| 摘要 |
PURPOSE:To suppress the disturbance generation of the 1st mixer by setting the 1st intermediate frequency not less than twice the upper limited frequency of the UHF band and not more than four times the lower limited frequency. CONSTITUTION:The oscillation frequency of the 1st local oscillation 13 is set higher than the 1st intermediate frequency fi1, and the oscillation frequency of the 2nd local oscillation 18 lower than frequency fi1 by the 2nd intermediate frequency fi2. Further, the 1st intermediate frequency fi1 is set not less than twice the upper limited frequency of the UHF band and not more than four times and lower limited frequency of the UHF band. Input circuit 10 of this tuner is provided with a trap attenuating frequencies fi2, fi1/2 and fi1/4 and the 1st mixer 12 suppresses the occurrence of disturbance of frequency fi1. Further, the 1st intermediate freqency filter 14 functions to suppress disturbance of fi1/2 in frequency and also has the BPF characteristics of a narrow band of approximate 8MHz to reduce cross modulation disturbance generated by the 1st intermediate amplifier 15, and filter 16 attenuates a frequency 2fi2 lower than fi1 to suppress image disturbance of the 2nd mixer 17. |
