| 摘要 |
PURPOSE:To constitute a device having a high privacy effect with small size and light weight by switching a normal modulation signal and a frequency inverting signal and transmitting them according to a specific bit pattern and allowing the reception side to apply the converse processing. CONSTITUTION:A frequency inverting signal 31 is generated from a modulation carrier frequency 61 of a modulation upper limit frequency 3kHz and a voice signal 21 through an LPF1 and a notch filter 2 through a double balanced modulator 3 in order to limit a band under the frequency 61 and eliminate the frequency being a half of the modulation carrier frequency, a synchronizing switch 4 is changed over by an output of a ROM5 in which a specific bit pattern is written to obtain a privacy call synthesis signal 41. An output of an oscillator 6 is divided into two, and a signal subject to proper frequency division by a programmable frequency divider 7 is inputted to a hexadecimal counter 8 and the output accesses the ROM5. An AND signal 91 between the signal dividing the frequency 61 into 1/2 and the carrier output of the counter 8 is added to the signal 41 as the synchronizing pilot and transmitted through an LPF10. The signal is demodulated by using the same frequency as the frequency 61 at the reception side to restore the voice signal. |
