GB1009491A - Transmission systems - Google Patents

Abstract

1,009,491. Telegraphy. INTERNATIONAL BUSINESS MACHINES CORPORATION. Nov. 21, 1963 [Dec. 18, 1962], No. 45923/63. Heading H4P. In a data transmission system in which the data is distorted prior to transmission to compensate for line characteristics, undistorted test pulses are transmitted initially and sampled at bit frequency at the receiver, where they are received distorted. The results of the sampling are returned to the transmitter where they are used to predistort the data to be transmitted. In a first embodiment, a distorted test pulse received from line 14 passes to unit 26 which senses the main peak and, via unit 29, enables gate 36 at the first peak in the distorted pulse. Unit 26 also generates bit rate clock pulses which step binary counter 34. After a K- bit delay (K = number of bit periods up to the maximum peak) the distorted pulse arrives at comparator 40. Comparator 40 is enabled at bit rate except during the main peak time and, when the distorted pulse differs from a certain potential, inhibits gate 36 via unit 29 and also passes a positive or negative pulse, indicating the sign of the difference, to register 46. Unit 48 now reads out the register, which also holds the binary count on counter 34 at the time the comparator pulsed, and the register's content is passed at slow speed to the transmitter where, by means of units 52, 60, 62, it modifies the next test pulse to be sent. This operation continues until counter 34 reaches full count, whereupon data may be transmitted, it being predistorted by units 52, 60, 62. A second embodiment, Fig. 2 (not shown), uses two comparators for positive and negative thresholds, the thresholds being gradually reduced to zero and the test pulses modified until the comparators give no output at each enabling pulse. Specification 1,009,493 is referred to.