| 摘要 |
PURPOSE:To perform the search preset and channel display at the same time, by detecting the normal signal in the output state of channel counter and using the horizontal synchronizing signal and AFC signal. CONSTITUTION:The counter 7 starts count with the operation of the preset switch 5. The output of the counter 7 is fed to the electronic tuner 10 to sweep the local oscillation frequency. Further, the local oscillating signal is frquency-divided into 1/n with the prescaler 15. After the preset counter 18 counts the number of presets, it is changed over to the hexa notation counter which changes the count state with one pulse per 1MHz. The preset counter 19 counts the output of the hexa notation counter and feeds the channel number to the display circuit 22. When the broadcast is received, the signal detection circuit 24 takes the AND between the detection signal of the normal tuning point and the horizontal synchronizing signal and horizontal blanking pulse to enable the normal tuning range by integration. |
