Patent GB-701328-A (GB)
Title: Improvements in or relating to transmission systems containing terminal stations andrelay stations
IPC: H04B7/155
Filed: 1951-04-27
Abstract: 701,328. Radio signalling. PHILIPS ELECTRICAL INDUSTRIES, Ltd. April 27, 1951 [May 2, 1950], No. 9977/51. Class 40 (5). [Also in Group XXXVIII] In a transmission system comprising terminal stations and one or more relay stations for the transmission of intelligence signals by means of carrier wave pulses, in which a relay station embodies at least one switch to be controlled from a terminal station, the carrier wave is modulated at a predetermined code frequency to produce a switching signal which extends into the intervals between successive pulses, while the relay station embodies a filter for selecting the received switching signal, which is fed to the control circuit whereby the said switch is controlled. As shown in Fig. 1 the transmitter of a terminal 1 comprises a stage 3 having several successively operative transmitting channels comprising pulse position modulators, the time multiplex pulses being applied to a carrier wave modulating stage 5 which is common to all the channels. The carrier wave pulses received from the terminal station 2 are supplied to the receiving portion 8, which supplies the receiving channels of the stage 10 which are successively released. The signals from the terminal 1 are received by the relay station receiver 14 and after amplitude detection are supplied to the transmitter 16, a receiver 19 and transmitter 20 transmitting the signals in the opposite direction. The switches 22, 23 and 24 are controlled from the terminal 1 and switch on, switch off, and supervise the relay station respectively. At the terminal 1 generators 25, 26, 27 and 28 for different code frequencies may be coupled through switches to the modulator 5 to produce switching signals. Tuned relays 33 and 34 are connected to the detector stage at the relay station and control switches 22 and 23, being respectively tuned to the code frequencies of generators 25 and 27. Initially the receivers 14, 14' of the relay stations are switched on by time switches 36, 36'. Upon closing switch 29 the relay 33 closes the switch 22 and switches on the relay station receiver 19 and transmitters 16 and 20, the relay station 12 being similarly switched on by the code frequency from the generator 26, by the relay 33'. Relays 33 and 33' are provided with holding windings. The code generator 27 switches off the relay stations 11 and 12 the tuned relay 34 being slower to respond than the relay 34<SP>1</SP> of the relay station 12. For supervising the relay station 11, a tuned relay 37 responding to the code frequency of generator 28 switches on a local switching-signal generator 38 comprising a modulator stage, a local carrier wave generator, and a local code frequency generator, the output of the generator 38 being supplied to the receiver 19 and via transmitter 20 to the terminal receiver 8. A tuned relay 39 is connected to the receiver 8 and operates a lamp 42 if the relay station 11 is operating satisfactorily. Relay station 12 is supervised in a similar manner from the terminal 2, by means of generator 28', but alternatively may be supervised from terminal 1. If the relay stations are of the type in which the incoming signals are transposed to an intermediate frequency and subsequently retransposed to carrier frequency the tuned relays may be connected through an amplitude detector to the I.F. amplifier. A terminal transmitter, Fig. 2, comprises a push-pull class C modulator stage 44, 44' which is normally cut off by negative grid voltage, and has a tunable Lecher output circuit 45 and tunable Lecher input circuit 46, the input circuit being inductively coupled to the carrier wave oscillator 48. Each time a pulse-shaped modulation voltage is supplied from the stage 53 the pentodes 44, 44<SP>1</SP> are released to produce corresponding carrier wave pulses. The code frequency generators 56 and 57 produce switching signals and when the switches 58 and 59 are closed, part of each positive period of code frequency oscillations is transmitted. If undistorted transmission is required, so that it may be utilized for service messages and the like, a tuned relay 61 is connected to a control oscillator 69 and operates a switch 62 which reduces the negative grid bias on the pentodes. The relay station, Fig. 3 (not shown), may comprise two amplitude detectors, one supplying the tuned relays 33 and 34, Fig. 1, and the other, operating as a threshold limiter to remove the switching signals, supplying the transmitter 16. An additional tuned relay at the relay station is operated from the terminal and switches the local signal generator 38 to the input of the transmitter 16 to operate the relay 37 and supply the supervisory signal to the receiver 19. The control of the tuned relay 37 may alternatively be effected by causing the threshold limiter to be temporarily inoperative when a tuned relay at the relay station responds.