| 摘要 |
PROBLEM TO BE SOLVED: To simplify a laying construction of a private broadcast system by using an existent speaker line as a transmission line. SOLUTION: In a private broadcast system, a broadcasting apparatus 2 and a speaker terminal device 4 are connected by a transmission line 6. In the broadcasting apparatus 2, a digital modulator 12 supplies a digital modulated signal resulting from modulating a carrier wave with a digital audio signal for the terminal device 4 to the transmission line 6. A drop commercial AC voltage dropped by a transformer 30 is superimposed on the transmission line 6. In the terminal device 4, the digital modulated signal from the transmission line 6 is demodulated to a digital audio signal by a digital demodulator 20, D/A converted by a D/A converter 24, amplified by an amplifier 26 and supplied to a speaker 28. The drop commercial AC voltage transmitted by the transmission line 6 is converted into a DC voltage by a power supply section 36 of the terminal device 4 and supplied to the demodulator 20, the D/A converter 24 and the amplifier 26. COPYRIGHT: (C)2009,JPO&INPIT
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