| 摘要 |
PURPOSE:To limit a receivable frequency range, by controlling the upper limit of the tuning voltage by a Zener diode and by setting the minimum value of the tuning voltage by a DC power source prepared separately. CONSTITUTION:Channel signal 32 is subjected to pulse width modulation in bit rate multiplier 51 and is supplied to voltage converter 52. The voltage-converted pulse signal is smoothed by low-pass filter 53 and is made into a DC to be taken out as a tuning voltage which has the peak value coinciding with the Zener voltage of Zener diode 7. Further, DC power source 8 is connected to tuning voltage applying terminal 12 of tuner 1, and the voltage value of DC power source 8 is so adjusted that a prescribed voltage can be applied to tuner 1 when the output voltage from channel selecting part 5 is lowered. |
