forum.tvfool.com/attachment.p...6&d=1422202514


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

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

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

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

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

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

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

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

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

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

http://forum.tvfool.com/attachment.p...8&d=1422238547


http://forum.tvfool.com/attachment.p...9&d=1422203105


More preamp test data to be posted later.

.

Fascinating read –well done!
 

tripelo,

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

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

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

The only amplifier that I’m aware of that filters that portion of the spectrum is the new Antennas Direct Juice. ADTech did an excellent write-up on that amp here:
http://www.digitalhome.ca/forum/show...01#post2406201

Looking forward to your follow-on.

Pete, thank you for your comments.

Your signal situation does seem particularly tough.

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

This DFW location is good for UHF test purposes.

That's a good idea.

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

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

Thanks for the info, looks interesting.

Compare Several Preamplifiers (cont.)
 

Referring to previous posts:

- Compare Several Preamplifiers OTA-DFW
- Compare Preamplifiers - Test Procedure & Configuration

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

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


http://forum.tvfool.com/attachment.p...1&d=1422653098


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

The highest output power is shown for the CM7777 versions:

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


http://forum.tvfool.com/attachment.p...3&d=1422653259


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

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

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

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

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

.

Some info please
 

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

Acme

Acme,

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

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

Homebrew 183Mhz
 

Compare Received Signal Strength of 5 UHF Antennas
 

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

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

Antennas:

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

Images of antennas at test location in a following post.

Test Location:

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

Test location TVfool info posted earlier:

Compare Preamplifiers - Test Procedure & Configuration

Test Equipment:

1. Sencore SLM1456 – Signal Level and MER measurements
(Scans channels one-by-one, dwells a few seconds per channel to lock and obtain a signal average, total scan time for 27 channels ~6-7 minutes)
2. DG8SAQ Vector Network analyzer -VNWA
(Measure scattering parameter S11 (complex input impedance->return loss/SWR)
3. Belden Coaxial Cable 1694A (40 feet)
4. Ferrite Cores at Coax to balun/antenna connection (Qty=4)
5. Balun for CM4228 (homebrew, hand-wound ferrite core, measured loss <1 dB)
6. Push-Up Telescopic Mast, 25+ ft.

Test Procedure

1. Calibrate VNWA, with the 40’coax cable (refers measurements to antenna/balun connection).

Starting with Terk HDTVi antenna:

2. Mount antenna w/coax and ferrites to mast, raise center of antenna to 25 feet
3. Align antenna for peak signal on Channel 29 (~central angle to DFW stations)
4. With 1456 scan all DFW UHF stations for signal strength and MER (record times)
(repeat scan, while in this configuration)
5. Take at least 2 Photos
6. Turn antenna ~90 degrees, disconnect coax from 1456, connect to VNWA
7. Measure S11 (input impedance, SWR/Return Loss) for the band
8. Lower Mast remove antenna
9. For each antenna repeat steps 2 through 8, finishing with a repeat of HDTVi antenna.

The test location and setup was similar to that described in previous posts:

Televes DAT-75 vs. Antennas Direct 91XG

UHF Signal Strength vs Antenna Height (AGL)

Compare Preamplifiers - Test Procedure & Configuration


Compared to previous tests, some differences in equipment, this test:

- No attenuator was used,
- Sencore SLM1456 instead of SLM1456CM
- Others, VNWA, etc.


Credit:

Forum member re_nelson provided much appreciated assistance throughout test planning, test, and follow-up.

RE_nelson also:

- Provided most of the antennas
- Provided the Sencore SLM1456
- Aligned antenna, operated the SLM1456, performed scans, & collected data.

Image below: RE_Nelson at the antenna test station with his Sencore SLM1456.


http://forum.tvfool.com/attachment.p...0&d=1461943453


The antenna mast is at far left behind the ladder and porch post. To aim the antenna, re_nelson observes SLM1456 and hand rotates antenna mast to maximize the signal strength indication.

(To be continued)

.

Images of 5 Antennas at Test site
 

(continued from previous post)

Part 2. Images of 5 Antennas at Test site

The following are images of the five antennas at the test site (antenna center height=25 feet).

Image below shows Terk HDTVi and CM4228 (old version)


http://forum.tvfool.com/attachment.p...1&d=1461943811



Image below shows Solid Signal HDB91x and Antennas Direct 91XG.


http://forum.tvfool.com/attachment.p...2&d=1461943818


Image below shows Antennas Direct DB8 (non-e).


http://forum.tvfool.com/attachment.p...3&d=1461943957


(To be continued)

.

Received Signal Strength Data Analysis
 

(continued from previous post)

Part 3. Received Signal Strength Data Analysis, Five UHF Antennas

Attached are four Graphs depicting a summary of data analysis.

1. Average Relative Gain, (Image below):


An average 2 scans of all channels for each antenna, relative to the HDTVi antenna.

http://forum.tvfool.com/attachment.p...4&d=1461944561


2.Average Relative Gain per Channel (image below)


A two-scan average of all antennas except HDTVi relative to HDTVi
(included four scans, two at beginning and two at end).

http://forum.tvfool.com/attachment.p...5&d=1461944568


3. Average SWR 5 Antennas (image below)


SWR was derived from measured S11 (Return Loss). The curves represent the
smoothed scan averages for each antenna.

http://forum.tvfool.com/attachment.p...6&d=1461944576


4. Mismatch Loss vs. SWR* (image below, see Note at end)


Table showing mismatch loss as a function of SWR.

http://forum.tvfool.com/attachment.p...7&d=1461944583



========== Comments ====================

The CM4228 had overall slightly higher signal levels, this was mainly due to better gain at lower channels.

The HDB91x delivered highest signal strength at mid and higher channels, and with exception at channel 20, 2nd highest at lower channels.

The 91xg pretty much tied with the HDB91x at very highest channels, with average levels at lower channels.

The DB8 was about average at lower channels similar to the two Yagis. At midband signal levels dropped and stayed lower thru upper band. The signal level loss at midband might be related to the SWR (approaching SWR=4, with nearly 2 dB mismatch loss).


Notes: SWR* & Mismatch Loss

SWR is a positive number representing how well the antenna impedance matches a transmission line. For Example: SWR=1 represents a perfect match, Antenna impedance transformed by balun or other means to 75 Ohms perfectly matches a 75 Ohm coaxial line. Greatly simplified a SWR of 2 could be that the antenna impedance is either 150 Ohms or 37.5 Ohms, either of which is mismatched by a factor of 2.

When there is an impedance mismatch at intersection of antenna and transmission line, there is a certain amount of signal that is rejected (cannot be transferred from the antenna into the transmission line). This loss is called 'mismatch loss'.

When modeling antennas in software (i.e. 4NEC2), to obtain the true gain (sometimes called 'net gain') the mismatch loss must be subtracted from the calculated gain.

When measuring antennas in field test or at an antenna range, the effect of SWR is incorporated in measured signal levels. So, no subtraction is required. One could add back in the mismatch loss and derive a gain-like number, this number would be the 'directivity' of an antenna.

In the case of the antennas above, if the mismatch losses were added back to the measured responses, then one would see that the 'directivity' of the DB8 might be nearer to the 'directivity' of the other antennas.


Derivation of SWR & Mismatch Loss

Scattering parameter S11 was measured with reference at antenna/balun terminals. S11 represents a complex (real and imaginary) reflection coefficient, which includes ‘return loss’.

From return loss (RL), both SWR and ‘Mismatch Loss’ (ML) can be can be calculated:

http://forum.tvfool.com/attachment.p...8&d=1461944589


(To be continued)

.

The HDTVi Antenna as a Reference
 

(continued from previous post)

Part 4. The HDTVi Antenna as a Reference

Another way of comparing gain of the antennas is to directly compare received signal levels to that of the HDTVi antenna. The HDTVi antenna was selected as a reference antenna mainly because it was thought that it’s gain would be relatively flat across the UHF band. Also it was thought that the SWR of the HDTVi would be relatively good (close to 1). Part of the reason for the above assumptions is that Log Periodic antennas can be designed to meet the criterion: flat gain and favorable SWR. The physical appearance of the HDTVI suggest as much.

A 4NEC2 analysis of the HDTVi tends to support the assumptions of flat gain and favorable SWR.

Below are images of the results of 4NEC2 analysis

http://forum.tvfool.com/attachment.p...9&d=1461945188


Top Image shows Gain in dBi (recall dBi=dBd+2.15), Lower image shows SWR


The above simulation SWR results agree favorably with the actual measurements. If the HDTVi gain were to be measured, likely it would also agree. If that were the case, than a direct comparison of the higher gain antennas with the HDTVi might provide insight.

Below is an image that shows the other four antennas compared directly with the HDTVi antenna:


http://forum.tvfool.com/attachment.p...0&d=1461945198



The above image illustrates the tendency of increasing gain of the four higher-gain antennas with increasingly higher frequencies.

As can be seen in this image and a preceding image, there is a discontinuity at channel 20 and channel 31. These two channels have lower signal strength than most of the others and also have been observed to exhibit multipath effects. The effects that were related to multipath were observed as part of a previous field test performed in May 2012, some results shown in a previous post (Ch 20 & 31 data were not presented).

UHF Signal Strength vs Antenna Height (AGL)

Omitting those points (Ch 20 & 31), the overall data might look smoother, but they were included for completeness.

The following image represents a best-fit linear approximation to the measured data and could illustrate some trends. Caution when interpreting this linear approximation; for a specific channel, it might be better to refer back to the raw data averages (shown earlier).

http://forum.tvfool.com/attachment.p...1&d=1461945205


Both Yagis show increasing gain with increasing frequency (channel number). The 8-bay bow tie, or panel array, antennas show a flatter response with some increased gain with increasing frequency.

CM4228 and DB8

Notable is the approximately 2 dB difference in gain between the CM4228 and the DB8. This difference could partially be explained by the increased SWR of the DB8 (about SWR=4 at mid band), an SWR of 4 could cause approximately 2 dB loss. Some of the signal strength difference and transmission line matching could be attributed to baluns. The DB8 balun was supplied by the manufacturer (Antennas Direct). The CM4228 balun was a homebrew hand-wound ferrite-core balun with a measured loss of less than one dB.

91XG and HDB91x

The measured signal level difference between the gains of the two Yagi style antennas is less pronounced. The HDB91x shows a clear advantage at the top end of the band, however this indication is partially an artifact of the linear approximation. Note the raw data average show signal levels from the two antennas to be fairly close near the upper end of the band. The reason for the overall differences is unknown, but could partially be related to a better impedance match to the transmission line. The S11 measurement of the HDB91x reveals a better impedance match starting at ~500 MHz (Ch 19) and upwards. It is known that the 91XG has an ~microstrip balun that in some ways resembles a usual half-wave loop (but is markedly different). The factory-supplied balun of the HDB91x has not been inspected.

After a first set of data on the 91XG was collected, it was thought something might be amiss. The 91XG balun housing was opened and inspected; a nut that holds the driven element to the balun seemed to not be tight. The nut was tightened and a second set of data was collected. The results of the second 91XG data set were close to that of the first set.

Overall, the appearance of the 91XG and the HDB91x seems similar. But, close inspection shows most component parts of the HDB91x are in some way different than the 91XG. There are measurable physical and electrical differences that may account for some of the difference in performance.

Test Location and Data Variability

Even though the test site is LOS to the DFW stations, some multipath has been observed with received signal on some channels. This is probably a result of the first Fresnel zone not being clear.

A repeat of each measurement probably helped reduce effects of brief transitory multipath effects. The individual data sets were fairly consistent. Measurements using the HDTVi at both beginning-of-test and end-of-test somewhat verified data consistency. The HDTVi final-measurements were about 0.2 dB lower in signal strength than the beginning-measurements. A scaled correction factor could have been incorporated into the data but was deemed unnecessary.

.

Compare: Antennas Direct C5 & Televes Yagi B-III
 

A series of antenna tests conducted on July 1, 2016.

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

Antennas:

1. Antennas Direct C5
2. Televes Band III Yagi

Antennas Direct C5: Driven element is a loop design (contains two loops, inner and outer) with reflector screen. The balun is ferrite core design.

Televes Band III Yagi: Folded-dipole driven element with reflector and five directors. The balun is sealed in metal can.

Images of antennas shown below:

Antennas Direct ClearStream 5 (C5)

http://forum.tvfool.com/attachment.p...9&d=1467817306


Televes Yagi B-III

http://forum.tvfool.com/attachment.p...0&d=1467817317



Test Location:

Garland, TX, ~30 miles line-of-sight to DFW stations, both VHF channels (8 and 9) located on same transmitting tower.

Test location TVfool info posted earlier:

Compare Preamplifiers - Test Procedure & Configuration

Test Equipment:

Same as previous*, except:

1. Sencore SLM1456CM instead of Sencore SLM1456
2. 3dB attenuator at input of Sencore SLM1456CM
(From antenna perspective, improves coax cable match to 75 Ohms)


*Previous similar test: Compare Received Signal Strength of 5 UHF Antennas

Test Procedure

1. Calibrate VNWA, with the 40’coax cable (refers measurements to antenna/balun connection).

Starting with Antennas Direct ClearStream 5 antenna:

2. Mount antenna w/coax and ferrites to mast, raise center of antenna to 25 feet
3. Align antenna for peak signal on Channel 8
4. With 1456CM scan DFW VHF stations (Channels 8 & 9) for signal strength and MER.
(repeat scan 9 times while in this configuration, record times).
5. Take at least 2 Photos
6. Turn antenna ~90 degrees, disconnect coax from 1456, connect to VNWA
7. Measure S11 (input impedance, SWR/Return Loss) for the band
8. Lower Mast remove antenna
9. Mount Televes Yagi B-III, repeat steps 2-8
10. Then again, for each antenna, repeat steps 2-9


The test location and setup was similar to that described in previous posts:

Televes DAT-75 vs. Antennas Direct 91XG


Credit:

Thanks to Stuart Sweet of Solid signal for providing the Televes Yagi B-III.

(To be continued)

.

Part 2. Images of the Two Antennas at Test site

The following are images of the two antennas at the test site (antenna center height=25 feet).

Image below shows Antennas Direct ClearStream 5 and Televes Yagi B-III.


http://forum.tvfool.com/attachment.p...1&d=1467817525


(To be continued).

.

Part 3 (continued from previous post)

Attached are Graphs depicting a summary of data analysis.

1. Average received power levels, (Image below):

An average 9 measurements of each channel (8 & 9) for each antenna (ClearStream 5 and Televes Yagi BIII).


http://forum.tvfool.com/attachment.p...3&d=1467817772


2. Average Relative Gain per Channel (image below)

A nine-scan average of both antennas.


http://forum.tvfool.com/attachment.p...4&d=1467817778


3. Average SWR 5 Antennas (image below)

SWR was derived from measured S11 (Return Loss). The curves represent the
smoothed scan averages for each antenna.

http://forum.tvfool.com/attachment.p...5&d=1467818016



For mismatch Loss vs. SWR, see previous post*.

*Received Signal Strength and Data Analysis


No mismatch loss for SWR equal to 1, a SWR of 2 results in a mismatch loss of about 0.5 dB.


========== Comments ====================

The Antennas Direct ClearStream 5 (C5) and Televes Yagi BIII provided nearly the same average signal strength for Channel 8 and 9, with an approximately 0.1 dB advantage for the Televes antenna. Since 0.1 dB is near the measurement accuracy limits of the test configuration, the difference may not be very significant.

The per channel data shows that the Televes antenna provides a higher signal on channel 9 (by about 0.2 dB) relative to the Antennas Direct antenna. This could be a result normally expected of Yagi type antennas, that is the gain increasing with increasing frequencies, up to the design limit.

Test Location and Data Variability

Even though the test site is LOS to the DFW stations, some multipath has been observed at UHF with received signal on some channels. However, effects of multipath have not been explored at VHF frequencies, and there have been no symptoms to suggest it might be prevalent.

Several repeats of each measurement probably helped reduce any effects of brief transitory signal variability. The individual data sets were fairly consistent. Measurements using the Antennas Direct ClearStream 5 at both beginning-of-test and end-of-test somewhat verified data consistency. The Antennas Direct ClearStream 5 final-measurements averages were within a few hundredths of a dB of the signal strength of the beginning-measurements average.



(To be continued)

.

Part 4 (continued from previous post)

4NEC2 Analysis and Discussion

Antenna simulation software (4NEC2) could be useful in comparing antennas. Generally, software analysis is not a substitute for field tests. Choices must be made of available approximations that are necessarily incorporated in software models. Without some field measurement data to guide the design of a simulation model, rarely does a simulation model account for all factors in an antenna design.

In cases where field data is limited, but available enough to help confirm the models and if one can be fairly sure the software model something close to reality, then software analysis can provide insight.

The physical dimensions of both antennas; the ClearStream 5 and the Televes Yagi B-III were measured and software models created in 4NEC2.

The gain values shown in the following 4NEC2 results do not include balun loss or mismatch loss.

Below are images of the results of 4NEC2 analysis

Top Image, Gain in dBi, Lower image SWR

(Recall dBi=dBd+2.15)


http://forum.tvfool.com/attachment.p...6&d=1467818232


The above simulation SWR results agree favorably with the actual measurements.

If the Antennas Direct ClearStream 5 gain were to be measured, likely it would also agree.

Below is an image that shows the Televes Yagi B-III antenna gain and SWR:


http://forum.tvfool.com/attachment.p...7&d=1467818239




The shape of the Televes SWR pattern above above is in reasonable agreement with actual measurements (see previous post). Overall, the SWR is lower than measured. No explanation has been found. It could be that the software model does not account for some factor that could alter the SWR values. Another possibility is that the balun (not modeled) could contribute to the SWR difference. For example; In some cases LC components are added to a balun to improve response at band edges at the expense of impedance match at center band.

The above image illustrates the tendency of increasing gain for higher frequencies, often seen in Yagi-type antennas.

These simulation results are also in fair agreement with data present at the two manufacturers websites:


Antennas Direct ClearStream 5

Gain and SWR (simulations of both, plus measured values of SWR at 10 ft AGL),

Located in this document:

https://www.antennasdirect.com/cmss_...with%20uhf.pdf


Televes Yagi B-III (Gain),

Located in this document:

https://www.televes.com/sites/defaul...ennas_en_0.pdf


Azimuth Beam Width

The following images show the computed azimuth (horizontal) antenna patterns of the two antennas at three frequencies representing lower end of the band (174 MHz), mid band (194 MHz), and upper end of the band (216 MHz).


http://forum.tvfool.com/attachment.p...8&d=1467818461



Note the C5 has a somewhat broader beamwidth, especially evident at the upper end of the band, than the Televes antenna.


http://forum.tvfool.com/attachment.p...9&d=1467818471

http://forum.tvfool.com/attachment.p...0&d=1467818478



The difference in gain at 216MHz is mainly related to increasing gain from the Televes B-III. The Televes B-III is advertised to cover up to 230MHz, so it is expected the gain would be higher at the upper end of the band.


(To be continued)

.

Part 5 (continued from previous post)

Specifications, Measurement, Analysis and Discussion

In an effort to reconcile the various gain and SWR numbers available for these two antennas, the following chart was composed.

For each of the two antennas and each channel (8 and 9), the gain and SWR are presented. The sources for the gain and SWR are listed in the left column.

The manufacturers numbers are derived from the technical documents found in the links provided in a previous post. Antennas Direct lists gain figures as dBi, very likely the Televes numbers are also in dBi.

The 4NEC2 results are from simulations described in the immediately previous post. The gain numbers (dBi) listed here are calculated to include mismatch loss due to SWR.

The DFW Measure numbers are a summary of actual measurements at 25 ft from a location in Garland TX (described in a previous post). The units of values listed as gain are dB, either positive or negative relative to that averages of the two antennas (per channel).


http://forum.tvfool.com/attachment.p...1&d=1467818654


Summary and Discussion

These two antennas are of different design, but for the channels tested yielded relatively close gain and SWR numbers.

The Antennas Direct antenna consists of driven element loops (inner and outer) with a screen reflector. The loop is made of relatively thick conductor that helps to broaden frequency response (flattens SWR). This design is in some ways similar to two stacked dipoles (top element fed at ends instead of center fed). This stacking effect tends to compress vertical beam width, thus for a given amount of total gain, allows for a slightly wider horizontal beam width. This C5 antenna being a relatively broadband design tends to have a flat gain and SWR response across the entire VHF high band.

The Televes antenna is a conventional Yagi design with folded dipole driven element. This design tends to have increasing gain with increasing frequency, up to the design limit. According to Televes literature the design limit is 230 MHz (the upper channel in the European band). Conventional Yagi designs tend to have a flattened oval shaped aperture (area over which signal is gathered). This flattened oval-shaped aperture shape means more of the antenna gain is a result of horizontal beam becoming narrow. So, one would expect the beam width of the Televes antenna to become more narrow at higher frequencies (where the gain is highest).

Since much of the data presented in the above preceding chart is in agreement.

The above chart for these two antennas tends to indicate:

1. Antennas Direct and Televes gain figures are consistent with each other.

2. Manufacturers gain numbers are consistent with 4NEC2 simulation results.

3. Antennas Direct SWR values are consistent with actual measurements (at 25 ft. AGL).

4. Computer simulations combined with field measurements can be used to characterize antenna performance, in some cases.

.

Compare: Antennas Direct DB8e & CM-4228HD
 

Antenna tests conducted on June 15, 2017.

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

Antennas:

1. Terk HDTVi (as reference)
2. Antennas Direct DB8e
2. Channel Master 4228HD

Terk HDTVi antenna measured as reference (see previous posts).

Both Antennas Direct DB8e and Channel Master 4228HD are panel type antennas, also known as 8-bay antennas.

Main differences between the two panel antennas are feed system design and reflector backplane.

Images of antennas shown below:

Antennas Direct DB8e

http://forum.tvfool.com/attachment.p...6&d=1498307192

Channel Master 4228HD (below)

http://forum.tvfool.com/attachment.p...7&d=1498307234


Test Location:

Garland, TX, ~30 miles line-of-sight to DFW stations.

Test location TVfool info posted earlier:

Compare Preamplifiers - Test Procedure & Configuration

Test Equipment and Test Procedure:

For details of test equipment & procedure, see previous similar tests:

Compare Received Signal Strength of 5 UHF Antennas

Compare: Antennas Direct C5 & Televes Yagi B-III


Credit:

Thanks to forum members ADtech and re_nelson for providing the Antennas Direct DB8e antenna.


(To be continued)

.

Compare: Antennas Direct DB8e & CM-4228HD
 

(Continued from previous post)

Part 2. Images of Three Antennas at Test site

The following are images of the two antennas at the test site (antenna center height=25 feet).

Image below shows the reference antenna: Terk HDTVi


http://forum.tvfool.com/attachment.p...8&d=1498307949


The image below shows both the Antennas Direct DB8e (left) and the Channel Master 4228HD (right).

http://forum.tvfool.com/attachment.p...9&d=1498307986

(To be continued).

.

Compare: Antennas Direct DB8e & CM-4228HD
 

(continued from previous post)

Part 3. Data Collection & Analysis

The amount of data collected represents:

Number of UHF channels: 23
Measurements per channel
DB8e4 and 4228HD: 9
HDTVi: 12

Total (individual channel measurements): 23 x 9 x 2 + 23 x 12 x1= 690

Attached are Graphs depicting a summary of data analyses.

1. Average received power levels, (Image below):

The image below represents an average of 23 UHF channels, nine measurements per UHF channel for each antenna (4228HD and DB8e), 12 measurements per channel for the HDTVi.


http://forum.tvfool.com/attachment.p...0&d=1498308360


The image below shows the received signal strength per UHF channel for the three antennas. Note signal strength is shown in dBmV (dB referenced to milliVolts in a 75 Ohms system. To convert to dBm (milliWatts) subtract 48.75. from the dBmV numbers.


http://forum.tvfool.com/attachment.p...chmentid=2751&


The image below shows the received signal strength of the DB8e and 4228HD antennas in dB, relative to the HDTVi antenna. The HDTVi signal strength is referenced to zero on the vertical dB scale.


http://forum.tvfool.com/attachment.p...2&d=1498308424


The image below shows a linear best-fit approximation of the received signal strength of the DB8e and 4228HD antennas in dB, relative to the HDTVi antenna.


http://forum.tvfool.com/attachment.p...3&d=1498308449


The following image shows SWR for the three antennas, it was derived from S11 (Return Loss), measured at 25 feet AGL.

The fuzziness of the lines in the SWR graph results from simultaneously receiving the broadcast stations in DFW with the Vector Network Analyzer. The reception of these strong signals caused some interference with the live impedance measurements. The antennas were not turned away from the stations as was done in previous measurements


http://forum.tvfool.com/attachment.p...4&d=1498308464


All three antennas have respectively good values of SWR. No mismatch loss for SWR equal to 1, a SWR of 2 results in a mismatch loss of about 0.5 dB.

Antennas Direct Technical data sheet indicates the SWR is less than 2 from 470 to 698 MHZ. The SWR measurement shown above for the DB8e is fairly well in agreement with Antenna Direct published specifications. Published SWR specifications for the 4228HD are not available.


For mismatch Loss vs. SWR, see previous post*.

*Received Signal Strength and Data Analysis


========== Comments ====================

The Antennas Direct DB8 provides highest overall signal strength, with an advantage over the 4228HD at high channels approaching 4-5 dB. TheCM4228HD performs well for channels below about channel 23, with an advantage of more than 1 dB at the lowest end of the band.

The 4228HD appears to have reduced gain as the frequency increases. The reason for this phenomenon was not investigated in this effort. However, it may be related to the transmission line feed for individual driven elements in the 8-element array, and particularly the feed between the two 4-bay segments.

Others have explored this 4228HD gain effect:

HDTV primer: Designed an improved antenna transmission line feed.

Antennahacks: Implemented an improved transmission line feed system.


Test Location and Data Variability

The test site is LOS to the DFW stations, however effects of multipath have been observed at UHF with received signal on some channels

Several repeats of each measurement probably helped reduce any effects of brief transitory signal variability. The individual data sets were fairly consistent. Measurements with the HDTVi, at both beginning-of-test and end-of-test, somewhat verified data consistency.

(to be continued)

.

Compare: Antennas Direct DB8e & CM-4228HD
 

(continued from previous post)

Part 4. Compare 6 antennas (DB8, DB8e, 4228, 4228HD, 91xg, HDB91x)

Having earlier measured four other high-gain UHF antennas relative to the HDTVi antenna, this could suggest that all six could be compared.

http://forum.tvfool.com/showpost.php...2&postcount=99

The main link between the two data sets is the measurements of the HDTVi antenna. The HDTVi was used as a reference antenna in both experiments. Realizing that errors can accumulate, a direct comparison of the two data sets might be somewhat useful.

Below is an image that shows the other four antennas compared directly with the HDTVi antenna:


http://forum.tvfool.com/attachment.p...5&d=1498309317


The Yagi antennas (91xg and HDB91x) stand out as having higher gain as the channel number increase. The two Yagis appear to have the highest gain available at the top of the UHF band.

It appears that the older CM4228 (non-HD) is a fairly good match to the newer DB8e, both show a wideband response with relatively high gain at the lower channels.

If the above graph were accurate for every channel (which is doubtful), one could add the gain of the HDTVi to every antenna, to obtain a total gain figures. Previous calculations show the gain of the HDTVi to be about 6.5-7 dBi.

Caveat: Keep in mind that real antenna gain patterns are rarely (if ever) linear, and the above chart (although based on measured data) is an approximation.

.

A Tower & Antenna Evolution
 

The tower shown in previous posts has been in use since 1971. It is located in Russell County, KY. The earlier posts showed some antennas that have been resident on the tower. Hopefully, a series of posts could show nearly all that antennas that have been on the tower and some rationale as to the purpose of those antennas.

In 1971, with the help of my younger brother, tower sections were individually lifted & assembled, then two antennas installed with a Channel Master rotator.

- Channel Master Crossfire CM-3600 VHF antenna
- Predecessor to CM-4228 UHF antenna (shown previously)

The image below shows the almost completed project of installing antennas just after the final tower section was placed. The 2nd image shows an excerpt from Channel Master literature describing the new 'Crossfire' antennas.

http://forum.tvfool.com/attachment.p...7&d=1514911861

http://forum.tvfool.com/attachment.p...8&d=1514911873


The next image shows the predecessor to what is now know as the old CM-4228 UHF antenna (previously posted).

http://forum.tvfool.com/attachment.p...9&d=1370105543


The objective was to receive stations from 3 cities:

- WAVE-3 Louisville (~101 miles, across typical hill & forested areas)
- WHAS-11 Louisville (~101 miles, across typical hill & forested areas)

- WLEX-18 Lexington (~77 miles, across typical hill & forested areas)
- WKYT-27 Lexington (~74 miles, across typical hill & forested areas)

By rotating antenna, receive:

- WATE-6 Knoxville TN (~93 miles, mountains in between)
- WBIR-10 Knoxville TN (~93 miles, mountains in between)

For most of the stations above, allowing for a bit of 'snow', reception was satisfactory mornings and night. Reception could be unreliable during day.

With the antenna rotator, this might have been a good setup for DX’ing. Stations could almost regularly be seen from various cities in Indiana, Ohio, Tennessee, Virginia, and West Virginia.

Maybe later, more details of subsequent antennas.

.

Best information available. THANK YOU
 

tripelo,

Really interesting material. I always look forward to your posts. Hope the New Year finds you & yours in good health.

Situation: 70-120 miles away from some very big signals (1 MW), but almost nothing less than 30 miles away. Everything is UHF except VHF 7 and 11.

Goal: Grab every signal I can; currently at about 75 virtual channels (but up to 100 are possible)

Baseline: Stacked AntennaCraft Yagis with WG7870 combiner CM7777 preamp. Due to wife's objections, these are at about 15' AGL (although we're near at the top of a hill, the signal has to pass through some treetops).

Hypothesis: Hotter antenna (think CM4251) would do the trick. But...why not go even bigger with the parabolic reflector? Acquired 10' C-band satellite dish, repurposed with bow-tie element.

Photos, measurements, and lessons learned: when it stops raining.

I've been working on a similar project, w/ a couple of 8 footers for the last couple of years.
I have the bowties and reflectors built, but will need to reconfigure the suspension conduits higher, or lower for focal point due to the bowtie placement conflicting w/ the same distance as where the old horn mount is.

Oh well, eventually.

First Impressions with 10 foot parabolic antenna
 

So, the first thing you have to realize is that the 10' C-band antennas are pretty solid, heavy and with a fair degree of wind resistance. As the reflecting surface is typically expanded metal with 2 mm perforations, this thing is going to present quite a wind load. Even after removing all the C-band electronics and unnecessary aiming motor, the parabolic and its mounting structure is probably 150 lbs...so this is not going up on a mast.

http://www.saleslogistix.com/IMG1.jpg

What it does get mounted on is 3" galvanized steel, and for obvious reasons that pipe needs to be at least 5' out of the ground. In my case, I went for 7 feet out of the ground...but that means 5' in the ground, surrounded by at least 300 lbs of concrete. Unless you have a really big augur, it's hard to do much more than that. Luckily, the ground drops off significantly from where the pole is, so it's effectively maybe 12' AGL.

Once the dish is mounted, configuring the antenna element is pretty straightforward. I live in an area with almost no signals in any direction, so I don't need a reflector behind the antenna element: it's just a matter of making the element (bow-tie) the right size and in the focus of the dish.

http://www.saleslogistix.com/IMG2.jpg

According to theory, the bow-tie is of infinite size...and I'd like to get down to to channel 7 so the wavelength is almost 2 meters. But the focus of the dish is probably less than a meter across, so there's not going to be any advantage to an bow-tie even that big. My first pass is with bow-tie wires 16" long. (I will experiment with solid bow tie and other variations in a week or so.) Through experimentation and measurement, I find the best distance for the bow-tie element and we're off to the races.

http://saleslogistix.com/IMG3.jpg

My main signal challenges are about 100 miles away, and my baseline for comparison metrics is a pair of yagis, with the bottom one about 12' AGL actual...but due to drop off of ground level effectively 17' AGL. According to the models, I shouldn't be getting much of anything...but with the stacked yagis and a nice preamp most of the time I get about 75 virtual channels (from about 20 transmitters). The new dish with a preamp gets nearly all the channels the same way, and the first pass of spectrum analysis (using the Nuts about Nets USB-based system on a PC) shows nearly identical signal strength. The dish is more directional than the Yagis (no surprise) but not as super-directional as I was worried about.

So now: how do I make the bow-tie outperform the Yagis? They are signficantly farther off the ground, which gives them a big gain advantage (I'm guessing 6 dB)...but the "collecting surface" of the dish should give the bow-tie even more than that.

The answers come next time I have time to mess with it.

I have a pair of 45' towers each sunk in 35 60# bags of ready mix and various engine blocks and bicycle frames, so I'm confident I can go up at least 2 sections. I just need to fabricate clamps.

Big dish on tower
 

Wow, well if you've got a 3000 lb+ foundation that's cool.
I'm not sure how you're going to get the dish very far up in the air--you'll need to set up some sort of winch system or use a very tall bucket. Just don't try it on a windy day--the dish becomes quite an unwieldy sail.

Thanks for the interesting photos of your dish.

Bowties are full wave dipoles. Since they are a collinear pair of dipoles spaced very close together, they don't have a lot of gain over a halfwave dipole. I suggest you use a stacked pair of halfwave dipoles, one above the other, fed in phase, for smaller size and greater efficiency at the focal point. A vertical spacing of 5/8 wave at the design frequency would give max gain. Adding a reflector behind the dipoles would give additional gain.

http://www.w1ghz.org/antbook/chap6-2.pdf

Thanks for the tips, and the reference to the antenna book! Seems like all of its characterizations are for transmission...but they should apply reflexively to reception.

I'll give the stacked dipoles a shot. In the "duh" department: won't I have an impedance mismatch when using stacked dipoles (I'm feeding a 300 ohm balun)?

Bowties are actually "supposed" to be solid (rather than "whiskers") for maximum gain...I'm going to be giving that a shot and will tell you the results.

However, given the special case of bowtie in the focus of a parabolic reflector I doubt that a reflector behind the bowtie (or dipoles) would help much: at that point, the waves are out of focus and bouncing off at a range of angles from 0 to about 120 degrees, causing a bunch of phase cancellations. Given I'm trying to use this from 170 to 700 MHz, I'm doubtful there's an optimum at all ;-) I don't have any issues with front/back ratio as there are no signal sources within 30 miles of me, and the landscape around me shields unwanted strays.

I'll give it a try and report back here.

Comparative designs, tests and results--the 10' parabolic
 

So with COVID-19 I have time on my hands at home and did a bunch of comparative measurements. Used Nuts About Nets spectrum analyzer to compare--the only variation in the configuration was the final antenna.

Note that the dish is mounted on a short pole (due to wind loading issues, couldn't go higher) but the ground level slopes off and the dish is effectively maybe 10 feet above ground level.

Also note that this would have to be called deep-fringe conditions--the nearest real station is 75 miles away and some of the stuff I'm shooting for is 125 miles away. Due to atmospherics, signal strength varies significantly during the day, so I always did my measurements within the same hour and comparable weather conditions.

Baseline was as shown in the photos above--very thin copper "whiskers". They are long because (1) I'm trying to get some VHF channels and (2) from what I read, making them longer doesn't significantly hurt the UHF.

Modified the whiskers to make solid triangular pieces. Within the variability of the signal/atmospheric effects, no measurable difference.

Put a reflector screen behind the active elements. No appreciable difference

Modified the whiskers and made "stacked" dipoles. Maybe 1 dB difference.

Took a Channel Master 4228 HD antenna and used that as the active antenna (facing in toward the dish). Depending on its location in the dish focal plane, got up to 5 dB of gain. The 4228 HD can be modded to improve its gain by another 3 dB (there are a couple of sites that describe how to do this)--I didn't make those mods, but I'll believe the claims.

But---the advantage of the parabolic, collecting a huge amount of signal, is fighting the disadvantage of "no altitude". And the measurements showed that it's a losing battle.

I took the Channel Master and raised it about 15 feed higher than the parabolic--and got more signal at every channel from the naked 8-bay bowtie at that altitude. Sigh.

Then I did a comparison of the Channel Master versus a pair of stacked broadband Yagis (AntennaCraft) and got surprising news: at almost every frequency, the Yagis beat the Channel Master. Obviously in VHF (actual channels 7, 8, and 11) there was no contest...but even in high UHF the Yagis were providing more signal, or were within a dB or two of the Channel Master.

So in this deep-fringe reception area, the lessons are pretty clear (even if somewhat counter-intuitive):

1. Altitude trumps everything else (duh)
2. If you need VHF channels, a Yagi or two is in your future
3. The 10-foot parabolics don't offer that much of a gain advantage at terrestrial TV frequencies (this was a surprise to me)
4. Modifying the active elements of the antenna didn't make as much of a difference as I'd expect
5. I'm glad I ordered the Channel Master via Amazon, as they allowed me to return it

Although this has turned out to be a wild-goose chase (I'm back with the Yagis I started with), hopefully my experience will persuade some of you to not go down this path unless you have a really strong tower to put your 10-foot, 100 pound parabolic on.