GB915765A - Telephone system comprising sound-powered receivers and microphones and a central ringing generator - Google Patents

Abstract

915,765. Direct call systems. STANDARD TELEPHONES & CABLES Ltd. July 16, 1959 [July 16, 1958], No. 24455/59. Class 40 (4). In a sound-powered telephone system in which substation transmit/receive transducers are capacitor coupled to a common line, a calling substation connects a voice frequency signal to the line from a common generator which is such that the signal increases in frequency or volume from an initial low level. In the arrangement shown, the common tone generator G is associated with a relay R which operates to a loop put across the line by calling buttons such as T 1 , T 2 , at stations F 1 , F 2 . With R operated, generator G is connected up and by virtue of a circuit V, which may be a simple R.C. circuit, the amplitude or frequency of the signal put on the line increases gradually. The coupling of a substation to the line may be such to make it resonate at the signal frequency and the transducer may be loaded with an acoustic resonator at this frequency. Substations may be portable plug-in sets, as at F 1 , and the calling button and coupling capacitor for each station may be provided in the plug or plug socket.