Measurement of short-term frequency stability of controlled oscillators

A method for measuring the frequency of a controlled oscillator as a function of time is described. Sometimes it is necessary to detect and measure small but fast frequency changes. This method can also be used to measure frequency-hopping radio transmitters or radar pulses. In these cases suggested measurement tools, e.g. spectrum analyzers or frequency counters cannot be used. The performance of the system depends mostly on the multimeter, whose accuracy, noise and speed set the limits for the measurements. So far we have been able to measure frequency changes of 5 Hz with sampling speed of 100 000 s^-1. The observed uncertainty is less than 2 Hz. With some further noise reduction better results are expected.