Re: Noise "Problem" at KPH/KFS

Phil Karn

These chirped signals are always radars of some form, most likely CODAR or similar for sea state surveillance.

Anybody know what ionosphere sounders look like? I often see chirp radar bursts all over HF, usually around the MUF, but I don't know if they're military over-the-horizon radars or civilian ionosondes.

Chirped FM is a traditional radar signal but there are many others. Most would look like high speed data or even broadband noise, most likely with a repeating structure. Any repetitive signal, no matter how complex, will consist of spectral lines spaced by the repetition interval. E.g., when HAARP was active on 6.8 and 6.9 a week ago, one of their signals consisted of spectral lines about 49 Hz apart occupying a total of maybe 50 kHz. The lines were so sharp that you could still see other signals between them despite their enormous ERP.


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