Can the FM stations audio be heard fairly clearly? If so, something in the repeater is demodulating it. If it were getting into the front end of the repeater it wouldn't be demodulated properly as the FM station is far too wide, usually at least plus/minus 75khz or more.
Could be some semiconductor junction being slammed with the rf... possibly in the controller. Bypass caps and/or ferrite chokes may be the answer, but it may require a lot of patience and experimentation. Star vat the repeater transmitter audio input, and work your way back through the controller to the receiver. If that doesn't get it, start the same routine with all control lines, grounds, etc.. Yah never know when you're dealing with that much of an RF field.. Been there, done that many times. Dave Fortenberry NA6DF Salem Communications Sacramento (kfia/ktkz/ktkz-fm/kkfs) etc, and further more.... 7treez! --- In [email protected], "Jeff DePolo" <[EMAIL PROTECTED]> wrote: > > > Question: The only way I see this happening is due to some AM > > component on radio station's transmitter. > > > > Thoughts? > > Virtually all FM transmitters have some residual/undesirable AM components. > If the AM follows the applied FM modulation, it's referred to as synchronous > AM, and is usually caused by bandwidth limitations. A properly-performing > FM broadcast transmitter will have synchronous AM products more than 40 dB > dB down, with -50 dB being a good goal to target. > > Transmitters, especially tube types, may also have asynchronous AM noise > which is often caused by residual ripple in the power supply(s) which has > nothing to do with the FM audio. > > If what you are truly seeing is a function of AM rectification due to RF > ingress into the repeater/controller/wiring, RFI filtering would be the way > to go. > > Does the "low level" audio persist even when the repeater receiver squelch > is closed, or is it heard only when there is user traffic? > > --- Jeff >
