| 摘要 |
PURPOSE:To attain excellent data communication by inserting a waveform shaping device to the post-stage of the modulator of an oscillating output section and converting a basic wave in the waveform asymmetrically, using a polarity switching device of a speaker, and erasing secondary distortion generated at a carbon microphone and a coupling section to improve S/N. CONSTITUTION:An input signal from an interface circuit 1 is used as a carrier by an F.S converter 2, formed into an asynchronous sinusoidal wave by a waveform shaping device 3, the 3rd harmonics and over are eliminated by a harmonic filter circuit 4 and inputted to a speaker 7 of the acoustic coupler via the speaker polarity switching device 5. Since the response to the pressing force or reducing force generated by the acoustic signal is nonlinear in the carbon microphone, the output waveform is reduced to an asymmetrical wave. Thus, the harmonic distortion is reduced by changing over the polarity of speaker by means of the speaker polarity changeover device 5. On the other hand, since the 2nd harmonic generated by the carbon microphone and coupling section of a handset 9 of a telephone set is leaked to a receiving side through a side tone preventing circuit, the distortion is offset with the 2nd harmonic by transmitting the asymmetrical wave including the double wave at the transmission side. |
