AUTOMATIC FREQUENCY CONTROL SYSTEM AND METHOD FOR FREQUENCY-SHIFT-KEY DATA TRANSMISSION SYSTEMS

摘要

The present invention provides a system and method of automatic frequency control (AFC) in a frequency-shift-key (FSK) data transmission system that allows a receiver to be used that has a bandwidth that approaches the requisite minimum bandwidth for a given data transmission rate and produces a substantial signal noise ratio (SNR) in the detected signal by the receiver. The invention includes a transmitter that outputs a SPACE signal and a MARK signal in a preamble that precedes the transmission data. The apparatus also includes a receiver (24) that uses the SPACE and MARK signals to adjust the freguency of the signal output by a voltage-controlled-oscillator (VCO) (42) to tune the receiver and thereby improve the signal-to-noise ratio (SNR) in the signals subsequently detected by the receiver.