| 摘要 |
PURPOSE:To expand the band of a voice signal by removing a tone signal by a signal synthesizing means. CONSTITUTION:An FM interphone adopting a tone type transmitting/receiving system has a transmitting system 2 and a receiving system 4. A voice signal S and a tone signal St are added by an adder 10 and FM-modulated and the modulated signal is sent to a lamp line 16. The received FM signal is demodulated by a demodulating circuit 20. A tone signal detecting circuit 22 takes out a tone signal from the demodulated signal. A waveform converting circuit 26 converts the waveform of a tone signal St into its reverse phase. The inverted tone signal -St is inputted to a signal synthesizing circuit 28. The circuit 28 adds the demodulated signal to the inverted tone signal -St and extracts the tone signal St component from the demodulated signal. Consequently, a normal voice signal is obtained. Since the signal synthesizing technique is adopted, a filter can be omitted and the system is reduced in size and produced unexpensively. |
