XP was one of the digital flavors of the Russian 7 operator. Active from 1993 until 2005, it was replaced by XPA starting in 2003.

Scheduling

Each XP schedule consisted of three broadcasts, spaced 20 minutes apart. The hundreds digits of each frequency of the schedule, when concatenated, give the schedule ID. Each schedule was weekly, and normally had a repeat transmission later in the week. The frequencies changed monthly.

Mode specification

XP was a 14-tone MFSK system, using two speeds within each transmission - 1 Bd for the intro, and 7.5 Bd for the message. The following is the list of tones used and their corresponding values:

Each transmission goes through several phases, in order: (all at 7.5 bd unless noted)

1. 1 Bd intro section: 3-digit ID, space (repeated thrice), number of messages ("000" - no messages, "1" - one message, "2" - two messages, etc.), space (repeated altogether 10 times)
2. Tones #13 and #14 repeated 10 times
3. 10 spaces, forming a continuous tone
4. Message: 5-digit groups, followed by a space
5. End of transmission: Tones #2 and #14 repeated 10 times in total

When no message was to be sent, the step 4 was skipped.

In the actual messages, the first group always started with "0", and the second group was the group count minus two. Multiple messages were separated by "00000 00000".