Patent GB-737617-A (GB)
Title: Improvements relating to impulse coded carrier remote control systems
IPC: H04B1/50
Filed: 1953-07-10
Abstract: 737,617. Electric selective signaling system. WESTINGHOUSE AIR BRAKE CO. July 10, 1953 [Sept. 30, 1952], No. 19176/53. Class 40 (1). In an impulse coded carrier remote control system for controlling from a central station the operation of devices at plural outstations by the transmission of an impulse coded first carrier frequency and for indicating the operation of a selected device at an outstation by the retransmission to the central station of an impulse coded second carrier frequency, a pilot signal at a third frequency is transmitted from the central station to the outstations, at which it is applied to frequency converters generating identical second carrier frequencies locked to the pilot frequency. Fig. 2 shows the central station apparatus for a railway signalling system selectively controlling the operation of track switches and signals over a common line to plural outstations, wherein one section of a double triode VT1 operates as a Hartley oscillator tuned by inductance 28 and capacitance 29 to a frequency of 9 kc/s. stabilized by resistance 35 in series with capacitance 36, and keyed over normally closed contact 11 of relay OT and normally closed contact 8 of relay OC in series with the anode supply. The oscillator grid is directly coupled over resistance 19 to the grid of the remaining triode section operating as a buffer amplifier feeding a bandpass tuning unit ICU comprising top capacitance coupled parallel tuned circuits 39, 40 and 41, 42 whose output is developed across a variably tapped potentiometer 44, the slider of which energizes the power amplifier VT2 comprising both sections of a double triode in parallel to supply keyed carrier to the common line 1LW, 2LW through a transformer Tl and a series inductance-capacitance filter F1 tuned to pass a 9 kc/s. signal. Triode VT3 operating as a Hartley oscillator tuned to 12.5 kc/s. by inductance 54 and capacitance 55 continuously supplies a pilot signal to line through transformer T2 and a series inductance-capacitance filter F2 tuned to 12.5 kc/s. Incoming indicating signals from the line are selected by a receiver IR comprising a filter-transformer F3 tuned to 25 kc/s. and applied to a variably tapped potentiometer 58 whose slider voltage is amplified by pentode VT4 feeding a bandpass tuning unit 2CU comprising top capacitance coupled parallel tuned circuits 67, 68 and 71, 72 whose output signal is rectified by a diode connected triode VT5 to a unidirectional negative-going voltage across load resistance 73 which cuts off the normally conducting triode VT6 on arrival of a signal pulse to release the code following relay OC. Coding unit OCU includes a master relay OM which when energized by closure of the contacts of a starting switch SB on the control-panel OCP, closes contact 129 in a stick relay circuit (not shown) to hold the relay energized until a complete code has been transmitted and closes contact 114 to energize transmitting relay OT through a known circuit network controlled by a known tuning chain of slow release relays (not shown) controlled by levers on control panel OCP to generate a selected impulse code train of long and short pulses in accordance with the required outstation switch or signal operation. Relay OT accordingly keys the transmitting oscillator by opening and closing contact 11 to transmit a corresponding code of 9 kc/s. carrier pulses to line. Fig. 3 shows the apparatus at one of a plurality of outstations wherein a receiver CR comprising a 9 kc/s. filter F4, a pentode amplifier, a 9 kc/s. bandpass filter, a diode detector, and a normally conducting triode cut off on arrival of a rectified carrier pulse to release relay FC, similarly to receiver 2CU in Fig. 2. The pilot signal is extracted by filter transformer F5 tuned to 12.5 kc/s. feeding a variably tapped potentiometer 87 whose slider signal is amplified by triode VT7 to energize an over-biased frequency - doubling triode VT8 whose anode load comprises an inductance 91 tuned to 25 kc/s. by capacitance 92. The amplified signal is limited by triode VT9 whose output is supplied through a bandpass tuning unit 3CU comprising top capacitance coupled parallel tuned circuits 99, 100 and 103, 139 and a variably tapped potentiometer R8 to a power amplifier PAM comprising two parallel triodes, transmitting an impulse coded 25 kc/s. indication carrier to line over output transformer T3 and a series inductance-capacitance filter F6. The cathode resistances of triodes VT8, VT9 are returned to earth over contact 124 of relay FT and over resistance R5 to the positive anode supply so that the tubes conduct when the contact is closed and are cut off when it is open, thereby keying-the 25 kc/s. carrier supplied to line. Each outstation apparatus contains a known station coding unit SCU similar to OCU in Fig. 2 in which relay FM is normally released. An incoming code signal from receiver CR impulses relay FC to control a known circuit such that the appropriate code signal is interpreted to selectively energize control relays, e.g. WSR, HSR to complete operating circuits for e.g. a track switch or railway signal motor. On completion of the operation, contact 121 is closed relay FM is energized to hold over its contact 123 and a known stick relay circuit (not shown) and to close contacts 122 to prepare a known coding relay circuit whereby transmitting relay FT is operated and released to key the 25 kc/s. carrier over contact 124 in accordance with a code representing the fulfilment of the operation. On completion of the appropriate code the stick relay circuit is released, and the system is prepared to receive further incoming pulse codes. At the control station, master relay OM has been released, and the incoming impulse coded indication carrier signals are extracted from the line and impulse relay OC to correspondingly open and close contact 116 to control a known circuit whereby the appropriate indication code signal for the performed operation is interpreted to selectively energize indication relays, e.g. RWK, NWK to complete operating circuits for indicator lamps NL, RL on the control panel OCP. Contact 8 of relay OC is also impulsed to key transmitter CT so that the indication carrier code is retransmitted at 9 kc/s. The carrier transmissions may be effected by radio or the pilot signal may be transmitted to the outstations by an independent line.