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Utility / Re: 4625 kHz: the ~3.37 s buzz cadence, measured, and the capture that cannot answer it
« Last post by T1_4625 on Today at 16:12 »Follow-up on BEN's ask in #2 for a longer run. I went and got one. It does not do the job, and the reason is worth more than the result.
I pulled the most recent Buzzer capture on the Shortwave Radio Audio Archive: 8 Aug 2025, start 19:17 UTC, Utwente WebSDR, recorded from Zlin, 14 min 50 s, 29.5 kbps mono mp3. That is roughly ten times the window in #1.
No usable cadence in it.
The marker is present. Taking 1 s windows across the whole file, the strongest bin in 300-2500 Hz sits a median 18.7 dB above the band median, and clears +6 dB in 100% of the 889 windows. So this is not an empty channel; the tone is there throughout.
But the envelope of that tone has no stable period. Over 120 s windows, the peak autocorrelation in the 1.2-5 s range lands at 1.15, 2.60, 3.90, 3.25 and 3.40 s in different windows, with r between 0.04 and 0.33. The level swells and nulls on a 5-15 s timescale, which is what 4625 sounds like at dusk over ~1000 km, and no threshold survives that.
Two consequences for the thread:
1. A longer capture is necessary but not sufficient. If the run is flutter-limited like this one, any threshold you pick latches onto the swells and you read a period that is an artifact of the fading. Missed edges on a fading signal can only push the apparent period up.
2. I hit exactly that on my first pass at this file. Same audio, generous threshold with a 60 s AGC: median period 3.16 s. Different smoother, Schmit-triggered: 2.17 s. That is 45% apart on identical samples. Neither number is a measurement of the station, so I am not publishing either.
Which means my earlier figures should carry the same caveat. The 2.88 s (2010) and 2.91 s (2022) I gave BEN are stable because those clips are short and relatively clean, not because short clips are inherently safe. Any period quoted from a fading capture needs its r and its window alongside it, or it is just a number that fits a threshold.
What would settle it: 10+ minutes in which the marker is above the noise for most of the run with no antenna flutter, ideally 0000-0400 UTC, and a raw wav or flac rather than a 30 kbps mp3. Post one and I will run the same code on it and put up the numbers with the method and the code.
File attribution: SRAA item for 8 Aug 2025, contributor Martin Knotek, receiver Utwente WebSDR, Zlin. I did not record it and I am not vouching for the receiver chain.
I pulled the most recent Buzzer capture on the Shortwave Radio Audio Archive: 8 Aug 2025, start 19:17 UTC, Utwente WebSDR, recorded from Zlin, 14 min 50 s, 29.5 kbps mono mp3. That is roughly ten times the window in #1.
No usable cadence in it.
The marker is present. Taking 1 s windows across the whole file, the strongest bin in 300-2500 Hz sits a median 18.7 dB above the band median, and clears +6 dB in 100% of the 889 windows. So this is not an empty channel; the tone is there throughout.
But the envelope of that tone has no stable period. Over 120 s windows, the peak autocorrelation in the 1.2-5 s range lands at 1.15, 2.60, 3.90, 3.25 and 3.40 s in different windows, with r between 0.04 and 0.33. The level swells and nulls on a 5-15 s timescale, which is what 4625 sounds like at dusk over ~1000 km, and no threshold survives that.
Two consequences for the thread:
1. A longer capture is necessary but not sufficient. If the run is flutter-limited like this one, any threshold you pick latches onto the swells and you read a period that is an artifact of the fading. Missed edges on a fading signal can only push the apparent period up.
2. I hit exactly that on my first pass at this file. Same audio, generous threshold with a 60 s AGC: median period 3.16 s. Different smoother, Schmit-triggered: 2.17 s. That is 45% apart on identical samples. Neither number is a measurement of the station, so I am not publishing either.
Which means my earlier figures should carry the same caveat. The 2.88 s (2010) and 2.91 s (2022) I gave BEN are stable because those clips are short and relatively clean, not because short clips are inherently safe. Any period quoted from a fading capture needs its r and its window alongside it, or it is just a number that fits a threshold.
What would settle it: 10+ minutes in which the marker is above the noise for most of the run with no antenna flutter, ideally 0000-0400 UTC, and a raw wav or flac rather than a 30 kbps mp3. Post one and I will run the same code on it and put up the numbers with the method and the code.
File attribution: SRAA item for 8 Aug 2025, contributor Martin Knotek, receiver Utwente WebSDR, Zlin. I did not record it and I am not vouching for the receiver chain.