|025||389||30||BT BT||92119 92119 06554 06554 ... 88317 88317||BT BT||389||30||0 0 0|
|3-figure ID||3-figure group, purpose unknown||Amount of 5-figure groups in the message||5-figure paired groups||3-figure group, purpose unknown||Amount of 5-figure groups in the message|
|Repeated for 4 minutes||Repeated twice||Repeated twice||Repeated twice||Repeated twice|
There frequently are minor variations to the above format, such as "BT BT BT BT" instead of "BT BT", and no BT's at all.
M01 can be heard on Tuesdays and Thursdays at 18:00 and 20:00, on Saturdays at 15:00, and on Sundays at 07:00 UTC. All of these use the same ID, which depends on the season of the year - it is "197" from November to February, "025" from May to August, and "463" on all the other months. Each time the message sent is different, and always 30 groups long. Rarely the messages are repeated a few days later. M01 does not adjust its transmission times to DST.
The Morse code on M01 is created by an automated machine with manual input from an operator, resulting in irregular pauses between the digits. The zero is sent as "T" - a single dash. The speed varies between 15 and 25 WPM.
M01 uses a distinct modulation type, with each tone being in fact two tones at once - 1000 and 2000 Hz.
M01 has been observed since 1970s. There used to be many more schedules in operation, with highly varied message lengths, and even multiple messages in one transmission. M01 settled on the six transmissions a week in early 2000s. Up until mid-2000s, the average message length was 40 groups, and was not fixed unlike now.
Prior to 2003, on the last week of each month, the transmissions were made in a special format - M01a. At one point, the last group of each month was the day of the month in the first two digits, the middle digit was 0, and the last two digits were the amount of groups counted from 0 - right now the last group is random.
- ENIGMA Newsletter #5 (May 1994), p. 23
- ENIGMA Newsletter #18 (January 2000), p. 11