| 摘要 |
PURPOSE:To enable to obtain optimum reception picture, by changing the center frequency of FM transmission BPF depending on the input level. CONSTITUTION:The input level of the television FM wave converted with the second frequency converter 12(taking the frequency as Fo) is detected with the AGC circuit 14 having the input signal level detector, and the output is fed to the voltage correction circuit 17. Further, the output of the circuit 17 is fed to the local oscillator 19 of which oscillating frequency is varied with the applied voltage of the second frequency modulator 12, or to the FM transmission BPF 13 in which the transmission center frequency Fo is changed with the applied voltage. Thus, the circuit 17 is operated so that the center frequency FBO of BPF is located at the region of the hatched parts i with the input level. The lateral axis DELTAFBO=FO-FBO. Accordingly, best video quality can always be obtained depending on the input level and greater effect can be made at low input level especially. |
