|Known counterpart stations||E18, G22, M13|
S04 belonged to one of Bulgarian intelligence agencies. The language was Bulgarian. Last heard in 2006.
|342||Nomer 222||Grupi 238||47175 18030 20166 ...||342||Nomer 222||Grupi 238||47175 18030 20166 ...||0 0 0|
|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|
|Repeated for 5 minutes||Repeated for 1 minute|
The serial number was increased each time a new message was sent on a given schedule.
The following pronunciation was used:
Little is known about S04. It was active in the 1980s, but has later fallen into disuse in favor of its Morse code counterpart, M13.
It was re-activated in November 1999, with one schedule - second Monday and Tuesday of each month at 21:45 UTC (winter 22:45), with ID 537 for messages 23 groups or shorter, or 342 otherwise. That was the only schedule of re-activated S04, that remained active until its demise in early 2006.