12 December 2018

CIS-79 "TANDEME" OFDM 79-tone

CIS-79 "tandem", OFDM 79-tone spotted on 10790.0 KHz/usb with bad SNR value. The signal is formed by 80 sub-carriers but the higher one (#80) is zeroed and unmodulated. The waveform uses QAM-64 modulation at symbol-rate of 30.5 Baud and 37.5 Hz channel step. No ACF value (=0) has been detected. Each symbol lasts 315 samples (256 +59). 
Note that a "control/service" symbol is sent each three tones using BPSK (Fig. 2): this feature was also commented here but in that case PSK-8 modulation is used. The signal was resampled at 9600Hz before to be analyzed.

Fig. 1

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