Abstract EN:

The long term frequency stability of hydrogen masers is generally degraded by the drift of resonant cavity. We have realized two electronic apparatus able to tune resonant cavities of 2 hydrogen masers with a short time constant, according to a method proposed recently. A square wave frequency modulated microwave signal, without carrier, is transmitted through the cavity. The amplitude of the transmitted signal is modulated when the mean value of the cavity resonant frequency is different from reference frequency. A synchronous detector provides an error signa1. After being filtered by a convenient transfer function, the voltage obtained is applied to the diode that controls the cavity resonant frequency. In these conditions, a tight control of the cavity resonant frequency is insured. The experimental results show that the apparatus does not degrade the short and medium term frequency stability, and allows a long term frequency stability of few parts in 10-15.