JPS57162549A - Analog privacy telephone set - Google Patents

Abstract

PURPOSE:To increase the intensity of privacy telephone, by multiplying the signals having the bipolarity and a random amplitude to obtain a privacy telephone signal after giving the sampleing and then the pulse amplitude modulation to an aural analog signal and then decoding the privacy telephone signal by carrying out an adverse operation at the receiving side. CONSTITUTION:The analog signal given through an input terminal 37 is sampled by a sampler 32 via a filter 31 and with a clock pulse CLK having a frequency doble the voice band and then supplied to a multiplier 33. On the other hand, the n-bit parallel random pulse train signal produced from a pattern generator 36 is supplied to a D/A converter 35 to be converted into an analog signal. This analog is supplied to the multiplier 33 and then multiplied by the output of the sampler 32 to be converted into the privacy telephone form and then to be sent to a transmission line through a filter 34. At the receiving side, the signal passed through an equalizer 41 is sampled by a sampler 42 and divided by a divider 43 by the signal obtained by giving a D/A conversion to the output of a pattern generator 46 that produces a random pulse same as the transmitting side. Thus the privacy telephone signal is decoded.