Radio-check bewteen voice callsigns GAMMA 130 and ROSTRO 530 (respectively It-GdF shore station and patrol-boat) followed by short MPSK blocks, most likely digital voice.
The MPSK signal occupies a bandwidth of ~2280Hz and has a FSK-2 600Hz shift preamble lasting 150ms (Fig. 1). Except for the 1st block, the FSK preambles of the following 3 blocks are similar. The 30 tones are 60Hz spaced: in the lower group of 20 tones the π/4-DQPSK modulation at 48.8Bd is used; in the upper group of 10 tones, a mix of modulations (MFSK, DBPSK and π/4-DQPSK) at same 48,8Bd speed is used (Fig. 2).
The MPSK signal occupies a bandwidth of ~2280Hz and has a FSK-2 600Hz shift preamble lasting 150ms (Fig. 1). Except for the 1st block, the FSK preambles of the following 3 blocks are similar. The 30 tones are 60Hz spaced: in the lower group of 20 tones the π/4-DQPSK modulation at 48.8Bd is used; in the upper group of 10 tones, a mix of modulations (MFSK, DBPSK and π/4-DQPSK) at same 48,8Bd speed is used (Fig. 2).
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| Fig. 1 |
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| Fig. 2 - upper group of 10 tones (credits to KarapuZ) |
The tone in between the two groups is modulated using DBPSK2 at 48.8Bd (same speed as above) and is used for for synch purposes. The 3 blocks have the same sequences transmitted in the sync channel (Fig. 3).
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| Fig. 3 |
This signal is similar to the Q-MAC HF modem waveform reported by radioscanner, except for the presence of the FSK preamble (Fig. 4). Indeed, a DXer from UDXF suggested the Telsy TCH01c rather than Q-MAC modem. Quoting form Telsy documentation [1]: "The TCH01c – Telsy Crypto Handset – is a unique and sophisticated encryption unit, combining an encryption module, a vocoder and a modem in a single handset." Well, in August 2009 Barrett Communications has announced its acquisition of Q-MAC Electronics:
http://www.barrettcommunications.com.au/.../
and it's interesting to note that Barrett recommends the Telsy TCH01c crypto handset for some of their transceivers:
http://www.italponti.it/_files/download/allegati/2090.pdf
That said, perhaps Telsy embeds the modem in their handset using a Q-MAC/Barret EOM license? I emailed Telsy but I did not have any reply.
http://www.barrettcommunications.com.au/.../
and it's interesting to note that Barrett recommends the Telsy TCH01c crypto handset for some of their transceivers:
http://www.italponti.it/_files/download/allegati/2090.pdf
That said, perhaps Telsy embeds the modem in their handset using a Q-MAC/Barret EOM license? I emailed Telsy but I did not have any reply.
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| Fig. 4 - signal by radioscanner (upper) and the signal being analyzed |
GAMMA 160: let's have a try with a 'passage' in red, I'll take you
ROSTRO 530: yes go ahead, take me up
usually "red" stands for not encrypted transmissions so it seems that they used a clear-text transmission for the modem check.
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