| 摘要 |
PURPOSE:To lower the zero-point frequency of an AFC voltage generating circuit even when the 1st IF frequency is >=100MHz, and to improve the stability of an AFC voltage and obtain the 1st IF frequency accurately and stably by providing the 1st and the 2nd frequency converting circuits, and supplying the output of the 2nd frequency converting circuit and outputting a control voltage corresponding to the zero-point frequency. CONSTITUTION:When movable contacts of switch circuits 6 and 7 are connected to, for example, a terminal A, an AFC loop is formed of a frequency converting circuit 2, a switch circuit 6, a frequency converting circuit 14, an AFC voltage generating circuit 4a, a switch circuit 7, a holding circuit 8, a VCO 3, and a frequency converting circuit 2. Then the frequency converting circuit 14 calculates difference frequencies (fIP1-fIF0') and (fIF0-fIF0') by using the 1st IF frequency fIF1 from the frequency converting circuit 2, the 1st IF reference frequency fIF0, and the 2nd IF reference frequency fIF0' from a reference frequency generating circuit 15 and those relatively low frequencies are supplied to an AFC voltage generating circuit 4a.
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