H.E. Peters, H.B. Owings, P.A. Koppang

Abstract: The stability of the free-running hydrogen maser is limited by pulling of the unperturbed hydrogen transition frequency due to instability of the cavity resonance frequency. Two automatic approaches to cavity stabilization have been used successfully in field operable atomic hydrogen masers in the past. One method is based upon the "spin-exchange" tuning procedure and was used in masers constructed at NASA's Goddard Space Flight Center. 1, 2 The other method is the cavity frequency switching servo used on Sigma Tau Standards Corporation (STSC) hydrogen masers, 3, 4, 5 While automatic spin-exchange tuning is in principle the more basic and accurate method, the required beam intensity switching and the long servo time constant result in reduced stability for measuring intervals up to 105 seconds. More importantly, the spin-exchange tuning method requires a second stable frequency source as a reference, ideally a second hydrogen maser, to get the best results. The cavity frequency switching servo, on the other hand, has very little effect on the maser short term stability, and is fast enough to correct for cavity drift while maintaining the cavity at the spin-exchange tuned offset required to minimize instability due to beam intensity fluctuations. Not only does the cavity frequency switching servo not require a second stable frequency source, but the frequency reference is the atomic hydrogen radiated beam signal, so that no extra RF connections need be made to the cavity, and externally generated signals that would perturb the hydrogen atom need not be transmitted through the cavity. In this paper we will discuss the operation of the cavity frequency switching stabilization method and will illustrate the transient response of the servo and certain other aspects of the technique that have potential for achieving improved basic accuracy. He also will give stability results obtained between masers at STSC and long term stability data obtained with STSC hydrogen masers at the United States Naval Observatory.
Published in: Proceedings of the 22th Annual Precise Time and Time Interval Systems and Applications Meeting
December 4 - 6, 1990
Sheraton Premiere Hotel
Vienna, Virginia
Pages: 283 - 292
Cite this article: Peters, H.E., Owings, H.B., Koppang, P.A., "HYDROGEN MASERS WITH CAVITY FREQUENCY SWITCHING SERVOS," Proceedings of the 22th Annual Precise Time and Time Interval Systems and Applications Meeting, Vienna, Virginia, December 1990, pp. 283-292.
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