Mutual Synchronization of Passive Hydrogen Masers

In the experiment frequencies of two passive hydrogen masers are mutually adjusted by means of PI-servo loop which obtains error value from the frequency comparator and controls synthesizer codes of the masers. As a result, output signals of both masers have got the same mean frequency and frequency stability is improved for the averaging times more than the control loop time constant value. It is also shown that summary signal of two mutually synchronized (and adjusted by phase) masers has better short-term stability and lower phase noise spectrum than the separate maser signals have. Simple theoretical and simulation analysis has been done to retrieve the conditions of frequency stability improvement or degradation in ensemble of two coupled clocks.