Posted by Bruce WA1HGJ on January 25, 2025 at 00:42:40.

In Reply to: Re: 47.9 kHz un-ID’d FSK posted by John, W1TAG on January 24, 2025 at 13:23:16.

Hi John, Thanks for the follow up, much appreciated. Very interesting potential explanation. Certainly, NAA on 24 kHz is stupendously strong here in our part of North America. However, the FSK station I'm hearing on 47.9 kHz cannot be explained by NAA's second harmonic, since the unknown FSK station is, at worst case, no more than +/- 10 Hz from 47.90 kHz. Here's why. Regarding NAA, I actually use it as a reference standard for both RF frequency and audio frequency of unknown FSK stations, by "parking" NAA in VFO B tuned to precisely 24.00 kHz (since we have certainty about its frequency), then tuning in the unknown FSK station in VFO A whilst toggling back and forth between A and B until the audio tones of the unknown station in VFO A precisely match those of the known NAA in VFO B. One may think it's impossible to precisely match the hyper-crazy FSK audio tones of two stations, but it's actually not difficult as you probably know yourself. This technique gives precise matches to the known frequencies of numerous FSK stations below 100 kHz, including NPM/21.40, GQD/22.10, NLK/24.80, NML4/25.20, TFK/37.50, NAU/40.75, FUG/62.60, FTE63/63.85 and FUE/65.80. So, the second harmonic of NAA at 48.00 cannot explain what I'm hearing on 47.90 (nor do I hear NAA's 2nd harmonic on 48, BTW), but I appreciate your proposing a solution. Bottom line is that this stuff in the sub-basement territory of the RF spectrum is pretty fun and fascinating. It's ironic to me that the LW spectrum seems like a new frontier now, when it's actually the well-trodden territory of the very earliest long ago days of radio. Thanks again, John. 73, Bruce WA1HGJ

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