Patent GB-753397-A (GB)
Title: Improvements in or relating to rhythmical telegraphy systems
IPC: H04L1/00
Filed: 1954-05-31
Abstract: 753,397. Code telegraphy. PHILIPS ELECTRICAL INDUSTRIES, Ltd. May 31, 1954 [June 3, 1953], No. 16063/54. Class 40 (3). In a synchronous telegraph system for the transmission of signals each comprising a group of a constant number of pulses of the same duration in which the incoming signal pulses are applied to..a delay register having a delay time equal to a multiple of the period of a signal pulse group and providing the output pulses, and in which a testing device, responsive to the reception of a faulty impulse effects the transmission of a signal to the transmitting station to repeat a number of complete signals and also disconnects the incoming signals from the register in which the stored signals circulate for the repetition time, the incoming signal pulses are fed to the input of a second delay register, the output of which is coupled to the first delay register. The delay of the second register is equal to a whole multiple of the duration of a signal element and the testing means, after having responded, is rendered inoperative for a time period equal to the repetition time minus the time delay of the second delay register. In the arrangement shown, marks and spaces sent by frequencies f1, f2 are received at 5 and produce from devices 6, 7 direct voltages which are fed to a testing device 12 responsive to voltage below a predetermined threshold value so that interference or fading operates the testing device. The marking pulses of the signals are passed via contact 8 to a delay device 9 having a period equal to that of a complete signal and over contact 10 to the distant teleprinter 11. The output of the device 12 operates a timing circuit 13 counting pulses produced at 20 ms. intervals by a pulse generator 14 and, in addition, operates the transmitter Z2 which is arranged to send a faulty signal, for example mark and space frequencies simultaneously, which at the receiver 01 operates the testing device to control a circuit 16 which moves contact 2 for a period equal to two full signal periods so that signals transmitted are also stored in a delay register 4 having a delay time equal to two full signal periods. The pulse generator 14 also produces a pulse at the end of each period of 140 ms., and in conjunction with a pulse from the circuit 13 triggers the device 15 which opens contact 10 at the instant corresponding to the end of a signal group during which a faulty element was received so that the previous signal group is passed to the teleprinter 11. When the circuit 13 becomes inoperative, a pulse from generator 14 at the 140 ms. period triggers the device 15 to close contact 10. Normally the timing device 13 counts fourteen 20 ms. pulses corresponding to the repetition period for two complete signals before returning the testing device 12 to its operative condition and switching contact 8 to the position shown so that the repetition of the pulse element previously found to be faulty, applied over contact 8, is correctly located in the sequence of pulses which have continued to circulate in the register 9. The essential modification of the system is the incorporation of the delay register 17 having a delay time equal to, for example, four element periods, and the timing device 13 is arranged to hold the testing device 12 inoperative for a period equal to fourteen minus four, i.e. ten, impulse periods so that a number of pulses prior to the pulse actually found to be faulty can be retested in case an apparently normal reception of a pulse produced by selective interference earlier in the transmission and during the period of a few impulses immediately prior to the detection of a faulty element, had given rise to the production of a faulty impulse element.