An odd receiver problem

[Floyd Sense]

Here's an unusual problem I've not seen before and at the moment I can't
carry the receiver out to the shop to try and locate the cause- so am
fishing for ideas:

The receiver is a National NC-300, completely recapped (not the micas),
properly aligned, all functions working properly.  It's extremely stable, I
can tune it to the boatanchor swap net on 40 SSB on Saturday mornings and
not have to retune it at all for the duration of the net.  Now for the
problem.  At seemingly random times while listening to a sideband signal in
the 3Kc selectivity position, a very "watery" sounding carrier appears near
the upper edge of the passband and it very slowly moves down across the
passband.  The signal is very weak.  If you've ever chased CW DX from Asia,
the signal has that same "watery" sound that those signals have, having
passed over the pole.  The signal is just wobbly enough in frequency that
the "Tone" filter in my Timewave DSP-599X filter won't lock onto it.  When I
first noticed it, it sounded like a DX station very slowly tuning his VFO
across the band.  If I tune to a dead spot in the band, the tone never
appears.  Have never heard it while listening to CW.  Listening to a net on
40 SSB, it appears every few minutes, but with no pattern.  Moving the
bandwidth control to 8Kc has no affect on the tone.  This phantom signal can
be heard with the receiver tuned anywhere in the 40 mtr SSB segment- don't
know yet about other bands.  Any ideas ?



K8AC
Floyd Sense in Angier, NC

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