--- In [email protected], "azandyca" <[EMAIL PROTECTED]> wrote:
"I am buiding a VHF repeater witha Motorola Quantar and am finding a
strange IM/Desense issue. .."
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You have the 2670 connected directly to the duplexer's receiver port
and you see these spurs when the Quantar is transmitting?
The Quantar is programmable for output power of 25 Watts to 125 Watts.
Assuming you have yours set for something above the minimum -
reprogram it for 3dB less power out and see if the spurs drop in
amplitude and if so by how much - 3 dB, 6 dB - or more. You can do
that on a per-mode basis so you can change power output 'on-the-fly'
just by changing channels.
Also - all VHF Quantars have a built in circulator. Adding an external
one may not be much help. After all - if you are seeing spurs at the
RX frequency - and if they were being generated within the Quantar PA
they would have to be sufficient in amplitude to make it past the
duplexer filtering - not a likely scenario - but one you can inspect
by placing an observation coupler [iso-T] in the line between the PA
and the duplexer and looking with your analyzer.
The next thing I would do is find some other device [e.g. MSF5000]
that could be programmed to your transmit frequency to serve as a
substitute signal source in place of the Quantar transmitter to see if
the same stuff is present indicating an external mix.
I have put several Quantars on 2 meters and never encountered anything
like your problem - surely there is an external situation
responsible.
I'm assuming this is a personal project or you would have looked for
internal Motorola assistance but there are a couple ST's in
Chicagoland who are pretty good RF guru's that might offer some advice
- even for a ham project.
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