Circuit for the measurement of small phase delays in MIT.

A single-channel MIT measuring system for obtaining phase delays is given. The circuit, which is described in detail, uses a high-frequency analogue multiplier to measure the phase difference between the signal and a reference signal. The noise in the phase measurement is approximately 1.5 millidegree when the time constant of measuring is 0.1 s, and the drift over about 1 day is approximately 10 millidegree.