Comparison of an Ammonia Maser with a Cæsium Atomic Frequency Standard

Abstract

SEVERAL atomic frequency standards of different types are now in use for comparisons with astronomically determined time. As the adopted frequencies of these atomic standards have been derived from the smoothed universal time U.T. ₂, which is itself variable in time¹, they disagree by several parts in 10⁹. In order to obtain a uniform base for the atomic times determined by the different standards, their frequencies have to be compared directly. This has been done between cæsium resonators at the National Physical Laboratory in Teddington and the Naval Observatory in Washington using the GBR 19.6 kc./s. transmissions. Later the same comparison was repeated between similar cæsium resonators at the National Physical Laboratory².