Variable-throughput digital modulator and its use in FM radio broadcasting

Variable-throughput digital modulator of a transmission digital signal e(t) comprising:

• means for time-based demultiplexing of said transmission digital signal e(t) into a first and a second elementary transmission signal e1(t), e2(t) respectively
• first and second baseband transmission filtering means corresponding in a first filtering mode to a first type of modulation at a first throughput and in a second filtering mode to a second type of modulation at a second throughput respectively, said first and second baseband transmission filtering means receiving said first e1(t) and said second e2(t) elementary transmission signal respectively, and delivering a first and a second filtered elementary signal, e1f(t), e2f(t) respectively;
• throughput switching control means for switching from the first to the second filtering mode, or conversely, in response to a throughput control signal;
• in-phase and phase-quadrature modulators of a carrier wave of frequency f0 receiving, on their modulation inputs, said first and said second filtered elementary signal respectively and delivering a first and a second modulated carrier signal respectively;
• adder means receiving said first and second modulated carrier signal and delivering a resultant modulated carrier signal;
• and
• filtering means centered on the frequency of said carrier wave f0 making it possible to eliminate the periodicity of the spectrum of said resultant modulated carrier signal in order to deliver a filtered resultant modulated signal for broadcast.