| 摘要 |
PURPOSE:To prevent the generation of cross modulation distortion, etc., generated when a broad-band receiving circuit receives signals of the UHF band and VHF band in common, by providing broad-band amplifiers at the prior stage and post stage of a broad-band variable attenuator. CONSTITUTION:A UHF or VHF signal inputted from terminal 1 is passed through a broad-band amplifier and variable attenuator 2, having the gain and attenuation extent controlled with an AGC voltage from terminal 14, in sequence and further amplified by broad-band amplifier 13 before being supplied to the 1st mixer 4. This mixer 4 is being supplied with an oscillation signal of the 1st local oscillator 5 and the received signal of the UHF or VHF band is frequency-converted into a signal of a band of about 2,500MHz, which is led to the 2nd mixer 7 via BPF6. This mixer 7 is being supplied with a local oscillation signal from the 2nd local oscillator 8 and the UHF or VHF signal having been frequency-converted into about 2,500MHz is further converted into an intermediate frequency signal of about 58, 75MHz, which is amplified by IF amplifier 9 whose output is sent out to terminal 11. |
