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Maybe only peripherally related to this discussion but here's a link to multiple ionosondes, managed by Terry Bullet, W0ASP , for Boulder Ionosonde (listed) and NOAA.
I believe that one is 4kW ERP pointed straight up perhaps repeated CW-like sweeps every 15 minutes, but there are many and some not listed. I get the impression that these are ill-coordinated by the FCC or anyone else, some may be academic institutions.
On 2022-04-21 11:13, Phil Karn wrote:
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.