| 摘要 |
PURPOSE:To stop disturbance to a pocketable bell, etc., of the middle band, by providing an input filter circuit at the prior stage of a variable attenuator provided in front of one mixer of a double-mixing system broad-band receiving circuit equipped with plural mixers. CONSTITUTION:A UHF or VHF signal from terminal 21 is led to high-pass filter 24 of about 55-60MHz (for the Japanese band) in cutoff frequency by way of the 1st band-stopping filter 23 that cuts off a frequency about a half the intermediate frequency and then led to the 1st mixer 29 by way of a series of the 2nd band- stopping filter 25 stopping the intermediate frequency band and 3rd band-stopping filter 26 stopping a band of a frequency adjacent to 25, 108-170MHz band and further broad-band variable attenuator 27 and broad-band amplifier 28. A signal frequency-converted by this mixer 29 is led to the 2nd mixer 32 via BPF31 and then converted into a signal of a video intermediate frequency of about 58, 75MHz with an oscillation output of the 2nd local oscillator 33. |
