This may not exactly fit the circumstances of the current thread.
However...
I was getting 800 MHz trunking interference on my 447.200 repeater receiver
some years ago. I was using a WP 678- R2 duplexer and a Hamtronics LNG-450
preamp on an Exec II. The thing was, there were no 800 MHz station
transmitters within five miles of the repeater site. Anyway, it seems that
enough of the 800 MHz signals made it through the duplexer pass cavities to
cause mixing in the preamp. In the end, the Exec II was really sensitive
enough standing alone. I also once knew a fellow who used an LNG-450 on one
of his MASTR Pro 460 MHz community repeaters. He had interference from a
co-located two-meter repeater. In the end, the ham repeater had to go away.
For him, that was more economical from both a time and expense standpoint
than solving the problem otherwise.
The bottom line is.. Where preamps are concerned.. Caveat Emptor!
Steve, AA5SG
----- Original Message -----
From: "Richard Sharp, KQ4KX" <[EMAIL PROTECTED]>
To: <Repeater-Builder@yahoogroups.com>
Sent: Wednesday, May 05, 2004 10:01 AM
Subject: RE: [Repeater-Builder] 2m repeater IMD issue
> > -----Original Message-----
> > From: Ken Arck
> >
> > <---What bothers me here about using a circulator is that you say it
only
> > occurs when your TX is active. This doesn't sound like IM to me, as that
> > would occur regardless of whether the tx was active or not (IM is
produced
> > when external RF comes down the TX line and mixes in the PA stages. This
> > does NOT require that the PA actually be making power).
>
> Good point. Yes, it only occurs when the 2m repeaters tx is on.
Basically,
> what I see on the spectrum analyzer (connected to the rx port of the
> duplexer) is several signals coming and going within the passband of the
rx
> cavity (+/- 300kHz approx). I can tune the analyzer to a specific carrier
> and hear either voice traffic or control channel. All of these signals
are
> around -90dBm at the rx port. As soon as the 2m transmitter is turned off
> the carriers on the rx port disappear.
>
> >
> > It sounds more like a classic case of mixing. Have you run all the freqs
> > involved to see where the possibles might be?
>
> At this point no. However, I'm in the process of obtaining all of the 800
> freqs to do a calc.
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
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