| 摘要 |
PURPOSE:To narrower the transmission band and to make effective use of the band, by controlling the level of the reception signal and the oscillation frequency of a voltage-controlled crystal oscillator through the reception linger signal. CONSTITUTION:A frequency shifting system linger signal including a control signal for measurement and data signal as well as a communication current voice current in a voice band is transmitted by a carrier suppression single side band system, and the linger signal is converted into a voltage corresponding to the difference from the reference frequency by a frequency discriminator 24. This voltage is compared with a reference voltage at a comparator circuit 25, and the output voltage of the circuit 25 is taken as a negative or positive reference voltage corresponding to the polarity to the reference voltage. The output voltage of the comparator 25 and that of the frequency discrimination circuit 24 are added via resistances R1, R2, and applied to a voltage-controlled crystal oscillator via a voltage amplifier 26 to control the oscillation frequency. The amplifier 26 produces a control voltage corresponding to the shift from the carrier frequency of the linger signal. As a result, a synchronizing pilot signal is made unnecessary. |
