17 August 2016

Ital-Mil FSK, FSK 1200Bd/800

FSK-2 1200Bd/800Hz waveform, approximately 1500 Hz bandwidth, used by Italian Military; in this record it's used by Italian Navy HQ (IDR Rome) on 12200.6 KHz/USB as unusual intro before STANAG-4285 1200bps/L transmission, receive peer had the tactical callsign AZWL. Since the PtP nature of that tansmission it could be that the initial FSK part act as a squelch ...but it's only a mine speculation.

fig. 1 ~1500 Hz bandwidth
fig. 2 - baudrate line
fig. 3 - involution module and shift between carriers
The main features of this signal are what seems a polarity change that occurs each 8 bits (fig. 4), as reported by radioscanner.ru and confirmed in this analysis, and, at least in this sample, its quite pronounced 232-bit period shown in figure 5.

fig. 4 - polarity change
fig. 5 - 232-bit period (fisrt part looks like a sort of preamble)


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