Nippon Telegraph and Telephone Public Corporation

Masaaki Terai

Makoto Yoshitoshi

Hideo Kishimoto

Ryoichi Matsuda

Kazuhiko Kakehi

Isao Kawashima

Giichi Ito

Kazumi Kato

There are provided a current detecting resistance element connected in series with a loop for supplying current to a telephone set, a switching circuit including a three terminal semiconductor switching element connected to be ON.OFF controlled by the voltage drop across the resistance element, and an impedance element controlled by the ON.OFF operation of the switching element to be connected across the loop for adding AC loss.

Automatic signal level adjusting circuits for use in telephone sets

Only one reversible electro-acoustic converter is used to act without a press-to-talk switch or the like as a transmitter and a receiver. The electro-acoustic converter is connected to a communication line through two 2 - 4 converters in the form of hybrid transformers which are interconnected to form a transmitting system and a receiving system.

Transmitting and receiving apparatus

Growing community of inventors

both Tokyo, Japan

Masaaki Terai