| 摘要 |
PURPOSE:To improve the separating characteristic for a reception frequency by changing the gain of an FM negative feedback loop in accordance with the reception frequency in a synthesizer receiver of the FM negative feedback system. CONSTITUTION:In the synthesizer receiver, a local oscillator 5 has such PLL constitution that the local oscillator 5 is controlled by the signal which is obtained by allowing the output of a phase comparator 9, which compares the phase of a signal obtained by dividing the output signal of the oscillator in a frequency divider 6 with the phase of a signal obtained by dividing the output of a reference frequency oscillator 7 in a programmable frequency divider 8, to pass an LPF10. The oscillator 5 forms the FM negative feedback loop where the output of a demodulator 4 is negatively fed back through an amplifier 17 to modulate the frequency. A resistance R3 of the amplifier 17 is short-circuited or opened by a switching circuit 20 to change the gain in accordance with the reception frequency band. The circuit 20 is controlled by the output of a detector 23 which detects the reception frequency band from the output of a channel selecting code generator 11 and turns on or off a transistor 22 to short-circuit or open the resistance R3. |
