GB308816A - Improvements in or relating to telephone transmission systems, particularly two way repeaters - Google Patents

Abstract

308,816. Telefonaktiebolaget L. M. Ericsson, (Assignees of Laurent, T.). March 21, 1928, [Convention date]. Two-way repeaters.-In a four-wire system speech transmission in one pair short-circuits the second pair. Speech over the pair I affects the device D (shown in full in Fig. 3) which enables direct current to flow between v1, v2, heating glow lamps G1, G2 and thus placing a balanced. short circuit for speech currents between d1, d2. Speech-frequency potentials from T3 super-added to the battery E3 cause a glow-lamp G3 to glow and thus alter the grid potential in the valve F3. The condenser C3 and resistance R3 damp out variations in the grid potential if a regular speech-frequency current (e.g. for signalling) is passed by T3 so that only the envelope of the speech curve is passed by F3 to T4, which is designed to transform these low frequencies to light G4. Condenser C4 and resistance R4 are designed to damp out these modulations as far as possible so that the grid of F4 obtains an almost constant voltage, and direct current suf6- cient to light the lamps G1, G2 passes between v1, v2. The transformers T1, T2, Fig. 1, provide a high-impedance section in the line II to render the short-circuiting of this line more effective. In Fig. 2 the short-circuit is across the secondary of a loop transformer and the charging time of the condensers C1, C2 is reduced by a choke L. The term " glow lamps " includes any device capable of independent discharge, such as a Neon lamp, but excludes thermionic devices.