Mystery Burst Transmission in the HF Ham Bands Smorgasbord / Kirt's Cogitations™ #349
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I was just thinking about these Mystery Bursts in the HF ham bands and thought
I would speculate what they are: Could they be QPSK modulation on a nearby Digital
TV broadcasting station (or far away considering the author is in the mountain
area) which is around 9 to 10 MHz switching frequency, and the mystery bursts are
the 3rd harmonic content of the fundamental Digital QPSK modulation frequency times
3 (9 MHz x 3) = in the CB radio band of 27 MHz.
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.
Click here to listen to the mystery signal present in the 10-
and 12-meter bands.
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.
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