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HF Mystery Signals / Re: UNID 6970 2019 UTC 19 NOV 2021--see waterfall
« on: November 24, 2021, 1736 UTC »2136 UTC - 23 Nov 2021, just noticed the "MFSK Oddity" on 6988 kHz USB, the thing is transmitting on four frequencies, looks to be 4Khz wide in total. At 2140 UTC it stopped ( deep fade?) and started back up at 2144 UTC, still going at 2149 UTC with S5 signal in WNY. It covers frequencies 6988 to 6991 kHz.
2152 UTC - Signal is fading in and out.
2210 UTC - Signal is now S9+5.
2235 UTC - Signal still S9+5.
In the next couple of days, with the long weekend, I will try to grab some images to add to this thread, to demonstrate what I am talking about below.
In the last couple years I have seen several different versions of this signal. Without a screen shot or a recording I am guessing at which specific variant of the signal you are seeing in your description above. So my below is a guess, based on your description, and one possible version of the signal that I see often.
The 4 kHz wide signal was a single transmission. I have seen this signal on up to 4 different frequencies at one time using bandwidths of 2, 3, 4, and 10 kHz for each frequency.
All of these versions can be found in various speeds, from very slow to very fast. Sometimes a very slow transmission will be a few kHz away from a very fast one.
In the 4 kHz wide version there appear to be 4 individual, 4FSK, channels. Arbitrarily I have called the 4 “data” channels inside the signal CH1, CH2, CH3, and CH4, with 1 being the lowest frequency set and 4 being the highest frequency set. Each channel has 4 shift tones. Generally the signal cycles in a 16 bit cycle. I mean each cycle has 16 pulses or combinations of shift tones, and then the cycle repeats, over and over.
One common rate is one set of shift tones every 100 msec. Since there are 16 bits or sets of shift tones in a cycle that means the signal cycles and repeats every 1.6 seconds. A faster version of this same signal, identical in every way except speed, sends a set of tones about every 10 seconds and completes a cycle in about 0.16 seconds.
All 4 data channels in a given transmission are in sync, and cycle together (pulses occurring simultaneously in CH1, CH2, CH3, and CH4) but the bit cycle is different for each channel. The same sequence is not being sent in CH1 as in CH2, or CH3, or CH4.
T!