| 摘要 |
PURPOSE:To provide a privacy telephone function when the information is transmitted by giving the double signal processing to an input signal. CONSTITUTION:The voice output is supplied to a reverse amplifier 2 which performs the inversion of amplitude for an input signal Vin. An amplitude modulator 3 gives the amplitude modulation to an output signal V1 by a carrier wave signal fo to obtain a modulation output signal V2. This signal V2 is demodulated by frequency signals f1 and f2 which are detuned by + or -3kHz against the frequency of the signal fo and transmitted. In other words, an upper side wave signal if transmitted is demodulated by the signal f2. Then the demodulation output signal Vo is supplied to a power amplifier 5 at the next state. In a reception mode the switches S1-S3 are switched as shown by the dotted lines. The radio waves are received by an antenna 1 and supplied to the amplifier 2, and the modulator 3 performs the modulation of amplitude by the signal fo. A demodulator 4 can perform the modulation with the same spectrum as that of the upper side wave signal by means of the signal f1.
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