IMPROVEMENTS IN OR RELATING TO THE TRANSMISSION OF INFORMATION

• Main Authors: LUCIEN HIX, PETER GEOFFREY LAW, HARRY HEGGIE OGILVY, JOHN EDWARD HARVEY BRICKNELL
• Format: Patent
• Language: English
• Published: 12.04.1972
• Subjects: ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; TRANSMISSION

1,270,109. Signalling on trains. RIPPER ROBOTS Ltd., and BRITISH RAILWAYS BOARD. 8 July, 1969 [8 July, 1968], No. 32403/68. Heading B7N. [Also in Divisions H3-H5] In a train audio information is transmitted on a high frequency carrier over a circuit provided for another facility, preferably a train lighting circuit. The information preferably frequency modulates a carrier of about 30 KHz. As described power from the lighting control circuit is applied via a conventional series regulator circuit, transistor VT1 to VT5, Fig. 1A, to supply a constant voltage to power the transmitter, Figs. 1A and 1B. The microphone input signal from terminal F is amplified in a differential amplifier, VT6 to VT9, and applied via a compound emitter follower, VT10 and VT11, to frequency modulate a magnetic oscillator including transformer T1 and multivibrator, VT12 and VT13. The oscillator output is applied to the power amplifier, VT15 and VT16, for application to the train lighting control circuit, via a gate formed by diode D8 and transistor VT14 which prevents a signal being applied to the power amplifier until a short time after the equipment has been switched on, due to charging of capacitor C10. At the receiver, Figs. 2A and 2B power derived from the lighting control circuit at terminals C and D filtered and stabilized by Zener diode D6, while signals are applied via transformer T1 to operate a Schmitt trigger, VT1, VT2, which cleans up the received waveform and fires a monostable trigger VT3 and VT4 which supplies charging pulses to an integrator C6 and R14. The appropriate frequency compensation for the integrator characteristic is provided in transistor VT5 from which the signal passes to a conventional amplifier feeding a loudspeaker in the rail coach. The arrangement provides public address, music distribution or intercommunication through a railway train without the use of special wires.