GB771302A - Improvements in or relating to communication channels conveying information in the form of a code - Google Patents

Abstract

771,302. Code telegraphy. STANDARD TELEPHONES & CABLES, Ltd. Dec. 10, 1953, No. 34416/53. Addition to 721,838. Class 40 (3). A telegraph receiver for equal length combinations of elements of two signalling conditions having a time scale circuit driven by regularly repeated pulses and providing pulses for examining the condition of the incoming signals at predetermined instants and effecting their regeneration comprises means for recording whether transitions from one signalling condition to another occur early or late in respect of their nominal positions in the time scale and means for momentarily stopping and restarting the time scale circuit independently of the transmitter and of the received signals and means for adjusting the position in the time scale at which the time scale circuit is restarted under control of said recording means. The arrangement is described in connection with the telegraph system of Specification 771,301 in which two check pulses are added to the normal five-unit code and in which the idle condition is represented by a continuous marking condition, whilst the seven-unit combination MMMMMSS is transmitted preparatory to the transmission of information. The transition from mark to space will therefore occur at 100 ms. from the commencement of the normal time scale in a cycle of 145 ms, if the seventh element is assumed to have a duration of 25 ms. In the rest condition, switch 12F has element 1 conducting and when the line changes to space, gate 101G passes a pulse to gate 105G which also receives a pulse 11fsp switch 11F which normally has its element SP conducting. Element ST of switch 11F is made conducting and produces a pulse 11ft which opens gate 102G since switch 23F is assumed to be in its position 23F4. The counter 11C which receives pulses at a frequency of 5Kc is started at position 102 ms. from zero. To guard against a false start occasioned by a space occurring in the normal idle signal the incoming signal is tested at 105 ms. and at intervals of 5 ms. up to 140 ms. by a gate 104G, and if a mark is present at two of these instants, a counter 12C is stepped to position 2 and via gates 108G, 107G operates switch 11F to make element SP conducting and close gate 103G to the stepping pulses - P. A pulse 11ft produced by the change-over of 11F resets the counting circuit 11C to position 102 and the counter 12C to the position 0. The received elements are applied to a switch 21F which produces an output at 21ft at each change-over, and pulses are applied to element E of switch 22F at times 10, 30, 70, 110, 130 ms. To element L of this switch pulses are applied to 0, 20, 40, 60, 80, 120 ms. so that in the case of a pulse which should occur at 20 ms., but occurs later the element L is operated. The element E is operated if the pulse element occurs before 20, 40 ... 120 ms. The switch 23F is reset to the position 23f4 at the instant 105 ms. in the time scale. If a pulse occurs early when 23F is in position 4 gates 206G, 207G are opened and the switch is changed to position 23F3, and if it should occur late 201G, 202G are opened and position 23F5 is energized. The positions 23F (1,2,3) indicate that the transition is late relative to the,time scale and the positions 23F (4, 5, 6, 7) are indicative of early transitions. After its initial operation the counter 11C is stopped at 100 ms. and restarted at 98 or 102 ms. according to the position assumed by the switch 23F in the meantime. At the time 11C0 the switch 12F is driven to position 2 and at 11C80 gates 115G, 116G are opened to step counter 12C to position 1. At time 100 ms., gates 106G, 107G are opened at switch 11F changed to position SP so that gate 103G is closed and stops the timing circuit. As the transition from space to mark which should have occurred at 0 ms. is late, the switch 23F will be in the position 5 and the pulse applied at 11ft when 11F changed over will restart the cycle at 102 ms., gate 105G being re-opened to restore the switch 11F to the position ST. If a marking element was found at one only of the examinations at 105, 110 ... 140 ms. the counter is in position 1 and is not stepped by the pulse at 11C80 so that the pulse is provided for opening gate 106G at 100 ms. If during signal transmission, the signal transits are early with respect to the time scale, gate 110G is opened at 100 ms. and the time scale counter 11C restarted from 98 ms. The switch 11F is not operated to position SP when the scale again reaches 100 ms. since the operation of 11F to the position SP produced a pulse 11ft restoring 12C to the position 0. The receiving equipment is brought to the rest condition by the reception of a predetermined number, e.g. nine, of signals consisting entirely of marks. The output of the element M of a switch 13F changed to S by a spacing pulse at times 10, 30... 130 ms. and restored, if necessary, to M by a pulse at 0 ms. is applied at time 135 ms. to a gate 112G so that the detection of nine successive all-marking signals will step the counter 13C to 13C9 and gates 107G, 108G will open to operate the element SP of the switch 11F so that the counter 11C is stopped. Also, pulses 13C9 and 11fsp open gates 114G, 113G to restore counter 13C to the position 0. Specification 692,411 also is referred to.