Hydrogen‐Maser Time and Frequency Standard at Agassiz Observatory

Abstract

A hydrogen maser was installed at the Harvard College Observatory‐Smithsonian 84‐foot radio telescope in Harvard, Massachusetts, for very long baseline interferometry (VLBI) experiments in October, November, and December of 1969. The maser is a compact unit (42 by 22 by 22 inches) of relatively low power consumption, designed specifically for field use; it is readily transportable. A precision 5‐MHz crystal oscillator that is phase locked to the maser provides all frequency and time references for the VLBI receivers, recorders, and clocks. The maser was tuned against a rubidium standard by a rapid flux‐switching technique; maser frequency resettability was estimated to be approximately ±3×10−13 with an over‐all accuracy of approximately ±1×10−12. Loran‐C was continuously monitored during the VLBI experiments, and the results of the Loran‐C maser comparisons are included.