Abstract
A comparison among three precise timing centers in the United States has been conducted for more than 1 year using three different synchronization methods. The timing centers involved were the United States Naval Observatory (USNO) in Washington, DC, Newark Air Force Station (NAFS) in Newark, Ohio, and the National Bureau of Standards (NBS) in Boulder, Colorado. The three methods were cesium beam portable clocks; Loran-C transmissions from Cape Fear, North Carolina, and Dana, Indiana; and ABC, CBS, and NBC network television broadcasts commonly received by the three timing centers.
Cesium beam portable clocks have the capability of accurately and precisely synchronizing remote clocks to within 0.1 μs. The Loran-C data involved a 3500 km (2180 miles) ground wave path – the longest Loran-C ground wave path that has been studied with the precision and accuracy reported herein. The long-term precision achieved was about 1 μs over 1 year. The accuracy is limited on occasion by inability to resolve the 10 μs ambiguity of the 100-kHz pulse train. The precision capability of maintaining remote clock synchronization within the majority of the continental United States using network television broadcasts was inferred to be about 5 ns·τ1/3 s-1/3 over the range of τ from 86 400 s (1 day) to about 107 s (324 days) but with definite accuracy limitations caused by such factors as occasional network re-routing of the television signals. Some estimates of the long-term frequency stabilities among the references used at the three timing centers were measured or inferred.