Patent GB-1003017-A (GB)
Title: Electrical signalling systems
IPC: H04Q1/38
Filed: 1962-06-15
Abstract: 1,003,017. Automatic exchange systems. STANDARD TELEPHONES AND CABLES Ltd. June 15, 1962 [June 20, 1961], No. 23117/62. Heading H4K. A transmitting station for an electrical signalling system includes a plurality of tunnel diodes, one or more of which may be connected to the output terminals of the station to characterize a signal to be sent. An electrical signalling system includes a transmitting station having tunnel diodes TD1 . . . TD10 and a receiving station. A monitoring circuit is closed via the contacts of push-buttons T1 . . . T10 in the position shown, when all push-buttons are unoperated. The monitoring circuit includes a rectifier D1 and, at the receiving station, a control relay S and battery and contacts of an auxiliary relay H. Contacts e 1 , e 2  of a switching device E are as shown when relay S is energized. In this condition relay S is energized and its contact s is open (shown dotted) which prevents relay H from being operated. On operation of one of the push-buttons, relay S is de-energized, relay H is energized via contact s and contacts R 1 , h 2 , h 3  switch over. A signalling circuit is then completed via an interrogation voltage generator AG, a resistor R, contacts h 1 , h 2 , one or more of the ten tunnel diodes and one or more of the push-button contacts. If push-button T1 is operated, only tunnel diode TD1 is connected into the signalling circuit. If push-button T9 is operated, tunnel diodes TD1 . . . TD9 are connected in series into the circuit. The tunnel diodes have different peak current values and are arranged in order of their peak current values with diode TD1 having the lowest value. The direction of current flow in the signalling circuit is opposite to that in the monitoring circuit. Voltage generator AG produces a unidirectional voltage which starts from an initial value when connected by contact R 3  and increases steadily up to a final value. When the current through one of the connected-in tunnel diodes exceeds its peak value there is a sharp increase in the P.D. across that diode and a corresponding drop in the P.D. across resistor R. This is temporary and is counteracted by the rise of interrogating voltage. Thus, as the interrogating current exceeds the peak current of each connected-in diode a voltage pulse is received across resistor R and is registered by counting device 1. For example, if push-button T5 is operated five voltage pulses appear in succession and are registered as the selected code signal. The width of the voltage pulses can be adjusted by a capacitor. When the final value of the interrogation voltage is reached the switching circuit is interrupted by release of the push-button and switching device E opens contact e 2  and closes contact e 1 . Relay H is de-energized and contacts h 1 , h 2 , h 3  return to the positions shown. Relay S is energized and its contact s returns to its original position. Switching device E then releases contacts e, e 2  and the receiving station is ready to receive a new signal. Alternatively, the current values of the interrogating current at which the voltage pulses are received can be used to determine the selected code signal. Alternatively two additional tunnel diodes provide a start pulse and a stop pulse, so that the time positions of the voltage pulses can be used to determine the selected code signal. In these arrangements only one tunnel diode need be inserted into the signalling circuit for each push-button. By combining the transmitting and receiving equipment at the same location a parallel-series converter is obtained. A modified system has two signalling circuits and operation of a push-button inserts one or more of a first set of tunnel diodes into a first signalling circuit and one or more of a second set of tunnel diodes into a second signalling circuit.