Mystery Burst Transmission in the HF Ham Bands
Smorgasbord / Kirt's Cogitations™ #349

<Previous                     Next>

A couple days ago, website visitor Bill P. wrote from his location in the western mountains of North Carolina to ask whether I have any information on a mysterious transmission he has been picking up in the 10- and 12-meter bands (28.000 to 29.700 MHz and 24.920 to 24.930 MHz, respectively) that "only appears when the bands are open." The signal has appeared intermittently for more than ten years. He included a link to a demodulated audio file of the captured signal. It sounds like a series of bursts at the same frequency. I do not recall ever having heard it.

Probably the best method for determining the source of a broadcast is to perform a spectral analysis of the demodulated signal to discover its constituent parts. I used a free audio analyzer package called WavePad, by NCH Software. The screen shot below quantifies a few of the primary parameters. It consists of 63 bursts at approximately 24 ms intervals. Each burst appears to be a CW signal of about 1,280 Hz (780 μS), although looking at the spectral waterfall most of the content appears to be in 1,100 Hz realm. The signal sample rate appears to be around 55 kHz. Bill did not say how often or at what intervals this series of bursts repeats.

Any thoughts?

WavePad Screen Shot of Mystery Burst Signal

This is NOT the infamous Russian Duga OTH radar broadcast. It also transmitted a burst pattern nicknamed the "Russian Woodpecker," but it sounds nothing like this HF mystery signal.

This sounds more like a Vietnam-era Huey helicopter than a woodpecker; a woodpecker's repetition rate is much higher than this.

Posted February 20, 2023