|Known counterpart stations||E18, G22, S04|
The transmission format is given below. The speed was 12 words per minute, and one dash was used for zero.
|458||BT||195||20||BT||95404 17097 16052 ...||BT||458||BT||195||20||BT||95404 17097 16052 ...||BT||Three long dashes
|3-figure ID||Serial number||Amount of 5-figure groups in the message||5-figure single groups||3-figure ID||Serial number||Amount of 5-figure groups in the message||5-figure single groups||"0 0 0"|
|Repeated for 5 minutes||Repeated for 1 minute|
The serial number was increased each time a new message was sent on a given schedule.
M13 was significantly more active than its voice counterparts. M13 transmitted every day, and constantly changed times and frequencies. All the transmissions took place in the 00:00-10:00 and 16:00-23:59 time frames. The average message length was 23 groups. The messages were repeated in one of the following patterns:
- On the same day, 1 hour later, on the same frequency
- On the same day, 1 hour later, on a different frequency
- On the next day, at the same time, on the same frequeny
- On the next day, at the same time, on a different frequency