Andy,
When you say you "see" this carrier, how are you viewing it? That is, are
you watching a spectrum analyzer with a pickup antenna, while the repeater
antenna is connected to the duplexer? Is this mystery carrier present all
the time, even when the Quantar is not repeating?
All of my Quantar service manuals are at my office, so I can't study the
possible leakages from the repeater until Tuesday, but I wonder if this
mystery carrier is leaking out of the repeater itself. Are ALL shields in
place and secured with every screw required? Are all components of your
repeater grounded to a known-good station ground?
Finally, how much desense are you experiencing, and how are you measuring
it?
73, Eric Lemmon WB6FLY
azandyca wrote:
> I am building a VHF repeater with a Motorola Quantar, and I am finding a
>
> strange IM/desense issue. When I attach an antenna to the system, I see
>
> a small carrier at +4.5 kHz from the carrier frequency. I have verified
>
> duplexer tuning, tried several antenna and feedline combos, and
> everything else I can think of to find/eliminate this issue, to include
> changing frequencies and retuning the whole mess. It works fine into
> the service monitor with no spurious emissions and no problem, only
> on the antenna system do I see this. There are no other emitters
> within several miles so it is not a local IM type thing. Has anyone
> else setting up a VHF Quantar seen this sort of issue? Could it be
> related to the Quantar itself with the 600k split? I am using a 6 can
> BP/BR duplexer and measure over 130dBm of isolation TX-RX...
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