priyom.org

Protocol

XPA2 utilizes a proprietary 16-tone MFSK waveform at the speed of 7.8125Bd, and the shift of 15.625Hz. Each tone represents one character:

Hz Character
1000.000 Space
1015.625 (Not used)
1031.250 Start of message
1046.875 End of transmission
1062.500 (Not used)
1078.125 Repeat previous character
1093.750 0
1109.375 1
1125.000 2
1140.625 3
1156.250 4
1171.875 5
1187.500 6
1203.125 7
1218.750 8
1234.375 9

Broadcast procedure:

  1. Precisely two minutes of 400 ms of the 9 tone (1234.375Hz), and 1600 ms of the space tone (1000Hz) repeating.
  2. The tone string 6666622662626 (forming continuous tones). (Note the use of a Barker sequence - possibly relating to synchronization in multipath propagation conditions.)
  3. The repeat and start of message tones alternating (20 tones in total).
  4. 10 space tones (continuous 1000Hz tone string).
  5. 5-digit groups, each separated by a space.
  6. The end of message and repeat tones alternating (20 tones in total).

Messages in the form of "0____ 00001 00000 _____" are null messages.

One broadcast can contain multiple messages. The messages are separated by "00000 00000".

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