It appears you have a good handle on it. The only thing I would suggest
trying is to put a Micor or MASTR II set of helicals on the front end of
your receivers. That would give you much more selectivity and could get
rid of the desense. Of course, being 220 it would have to be a modified
set.
BTW, a couple of feet should make no noticable difference as far as
coverage, but could greatly improve the isolation between the repeaters
since the antennas overlap now.
Joe M.
Michael Singewald N1PLH wrote:
>
> You guys were very helpful with our last co-location problem (147.225-
> and 146.925+), now I have another.
>
> Now another gentleman put up a machine on 224.340/222.740 near a
> machine on 443.550/448.550. When 220 comes up, it keys the 440
> machine. When 440 comes up it desenses the 220.
>
> Both have Stationmasters on the same tower and the antennas overlap
> about 2 feet (440 is above 220). I believe both are using BpBr
> duplexors. 220 is running around a 90 watt amplifier. 440 is at
> about 20 watts. 220 has a preamp with some sort of filter in front
> of it. 220 is a Hamtronics, and 440 is a Kendecomm. I know the
> solution could involve switching to Moto/GE but before they do that,
> what can be done first to work with what is available?
>
> I bench tested the 220 rx at .15uv for 12db sinad without the
> preamp. So I told the guy to first ditch the preamp and see if that
> helps his desense on 220.
>
> I thought a bandpass on each machine might help but I don't know what
> effect it would have on what I suspect is the culprit, the harmonic
> of 224.34 which is 448.68...very close to 448.55 the input on 440.
> Also, Tx/Rx says they don't make a 220 bandpass.
>
> Moving the 220 antenna down 10 feet might do the trick also, but I
> think this guy wants to keep all the height he can since this is only
> a 75ft tower to begin with and he is side mounted at about 60.
>
> BTW, this hill has 2 VHF, 2 220 and 2 440 machines on two towers. I
> suspect that makes it a prime location for some commercial (Moto/GE)
> equipment, but my Hamtronics station is doing fine, for now, and I am
> just trying to help my neighbors with their problems.
>
> PS. You guys make me look good! Thanks for all the "lessons".
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