Abstract: A mixer circuit using a rat-race constituted by disposing microstrip lines on one surface of a substrate to provide a loop-shaped transmission line and four transmission lines connected to the loop. In the rat-race, two of the four transmission lines are disposed within the loop of the loop-shaped transmission line. A conductor penetrates the substrate at the center of the loop of the loop-shaped transmission line, and a pair of diodes are connected respectively between this conductor and the two transmission lines disposed within the loop so that an intermediate frequency signal obtained by subjecting a high frequency signal to frequency conversion can be derived from the conductor at the other surface side of the substrate.

Abstract: A device for frequency-converting multi-channel broadcast signals consists of a local oscillator for generating at a time a single oscillation frequency, a mixer and a frequency discriminator for automatically controlling the oscillation frequency of the local oscillator. The frequency discriminator delivers a dc zero voltage when the frequencies of plural signals applied to the discriminator coincide with those of the carrier waves of the frequency-converted multi-channel broadcast signals. If the frequencies of the plural signals applied to the discriminator differ from those of the carrier waves, the discriminator delivers a dc output voltage whose amplitude depends upon the difference.