--- courir26 <[EMAIL PROTECTED]> wrote:
> I'll rephrase the question, what is the min
> frequency separtation for
> a 10W repeater with two ants, no vertical
> separation, horizontal sep
> of about 100'.
>
> I'm guessing it would have to be 2 MHz or more, but
> that is what I'm
> asking.
>
> Please don't answer .600 and 200' vertical because
> that is not the
> question.
>
> I'm referring to an emergency or garage repeater
> with odd split.
>
> Thanks!
>
> Tom N5OFF
>
OK, let's just look at theoretical numbers here. 100
ft of horizontal separation between 2 dipoles at 2M
would give you 41 dB of isolation. If you have a 10
watt TX, that is putting out +40 dBm, which would put
a -1 dBm into your RX (at the TX freq). The further in
freq you get from the TX, the more your sideband (or
phase) noise will be reduced. Since your RX can
probably hear down to -120 dBm, you will need that
much TX phase noise suppression at your RX frequency.
Most good quality (non-ham) transmitters may acheive
this at a 2 to 3 meg separation, some ham models may
also do this. Now, your RX front end needs to suppress
the TX freq by a certain amount, to avoid overload.
Most radios will overload at about a -30 dBm, so your
helicals need to suppress the TX freq by at least 30
dB, reference the RX freq. A Micor or MII, or other
good RX will probably do OK in that field, since they
have "tight" preselectors. Most ham grade radios will
not work, since everything in band comes right
through. You might be able to put on an external
preselector and make a ham RX work.
Bottom line, 2 megs might be too close, 3 megs might
be where things start to work OK, and further the
better. Most of the figures you would need to test
this aren't published, and you would have to
experiment to find out what did and didn't work. Like
I said previously, we had a commercial 161MHz Micor on
a 150 KHz split that worked without cavities, and only
about 60 ft vert between antennas. If I hadn't seen it
working, I would never have beleived it. But 60 ft
vertical is 28 dB better than 100 ft horizontal.
Joe
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