AUTOMATIC EQUALIZATION METHOD AND APPARATUS

This invention relates to a method of and an apparatus for providing equalization to frequency dependent delay and amplitude distortions in a transmission line. The apparatus includes an adjustable equalizer having a plurality of delay networks, an amplifier, a peak-to-average difference detector, and a control logic for selectively switching the delay networks and amplifier into and out of the path for the incoming signal. Adjustment of the equalizer to a given transmission line is carried out under the control of the control logic and in response to peak-to-average difference signals supplied by the detector. To that end, a train of test pulses is transmitted to the equalizer via the transmission line, and the delay networks and amplifier are selectively switched into and out of the signal path in timed synchronism with successive ones of those pulses, thereby providing different combinations of phase and/or amplitude compensation for such pulses. The peak-to-average difference detector responds to the compensated pulses to identify the particular delay network or delay network/amplifier combination that best compensates for the distortion introduced by the transmission line, and the control logic locks that combination into the signal path. In the case where the equalizer is used in an FM transmission system, it is interposed between the transmission line and the FM demodulator so that the equalization takes place prior to the recovery of the demodulated baseband signal.