Radio receiver for carrying out self diagnosis without interference

Claim 1

A circuit arrangement which is selectively operable in a normal mode and a diagnosis mode in response to a circuit input signal and a diagnosis input signal generated in said circuit arrangement, respectively, and comprises a controller for producing a control signal selectively indicative of said normal and said diagnosis modes, processing means responsive to said control signal for processing said circuit and said diagnosis input signals into a processed signal of a processed level when said control signal indicates said normal and said diagnosis modes, respectively, and squelch signal producing means responsive to said processed signal and a reference signal of a reference level for producing a squelch signal when said processed and said reference levels have a predetermined relationship, wherein the improvement comprises: first threshold signal generating means for generating a first threshold signal of a first threshold level; second threshold signal generating means for generating a second threshold signal of a second threshold level which is lower than said first threshold level; selecting means responsive to said control signal for selecting said first and said second threshold signals as a selected threshold signal when said control signal indicates said normal and said diagnosis modes, respectively; and means for supplying said selected threshold signal to said squelch signal producing means as said reference signal, said squelch signal producing means using said first threshold level as said reference level when said control signal indicates said normal mode, said squelch signal producing means using said second threshold level as said reference level when said control signal indicates said diagnosis mode.