Unid datalink protocol(s) over a PSK8 ST and STANAG-4539 (2)

i56578-swl.blogspot.com 8 miesięcy temu

I had the chance to evidence another transmissions on 3712.70 KHz/USB and - besides 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 usage 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 present (Figs 1,2): therefore, the GMSK-MFSK-8 signal is the Thales Systeme-3000 "Skymaster ALE", utilized in TRC-3500 and TRC-3600/TRC-3700 series radios (HF 3000 family).

Fig. 1 - Thales Systeme-3000 GMFKS+MFSK8

Fig. 2 - Thales Systeme-3000 GMFKS: bitstream after differential decoding and 50ms bitmap

As you see in Figure 2, I utilized 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 besides utilizing the "classic" FSK approach (Figure 3).

Fig. 3 - usage of the SA MFSK dem

For what concerns the 2 PSK8 Serial speech waveforms A & B [1], they besides could be proprietary ones (Thales); indeed, quoting TRC-3600 datasheet: "Thanks to its digital advanced technology, the TRC 3600 offers fresh embedded services: safe advanced data rate and digital voice transmissions. It integrates a advanced data rate, multiwaveform, single speech modem (from 75 to 5400 bps) and a vocoder (800 - 2400 bps) associated to a advanced safety 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.