Patent GB-1038709-A (GB)
Title: Improvements in and relating to communication systems
IPC: G08C19/14
Filed: 1964-03-19
Abstract: 1,038,709. Electric selective signalling. GENERAL SIGNAL CORPORATION. March 19, 1964 [April 4, 1963], No. 11788/64. Heading G4H. In a signal transmission system a combination of frequencies is transmitted repeatedly as a series of randomly recurring bursts of frequency modulated carrier signal. An address signal is transmitted, to select a field station, together with a command signal. There may be more than one transmitter working on the same carrier frequency and the use of randomly recurring bursts of signal reduces the likelihood of interference between the signals of two transmitters transmitting at the same time. Transmitter (Fig. 2, not shown).-Manually operable push-buttons 11 apply a signal to a diode matrix 12 which energizes a combination of mark and space leads. The switches are series connected so that the operation of any one de-energizes preceding switches. The highest numbered switches are reserved for the most important operations. For each lead there is an oscillator in unit 13 so that the command is represented by a combination of frequencies, there being a mark and space frequency for each bit. The outputs are applied on a single lead via amplifier 18 to the transmitter 10 together with another combination of frequencies controlled by the address selector 15 and produced by oscillators 14. Unit 18 comprises a series of differentiating circuits each of which gives a pulse when the corresponding oscillator changes its output. Any change of command produces an output which is applied to amplifier 31 to key the transmitter. Random pulses produced by generator 17, are also applied to amplifier 31. The generator produces a pulse in each of a succession of equal intervals, the timing of the pulse within its interval being random. The signal transmitted is shown in Fig. 1C, extra bursts of signal being produced when the command switches are first operated and when they are released. Receiver (Figs. 4A, 4B, not shown).-The signal is demodulated at 100 and the component frequencies produce signals from corresponding filters in unit 106. The address signals are applied through a plug-board CP to an And gate comprising for each mark/space pair a diode and an inverter, Fig. 5 (not shown). The signals from each pair are applied directly or in reversed order according to whether in the address of this field station the corresponding bit is " 1 " or " 0 ". The command signals are similarly extracted and each mark/space pair is applied to an Exclusive Or gate which gives an output only if one or the other lead is energized. Signals from these gates pass to And gate 103 and an output is produced only if the correct address combination is received and a command signal having the correct number of bits. The other outputs from the Exclusive Or gates comprise signals on a single lead having one amplitude for a " 1 " and another for " 0 ". Switches 118 reproduce a mark/space representation on two leads and these are again tested in Exclusive Or gates 123 to control gates 124. The output from And gate 103 causes a pulse detector 125 to open gate 128 so that a signal can pass via inhibit gate 127 to gates 124. While there is no pulse detector 126 closes gate 127 to prevent any output. When gates 124 pass a signal gates 121, 122 are opened to pass the command signal on mark and space leads to the controlled equipment. This may be a locomotive.