rjr@mgweed.UUCP (10/14/83)
I ran some tests on the tv system here over last weekend. Since i made an inquiry on tv signal distribution on the net and some of you kindly responded, I thought I would pass along some findings: I am 40 miles west of the transmitting stations, which are in Chicago. Most, if not all, are on the Sears tower and are almost line-of-sight here but the signals must be blocked somewhere since the levels are so low. The signal strengths are as follows: chan uv (300 ohms) 2 600 5 600 7 500 9 600 11 300 20 300 26 1000 32 1000 38 1000 44 500 60 1400 66 400 This was with the UHF and VHF antennas combined with the Winegard "antenna coupler" I mentioned previously. The signal is then split 2 ways via a passive 2-set coupler. Even considering that I am loosing half the signal to each set, the signals are not all acceptable. I believe that 300 uv is considered minimum usable on a 300 ohm system. Next I added a Winegard 4-set amplifier ahead of the field strength meter. It was a 75 ohm unit, so I preceeded and followed it with a pair of baluns. It exibited about 10dB of gain on VHF. On UHF, however, I had 8dB loss!!!!! This loss was caused by the baluns, determined by other tests. I also replaced the "antenna coupler" on the roof with a Radio Shack VHF/UHF splitter. I had previously checked it out and found no measurable loss through it. With the splitter in place, the signal strength (no amplifier) increased about 3dB. Conclusion: Baluns have about 4dB loss on UHF! (I tried other brands besides the original 2 also). Splitters work well backwards as antenna combiners for combining VHF and UHF antennas to one down-lead. My intended solution to the low signal levels will be to add a 300 ohm, 4-set amplifier. (By the way, hams, this Winegard amp rolled off rapidly below channel 2 so should help TVI situations). Bob mgweed!rjr K9EUI