7 May 2018

Telsy/Q-MAC MPSK 30+1 48.8Bd 60Hz
i56578, DF3LZ,KarapuZ


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).

Fig. 1
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). 

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.
 
Fig. 4 - signal by radioscanner (upper) and the signal being analyzed

It's also interesting to note that the digital signal was preceded by the following comms:
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.