| 摘要 |
PURPOSE:To eliminate the interruption of a call, by detecting the carrier wave which is always fed from a modulator at the receiving side in the privacy call mode and automatically switching the normal call to the privacy call by a switching operation of the talking subscriber. CONSTITUTION:In the normal call mode, the call signal given from a telephone 1 is converted into 4 wires through a 2-wire/4-wire converter plus a ringing tone generator 2 and then transmitted to an FDM device via changeover switches SW1 and SW2. The call signal supplied from the remote side is converted into 2 wires by the generator 2 to be fed to the telephone 1. In the privacy call mode, the call signal is coded by a voice coding device 3 by switching changeover switches SW1-SW4. Then the regular scramble is applied by a privacy device 4. Thus the code is converted into an analog signal through an MODEM5 to be transmitted to the remote side. When the switching is carried out between the privacy call and the normal call, the carrier wave is detected by a carrier detecting circuit 6 of the receiving side to be applied to an OR circuit 8 via an AND circuit 7. The switching is automatically carried out between the privacy and normal calls by operating a privacy call setting button B1 and a normal call setting button B2 respectively. |
