Circuit arrangement for signal equalization in wide-band transmission

Abstract

A transmitting station for wide-band signals at one end of a line such as a bifilar or quadrifilar cable includes a generator of test frequencies lying between several sub-bands--such as carrier-frequency telephone channels--normally used for message transmission. A pilot wave outside the range of message frequencies, generated at the transmission station, is modulated under the control of a transmitting-side programmer to indicate the start of a test sequence during which the several test frequencies are sequentially emitted, except when a message to be transmitted (e.g. a TV program) spans several sub-bands and requires suppression of the intervening test frequencies. At the other end of the line, a receiving station includes an equalizer with a number of individually adjustable stages pertaining to respective frequency bands centered on the several test frequencies. A receiving-side programmer, started by the extracted pilot wave, controls a generator of heterodyning frequencies which differ by a predetermined beat frequency from the respective test frequencies and are sequentially produced for mixing with the incoming test frequencies. The amplitude of the resulting beat frequency is detected and compared with a reference voltage to generate an error signal which is fed to a storage cell of a memory working into the corresponding equalizer stage for adjusting same until the error signal disappears. If the transmitting-side programmer is instructed to skip one or more test frequencies, their absence is communicated by the beat-frequency detector to the receiving-side programmer which then switches immediately to another heterodyning frequency.