X06^[a] is a proprietary selective calling system, used exclusively by the Russian diplomatic service.

Waveform

The signal consists of a sequence of 6 tones in succession, 333⅓ ms long each, followed by a ~1320 ms pause, repeated over and over. The tones are assigned to the following audio frequencies in hertz: (±5 Hz)

Operation

X06 broadcasts are made solely by MFA Moscow. Each tone sequence uniquely identifies a single Russian diplomatic mission, and has its own pool of frequencies on which it may be broadcast; only one frequency is used at a time.

While X06 is being broadcast, Moscow is waiting for the target to initiate a point-to-point link using Perelivt on any of its frequencies; in case no such attempt is received, the X06 broadcast may be moved to a different frequency from the pool.

There are 54 tone sequences known to correspond to diplomatic missions:

Other uses

X06 is sometimes used to emit test sequences like 123456, 111666, 121212, or 111111. Notably, such sequences are emitted about an hour before the Moscow-based E07, M12, XPA, XPA2, and XPB schedules, successively broadcasting on each frequency that will be used in ascending order (regardless of the order used on the schedule).

Notes

1. X06 is the ENIGMA ID. Western sources often use the name Mazielka, which is a made up word invented in the 1980s by one of the Western military forces. The actual name of the system is unknown.