| 摘要 |
PURPOSE:To simplify the circuit constitution by selecting the oscillation frequency of the 1st local oscillator more than double the higher limit frequency of the reception frequency at the VHF band and thus reducing the image disturbance as well as decreasing the number of the switching circuits. CONSTITUTION:The TV signal of the VHF band applied to VHF input terminal 1 is added to 1st mixer 23 and then mixed with the signal of 1st local oscillator 26 to be converted into the 1st intermediate frequency of the UHF band. At the same time, the UHF band signal supplied to UHF input terminal 4 is applied to switching circuit 7 via amplifier 6. The 1st intermediate frequency of the frequency-converted VHF is applied to circuit 7 via mixer 23, and the signal processing is given to the outout switched through circuit 7 via tuning circuits 18 and 20 featuring the variable frequency plus 2nd mixer 21. And the 2nd intermediate frequency signal is delivered to output terminal 22. The oscillation frequency of oscillator 26 is selected more than double the higher limit level of the reception frequency of the VHF band supplied through terminal 1. In such way, the image disturbance is reduced, at the same time decreasing the number of the switching circuits. |
