Radio loudspeaker telephone device capable of automatically preventing howling on execution of calling operation

摘要

In a radio loudspeaker telephone device (30) having a radio controller (18) which makes a radio transmitter (15, 17) transmit to a radio channel a dial signal representative of a destination subscriber telephone set, the radio controller produces a timing signal representative of a first time instant at which the radio controller receives a response signal through a radio receiver (16, 17) from the radio channel. The response signal indicates that the destination subscriber telephone set is not busy. A detecting circuit (33) produces a ring-back tone detection signal while the detecting circuit detects a ring-back tone signal which is received through the radio receiver from the radio channel and which indicates that the destination subscriber telephone set is called by the telephone device. A switch unit (32) usually connects a microphone (11) to the radio transmitter. A switch controller (34) makes the switch unit disconnect the radio receiver from the microphone a time duration from the first time instant of the timing signal up to a second time instant at which the ring-back tone detection signal disappears. First and second attenuating circuits may be connected between the microphone and the switch unit and between the radio receiver and the loudspeaker, respectively.