Data transmission system using two frequency modulation - has simplified modems by using same clock for modulation and demodulation

摘要

The data transmission system, using two-frequency modulation, requires less complicated modems than similar existing systems and can also handle mobile stations. The two frequencies each represents one binary state, ie. the first's full period for first state and the second's half period for second state. The individual transmission stations generate a clocking signal corresponding to the first modulation frequency using a quartz oscillator and frequency dividing multistage sync counter. This clocking signal acts both for the transmission modulator and for the sampling demodulator. The sampling signals are synchronised with the received signal edges by a comparator.