2023-04-24, 09:12
Looking at the trace of that graph makes me think it's very likely that I have experienced the same phenomena using a different method.
Many years ago, in the 1980s I was very active of the HF bands. On several occasions during afternoon thunderstorms I noticed that while monitoring on 21MHz there was a slow buzzing sound which built up in amplitude and buzz rate to be abruptly terminated with the typical sferic sound concurrent with a local lightning flash. This was using a 1/4 wave vertical antenna in the centre of the corrugated iron roof of the house. I still have audio recordings of this on a cassette tape somewhere in storage but no tape player.
Regards.
Many years ago, in the 1980s I was very active of the HF bands. On several occasions during afternoon thunderstorms I noticed that while monitoring on 21MHz there was a slow buzzing sound which built up in amplitude and buzz rate to be abruptly terminated with the typical sferic sound concurrent with a local lightning flash. This was using a 1/4 wave vertical antenna in the centre of the corrugated iron roof of the house. I still have audio recordings of this on a cassette tape somewhere in storage but no tape player.
Regards.
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