Patent GB-777195-A (GB)
Title: Improvements in or relating to telegraph systems
IPC: H04L5/14
Filed: 1955-08-29
Abstract: 777,195. Telegraph systems. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Aug. 29, 1955 [Sept. 1, 1954], No. 24722/55. Class 40 (3). In a telegraph system in which each telegraph signal comprises a start element and a stop element which normally have fixed but opposite polarities, service signals are produced for transmission by reversing the polarity of the start element and/or the stop element, and the receiver end incorporates means responding to the reversed polarities of the start element and/or the stop element. The signals from the tape transmitter BZ are passed to the line RZ under control of a series of gas-filled tubes B12 ... B18 to the ignition electrodes of which pulses are applied at intervals of 20 ms. from a generator SG, a tube which is conducting priming the next tube which is fired by the next pulse from SG which also operates through anode resistor R27 to cut off the tube which was previously conducting. For the start impulse, assumed to be positive, the tube B12 is in conducting condition and a positive pulse is applied from cathode resistor R28 via rectifier G1 to the point ZP connected by resistors R21, R22 to the ignition electrode f1 of tube B11 and the cathode of tube B10. When ZP is positive, the next pulse from SG fires tube B11 so that a positive pulse is passed to the line RZ from its cathode resistor R25. For the five selecting (information) elements of the signal, positive pulses are applied from the tubes B13 ... B17 via rectifiers G2 ... G6 to the transmitter BZ and if tape-controlled contacts are closed a positive potential is applied to the point ZP so that tube B11 is made conducting to send positive pulses to the line RZ. If the contacts are open a low potential is applied via rectifier G1 to the point ZP-since the tube B12 is not conducting-and the next pulse from SG fires the tube B10 and cuts off the tube B11 so that a negative pulse is applied to the line RZ. During the stop impulse period, B18 is conductive so that B12 is non-conductive and a low potential is applied at ZP so that the next pulse from SG ignites B10 if it is not already operated. The tube B18 primes the tube B12 and also passes a pulse over the line TL to step the tape in the transmitter BZ for the transmission of the following signal. When a service signal involving the reversal of the stop polarity is to be sent, the closure of a switch Cd primes the tube B20 which is fired by each pulse from the generator SG. The firing of the tube B20 primes the tube B19 which is fired when the tube becomes conductive during the stop element period. The firing of B19 applies a strong positive pulse to the ignition electrode f2 of the tube B11 which fires although the output voltage at ZP is low and the firing of B10 attempts to cut off B11. Receiver arrangement. The circuit for detecting the service signal in which the polarity of the stop element is reversed, i.e. transmitted with positive polarity, comprises tubes B1 ... B7 constituting a counting circuit for the seven elements of a received signal, the tubes B2 ... B7 being triggered from a source IB producing pulses at intervals of 20 ms. and the tube B1, when primed by the tube B7 in conductive condition, being fired by a positive impulse derived from the differentiated input at terminal IK when the signal changes from negative to positive. If the counter is out of synchronism with the incoming signals, it gradually adjusts itself automatically since the only regular change from negative to positive occurs at the transition from the stop element to the start element. When the counting circuit is in synchronous operation, the tube B8 is invariably ignited by the first pulse from IB after the tube B7 has been ignited, which corresponds to the end of the signal, and the tube B9 is primed. Since the stop pulse at IK is of positive polarity in the survice signal, the tube B9 is fired and operates relay DR which initiates further switch - ing action or operates an indicator. The firing of the tube B9 passes a pulse via capacitor C18 to the ignition electrode of the tube B1 which fires so that the counting circuit operates without interruption.