Electronic circuits showing a level-independent phase shift for hydrogen-maser work applications

The origin of spurious level-dependent phase shifts occuring in amplifiers is analyzed. The effects of nonlinearities in transistors and of a bandwidth limitation are stated. Rules for the design of electronic circuits in which this effect must be minimized are given. Experimental results related to a 40-dB amplifier and to an amplitude limiter, both at 5.75 kHz, are described. The tuning of a hydrogen-maser cavity with the condition that the phase of oscillation does not depend on the amplitude of oscillation is considered. A preliminary precise test of the method is reported and discussed.