Our group has substantial technical knowledge and experience, but we've been
just about beaten down by a problem with our repeater. A brief overview of
our situation follows.
We have a 222 MHz repeater comprised of a converted Micor mobile, Telewave
TPRD-2254 BpBr duplexer, AM-6155 PA modified for class C operation at 250W,
and a DB-264JJ antenna at 80 ft. fed by 1/2' Heliax on a commercial FM
broadcast tower . With the duplexer terminated into a load, we have about 1
dB degradation in sensitivity when transmitting. However, with the antenna
connected to the duplexer, we experience in excess 15 dB of desensitization.
We have eliminated other narrowband transmitters and analog TV transmitters
as contributing factors. We are left with a channel 12 digital TV
transmitter at an adjacent site as a key contributor to the problem. Our
hypothesis is that we have broadband IMD products from the mix of our
transmitter and the DTV transmitter that are appearing in and near our
receiver passband. Is it a "rusty bolt" problem or is there some other
non-linear component somewhere on the site or in our system that is the
mixing point - we don't know.
I'd be interested in beginning a dialog with anyone who might be able to
give us some further insight into this problem.
Regards,
Stu Benner
W3STU
Boonsboro, MD
