AVS Special Member
Join Date: Nov 2001
Location: College Park, MD
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There's an insertion loss of the bandpass filter that might be dropping your signal strength below an acceptable level. It varies from one unit to another. It has been a long time since I seriously experimented with UHF jointennas on a bench, but I think the insertion loss of the bandpass path commonly varied from about 2 to 5 dB.
The other thing is, the band reject filters aren't very narrow, and the channel 23 band reject circuit could attenuate channel 20 on the thru path, and the channel 20 filter's reject circuit could reject the channel 23 on its thru path, so it is important to couple the weaker, problematic signal last in a string of jointennas. You might also benefit from lightly amplifying the channel 23 lead by 10 to 12 dB before inserting it into a filter, but whether you can get away with doing that will depend on the relative strength of the other signals coming off that line. If you only have a 15 to 20dB amplifier available, you can use it to preamplify the channel 23 line, but if you do, you might need to "double up" your two channel 23 Jointennas, using the first one on the preamplifier output just as a bandpass filter and using the second one for coupling.
Do you have a TV fool plot we can look at?