Abstract: A signal transmitter-receiver system comprising first and second transmitter-receiver units interconnected by a signal transmission line, a first transmitter-receiver unit including a first transmission circuit for delivering a selected one of a plurality of a.c. signals each having a distinct phase difference with respect to a reference a.c. signal to the signal transmission line at each of successive predetermined communication time interval, the second transmitter-receiver unit including a second receiving circuit for identifying the phase difference of the a.c. signal or the signal transmission line with respect to the reference a.c. signal at each communication time interval, the second transmitter-receiver unit including a second transmission circuit for changing the combination of positive and negative amplitudes of the a.c.

Abstract: A group modulator provided a plurality of digitally modulated signals with frequency division multiplex, having a time division multiplexer (11) for multiplexing a plurality of input data (#l through #n). A mapping circuit (12) provides an I-channel signal and a Q-channel signal according to a pattern of the multiplexed signal and the modulation system. A pulse shaping circuit (13) restricts bandwidth of the I-channel signal and the Q-channel signal. A frequency shift circuit (14) shifts frequency of the I-channel signal and the Q-channel signal by the frequency defined by the carrier control signal (i) for each input data. An accumulator (21,22) accumulates each of the I-channel signal and the Q-channel signal of the output of the frequency shift circuit (14) during a predetermined period (T). A D/A converter (31, 32) converts the output of the accumulator from digital form to analog form. A low pass filter (41, 42) is provided at the output of the D/A converter.