Patent GB-780948-A (GB)
Title: Synchronizing control arrangement for pulse-code-communication system
IPC: H04L7/04
Filed: 1954-03-23
Abstract: 780,948. Code-telegraphy; electric synchronous movements. HAZELTINE CORPORATION. March 23, 1954 [March 30, 1953], No. 8413/54. Class 40 (3). In a pulse code communication system a group of code combinations of elements representing a number of characters is prefixed by a group of pulses forming a synchronizing signal for the receiver. The group is formed of two dissimilar sets of pulses, each of which is individually different from any character combination, and the receiving arrangement is arranged to respond to either set of pulses so that reception takes place if one or the other set of pulses is mutilated in transmission. Additionally, the receiver is set into operation if predetermined impulses selected from the respective sets are correctly received. In the transmitting arrangement, Fig. 1, the start element of a signal from the automatic transmitter 50 releases relay 62a which at contact 62b energizes for a period of a complete signal a pulse generator 63 operating relay 52a, which at contact 52c brings in a generator 64, and at contact 52b extends the output of the transmitter 50 to contact 53b of a relay 53a operated by sampling pulses from the generator 64. The code elements are passed over operated contact 53b to a storing device 25 of a shifting register 51, and each sampling pulse is followed by a shifting pulse so that the elements of five consecutive signals are selectively stored on the devices 1 ... 25 of the register 51. The sampling pulses are also passed to a counter 65 which after 25 pulses operates a keying pulse generator 66 causing the pulses in the register 51 to be transferred simultaneously to a message tegister 54, and also actuating mechanism 57 controlling the operation of a distributer 55 with an arm 58 moving over segments 56a . . . 56l to generate the synchronizing signal and subsequently over segments 1a, 2a ... 25a, connected to the register 54 to transmit the message signals. The segments 56a . . . 56# are connected to produce alternate spacing and marking pulses, the second marking impulse having a length of 1¢ units. The segments 56g ... 561 are connected to provide alternate marking and spacing pulses with the second spacing element having a length of 2¢ units. The pulse from the counter 65 is also applied to the reset pulse generator 67 which, after a predetermined delay, resets the elements of the digit register 54 in preparation for the pulse elements of the subsequent five character signals. At the receiver, Fig. 2, the pulses are initially applied over back contact 76b to a circuit 84 which in response to the synchronizing signal operates a generator 85 actuating relay 76a to move contact 76b to pass the output of the receiver 74 via contact 77b of relay 77a, operated by sampling pulses from the generator 85, to the shifting register 75 which is also stepped by pulses from the generator 85. After a prescribed interval, the pulses stored in the register 75 are simultaneously transferred to elements in the register 78 and at the same time mechanism 81 is operated to control a distributer 79 so that the arm 80 rotates over segments 1b . . . 5b . . . connected to the register, stop and start segments being included between the consecutive groups of five segments. After a predetermined interval, a pulse from generator 85 restores the register 78 to its normal condition. In the arrangement, Fig. 3, for detecting the synchronizing signal, the impulses are applied to a magnetic tape 92 fed past a recording head 91 by rollers 93, 94. The impulses are picked up by coils 96 ... 101 and 109 ... 113 spaced according to the leading and trailing edges of the pulse pattern shown, and associated with generators 121 ... 131 interconnected with three groups of rectifiers 102 ... 107, 114 . . . 119 and 132 . . . 137 connected at points 108, 120, 138 to resistors 139, 140, 141 and via rectifiers 142, 143, 144 to a relay winding 145a. The coils 97, 99 ... associated with the trailing edges of the pulses are reversed so that the generators 121 ... 131 all produce positive pulses. If all the rectifiers of one or more of the groups 102 ... 107, 114 ... 119 or 132 ... 137 are made non-conducting, current flows through one or more of the resistors 139 . . . 141 so that the winding 145a is energized to close contact 145b and operate the pulse generator 85, Fig. 2. The three sets of rectifiers are provided so that the winding 145a is energized if the first or second part of the synchronizing signal is received undisturbed, or if mutilation is limited to the beginning and end of the first part and the beginning of the second part respectively of the composite synchronizing signal. Specification 780,947 is referred to.