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Old 06-07-2013, 10:58 AM   #12  
Pete Higgins
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Join Date: Aug 2012
Location: California, 58 miles @112 degrees from Mt. Wilson
Posts: 242
Default HDB8X vs CM-4228

I do not claim to “scientifically” test or even fairly compare multiple antennas. I can, however, report my real world results, recognizing the constraints I’m faced with. Make what you will of the information. I can confirm that lugging antennas and climbing ladders was a lot easier 50 years ago. It must be something in the water?

Since I can’t raise or lower my pushup mast by myself, I fixed mounted the new Solid Signal HDB8X on it below the rotor. The bottom of the HDB8X is @ 21’ 7” AGL, 5’ 9” below the bottom of the 40 year old Channel Master CM-4228 (not a new “HD” model). For the last several weeks, the CM-4228 has been connected through a new white 17’ RG-6 cable to the base of the pushup mast, an F-81 F-F barrel, 50’ of new white Magnavox M61210 RG-6 to a coax switch in the garage. My Winegard YA 1713 was similarly connected through a new black 17’ RG-6 cable, an F-81 F-F barrel to a 32 year old piece of RG-6 that also ran to the coax switch in the garage. During amplifier testing I verified there was no SNR variance @ UHF frequencies between using the new white vs using the old black garage coax runs.

I disconnected the black garage RG-6 cable from my YA 1713 and used that piece for testing the new HDB8X. The garage coax switch was used to switch between the CM-4228 & the HDB8X. The single output of the garage coax switch is connected to a new ~75’ thru-wall RG-6, run to my office computer and Hauppauge HVR-1800 tuner card used for this comparison. In other words, everything from the coax switch in the garage to the point of measurement was common for both antennas.

Using the rotor, I “bump” aligned the CM-4228 for maximum SNR on LA channel 36 (4.1 KNBC) and then, by eyeball, “fix” aligned the HDB8X to match. I purposely did not try to introduce the variance of two separate amplifiers although looking at my TV Fool report amplification is certainly called for:

The HVR-1800 was tuned to a channel & the SNR recorded, I then ran to the garage to throw the switch, returnd and record the new reading, tuned to the next channel, record it and repeated the process. Measurements were alternated between antennas so that each antennas value was recorded 20~30 seconds apart.

I also included measurements from my <1 year old Antennas Direct 91XG/Antennacraft Y10-7-13. These antennas are tower mounted @ ~40’ AGL and have individual +15 dB PCT MA2-M drop amplifiers connected via either an F-71 M-M barrel for the 91XG or a 300 ohm to 75 ohm BALUM and short piece of RG-6 for the Y10-7-13. The output of each amplifier connects to a UVSJ feeding ~125’ of new RG-6 that connects in my garage to a PCT MA2-4P +8dB/output per leg distribution amplifier one leg of which feeds a separate new run of RG-6 into my office. A different HVR-1800 tuner card & computer were used to take these readings. This is clearly an apple to oranges comparison, but is in-part justified by the fact that when I swapped the 91XG & CM-4228 last summer there wasn’t a significant difference in amplified performance. If nothing else it should be predictive of what I might achieve by adding a +23 dB amplification chain to the HDB8X and mounting it on the tower.

If it were still made, I would certainly recommend the Channel Master CM-4228 over the HDB8X if for no other reason than its High VHF capabilities. Within its design frequency range the unamplified HDB8X average UHF SNR of 13.975 compares favorably to the 13.7429 of the unamplified CM-4228. .23 difference is well within my margin of reading error since the tenths digit for both antennas was constantly changing. Had I been able to align the HDB8X with a rotor I may have been able to improve its SNR, especially for the San Diego stations. Last summer when I swapped out my brand new tower mounted 91XG with the CM-4228 I was really surprised when it matched the 91XG SNR’s within 1-2 dB on all channels. The 91XG was better on slightly over half of the channels but the CM-4228 definitely held its own. For that test I replaced the 91XG’s F-71 M-M barrel to PCT MA2-M connector with an ~18” piece of coax to the CM-4228’s 75/300 ohm BALUM keeping the amplifier, UVSJ and coax paths to the measurement computer fundamentally the same for both antennas. Extrapolating those results to today’s tests leads me to conclude that at my location there isn’t a significant UHF performance difference between the three antennas.
Attached Images
File Type: jpg HDB8X Test 6 June 2013.jpg (105.1 KB, 52 views)
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