Carrier waveform phase modulation and prefiltering - provides data transmission with good carrier recovery with multiplexer controlled by counter

摘要

The method of generating a filtered and phase modulated waveform for transmitting packets of data has the advantages that it reduces the number of possible waveforms of a signalling element which may be associated with a packet of bits, and greatly reduces the sensitivity of carrier recovery to data sequences and transmission induced distortions. In the example given, data input (1) is modulated by a differential phase modulator (2), divided by a resistive potentiometer derived from a multiplexer (9) and the modulated output is available after the voltage follower (3). The up-down counter (18) controlling the multiplexer and the resistor values are chosen to multiply the data modulation by a symmetrical ramp waveform which has zero amplitude at the moments of phase jumps in the data modulated carrier. The signalling period is 1.5 times the carrier period.