Determining Optimum C-Field Settings that Minimize Output Frequency Variations in Cesium Atomic Frequency Standards
AEROSPACE CORP EL SEGUNDO CA ENGINEERING AND TECHNOLOGY GROUP
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De Marchi at the National Institute of Standards and Technology NIST performed an experiment on Hewlett-Packard cesium Cs frequency standards, in which he showed that there exist optimum values of the C-field that make the output frequency insensitive to variations in microwave power. Moreover, and most important, De Marchi demonstrated that the long-term stability of the Cs standard was improved at these optimum values of the C- field. To see if these results could be obtained with standards made by different manufacturers and having different modulation schemes and Cs tube designs, we performed a similar study using a completely automated measurement system on four Cs standards made by two other manufacturers. Our results, similar to those of De Marchi, showed that there are similar optimum C-field settings in these standards furthermore, they showed that it may be more important to tune the microwave cavity precisely to the center Cs resonance frequency fo than it is to set the C-field at an optimum value. The best procedure, of course, is to do both, i.e., tune the cavity to the Cs resonance frequency as well as set an optimum C-field.
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