| 摘要 |
PURPOSE:To simplify the system constitution by providing a signal switch to the pre-stage of a modulator and switching the connection between the modulator and the pre-stage equipment at the reduction in the received electric field and at a fault of the pre-stage equipment to interrupt the faulty equipment. CONSTITUTION:When a reception input electric field of a receiver 1 reaches a threshold level or below, the receiver 1 switches the switch 3 by using a control signal outputted from the demodulator 2 to interrupt the input signal to the modulator 4. Thus, no input signal is given to the modulator 4, a signal from a carrier oscillator 16 is outputted to an output terminal 18 while being not subject to modulation by the modulator 4 through the interruption of the input signal, the signal is sent from the output terminal 8 through the frequency converter 4 and the amplifier 6 to execute squelch transmission. Thus, it is not required to provide especially a high frequency oscillator for squelch and the system is simplified.
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