Results with the special-purpose ammonia frequency standard.

A special purpose ammonia frequency standard and clock have been developed on the basis of the 3-3 transition in ammonia providing the frequency reference for an 0.5 GHz oscillator. The output is multiplied in one step to K-band and the resulting output is passed through a waveguide cell containing ammonia. The oscillator is frequency modulated at about 10 kHz and locked by nulling the third harmonic of the detected output. Digital demodulators in the feedback networks reduce servo off-set problems. Operation at pressures where collision broadening makes up part of the linewidth makes it possible to null out pressure shifts. Shifts of less than 5 x 10 to the -10th power/micron have been observed.