13 December 2016

unid FSK 300Bd/500, 255/360 bit period


The signal was copied on 06775.0 (cf) at 0954 UTC of 7 December. The FSK-2 modulation exhibits a constant 300 symbols/sec speed and shift of 500 Hz (Fig. 1).

Fig. 1
The most interesting feature is the switch of the period lenght most likely in corrispondence of switching from idle and traffic mode. In the fist case the ACF has the value of 850.55 msec that corresponds to a 255-bit period length (Figs 2,3):

Fig. 2
Fig. 3
In the second case, likely when the signal transports data, the ACF exhibits the value of 200.13 msec that corresponds to a 360-bit period length (Figs 4,5) or, better, to a 60-bit frame which is repeated six times.

Fig. 4
Fig.5

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