This signal employs 8-ary phase-shift keying (PSK-8) on a single 1800 Hz carrier, the modulation of this output carrier is a constant 2400 symbols/secs waveform: a quite common mode largely used in HF (pic. 1). I spotted this transmission on 15062.0 KHz on USB.
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| pic. 1 |
The period of the waveform has a duration of ~1013 ms that in turn makes 7296 bits or 2432 PSK-8 symbols @2400 Baud (pic. 2)
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| pic. 2 |
This (long) period length could be misleading but looking at the STANAG-4538 table 13-1 (LSU Burst waveform characteristics, pic. 3) we see that it matches the lenght of the BW5 waveform:
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| pic. 3 |
Looking at the diagram of the ACF we see that the single BW5 burst has been transferred 14 times in a row in the third segment of the trasnmission as confirmd in the bitstream (pics. 4,5). Since the manufacturer of the equipment may modify the standard if it does not impair its performance, perhaps we are dealing with a modification of the STANAG-4538 BW5.
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| pic. 4 |
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| pic. 5 |
To avoid confusions, MIL 188-141C Appendix C third-generation ALE is termed Link Set-Up (LSU) in STANAG 4538. Two non-interoperable protocols for link establishment are specified in STANAG 4538: Fast LSU (FLSU, smaller, lightly-loaded tactical networks) and Robust LSU (RLSU, large networks and heavy traffic). The specifications previously contained in the Appendix C have been replaced with reference to the essentially identical NATO STANAG 4538.
