[CW] Mystery interference

[Donald Chester]

A few days ago, a new interference appeared on 80m.  It consists of rough, 
60kHz modulated carriers, spaced at 15.7325 kHz intervals.  At first I 
thought it might be a touch lamp, but the carrier frequencies are extremely 
stable, despite the rough sounding modulation.  The strongest carrier 
appears to be at 3579.55 kHz.  Carriers are clearly audible from 3406.48 kHz 
to 3736.9 kHz, with vestiges detected above 4 mHz.  The sound of the 
modulation changes every few seconds, and the signal strength varies as the 
modulation changes.  At its strongest point it is about 10 dB above S9.  I 
get the strongest signal on the 160m. beverage, but it is audible on the 
10m. ground plane and indoor loop.  The signal is weakest on the 
transmitting dipole.

I measured the frequencies using a DDS vfo with 1 Hz resolution.  Individual 
frequencies may be inaccurate due to the difficulty in finding zero-beat in 
the presence of the rough 60Hz modulation, but the spacing of the signals 
was determined by averaging the difference in measured frequency between 
adjacent carriers throughout the band.  At the time, the DDS vfo was 
zero-beat with WWV at 10 mHz.

Readings were taken at the following frequencies:

3500.88
3516.662
3532.25
3548.15
3563.69
3579.55
3595.29
3611.02
3626.74
3642 (approx)
3698 (approx)
3674 (approx)
3690 (approx)
3706 (approx)
3721 (approx)
3736.9


I am hoping someone might save me from having to re-invent the wheel in 
chasing down this interference, by identifying a probable source based on 
the above data.

73 de K4KYV


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