| 摘要 |
PURPOSE:To prevent detrimental failure on the frequency characteristics caused in the band of an intermediate frequency, by constituting an impedance viewing from an intermediate frequency block circuit to a high frequency signal input terminal so as not to form a resonance characteristic in the intermediate frequency band so that the intermediate frequency signal blocking circuit does not act like a coupling capacitor. CONSTITUTION:The intermediate frequency block circuit 8 is provided on a main line 2 at a distance being about 1/4 wavelength of an intermediate frequency signal from a mixer diode 3, and one end of a low-pass filter 10 is connected to a high impedance point C of the main line 2 at an intermediate/high frequency signal input terminal 1. Since the point C on the main line 2 is a high impedance point at the intermediate frequency and a low-pass filter 10 terminated with a resistor is connected to the point C, even if an resonance circuit is formed at the high frequency signal input terminal 1, the signal is damped with the resistor. Thus, no resonance characteristic appears at the impedance viewing the intermediate frequency signal block circuit 8 from a terminal B of the mixer diode 3, the terminal B is short-circuited surely at the intermediate frequency, allowing to prevent the detrimental failure produced in the mixer circuit. |
