| 摘要 |
PURPOSE:To prevent the variation of capacity to suppress the change of the lead-in range and frequency even in case the modulation sensitivity of a voltage control oscillating circuit changes in response to the oscillation frequency, by providing a variable gain amplifying circuit within a loop of an automatic frequency control circuit. CONSTITUTION:The control voltage is supplied to the 1st terminal 8 of a voltage control oscillating circuit 2 to set the oscillation frequency, and at the same time a signal is supplied to the 2nd terminal 7 to control automatically the frequency. While the received signal is supplied to the 1st terminal 1 of a mixing circuit 3, and at the same time the output terminal of the circuit 2 is connected to the 2nd terminal of the circuit 3. Then the intermediate frequency signal underwent the conversion of frequency through the circuit 3 is supplied to a frequency discriminating circuit 5 to detect the variation of frequency. The output of the circuit 5 is supplied to an LPF6 to obtain the frequency error voltage. This voltage output is supplied to a variable gain amplifying circuit 9, and the gain of the circuit 9 is controlled by the oscillation frequency setting voltage which is applied to the terminal 8. The output of this control is applied to the circuit 2 in the form of a signal which controls the frequency automatically. |
