GB1036262A - Improvements in or relating to intercommunication systems - Google Patents

Abstract

1,036,262. Interconnection systems. STANDARD TELEPHONES & CABLES Ltd. Feb. 5, 1965, No. 5094/65. Heading H4K. In an interconnection system subscriber subsets are connected directly to a common highway and communicate in a time division multiplex manner, each time slot being allocated to one subscriber and a connection being made by adjusting the calling subset equipment to transmit and receive in the time slot of the wanted subscriber. The multiplex pulses may be modulated by amplitude, or width or comprise pulse codes. In a first embodiment the highway comprises a coaxial cable or balanced pair with the subsets tapped along its length and the ends terminated with matched impedances. Each subset may be connected over a balanced circuit or be provided with a multiplex pulse position having separate go and return portions. A signal generator supplies the highway with a synchronizing pulse followed by the channel pulses in each exchange cycle. Alternatively the pulse generator may provide only the synchronizing pulse which triggers the subsets into the production of their associated channel pulses. In this arrangement the channel pulses of idle subsets may be of reduced width so as to reduce the length of the exchange cycle. In a second embodiment separate go and return highways are provided with separate arrangements for producing the channel pulses on each highway. The subsets require separate facilities for transmission and reception and may be connected into the highways as repeaters. An arrangement of the subscriber's set is shown in Fig. 4 in which a circuit SS identifies a synchronizing pulse to reset a binary counter BC, the counter being stepped by the channel pulses on the highway. When the channel pulse associated with the subset is reached the counter opens a gate AG to connect the transmitter TD and receiver RD to the highway. To call a wanted subscriber a dial or pushbutton device is operated to cause the counter BC to open gate AG in the wanted subscriber's pulse position. A tone signal generator transmits intermittently to call the wanted subscriber, some of its signal being fed back through the call set to indicate that the signal is being received. A calling signal outside the audio range can be employed to trigger a buzzer at the called set. Once a wanted pulse position has been selected the calling condition is subjected to a delay so that any conversation on the channel blocks transmission from the calling set and produces a busy signal.