M05 was a station that was only heard for two days - on October 5th and 6th, 1993 - possibly linked to the Moscow coup attempt. Very strong signal strengths reported by British monitors suggest the UK as the country of origin.

The Morse code pitch was 800 Hz. The speed was described as very slow. Standard five dashes were used for zero. The transmission format was complex; for most of the time, sets of 6-figure groups were sent, followed by "000000/". Example sets:

The sets would have been repeated for anywhere between 30 minutes and a few hours. Note the sequences of repeated digits in groups. Occasionally either "K", "KK" or "KKK" preceded the sets.

M05 operated 23 hours a day, on the following schedule:

References

ENIGMA Newsletter #7 (January 16th, 1995), p. 36 - read a scanned version here