Abstract: A discriminator having a power divider that divides a signal under test into a signal channel component and a reference channel component. A tunable delay line, such as a magnetostatic wave delay line, inserts a delay into the reference channel. A multielement input transducer selects a narrow band of spin wave wavelengths that are activated, thereby producing frequency discrimination. A phase detector is responsive to both channels to produce an output signal to a spectrum analyzer. A feedback loop, responsive to the output signal of the phase detector automatically places these two components into a quadrature relationship. The discriminator is automatically calibrated by tuning the delay line to values away from the quadrature condition in order to determine the discriminator consant.