> Randy,
>
> There could be 2 problems why you get desense. 1.overload by
> the other repeater tx, but more likely 2. his wide band tx
> noise, down maybe 85 db, is getting into your receiver...the
> wide band noise is actually on your rcvr freq.
I thought about that issue (Tx noise from the repeater) when I wrote my
original reply but didn't bother to comment on it. The offending
transmitter is a repeater, transmitting low (444.6) and receiving high
(449.6). Its duplexer, assuming it's pass/reject, and I can't imagine it
wouldn't be if it's at a commercial site, should provide a fair amount of
noise supression at the vicitim's receive frequencies in the 446.7ish range,
though not the full 90 dB or thereabouts that it provides on the repeater's
receive channel at 449.6. Maybe it's affording 40 dB or so of attenuation
at 446.7 as a WAG. When combined with the spatial isolation between
antennas (20 or 30 dB as another WAG), there should be a decent amount of
noise attenuation already.
In contrast, the victim receivers have no protection from the high-level
signal from the repeater transmitter, hence I would expect the lack of
carrier supression to be the first evil to combat. But, Tx noise supression
via additional filtering on the repeater Tx may ultimately need to be added
later if protecting the receivers from overload doesn't cure the problem.
Again, without having measurement data to work with, it's hard to say for
sure, but starting with filtering on the link Rx's seems like a logical
first step.
--- Jeff WN3A
