Jeff,
Please advise the make and model of your repeater, and its operating
frequencies.
A local repeater once had a similar problem, wherein an AM station's
104th harmonic was beating with the UHF MICOR's exciter output (which is
at VHF) and was then slope-detected by the repeater's receiver. The guy
who maintained (note the past tense!) the 70cm repeater was rather
sloppy, and had not replaced the shield plates on the unified chassis.
Once all of the shields were replaced and properly secured with all
required screws, the problem went away.
I am not suggesting that this is the cause in the instant case, but from
the meager information presented, it appears to be slope-detection of an
AM signal. The challenge is now to track down what other oscillators
are running when the problem occurs. Since the AM station is heard
clearly, the beating frequency is MOST likely being generated by a
constantly-running crystal oscillator that is poorly shielded. Whether
this oscillator is nearby or a mile away is unknown. We'll see...
73, Eric Lemmon WB6FLY
W2JRT - Jeff wrote:
>
> I have a 70cm repeater that is located about .75 mile from a commercial radio
> station.
>
> I was using a Celwave notch-type mobile duplexer, and experienced no problems
> whatsoever. Recently, I purchased a new Sinclair Bp/Br Q318GR, 4 cavity
> duplexer and replaced the Celwave. This morning, I have noticed that the
> nearby radio station is now coming through on the repeater's transmitted
> signal...
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