As the stability of frequency standards have been improved, it becomes desirable to have less noise in the measurement system than the composite noise in the pair of standards to be measured.
This paper describes the system and the way of improving frequency stability measurements in the time domain, using the beat frequency method for τ<10s and the phase comparison method for τ<10s. (τ is the averaging time of the measurement.)
With regard to the beat frequency method, it became clear that the trigger error of the counter is an important factor for the precision of measurement, and that, in order to make the influence small, the multiplication of the signal frequency is effective.
Using a phase meter with a voltage-frequency converter, a frequency stability of 1.0×10
-14 was obtained, which corresponds to the noise of this measurement system at an averaging time of 100s.
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