| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent unrequired enlargement of a transmission band and to stabilize a transmission output level in a low-speed frequency hopping AM transmission system. SOLUTION: Voice signals are turned off by a timing signal S2 before and after switching a frequency and a waveform for smoothly connecting the turned- off signals at both end parts of the off period to an off level is generated by a timing signal 3 and a waveform shaping circuit 9 and added to the voice signals by an adder 10. Then, during a voice signal off period, the output of a synthesizer 2 is turned off by a timing signal S4 and the frequency is switched by a timing signal S5. In such a manner, the voice signals are prevented from being superimposed on a carrier wave changeover part and band enlargement is prevented. Also, an APC voltage is fixed in a sample-and-hold circuit 8 before and after the point of time of changeover so as not to distort the waveform of the on/off part by APC.</p> |
