Patent GB-576352-A (GB)
Title: Printing telegraph system
IPC: H04L27/26
Filed: 1944-02-18
Abstract: 576,352. Type - printing telegraphy. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). Feb. 18, 1944, No. 3055. [Class 40 (iii)] In a printing telegraph system the transmitter is arranged to send an invariable frequency as a start element and a number of different frequencies corresponding to the code elements of a character which are transmitted simultaneously. During idle periods, a frequency slightly different from the start element frequency is transmitted and units and spaces are differentiated by frequencies differing by a small amount. In the transmitter arrangement, Fig. 1, one frequency is radiated by an oscillator 06 during idle periods, and the depression of a key 6 ... controls motor 11 and shaft 10 so that contact 14 is closed and oscillator 06 radiates slightly different frequency as the start element. Further rotation of cams 12, 13 opens the circuit of oscillator 06 and at contact 15b simultaneously connects the oscillators O1 ... 05; the particular frequency corresponding to a mark or a space being determined by the selective operation of contacts 16 ... 20 by code bars 1 ... 5. At the receiver, Fig. 2, the input is applied to valve 31 which acts as a limiter and over contacts 35a to a circuit 36, 37 tuned to a frequency midway between the idle period frequency and the start element frequency. The signals passed by this circuit are applied to circuit 43, 44 tuned to frequencies slightly above and below the stop and start frequencies so that the start frequency acts differentially across detectors 45, 46 to operate relay 21 over contact 50 closed by cam 24 on shaft 22 in its rest position. When relay 21 operates, shaft 22 is rotated, the circuit of relay 21 is broken and the output of valve 34 is connected simultaneously over contact 35b to circuits 51 ... 55 tuned to a frequency midway between the marking and spacing frequencies of the five code elements. The output, as shown, for example, from tuned circuit 51, is applied to a valve 56 and circuits 61,.62 tuned to frequencies just above and below the marking and spacing frequencies of the first code element so that a marking frequency differentially operates relay 67. Differential circuits and relays similar to 67 are provided for the remaining elements of a code combination, A shaft 25 carrying cams 28, 29, 30 is rotated at half the speed of shaft 22 through gears 26, 27. When a marking element is received, relay 67 operates and over contacts 68 registering relay 70 is energized and locks over contact 71 during the revolution of shaft 25. During the subsequent half-revolution of shaft 25, contact of relay 67 is connected to a second registering relay 72 by springs 69 on the opposite side of the cam, and, relay 72, if operated, locks up over springs 81. At the same time contact of relay 70 is connected by spring 74 with a spring 75 operated by cam member 24 so that the indication on relay 70 is transferred to relay 21 which sets the first member of the printing selector. The other four code elements which had been simultaneously applied to relays similar to 70 are sequentially applied to relay 21 through springs 76 ... 79. During the transfer of the code elements of the first character to relay 21, the second code combination is applied to relay 72 and four similar relays. Towards the end of a revolution of the shaft 25, contact 71 is opened and relay 70, if operated, is thereupon released in preparation for the first element of the code combination of the next character. The printing of the first character takes place whilst the third character is being registered by relay 70 and the four similar relays.