  We report the measurement of intermodulation gain in NbN superconducting
stripline resonators. In the intermodulation measurements we inject two unequal
tones into the oscillator, the pump and signal, both lying within the resonance
band. At the onset of instability of the reflected pump we obtain a
simultaneous gain of both the idler and the reflected signal. The measured gain
in both cases can be as high as 15 dB, whereas to the best of our knowledge
intermodulation gain greater than unity in superconducting resonators has not
been reported before in the scientific literature.
