Originally Posted by Dee Barvo
With the DVR, most of the SF stations disappeared, but currently watching KTVU, 2 out of Oakland, and I have a perfect picture and no dropouts. This with the antenna aimed due north.
I performed a simple test inside the house to check my theory that the antenna pattern would be messed up if only one side of the coax was connected.
I set up a signal generator on UHF with a dipole as the transmitting antenna in a bedroom at the end of a hall that I could see in the kitchen 30' away. This reduced the reflections that could reach the receiver since the signal had to pass through a doorway. I used my little 8 element UHF LPDA as the receive antenna connected to my spectrum analyzer so I could measure the signal strength. I verified a normal antenna pattern with coax connected to the antenna. IOW the strongest signal occurred with the antenna pointing at the transmitter.
Then I connected a piece of coax that only had the center conductor making contact. The shield was open. The antenna pattern was completely changed and the signal was about 20 dB weaker. The weakest signal was when I was almost pointed at the transmitter. The strongest signal was when the antenna was off-pointed about 45°.
Since the 91XG is a different design than my LPDA, it would not be unexpected that the pattern with only half the coax connected would be much different.
My best educated guess is that you have an open connection somewhere in your system. It could be the cable. It could be the antenna balun.
Your symptoms fit the test results; best signals with the antenna off-pointed from the transmitters and weaker stations are not receivable. Also this would explain VHF reception. The antenna is not rejecting VHF as it should.
Because your Noise Margin on the Sacramento stations is so high, you can still receive them even with an antenna that has loss instead of gain. If you fix this problem you'll probably recover all the lost SF stations. It may very well kill VHF reception since the antenna will be working as designed and you'll have to add a VHF antenna.
I'd come up with something other than adding ropes and plastic to the 91XG to keep the TV's off of it. Maybe you could extend the mast just above the 91XG with PVC pipe and use a Tee junction with more PVC to be the same length as the 91XG boom and prevent the TV's from landing on it. You could use the end of the boom as a support for the long PVC. They could sit on the upper PVC.