40m Pulse Signal

Since about August 20, 2005 myself and others have been receiving a pulsed signal on the low end of 40m. I've read complaints about the signal from others on various radio related e-mail reflectors. I've heard it from about 7.000 to 7.050 MHz and others have heard it from 7.030 to 7.070 MHz at other times.

The signal isn't on all of the time but when it is on it is often on for hours at a time. I've heard it well in the afternoon and at night from here in north Texas. Given the pulse modulation and wide bandwidth I suspect that it is some kind of Over The Horizon Radar transmission. During a long recording that I made selective fading is very evident on the signal so it is pretty obvious that it is a skywave signal and not just local RFI.

Here are the technical parameters the best I can tell using a maximum detection bandwidth of 3 kHz:

At this time it is just an irritating nuisance much like the old "Woodpecker" of years gone by. Below is a 5 second clip of the signal recorded on 7.043 MHz at 2313 UTC on September 4, 2005:


Signal's Spectrum
aa5tb_072.mp3's Spectrum


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Last updated on August 20, 2006.
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Originally posted on September 4, 2005