| 摘要 |
<p>A loudspeaker telephone system is comprised of a voice switching circuit, hybrid, and power supply circuit. The voice switching circuit is provided with the comparators for comparing the speech through the main paths with the side tone through the auxiliary paths, the time constant circuit for controlling exponentially a pair of the variable gain amplifiers for making or breaking the sending and receiving signals, and four band pass filters arranged in each input of the comparators for rejecting the indoor noise as well as the line noise coming into the loudspeaker telephone system through the lines. Accordingly, the howling effect between the microphone and the loudspeaker is inappreciable, the transfer from the sending mode to the receiving mode is easily made while maintaining a naturality of the voice. Also, with the construction of the impedence matching elements in the conventional hybrid, the hybrid can be used in common either in the present loudspeaker telephone system or in the conventional telephone system. In the loudspeaker telephone system, the line current is used as a bias voltage by the construction of the power supply circuit, therefore there is no need for providing an additional power supply source.</p> |
