GB253697A - Improvements in signalling (ringing) arrangements for carrier wave systems - Google Patents

Abstract

253,697. Western Electric Co., Ltd., (Western Electric Co., Inc.). May 20, 1925. Wired wireless systems; calling systems and apparatus. - An arrangement to ensure the transmission of calling or ringing signals between two distant stations on a carrier-wave system comprises means whereby the initial low-frequency ringing current is caused first to change the normal frequency of the local carrier-wave oscillation-generator, tn a new value which lies within the transmission range of the line, and then to modulate the new carrier at audible frequency. At the receiving end a branch circuit, shunting the ordinary terminal apparatus, receives the rectified calling-wave and causes it to operate a local ringing-source As shown in the Figure, a circuit 10, shunting the input network 3 to the modulator M, intercepts ringing-current on the line L of a frequency of approximately sixteen cycles, and causes a relay 11 to bring a condenser 12 in or out of the main oscillatory circuit 4, 13 of the carrier generator G, thus changing the normal carrier-frequency and simultaneously interrupting the changed frequency at sixteen cycles. At the receiving end, the interrupted calling-frequency passes through a band filter RF, and is detected at D and amplified at A. The resultant impulses are collected by a tuned circuit 15, 16 branched across the ordinary speaking-channel RF1, and pass through a rectifier R to operate relays 18, 19, which disconnect the terminal network 3 and insert a ringing-source 2 in the line L to call the distant subscriber. Owing to the tuning of the circuit 15, 16 it has no appreciable shunting action on received speech currents which pass into the speech filter RF1 and through the network 3 into the low-frequency line L. A similar calling-arrangement may be applied to a standard four-wire circuit comprising push-pull modulators and rectifiers, the frequency-changing relay 11 being also adapted simultaneously to break or unbalance the push-pull couple. A system is also described in which an intermediate carrier frequency is independently generated and then modulated by low-frequency ringing-currents, the resultant complex being used to modulate the normal carrier-wave frequency.