| 摘要 |
PURPOSE:To extract a voice signal with good quality by detecting a tone signal or an inverted phase tone signal obtained from a receiving tone synthesizing signal and controlling the tone signal in response to the received tone signal level. CONSTITUTION:A tone synthesizing signal S0 is formed by adding a sound signal S given from a signal source 6 and a tone signal St given from a signal source 8 at an adder circuit 10. A carrier (f) is modulated by the signal S0 at an FM modulation circuit 12 and transmitted to a lamp wire 16. The signal received at a receiving system 4 and detected via a high-frequency amplifier circuit 18 and an FM demodulating circuit 20 is inputted to a tone signal detecting circuit 22 to detect a tone level signal St' in response to the receiving level of the signal St and the inverted phase tone signal St' having opposite phase to the signal St. The signal St' in response to the receiving tone signal is added with the signal S0 at a sound signal detecting circuit 24 and inputted to a speaker 32 via a muting circuit 30. |
