ginal synchronizing signal, whether the call-data has been modulated by the n values and transmitted at the first transmission rate or modulated by (n+2 m) values (where m is a natural number) and transmitted at a second transmission rate that is double the first transmission rate; an n-value demodulator for demodulation an n-value modulated signal to 1, 0 data; an (n+2 m) demodulator for demo