|Emission mode||AM; 14-tone MFSK, 1 Bd and 7.5 Bd|
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.
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:
|2||319||Transmission end tone|
|13||495||Message start tone|
|14||511||Repeat previous tone|
Each transmission goes through several phases, in order: (all at 7.5 bd unless noted)
- 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)
- Tones #13 and #14 repeated 10 times
- 10 spaces, forming a continuous tone
- Message: 5-digit groups, followed by a space
- 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".