XPA

This is a Russian mode believed to be used by at least one of the Russian intelligence services. It transmits data at either 10 baud (most commonly) or 20 baud using 17 tone MFSK (Multi Frequency Shift Keying).

Rivet can decode XPA live from a radio (using your soundcards line in input) or from . WAV file recording which is mono and with a sample rate of 11024 KHz or 8000 KHz. The program begins its operation by hunting for the XPA synchronisation sequence by looking for four tones (tone #1 , tone #2 , tone #3 and tone #4) it then checks that tones #1 and #3 are the same and that tones #2 and #4 are the same, finally it then checks that there is 760 Hz difference between tones #1 and #2. At that point the program calibrates its timing and the frequency offset of the transmission. Once Rivet has done this do NOT change the tuning of your radio.

A decoded XPA message looks like this ..

13:13:58 XPA Start Tones Found (correcting by 36 Hz)
13:14:03 High sync tone found
13:14:03 Symbol timing found
Block Sync
4444444444
Block Sync
101 101 101 1 101 101 101 1 101 101 101 1
4444444444
Block Sync
6
Message Start
00857 00097 93286 71395 40333 00714 17852 48857 77718 50780 37834 00215 21772 68734 13603
85646 14094 40723 82696 11038 43675 98847 50732 30954 17592 54577 90765 62197 87165 86007
68736 35714 24007 86209 96271 89625 35714 19269 81590 60485 02469 82980 59119 82461 77523
86731 22993 12521 52548 97909 55084 10648 78945 97123 16673 97138 83388 34822 60415 93306
50071 38438 27154 80657
Block Sync
82050 37623 04296 14200 72261 30215 93943 34679 68188 53956 79136 08478 30933 72586 38826
06910 55823 18377 89051 96813 05847 91457 30993 17025 36671 20034 7380 08659 34217 05873
30813 11871 61634 20351 39596 7426
13:14:03 XPA Decode Complete

There is a WAV file recording of a XPA transmission on the Rivet sound samples page here.