  An analog crystal filter based cavity emulator is modified with reverse
biased varactor diodes to provide a tuning range of around 160 Hz. The piezo
drive voltage of the resonance controller is used to detune the cavity through
the bias voltage. A signal conditioning and summing circuit allows the
introduction of microphonics disturbance from a signal source or using real
microphonics data from cavity testing. This setup is used in closed loop with a
cavity controller and resonance controller to study the effectiveness of
resonance control algorithms suitable for superconducting cavities.
