Patent GB-255581-A (GB)
Title: Improvements in and relating to electric telegraphy
IPC: H04L25/04
Filed: 1925-05-15
Abstract: 255,581. Jacob, W. G. R., and Eastern Telegraph Co., Ltd. May 15, 1925. Restoring or modifying imperfect signals; repeating systems using contact-making relays ; transmitting systems; synchronous movements.- In an arrangement for receiving alternating-current signals, employing mechanism which is synchronized with the current alternations, means are provided for re-shaping the received signals prior to recording a retransmission. The invention is particularly applicable to a system using code elements distinguished by phase of alternating current as described in Specification 234,529. Fig. 1 shows an arrangement for retransmitting cable code signals employing signal shaping means similar to that employed with the transmitter described in Specification 19099/05. The alternating-current signals are received by apparatus such as is described in the above Specification which delivers corresponding directcurrent signals to a relay 2 controlling a similar relay 3. On receipt of a dot the tongue of relay 3 moves to the left to close a contact in a circuit from battery 1<1> through relays 4 and 6 in parallel and a contact 5 closed intermittently by a cam on a shaft 1 making one revolution per signal element. On receipt of a dash, relays 9 and 8 are similarly energized. The relays 4 and 8 retransmit dots and dashes respectively into the circuit LE. The phase of the cam action is such as to close the contact 5 at about the middle of a received signal thus making the maximum allowance for distortion. The relays 6 and 9 serve to close hold-on circuits for the relays 4, 6 and 9, 8 respectively from the battery 1<1> through a contact which is opened intermittently by a second cam on the shaft 1 to terminate the signal in the circuit LE. The phase of this cam determines the degree of curbing of the re-shaped signals. In the application to Morse or Baudot signals the relays 8 and 9 are dispensed with. Alternatively a re-shaping arrangement as described in Specification 215,434 or 234,894 may be used. Means are provided for ensuring a constant phases and speed relation between the signals and the alternating current employed for their retransmission. For this purpose a third cam on the shaft 1 may actuate contacts in the circuit of a phonic motor controlling the speed of an alternator of which the field is excited by the re-shaped signals, or the cam may actuate contacts used in conjunction with a transformer and a direct current battery to produce an oscillating voltage for the retransmission. Fig. 3 shows an arrangement, applicable to the system described in Specification 234.529, for ensuring that, on resumption of signalling after a pause, the retransmitted signal elements shall have the correct algebraic sign notwithstanding loss of synchronism of the retransmitting shaft during the pause. The alternating-current signals received over leads 18, 19 are delivered to commutators 16, 17, operating 90‹ apart, on a shaft 33. The commutators are employed, in conjunction with relays 29, 30, 31, and 32, motor 34, and differential gearing 35, as described in Specification 234,529, to maintain the shaft 33 in phase with the received current. The commutator 16 thus delivers rectified current to a relay 20 which causes corresponding + and - currents from battery 20<1> to traverse polarized dot and dash relays 21, 22 respectively and the relay 29. When no signals are being received, the tongues of the relays 21 and 22 remain on their back contacts and close a circuit from a battery 24 through an electromagnetic clutch 25 of which the shaft 26 is geared to the shaft 33. The clutch thus acts to close contacts 27 and 28. The contact 27 disconnects the battery 36 from the tongue of the relay 30, and connects it directly to the relay 32, thus causing the motor 34 and differential 35 to rotate continuously in one direction. The contact 28 shortcircuits the relay 22. Resumption of signalling is preceded by a prolonged series of dots, whereupon the circuit of the clutch is opened as soon as the commutator 16 is brought into such phase relation to the alternating current as to deliver dot signals to the relay 20, and the retransmitted signals then have the correct algebraic sign. The arrangement of Fig. 3 obviates the necessity for a continuous transmission of current or of a series of signals to maintain the synchronism of the shaft 33 during a pause between messages, and consequent unnecessary operation of the stripperforating receiver. Alternatively if such a synchronizing transmission is used, the receiving operator, observing its receipt, may open a switch to disconnect the perforator. Resumption of the message signal is then preceded by a cessation of the synchronizing transmission, and such cessation is utilized as in the arrangement of Fig. 3 to energize a clutch or other electromagnetic device tn trip the switch. The subject-matter claimed in Specification. 248,941 is disclaimed.