GB325274A - Improvements in and relating to telephone systems - Google Patents

Abstract

325,274. Burovox, Ltd., and Smith, S. C. Winfield-. Nov. 15, 1928. Direct call systems. - In a system in which a principal may call a subordinate or other party, receive the answering call on a loud speaker, and speak from a distance into a sensitive microphone, a visible or audible signal is operated by current fed to the principal's microphone when the called party is in a position to listen. Thus the principal is warned when conversation in his room may be overheard and he may be provided with a switch to open his microphone circuit. In the arrangement shown in Fig. 1, the loud speaker a and microphone b at the principals station A are respectively connected in series with the transmitter e and receiver f at the subordinate's station B. The operation of key c completes the circuit of a buzzer or other calling device h at B, and when the called party replies by lifting his receiver off the hook i, speaking circuits are completed, and signal device d, which may be directly or indirectly operated by microphone current, warns the principal who may break his microphone circuit by restoring c. The party at station B may call A by removing his receiver and speaking into his transmitter. In the modified arrangement shown in Fig. 2, three. stations A1, A2, A3 similar to A, Fig. 1, but provided with separate calling and overhearing- preventing keys o, p, and installed for example in ships' cabins, may communicate with a station B1, in the steward's cabin for example. Station B1 is equipped with a buzzer &c. h, indicators u and a two-wiper switch s, t, constructed as described in Specifcation 319,861, by which the party at B1 completes the speaking circuits. The Provisional Specification also describes the signal device as being in the principal's receiver circuit.