Paired Operation of Telephones

Paired Operation of Telephones


a system for operating two telephones, each with a different number, on a single subscriber line. The system ensures discriminatory ringing and privacy while also meeting all the technical requirements for telephones of general use. Simultaneous operation is effected with either frequency- or time-multiplexing apparatus, which is installed at the automatic exchange and at the subscriber’s premises. Frequency-multiplexing apparatus permits the simultaneous transmission of two telephone conversations on a single line; one conversation is transmitted in the audio-frequency range, while the other is transmitted at higher frequencies with the use of modulation of oscillations. With time-multiplexing apparatus, the subscribers’ telephone channels are separated in time.

In the USSR, relay selectors and devices with diode-switches are among the most common devices for time multiplexing. With the former, relays are used to connect one telephone to the line and disconnect the paired telephone. With devices having diode-switches, the mutual blocking of the paired telephones is realized through the use of isolating semiconductor diodes in the telephones’ line circuits. The diodes are connected in such a way that they connect one telephone and disconnect the other depending on the polarity of the voltage supplied by the battery at the automatic exchange.


Abene, V. A. Blokiratory dlia sparennogo vkliucheniia telefonnykh apparatov. Moscow, 1959.
Gubrenko, I. M. Diodnotriodnyepristavki dlia sparennogo vkliucheniia telefonnykh apparatov: Sbornik nauchnykh trudov TsNIIS, fasc. 5. Moscow, 1970.
Gurvits, Sh. F., and Iu. E. Gontkovskii. Ustroistvo SUS-54 dlia sparennogo vkliucheniia telefonnykh apparatov v ATS-54. Moscow, 1971.