The Use of GPS Disciplined Oscillators as Primary Frequency Standards for Calibration and Metrology Laboratories

An increasing number of calibration and metrology laboratories now employ a Global Positioning System disciplined oscillator (GPSDO) as their primary standard for frequency. GPSDOs have the advantage of costing much less than cesium standards, and they serve as “self-calibrating” standards that should not require adjustment or calibration. These attributes make them an attractive choice for many laboratories. However, a few of their characteristics can make a GPSDO less suitable than a cesium standard for some applications. This paper explores the use of GPSDOs in calibration laboratories. It discusses how GPSDOs work, how measurement traceability can be established with a GPSDO, and how their performance can vary significantly from model to model. It also discusses possible GPSDO failure modes, and why a calibration laboratory must be able to verify whether or not a GPSDO is working