> The repeater might be getting into the PA stage of the APRS
> radio. Try
> powering off the APRS radio during the time that you hear the weird
> noise. I would bet that the noise goes away as soon as the APRS radio
> in powered off.
What kind of radio is being used for APRS? If it's something like a
ham-grade transceiver, it's almost guaranteed to have a PIN diode for T/R
switching. When crunched by the high-level RF from the repeater
transmitter, it's probably making a racket...
As others have said, you simply don't have the filtering you need to make
this work right. Isolators on both transmitters would be a good start given
the tight coupling between antennas; to add an isolator to the APRS radio
may mean having to switch to another radio (perhaps a better one) that has a
real T/R relay or other means for getting the isolator into the transmit RF
path.
Then start looking at what it's going to take in terms of filtering to get
the carrier and noise rejection required, which will vary depending on what
you're using for radios, how much isolation you have between antennas
(should be *measured*, not guessed at), etc.
Why are the two antennas in the same plane to start with? Can't they be
relocated to get some vertical separation?
--- Jeff WN3A
