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Old 1-Feb-2016, 11:48 AM   #1
Hamilton Ham
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Join Date: Dec 2014
Location: Hamilton ON
Posts: 12
Change cable lengths-channels disappear

I finally got around to cleaning up the rats-nest of cables, A-B switches, splitters, pre-amps etc...After the cleanup, which essentially consisted of shortening up the cabling interconnecting the various components mentioned above, one or two channels would disappear from one TV, different channels would disappear from another TV etc. I feed 4 TVís from the antenna ďfarmĒ. The TV closest to the ďwiring jungleĒ suffered the most loss. I was trying to replace 3 or 4 foot cables with shorter ones of about 6 inches to a foot in length. After endless trips up and down the stairs, I ended up with the cabling lengths that I started with. It was the only way I could get all channels on all TVís at the same time. My question is, whatís going on here? Why does the length of the interconnecting cables affect the channels received? Is this some kind of SWR issue? Any clues as to what I should be looking for? The most troubling thing is that maybe in the past when I was chasing those elusive channels, maybe all I had to do was change the length of some cable somewhere! I wonder if some of those common problems with missing channels that so many others have reported, could be solved with cable length changes. Any comments or advise would be appreciated.
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Old 1-Feb-2016, 2:57 PM   #2
rickbb
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Join Date: Dec 2014
Posts: 338
Do you have an amp? The shorter cables could put it just over the threshold for overloading the tuners. At least that's my best guess.
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Old 1-Feb-2016, 7:19 PM   #3
Hamilton Ham
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Join Date: Dec 2014
Location: Hamilton ON
Posts: 12
I have an RCA preamp that makes up for cable losses in my longest run. Thatís where I get my best overall reception. My strongest signal is ch 35, -52dbm as measured at the antenna terminals. My weakest is ch 44 at -85 dbm. The next measurable signal up in frequency is about -80 dbm near 728 Mhz. By the shape of the waveform Iím guessing it is a cellular transmitter. On the lower end of the UHF band are some commercial repeaters in and around 460 Mhz. The strongest there is about -72 dbm. I have no problem with VHF Hi as there is only one station on ch 9 with a strength of -58 dbm. It, along with most of my UHF come LOS from the CN Tower 30 miles to the NE. Intermod does not seem to be a factor. The waveforms even around ch 35 are very clean. Iíve seen what intermod does when I tried to put too much amplification in the system. Also I donít know what the bandwidth is of a typical TV tuner. I have no idea what the rejection would be for out of band signals. I know at my location multipath is a significant factor. Aiming antennas is a challenge. A degree or two can make or break reception of a specific channel. My only thought is that the cable length problem is producing out of phase reception similar to multipath when a signal hits the TV antenna input. Again, any thoughts on the matter would be appreciated.
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