HFU HF Underground
Loggings => HF Mystery Signals => Topic started by: alleycat on November 29, 2020, 0211 UTC
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I'm guessing this is a natural HF phenomenon (meteor?), but I suppose it could be a propagation check of some kind? When I used to monitor radio in the traditional fashion, I'd hear a "swoop" every once in a while - sounded like a carrier sweeping up (and I think it's always up) through the frequency I was monitoring - and once I started SDR'ing, I verified my hunch visually:
(https://www.lutins.org/temp/rf_sweep.jpg)
Anyone know for certain what this is? Thanks & 73 de KC2KLC
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No, this is not natural, this signal is a type of ionosonde called a chirp sounder. And yes, they are propagation monitoring tools. They start from some defined frequency and transmit continuously (sometimes except for specific skipped frequencies, which vary per installation) to another defined frequency. For example, it might start at 5000 kHz and chirp up to say 28000 kHz, at 100 or 150 kHz per second. In one example, 5000 kHz to 28000 kHz at 100 kHz / sec, it would take about 230 seconds, just under 4 minutes, to make the entire sweep. Since the target set is the ionosphere, and that is pretty slow to change, it does not have to do this very often, a few times an hour is enough to keep up with changes.
It absolutely can be thought of as a radar for tracking what is going on in the ionosphere. And there are dozens of these scattered around the World, so you often can hear two or three zipping by a given frequency in just a few minutes.
T!
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I often see two running at the same time several seconds apart. It is interesting to see that some of them will actually skip certain segments of the HF spectrum. Open the waterfall up as much as you can and you'll start to see the whole sweep and the lower and upper levels you can receive.
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Over 4 decades of monitoring the airwaves, and I'm still learning something new about them on a regular basis. Thanks!