digital modulator with variable data transmission rate and its application in vhf radio

摘要

The invention relates to a digital modulator with variable bit rate. It comprises, after time-division demultiplexing (1) of the transmission signal e(t) into a first and a second elementary transmission signal e1(t), e2(t), a first (21) and a second (22) circuit for filtering by modulation of first and of second type, corresponding to a first and a second bit rate delivering a first and a second filtered elementary signal e1f(t), e2f(t). A circuit (20) for control of bit-rate changeover by switching over from the first to the second filtering mode is provided. A phase-quadrature phase modulator (3) receives the first and the second filtered elementary signal in order to modulate an RDS-compatible carrier f0 and a filtering circuit (5) delivers a filtered signal for broadcasting. Application to broadcasting of additional data in FM broadcasting. IMAGE