View Single Post
Old 30-Jun-2013, 1:21 AM   #40
Pete Higgins
Pete Higgins's Avatar
Join Date: Apr 2013
Location: California, 58 miles @112 degrees from Mt. Wilson
Posts: 83
HDB8X multi-direction progress update

tripelo & all,

I wanted to update my progress to show how I had the HDB8X configured for multi-directional reception. For some reason, I haven’t been able to connect to the TV Fool or FM Fool sites for the last several days. (“the site TV Fool is not responding”)

At my location, I really needed the extra gain of an 8-Bay vs. a 4-Bay, but when the signals aren’t faded this configuration seemed to work very well –without a rotor. When they are, even my CM-4228 & 91XG tend to drop in & out.

A couple of things worth noting are:

1. I am powering both amps. through the two panel signal combiner that came with the HDB8X.

2. The NF-471 completely removes RF channel 26 @ -15.6 dBm with the LA panel pointed right at it and the amplified & unfiltered San Diego panel that’s rotated ~123 deg. is also completely rejecting KVCR. I wasn’t expecting this. This panel does bring in RF channel 30 (KPBS @ -96.3 dBm) from San Diego with an SNR in the mid 20’s, so it obviously has good forward gain near channel 26 and very good rejection of it to the rear.

As you can see from my TV Fool report, RF channel 26, 294 deg.@ -15.6 dBm (plus I also have an FM station on 99.9 MHz also @ 294 deg. & -13.4 dBm) would severely overload my pre-amps., but all the rest of my San Diego (~168 deg.) and LA (~292 deg.) stations are 1 & 2 edge @ -85 dBm and below. That’s why I added the Channel Plus NF-471 notch filter that rejects off-air UHF TV channels 24 to 29 and the Antennas Direct FM Band reject filter to the AP-2870 LA panel amp.

Subsequent to the single HDB8X multi-direction experiments, I decided to try the CM-4228 in conjunction with the HDB8X. My reasoning being that the theoretical 3 dB of additional gain (~ doubling the signal power) would help compensate during the signal fades that always seem to interrupt the San Diego evening news.

Because it was the only device I’d found that would pass power to both amplifiers from a single coax, I queried Solid Signal about purchasing an additional HDB8X Frequency Mixer. They currently don’t list them for sale, but generously offered to send me one (@ no cost) from an antenna damaged in shipping.

I wanted to reconfigure the test installation to raise the HDB8X above the rotor to the same height as the CM-4228 so I could align its pattern for best SNR but unfortunately I can’t bring down my pushup mast by myself. When originally implemented I had two sons, a teenager and a college student, living at home to help. Now, one lives in Oregon and the other retired last year and lives 60+ miles away. Undaunted, I revamped the test configuration as shown below:

As with previous testing, I “bump aligned” the CM-4228 for best SNR on LA RF channel 36 (4.1 KNBC @ -107.4) and using its alignment as a guide, aligned the HDB8X as close as possible to the same direction. (This makes the assumption that as mounted, both antennas have the same radiation pattern –which may or may not be valid.)

After everything was in place & hooked up, with both antennas pointed towards LA, I measured an SNR of 24.7-25.3 for RF channel 36 (4.1 NBC). I also measured a SNR of 30 (as high as my meter registers) for RF channel 26 (24.1 KVCR) the -15.6 dBm PBS station 3.5 miles from my house and in line with all the LA stations.

Next, I rotated the CM-4228 towards San Diego, stopping @ ~168 deg. As the CM-4228 turned I noticed 2-3 dB fluctuations in SNR. I “bump aligned” the CM-4228 for best SNR on San Diego RF channel 40 (39.1 KNSD @ -95.2 dBm). I went back and measured an SNR of 23.1-23.4 for RF channel 36 (4.1 NBC). Interestingly, having both 8-Bays pointing the same direction added an additional 1.6-1.9 dB to the SNR. As with previous testing, with the CM-4228 8-Bay turned 123 deg. away from my local PBS station, it didn’t show any back lobe response. Unfortunately LA RF channel 31 (5.1 CW @ -103.5) falls within the Channel Plus NF-471 notch filter’s skirt and was lost. (Rotating the CM-4228/HDP-269 back towards LA brings channel 31 back without any signs of overload)

UHF signal-to-noise ratios from both LA & San Diego are usually 20 dB or greater and appear to stay about the same as a single 8-Bay when aligned with a rotor. More importantly, with a sample size of three afternoons, my San Diego news station dips from an SNR of ~25 to a low of ~18-19 in late afternoon to early evening. It had been dropping into the low 15.x’s where signal was lost. Most nights it holds the 18-19 and stays error free, climbing back up after sundown.

With my limited evaluation capability, last summer my new 91XG performed only slightly better than my “original” CM-4228. This spring my new HDB8X, similarly, performed slightly better than my “original” CM-4228. Therefore, I have to conclude that for my location there isn’t a significant performance difference between the three designs. It also suggests that the advertised gain is very optimistically over stated. Unlike long Yagi’s or LPA’s, Bow Tie designs are easily mounted to a tower leg or off the side of a house or balcony (J-Pole). Hinged designs, also afford convenient reception of multiple markets where a 4-Bay is sufficient.

Because of their price and observed performance, if I needed to design a system from scratch to feed UHF to multiple TV’s without the inconvenience of turning a rotor to view different markets, depending on TV Fool’s reported values, I’d be real tempted to try an unamplified HDB8X with the panels aligned for both markets. If signals were such that you couldn’t tolerate the “re-radiation loss” I’d order two HDP-269’s to help isolate the panels and overcome combiner, coax & splitter loss. Finally, if signals are really weak, (deep fringe) combining two HDB8X’s with two matched pre-amps. (HDP-269’s in an overload prone environment) might offer a cost effective solution. I did find this Splitter/Combiner which should support powering two pre-amps. through a single coax. lead-in:

SNR and antenna gain are not the same thing. I would really like to see gain comparisons and real world test results between the HDB8X that I have and some of the other hinged designs –some costing almost 4 times as much.
Attached Images
File Type: jpg HDP8X Multi-Setup -3.jpg (61.5 KB, 9499 views)
File Type: jpg 2 Ant Test-04.JPG (66.6 KB, 9007 views)

Last edited by Pete Higgins; 30-Jun-2013 at 1:24 AM.
Pete Higgins is offline   Reply With Quote