I kind of notice the same thing on extremely strong AM signals (30+ db
over S9), but not sure if it's on the signal itself (i.e. lact of
spectral purity of the transmitter) or in the receiver. Just be sure
that the test signal you use is spectrally pure. Potentially, a very
hot signal entering the ANT connector could be 'blowing' past early
filter stages and leaking into final IF. Don't know. Don't hear
anything like it on my trusty old Drake R4C! Can't beat tubes for
dynamic range, no matter what anyone says. (-:
Jim N4BE
sellington wrote:
>
> Thanks to all who responded. Sorry I didn't think to point out that, yes,
> the noise blanker was off.
>
> I made some more measurements last night, and it looks like the problem
> may be high order spurious responses within the roofing filter passband.
> I applied a single input signal of about 10 mV (-27 dbm), and found some
> spurious responses only about 50 dB down. Depending on the precise
> frequency, the spurs were 500 to 1000 Hz from the signal. Their strength
> varies linearly with input, so they're not intermod products. They tune
> faster than normal, so must be related to VFO harmonics. In some cases
> they have a strange slow beat note, which could be what sounded like
> intermod. I don't know the cause yet, but there's something strange
> happening.
>
> 73,
>
> Scott K9MA
>
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