> "Bob A" <[EMAIL PROTECTED]> wrote:
> Thanks Skipp and Paul for input so far- I suspected that
> this would be a bit marginal. However, we're only
> running 40 watts,
40 watts, 600KHz away from your receiver is something
you have to respect. It's actually quite a bit of
signal in the relative world.
> ..and the rx selectivity seems pretty good. It's an
> older Motorola, and it has 4 small cavity filters at
> the input of the rx inside the box.
Although you didn't mention the specific receiver model,
I can tell you the 4 cavity front end is not nearly as
much as you expect it to be. Many of the Motorola base
and repeater front ends are pretty wide when you look at
them in detail. But their respective receiver front ends
have good out of band area (as defined as more than a
few MHz on each side) rejection.
> Running 600 kHz split with 2 antennas now, and I can
> find spots for the rx antenna in which the system
> works OK for local communications.
Nulls in the transmitter to receiver antenna path...
> To Skipp's question, the old cavities have tee
> connectors attached direct to the ports, and
> they are all SO-239.
You can add lengths of coax in series with the Tee
Connectors to the top of the cavity port (loop), which
extend the notch depth (to say 25 to 30 plus dB, the
direct original notch depth is only 15 to 18 dB ...
from memory)
> And, if these old cans are single port, no shunt
> Ls or Cs, does this mean they will notch as-is or
> will they need external help?
You could make them notch pass with loop to probe
modifications, but you probably wont the get preformance
you seek without major work and tweaking. Plus you'll
need at least 4 cavities.
You should leave them as notch only cavities and
add series coax stub lengths to get the max notch
where you can. Decibel does/did a narrow space
duplexer using a number of these cavities. I have some
pictures of said taken from ebay auction pics. The
duplexers were 6 or 8 cavities...
cheers,
skipp
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