XPA2

XPA2 is a Russian mode believed to be used by at least one of the Russian intelligence services. It transmits data at the unusual rate of 7.8 baud using 14 tone MFSK (Multi Frequency Shift Keying).

Rivet can decode XPA2 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 234 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 alter the tuning of your radio.

A decoded XPA2 message looks like this ..

13:49:52 XPA2 Start Tones Found (correcting by -1 Hz)
13:50:29 Symbol timing found
02435 00146 98804 73855 93507 32951 32279 89275 85524 53888 95942 92198 90557 04769 54888
20926 94351 53313 31155 63773 55936 08424 26549 01634 43739 83041 11786 65426 09526 69705
28433 53534 59595 88768 38470 64642 94623 09572 01779 46864 48326 44457 80870 13778 58331
70218 02211 33066 78858 82209 34788 24458 27877 14600 16550 66300 53399 36220 66529 80022
84492 18763 77921 74517 06590 40668 78325 11660 78097 35235 66565 05193 08038 23858 02838
96632 12334 57529 31361 97524 06251 73501 56953 86309 65431 43780 17915 56730 12549 07132
34694 22306 01444 55806 17712 69823 33014 07770 37248 06682 33638 30834 75725 02321 58679
91992 44526 72421 05908 33798 91084 28280 23088 32018 74665 75705 58256 00465 27697 04388
37650 93575 06837 46454 84140 47744 88681 77535 49948 27777 43165 11011 80486 68013 91912
97794 76189 68125 99885 31533
13:50:30 XPA2 Decode Complete

There is a WAV file recording of a XPA2 transmission on the Rivet sound samples page here.