PURPOSE: To eliminate the use of a common mutual calling relay and to improve the general-purpose properties of a subscriber circuit, by transmitting intermittently call signals and then transmitting a call signal individually to each telephone set of a party line telephone in accordance with actuation of a polarity inverting means.
CONSTITUTION: With a common mutual calling operation of a telephone 6, a continuous call control signal (a) and a polarity inversion control signal (b) which is intermittent with a prescribed cycle are supplied to a subscriber circuit 1 by a command of a central controller. Then relays RG and RV are actuated continuously and intermittently respectively. As a result, a call signal (r) is transmitted alternately and intermittently to lines 5a and 5b of a call wire 5 to ring bells 8 and 9 alternately. When a telephone 7 gives an answer, a ring trip circuit 2 detects the answer and stops the transmission of a call control signal to the relay RG. Thus the ringing of the bell 8 is stopped, and at the same time an answer signal (c) is transmitted to the central controller. Then the input of signals (a) and (b) is prevented to the circuit 1.
TABU TAKASHI
NAKANO YOSHIAKI
MASUDA NOBUYUKI
