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I have been meaning to write up something on the MFSK Oddity that has been being reported by multiple people to this forum over the past year+.  Unfortunately, real life has gotten in the way and I have not had time to do it.

So I am going to pull all (well, all I can find) the threads together under this one thread and include a couple recordings I have made.

(edit)  Well, that did not work.  I will link the other threads to this one, not merge the threads.

For those not familiar, the MFSK Oddity is a signal that has been showing up since at least mid 2020, and I suspect it was around a bit before that.  Further, I think some of the phantom "1 PPS" signals before that time may be related.

Some listeners tie this signal to HFT (High Frequency Trading).  I do not think that has been proven, but geolocation via TDOA and HFDF, searches of related frequency authorizations for HFT license, and similar frequency use / habits of other HFT tied signals make the HFT association very possible, if not probable.  If not quite proven it is a best guess.  10Band LLC and related businesses are likely candidates.

The arguments against HFT are that the data rate is too slow to be useful for that service, and the data also appears static, unchanging, for very long periods of time.  If you are leveraging RF vs fiber to gain microseconds of advantage, why use a data format that sends bits in 10's or 100's of millisecond intervals?

I have measured bandwidths of about 2.6, 4, and 10 kHz, I have seen other bandwidths but they have been too weak for me to get a decent estimate of the occupied bandwidth.

I have seen pulse rates of between 200 Hz (5 msec pulse interval) to 1 Hz (1 second pulse interval).  I have seen repeating "bit patterns" (for lack of better term) of 8, 16, and 32 bits.

The signal appears to be MFSK like.  Since late 2020 it has generally appeared to be 4 channels of data (prior to that it was 3 channels, or less), each channel with 4 FSK like steps.  There may be some other modulation on each pulse, but if so I have not been able to confirm it.  Arbitrarily, for my notes, I have called the lowest frequency channel of data Ch1, and moving up in freq Ch2, Ch3, and Ch4.  Within each channel I have called the tones, again low freq to high, 1, 2, 3, and 4.

These signals move frequencies regularly, probably as needed for propagation.

Some videos below, sorry, they are not nicely annotated or explained, but at least they are recordings.  The frequencies listed are center frequency.

4 kHz bandwidth, 4 Channel, 16 bit, 1000 msec interval, 15910 kHz

4 kHz bandwidth, 4 Channel, 16 bit, 100 msec interval, 14903 kHz

4 kHz bandwidth, 4 Channel, 16 bit, 66.7 msec interval, 10160 kHz

4 kHz bandwidth, 4 Channel, 16 bit, 50 msec interval, 10170 kHz

4 kHz bandwidth, 4 Channel, 16 bit, 33.3 msec interval, 13909 kHz

4 kHz bandwidth, 4 Channel, 16 bit, 20 msec interval, 13928 kHz

4 kHz bandwidth, 4 Channel, 16 bit, 10 msec interval, 10807 kHz

4 kHz bandwidth, 4 Channel, 32 bit, 100 msec interval, 15905 kHz

4 kHz bandwidth, 4 Channel, 32 bit, 5 msec interval, 14500 kHz

2.6 kHz bandwidth, 4 Channel, 3 step, 16 bit, 100 msec, 6993 and 6988 kHz

2.6 kHz bandwidth, 4 Channel, 3 step, 16 bit, 50 msec interval, 14480 kHz


Related threads:

UNID 9060 Digi

UNID 6940.0 kHz (CF) 00:00 UTC 01 FEBRUARY 2022

UNID 6985 (CF) 1310 UTC 09 JAN 2022

UNID 6988 USB 2223 UTC 09 DEC 2021

UNID 6965 (CF) 2200 UTC 09 DEC 2021

UNID 6970 2019 UTC 19 NOV 2021--see waterfall

Spy Numbers / MOVED: Don't know fershure
« on: February 01, 2022, 1412 UTC »

HF Beacons / Possible new'ish beacon on about 4096.39 kHz
« on: August 20, 2021, 0017 UTC »

I have been seeing what may be a beacon on about 4096.39 kHz.  I have seen this for several months, possibly over 6 months (will have to check recordings to confirm) and it feels / looks / acts like a possible beacon.  But I am not sure, and if it is not a beacon then I do not have a good guess as to what it is.

I have never gotten this signal very strong, so I still have a lot of questions about it.  The following are approximates, since I have yet to get a good enough SNR on the signal to confirm some of them.

The freq is about 4096.39 kHz and appears stable, the signal may be about 34 Hz wide, and could be an approximate 22 Hz shift FSK.  I cannot confirm it is FSK, but it sounds and looks like it could be.  And the signal certainly has some kind of width to it, but again, I have not had a good enough signal to get much detail.  I have been waiting to get a good sig before reporting this, but it seems I may never get a decent signal on it so I thought I would put it out for others to keep an eye open.


Chinese (Tawainese) numbers station V13 (New Star Broadcasting) on 8300 kHz, H3E mode (USB + carrier), 1300 UTC, June 5, 2021 with its normal programming.

Carrier came up at 1300z.

I have this frequency in my logs for V13 in 2013 and 2014, so it is not new for them to use this freq, but I do not believe they have used it recently.



I have put up a few new videos on my YouTube channel, today they were all associated with the US military, USAF operated, HF-GCS (High Frequency Global Communications System), including what might be the last SkyKing transmission and a rather lengthy EAM.

For those not aware, the HF-GCS appears to have stopped sending SkyKing messages in late 2019.  Other message types have continued to be used as before, but it appears that possibly there are no more SkyKings being sent.

What I can say for sure is that there have not been any SkyKings recently reliably reported in the regular forums and mailing lists.  There have been some reported overall (such as on YouTube), but on further review of recordings/descriptions, etc, they were either definitely, or probably (in the case of no recordings) not actually SkyKings, but rather miss-identified EAMs.  I have not heard any SkyKings myself since October of 2019, and while I don't spend a great deal of time monitoring the HF-GCS, I typically would hear several a month prior to that date.

This is my last recorded SkyKing, and I have not yet seen a confirmable more recent recording:

Only time will tell, but has the SkyKing message format on the HF-GCS gone the way of other Cold War signals?

A rather lengthy EAM, of 164 characters.  To be sure, I have heard longer EAMs (the longest I have completely recorded is 278 characters, but I have heard the tail end of one over 300 chars), but this is definitely longer than average:

And a recent format SKyKing transmission from a couple years ago.  I included this video in the channel only because tomorrow I will release a video of an older format SkyKing, a format that they stepped away from in about 2016.


I have put up a new video on my YouTube channel, this one is of the Chinese oddity station MC03, the Morse code sister station to VC01.  This outlet of MC03 appears to have a very chirpy transmitter, and I have heard it (MC03) broken like this on several frequencies for more than 6 months.

This station appears to carry traffic very similar to VC01, and is also assumed to be related to air defense or air tracking.  In the video I annotate a couple minutes worth of the changing data, including time tags.

I find the time tags interesting.  There is one official time zone in China, Beijing Time (UTC +8).  However the time tags appear to be UTC +7, which would be Kansu-Szechuan time.  I have seen this pretty regularly with MC03, although I have also seen other time zones in use.  I assume I hear different time zones depending on where the node I am then hearing is located.  But why don't they all use BJT?



Spy Numbers / New video up, Chinese oddity station VC01
« on: April 24, 2021, 1740 UTC »
I have put up a new video on my YouTube channel, this one is the Chinese oddity station VC01.

For those not familiar, VC01 is also called the "Chinese Robot". It is a female voice, machine generated but possibly human recorded, reciting strings of numbers. It is at a very fast rate, too fast for reliable human interpretation. Absolutely the numbers are understandable, but for a human to reliably transcribe the numbers for extended periods is probably not realistic.

The station has been observed for at least a couple of decades, and is presumed to be related to air defense tracking. It has a sister station, assumed to be the same tasking, in Morse code, called MC03.



HF Mystery Signals / MOVED: UNID 4724 KHZ
« on: February 15, 2021, 0017 UTC »

HF Mystery Signals / MOVED: UNID 10340.10 KHZ USB
« on: December 13, 2020, 0456 UTC »

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