Abstract
A null detector for use with audiofrequency capacitance bridges is described. A superconducting inductor is used in a matching network at the input of the detector. Capacitive feedback in the preamplifier of the detector determines the bandwidth. For a bridge with an output capacitance of 1 nF operating at a frequency of 1592 Hz ( omega =104 rad s-1), the noise contribution from the detector is negligible compared with the noise contributed by the output conductance of the bridge (about 1.5 nS).

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