GB1353018A - Automatic transversal equalizer - Google Patents

Abstract

1353018 Automatic equalizers XEROX CORP 20 April 1971 [21 April 1970] 19039/70 Heading H4R An automatically adjusting equalizer has a transversal filter with its taps fixed to give an amplitude frequency response having a rising characteristic, following a raised cosine curve, between 600 and 3000 Hz. The output, 30, from the transversal filter is fed via a potentiometer 56 to a summing amplifier where it is added to the signal appearing at the centre tapping 40, of the transversal filter delay line. The potentiometer is automatically adjusted to provide equalization for two different frequency pilot signals transmitted over the transmission system and fed through the equalizer. As described with respect to Fig. 8 the full equalizer comprises a transversal filter including delay line sections T with the signal appearing at the input, output, and middle, taps fed through respective resistors 24, 26, 28, to an inverting amplifier 50. The output of amplifier 50 is mixed with the signal appearing at the two other taps, fed through respective resistors 25, 27, at the input to a second inverting amplifier 54. The resulting signal, constituting the output of the transversal filter, is fed through a variable resistor 56 to be mixed with the signal appearing at the centre tap of the filter at the input of a third amplifier 58, the output from which constitutes the equalizer output. The received signal includes two reference or pilot signals at 1200 and 2400 Hz, the relative levels of which, at the transmitter, are known; these reference signals are separated by filters 67 and 68, amplified, and rectified to provide opposing D.C. voltages at the input of amplifier 72 to provide a control signal for driving motor 73 in such a way as to adjust potentiometer 56 to restore the relative levels of the two pilots to the values they had at the transmitter.