| 摘要 |
PURPOSE:To improve the attenuation characteristic without deteriorating the efficiency of receiving sensitivity, etc., by providing the first and second wide band variable attenuators on the pre-stage of the first mixer, and controlling both the attenuators simultaneously or independently. CONSTITUTION:A television signal which has been input is controlled by control voltage from the automatic control terminal 10 through the driving circuit 14 so that the respective output levels can be constant by the first and second wide band variable attenuators 12, 13 which are able to control the gain. The attenuation characteristic to the frequency in case when both these attenuators have been driven simultaneously by the circuit 14 shows the attenuation amount of 70dB or so extending from VHF band to UHF band, within the range of 10-1V of AGC voltage. Accordingly, since a sufficient attenuation amount can be obtained according to said receiving system, no receiving becomes difficult due to distortion disturbance caused by the wide band amplifier 3 and the first mixer 4, even in case of a high input signal exceeding -25--15dBm. |
