21 January 2017

ROHDE & SCHWARZ 225Bd FSK burst system

Thanks to my friend cryptomaster from radioscanner.ru for the identification of the signal (it was previously tagged as unid).
This transmission, most likely a caller or an ALE system, has been copied on 11092.0 KHz/USB (1Khz offset) at 1503 UTC and consists of repeated series of five FSK bursts each burst with a duration of 680 msec and 2 seconds spaced (at least in this sample). Looking at the spectrogram in Fig. 1, bursts have start and ending tones which last respectively 50 and 100 msec and alternate their value in 957 and 1129 Hz at each transmission unless in the last two bursts where the final tone remain unchanged (Fig. 2): this is probably a characteristic format of the signal.

Fig. 1
According to the Figs. 3,4  the signal has a transmission rate of 225 bps and 175 Hz shift and in some way it resembles the Kantronics G-TOR standard.

Fig. 3
Fig. 4

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