| 摘要 |
1412386 Radio signalling MOTOROLA Inc 17 Jan 1974 [29 March 1973] 2161/74 Heading H4L In a radio communication system, a portable transmitter-receiver operates on different carrier frequencies in each direction to provide duplex speech communication via a base station which may be linked to a telephone exchange, the portable transmitter-receiver includes a detector coupled to the microphone circuit of the transmitter which renders said transmitter operative only in the presence of speech (or a calling signal) and at the base station the base station receiver is muted in the absence of received signals. The arrangement provides battery saving at the portable station. As described, the radio link uses frequency modulation. A plurality of push-buttons control corresponding oscillators to provide the calling signal. |
