| 摘要 |
PURPOSE:To improve a signal-to-noise ratio when a voltage is high by controlling the loop of a voltage control oscillator in a narrow-band reception state simultaneously with band switching. CONSTITUTION:After being mixed 3 with a local oscillation signal, a FM reception signal is supplied to the 1st IF amplification part 4 and a FM intermediate-wave signal which has been amplified to a fixed level with broad-band characteristics is detected 7 from the W side of band change-over switch 15 through BPF5 and the 2nd IF amplification part 6. In the narrow-band reception state at the N side of switch 15, on the other hand, the output of amplification part 4 is sent to PLL part 17 via narrow-band BPF8 and the 3rd IF amplification part 9, a carrier component from voltage control oscillator 12 is compared with FMIF in terms of phase, and the phase difference is changed into a DC component through LPF11, thereby making the loop control so that the phase difference will be eliminated. Consequently, the S/N ratio can be improved at the time when the voltage is high. |
