Superconducting filter apparatus and wireless receiving amplifier having an abnormality discriminating circuit

A wireless receiving amplifier for amplifying a signal of a prescribed band in a signal received by an antenna and outputting the amplified signal, comprising:

• a superconducting filter that exhibits a prescribed pass-band characteristic when cooled to cryogenic temperatures;
• a low-noise amplifier connected to the output of the superconducting filter for amplifying a signal that is output from the superconducting filter;
• a refrigerator for cooling said superconducting filter and low-noise amplifier to cryogenic temperatures;
• a first pilot signal generator for generating a first pilot signal having a frequency that is outside said pass band characteristic and inputting said fist pilot signal to the superconducting filter together with an antenna receive signal;
• a second pilot signal generator for generating a second pilot signal having a frequency that is outside said pass band characteristic and inputting said second pilot signal to the connection portion between said superconducting filter and said low-noise amplifier;
• and
• a discriminating unit for detecting the level of the first and second pilot signals contained in a signal that is output from the low-noise amplifier and for discriminating abnormality in the refrigerator and low-noise amplifier based upon the level of the first and second pilot signals, respectively.