Patent GB-618775-A (GB)
Title: Improvements relating to radio communication and signalling systems
IPC: B61L15/00
Filed: 1946-03-05
Abstract: 618,775. Railway signalling. TRIGGS, W. W. (Farnsworth Television & Radio Corporation). March 5, 1946, No. 6875. [Class 105] [Also in Group XL (c)] An electric signalling system comprises a control station with a receiver and a transmitter, means for transmitting energy at periodic intervals and means associated with the receiver for preventing transmission during reception. A system is described which provides two-way radio transmission between a control station and a number of mobile stations suitable for traffic control use in a railway marshalling yard, whereby the periodic transmission is utilized to provide a warning of any apparatus failure. Fig. 1 shows a block schematic diagram of the control station equipment. The antenna 23 is connected to receiver 21 when antenna relay 24 is normal or to transmitter 22 when relay 24 is operated. Modulating signals are applied to transmitter 22 from an audiofrequency signal source 27 when transfer relay 31 is normal, or from a microphone 26 when relay 31 is operated. The H.T. supply is connected to the receiver 21 when power supply relay 33 is normal or to the transmitter 22 when relay 33 is operated. The valve heater supply is connected to both transmitter and receiver independently of the position of relay 33. An automatic keying device 34 operates both relays 33 and 24 at recurrent intervals and thus provides intermittent transmission of checking impulses consisting of carrier wave modulated by signals from source 27. In the periods between the short impulses, the system is available for the reception of incoming signals. For speech purposes switch 32 is depressed to operate transfer relay 31, which energizes power transfer relay 33 and antenna relay 24, so that speech modulated signals may be transmitted. When receiving, demodulated signals from receiver 21 are applied to loudspeaker 25. When an incoming signal is being received, a lock-out relay 42 which is associated with the audio-amplifying stages of receiver 21 operates, thereby disconnecting the control circuits to power transfer relay 33 and antenna relay 24, so that these relays remain unoperated, and reception continued uninterrupted. Pilot lights are provided .as a visual check. A demodulator unit 36, which is inductively coupled to the transmitter output circuit, comprises a signal rectifying circuit which controls the operation of relay 37. Relay 37 controls lamp 35 which thus lights when a modulated carrier wave is being transmitted. Indicator lamp 41 is energized when power supply relay 33 is operated and thus indicates that power is being supplied to the transmitter. Lamp 43, which indicates an incoming signal, is energized when lock-out relay 42 is operated. Fig. 2 is a schematic diagram of the mobile station equipment. The antenna 51 is connected to receiver 53 when antenna relay 55 is normal, or to transmitter 52 when relay 55 is operated. The H.T. supply is connected to receiver 53 when power transfer relay 64 is normal or to transmitter 52 when relay 64 is operated. Modulation signals can be applied to transmitter 52 from microphone 65. When receiving, demodulated signals from receiver 53 are applied to filter 56 which selectively applies speech signals to loud-speaker 57, and the periodic check impulses which are at a low audio-frequency, to rectifier 61. The output from rectifier 61 operates relay 62 which energizes lamp 63. Lamp 63 thus flashes in synchronism with the checking impulses and confirms that the system is operating. A portion of the checking impulse energy may also be applied to loud-speaker 57 to provide an aural check. When transmitting from the mobile station switch 54 is actuated which operates antenna relay 55 and power transfer relay 64. Relay 64 also lights lamp 66 to indicate that the transmitter is energized. In addition, code signalling may be provided by operating switch 54 to transmit impulses of unmodulated carrier wave energy, which will cause lamp 43 to flash at the control station. Fig. 3 (not shown) describes the circuit of the transmitting and allied apparatus at the control station. Relays 24, 33, 42, 31, 37 operate as described with reference to Fig. 1. The input power supply is applied to terminals 71. The transmitter comprises a crystal-controlled oscillator 85 and power amplifying valve 92. The primary circuit of the H.T. transformer 73 is controlled by relay 33. The audio-frequency signal (source 27 of Fig. 1) is derived from the main power supply by means of the voltage developed across resistance 103 in the lead to the H.T. supply smoothing filter 77, which is applied through relay 31 to valve 106 and valve 111, the output from which is applied to valve 92 to modulate the carrier. The automatic keying device 34 of Fig. 1 is provided by a motor-driven cam arrangement 82, which intermittently operates relays 33 and 24. A bridge rectifier circuit 101 supplies the voltage necessary for operating relays 31, 33 and 24. The demodulator 36 of Fig. 1 is provided by inductive coupling 121 and valves 125, and signal rectifying valve 131. Fig. 4 (not shown) describes the circuit of the receiving portion of the control station. Terminal 142 is connected to antenna 23 through relay 24 of Fig. 3. The receiver comprises radio-frequency amplifier 153, oscillator 156, mixer valve 155, intermediate frequency ampli-. fiers 163, 165 and detector valve 166. A second diode portion in valve 166 in series with condenser 175 is connected across diode load resistor 171 to form a noise-limiting circuit. The output from resistor 171 is applied to valve 181 which also comprises a second triode portion acting as a muting circuit which is released when a carrier is received. The output from valve 181 is applied to power amplifier 185 and thence to loud-speaker 25 and earphone terminals 191. Automatic volmne control is provided by valve 165 and the output from valve 181 is also used to operate lock-out relay 42. The primary circuit of the H.T. transformer 144 is controlled by relay 33 via terminals 143. Fig. 7 (not shown) describes the circuit of the mobile station equipment. The receiver is similar to that described for the control station. The transmitter comprises valves 282 and 285, and valve 295 acts as the modulator valve. The H.T. power supply is provided by a motor generator M/G supplied from the locomotive power supply which is connected to terminals 204. Relays 55 and 64 of Fig. 2 are shown with a single energizing coil 274, and these relays together with relay 272 are operated by switch 54. Relay 272 controls lamp 66 and completes the microphone input circuit of modulator valve 295. Fig. 8 (not shown) shows the circuits corresponding to the filter 56, rectifier 61 and relay 62 of Fig. 2. Details of the mountings and arrangement of the microphones, signal lights, &c. in the control room and the locomotive cab are also described. The system may be used for fire, police, traffic control or other communication applications, and may involve separate transmitter and receiver aerial systems and separate carrier frequencies.