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Old 06-26-2013, 10:02 PM   #30  
Pete Higgins
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Join Date: Aug 2012
Location: California, 58 miles @112 degrees from Mt. Wilson
Posts: 265
Default Two Antenna Test (1- CM-4228, 1-HDB8X)

As I said in my last post, “At my location, I really need the extra gain of an 8-Bay vs. a 4-Bay”. 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 evening news.

Because it’s the only device I’ve found that will pass power to two amplifiers over 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 (Thank you Stuart).

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 an 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 8-Bay turned away from my local station, it showed no back lobe response.

This afternoon, UHF signal-to-noise ratios from both LA & San Diego were 20 dB or greater and appeared about the same as a single 8-Bay when aligned with a rotor. More importantly, with a sample size of one afternoon, my San Diego news station dipped from an SNR of 24.9 this afternoon to a low of 18.5 around 6:20 PM. It had been dropping into the low 15.x’s where signal was lost. Tonight it’s holding @ 18.9 and error free.

If I wanted to design a system from scratch to feed UHF to multiple TV’s without the inconvenience of turning a rotor to view different markets, I’d be real tempted to order one or two HDB8X’s & two HDP-269’s depending on how much antenna was need for a given location. Of course that’s predicated on a source of power passing signal combiners becoming available. Solid Signal -Hint, Hint.

Last edited by Pete Higgins; 06-27-2013 at 10:42 AM..
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