GB1161003A - Improvements relating to Data Transmission Systems - Google Patents

Abstract

1,161,003. Digital transmission systems. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 12 Dec., 1967 [22 Dec., 1966], No. 57481/66. Heading H4P. Serial digital data is transmitted over a telephone line in the form of multi-amplitude signals on a number of channels, the signals in each channel being vestigial side-band. In the embodiment described serial data at bit-rate b is fed to a 3-bit shift register from which parallel signals are read out at rate b/3 to a coder which develops on two channels simultaneous signals, each having one of three amplitude levels. The signals on both channels pass via respective low-pass filters to modulators which develop vestigial side-band signals: one channel contains the upper side-band of one multi-level signal and has a carrier f 1 , and the other the lower side-band of the other signal and a carrier f 2 . At the receiver the signals in the two channels are demodulated and passed to a level-decision circuit which develops from its distorted input undistorted three level signals at rate b/3. These signals are converted to 3-bit parallel form and passed to a shift register which provides the original data at rate b. The receiver includes a digital circuit which generates clock signals under control of a signal f 2 -f 1 derived from the demodulators.