> 50 ohms is ONLY at the pass frequency. The concern here is
> that the wrong
> cable length between the pass cavity & duplexer can cause
> undesired effects
> at reject frequencies.
'zactly.
Although a bandpass cavity (or multiple cavities) is always a good idea in
front of any receiver, the original poster may want to take a look at what's
actually getting to the receiver in the current configuration. Lack of
attenuation of your own repeater transmitter carrier due to inadequte
duplexer isolation can result in overload of your receiver's first mixer (or
first RF gain stage, if it has one), aggrevating receiver-induced intermod
when other nearby transmitters key up. I've seen a number of repeaters that
seemed to play just fine without a hint of desense when running in a quiet
environment, but when other signals came down the hose, even ones that would
typically be considered "harmless" in terms of their low amplitude, suddenly
intermod was realized. In such a case, adding a pass cavity could help by
keeping the other signals out, but the crux of the problem is really too
much of your own transmit carrier hitting the front of the receiver.
--- Jeff
