| 摘要 |
PURPOSE:To prevent interference between adjacent channels, by detecting the shift of intermediate frequency and controlling a local oscillation frequency. CONSTITUTION:A detected output of an FM detection circuit 3 is inputted to an MPX circuit at the next stage, and a DC voltage in response to the shift of intermediate frequency is outputted and inputted to an AFC lock circuit 10, which consists of a DC voltage amplifier 11, a window comparator 12, a tuning gate 13 outputting L during the channel selection of an FM receiver and H after the channel selection, and an AND circuit 14 giving a control signal to an AFC gate based on a muting output of an FMIF stage 2, an output of the window comparator 12, and an output of the tuning gate 13. The AFC gate 15 is activated when the level H is inputted to its control terminal to input an output DC voltage of the voltage amplifier 11 to an AFC circuit of a local oscillator 4. |
