Thought I might take a minute to contribute a success I had with an inexpensive product. I live in the San Francisco Bay Area. I have two antennas on the same mast, without a rotor. We receive almost all channels from 2 main directions. Sutro Tower in San Fran and the NBC affiliate who recently moved to San Jose. Around here, a "cut" antenna for VHF Ch. 12-only, has become very popular, since the affiliate moved.
I live within 20 miles of San Fran and can see the tower from my roof. My area is bombarded with a lot of strong signals on both UHF and VHF.
I was getting a lousy signal strength on my Ch. 12 antenna. I tried about a million things to try and improve it. Nothing really worked. One of the guys at Schad Electronics in San Jose recommended that maybe I should install a channel 12 Channel Master product called Join-Tenna. Primarily, it is used for people who had a VHF/UHF combo and then added a Ch. 12 VHF antenna. The Join-Tenna not only combines the two to a single downlead, but also cuts the multipath problem of two, same band antennas.
It also has a wiring diagram to use the Join-Tenna for filtering. On the internal "signal strength" meter on my Hughes HDTV DirecTV receiver (which I know does not measure signal-to-noise, just db) I was getting about 30 before and after hooking up the Join-Tenna to "filter" other signals (or noise), the signal strength went up to 90. The drop outs have disappeared and the picture has improved wuite a lot.
Channel Master makes these tuned Join-Tenna's for other specific channel.