Single channel duplex communication system

摘要

A single channel duplex transmitter/receiver utilizing digital frequency shift keying (FSK) signals. An analogue-to-digital converter frequency modulates the output of a local oscillator whose output is coupled via a mixer/combiner/splitter network to an aerial. FSK signals received from the aerial in the receiver are mixed with the local oscillator output in network to provide quadrature signals which are low-pass filtered before being demodulated in a zero IF demodulator to give a digital output. To avoid unwanted sidetone the output of the A/D converter is fed through a delay to a digital network where it is subtracted from the corresponding signals fed back through the demodulator. The digital signals are then fed to a D/A converter.