Superaudio Telegraphy

a method of primary multiplexing of wire communications lines in the superaudio frequency range (3–10 kilohertz [kHz]). It is used in intraregional communications systems if the load conditions require more than two telegraph channels (up to four are possible). Transmission and reception of messages in superaudio telegraphy are basically the same as in voice-frequency telegraphy.

In 1930 the Soviet engineers V. A. Dubovik, G. V. Dobrovol’skii, and others developed apparatus for superaudio telegraphy that used amplitude modulation. It was capable of providing three two-way telegraph channels in a two-wire circuit; the channels occupied the frequency band from 6.1 to 9.1 kHz. The apparatus was originally installed in the telegraph lines connecting Moscow with Leningrad, Vologda, Sverdlovsk, and other cities. In the late 1940’s the NT-4 superaudio telegraph apparatus became the most common type. It uses frequency modulation to provide four two-way telegraph channels in the frequency band from 3 to 5.5 kHz.