[AMRadio] Strange interference


Donald Chester k4kyv at hotmail.com
Sat Jan 1 00:42:46 EST 2005


I first noticed this 24/7 interference a couple of months ago.

The interference covers the entire HF spectrum - from 80m to 30 mHz.  It is 
spaced intervals of approximately 30.475 kHz.  On an AM detector it sounds 
like a tone modulated carrier, but careful observation shows that there are 
two distinct carriers heterodyning against each other; one is unmodulated 
and the other has a spastic but barely perceptible frequency shift of a few 
Hz, and each shift initiates with a click. The frequency shift averages 
about twice a second.

The higher in frequency, the greater the spacing of the carriers.  At 30 
mHz, they are a little over 800~ apart, on 20m. they are a little over 400~ 
apart, on 40 they are 200+ hz apart, and on 80m about 100~ apart.  Although 
the signals appear approximately every 30.475 kHz, some frequencies are much 
stronger than adjacent ones.  There are a few holes in the pattern, where 
nothing is audible on the expected frequency.

The signal appears to be local, since it comes in on 10m all the time, and 
the S-meter remains stationary, thus excluding  the liklihood that it is 
skywave.  The higher in frequency, the stronger the signal.  It is louder 
than my xtal calibrator on 10m, but on 80m it is almost buried in the noise.

Here are a few of the frequencies I measured that  fall inside the ham 
bands:

29.998826/29.999660 mHz

14.884912/14.885340 mHz

7.373734/7.373935 mHz

3.618225 kHz

The signal is extremely stable; I notice no drift over a 24-hour period.

It is not something in the house, since I cut the a.c. power at the main 
utility entrance and the signal is still there.
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Anyone ever heard anything like this?

Don K4KYV





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