| 摘要 |
PURPOSE:To reduce noise and distortion by suppressing spurious disturbance, by using the difference between an input signal frequency obtained through the frequency conversion of a mixer and the frequency of a voltage-controlled oscillator as an intermediate frequency. CONSTITUTION:An input signal from terminal 40 is inputted to the 1st input terminal of the 1st mixer 45 via filter 41 and RF amplifier 43, and the output of voltage-controlled oscillatot 47 is amplified by amplifier 46 and then inputted to the 2nd input terminal of mixer 45. Then, the difference between the oscillation signal frequency of voltage-controlled oscillator 47 and the frequency of the input signal is set as the 1st intermediate frequency. In this case, the 1st intermediate frequency is set within the range of 2,520-2,700MHz, so the frequency of voltage-controlled oscillator 47 is set within the range of 2,613-3,287MHz. Consequently, spurious disturbance in the signal band of the 1st intermediate frequency is narrowed down to the secondary and tertiary higher harmonic disturbances occuring in the RF amplifier and the 1st mixer and an interchannel beat disturbance, and for this purpose, they are eliminated by the following circuits to reduce noise and distortion. |
