| 摘要 |
PURPOSE:To attain individual station selection and mutual simultaneous talking even if a multi-station type is used with a 2-wire or a lighting distribution line by using a carrier f1 for a channel selecting signal for both transmitting and receiving stations, using the f1 for transmission for the transmission station and using f2 for transmission for the receiving station. CONSTITUTION:In case of transmission, when an opposite address is transmitted by channel selecting switches SW1-3, a processor Q2 brings a call signal transmission/receiving circuit Q1 to the transmission mode. An output of a gate G5 is subject to tone burst modulating by an AM modulating circuit AM and modulated by a frequency f1 by means of an FM modulator F1 through a switch AS4, and transmitted to a line (l) through a BPF.BP1. In transmitting a call tone, the processor Q2 opens a switch AS3, FM-modulates an output of a call tone generating circuit CP by the f1 and transmits the result to the line (l). When the opposite party hooks up, an output signal CD2 of an FM demodulator FD2 is supervised and the opposite station transmits a talking signal in a frequency f2, then the talking state is attained when the signal CD2 exists. The sound signal FM-modulated by the f2 from the opposite station is demodulated by the FD2 through a BPF.BP2. |
