INTERMODULATION DISTURBANCE DETECTING UNIT
There are provided a notch filter 21 for carrying out a filtering processing for inputting a broadband IF signal which is output from a frequency converting circuit 4 and attenuating a frequency component of a desirable wave and an amplifier 22 for amplifying and outputting a signal output from the notch filter 21 , and a presence/absence of an intermodulation disturbance is detected depending on whether a signal having an equal frequency to the frequency of the desirable wave is output from the amplifier 22 or not though the frequency of the desirable wave is attenuated by the notch filter 21 . Consequently, it is possible to easily detect the intermodulation disturbance irrespective of a level of a received signal or a desirable wave included therein without carrying out a complicated processing such as an amplitude modulation of the received signal.
1 . An intermodulation disturbance detecting circuit comprising:
a filter portion for carrying out a filtering processing for inputting an intermediate frequency signal converted from a radio frequency received signal and attenuating a frequency component of a desirable wave;
an amplifying portion for amplifying a signal output from the amplifying portion and outputting the signal thus amplified; and
a detecting portion for detecting a presence/absence of an intermodulation disturbance depending on whether the signal output from the amplifying portion has an equal frequency component to the frequency of the desirable wave.
2 . The intermodulation disturbance detecting circuit according to claim 1 , wherein the filter portion is constituted by a notch filter.
3 . The intermodulation disturbance detecting circuit according to claim 1 , wherein the amplifying portion is constituted by a linear amplifier having a dynamic range set to be smaller than a predetermined value.
4 . The intermodulation disturbance detecting circuit according to claim 2 , wherein the amplifying portion is constituted by a linear amplifier having a dynamic range set to be smaller than a predetermined value.