| 摘要 |
PURPOSE:To achieve sufficient isolation easily by changing over a vertical polarized signal and horizontal polarized signal by lowering the frequency through frequency conversion and then by controlling the attenuation of an AGC circuit. CONSTITUTION:An input vertical polarized signal is frequency-converted by frequency converting circuit 21 into the 1st IF signal, which is inputted to automatic gain control AGC circuit 26 and the attenuation is controlled with an AGC signal from switching circuit 29 to maximize the attenuation of circuit 26 in the reception of a horizontal polarized signal. The horizontal polarized signal is inputted to frequency converting circuit 22. The 1st IF signal is inputted to AGC circuit 27 and the attenuation is controlled to a constant level with an AGC signal from circuit 29 to maximize the attenuation of circuit 27 in the reception of the vertical polarized signal. Then, IF signals from circuits 26 and 27 are used to select a signal of a desired channel through filter 10, and conversion is performed to lower the frequency of this selective signal; and level detector 14 generates the AGC signal to control circuits 26 and 27 through circuit 29. |
