| 摘要 |
PURPOSE:To prevent the radio interference to adjacent homes or rooms and the wiretap by performing the communication between a telephone set body and a handset with brightness-modulated infrared rays and adopting frequency division or/and wavelength division. CONSTITUTION:A circuit equipment A is provided in the telephone set body side, and a circuit equipment B is provided in the handset side. In the equipment A, a light emitting part 6 radiates brightness-modulated infrared rays. A light receiving part 7 receives brightness-modulted infrared rays radiated from the handset side and converts them to an original electric signal of modulation. A demodulating circuit 10 demodulates this modulated electric signal to convert it to a voice signal, and this voice signal is transmitted to a telephone line through a balancing network 1. In the equipment B, a receiving part of the handset receives radiated modulation infrared rays and onverts them to a voice signal to generate voice from a receiver 17, for example, a speaker. Meanwhile, voice applied to a transmitter 18, for example, a microphone is modulated by a modulating circuit 22. Since the carrier frequency is changed to f1 and f2 between the transmission from the telephone set body to the handset and the transmission from the handset to the telephone set body, bidirectional calls are secured. |
