I had the opportunity to record other transmissions on 3712.70 KHz/USB and - also following the comment of my friend KarapuZ - I can state with reasonable certainty that the waveforms analyzed in the previous post [1] come from Thales equipment.
As mentioned, both Thales and L3Harris use the GMSK-MFSK8 waveform to handle HF links but the L3Harris bitmap/bitstream have a very recognizable pattern that is not present in the bursts recorded today (Figs 1,2): therefore, the GMSK-MFSK-8 signal is the Thales Systeme-3000 "Skymaster ALE", used in TRC-3500 and TRC-3600/TRC-3700 series radios (HF 3000 family).
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| Fig. 1 - Thales Systeme-3000 GMFKS+MFSK8 |
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| Fig. 2 - Thales Systeme-3000 GMFKS: bitstream after differential decoding and 50ms bitmap |
As you see in Figure 2, I used the OQPSK "view" to demodulate the preamble of the Skyaster ALE signal: however, the differential decoding clearly show a 2-state keying (precisely GMFSK) that can be demodulated also using the "classic" FSK approach (Figure 3).
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| Fig. 3 - use of the SA MFSK dem |
For what concerns the two PSK8 Serial Tone waveforms A & B [1], they also could be proprietary ones (Thales); indeed, quoting TRC-3600 datasheet: "Thanks to its digital advanced technology, the TRC 3600 offers new embedded services: secure high data rate and digital voice transmissions. It integrates a high data rate, multiwaveform, single tone modem (from 75 to 5400 bps) and a vocoder (800 - 2400 bps) associated to a high security digital COMSEC chip".
The data link protocol could be the digital voice vocoder (new MELP/LPC10), given the similarity of the bitstream with its L3Harris analogue, but that is just an unconfirmed hypothesis of mine.
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| Fig. 4 - bitmaps of the two PSK8 ST waveforms | |
https://disk.yandex.com/d/6NK6xYRAWzjzEw
[1] http://i56578-swl.blogspot.com/2024/04/unid-datalink-protocols-over-psk8-st.html
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