Allan Deviation Analysis of WWV Doppler Shift Measurements recorded with the HamSCI Grape 1 Receiver

The Allan deviation (ADEV) is a well-established metric, recognized by the IEEE and other standards organizations, for estimating the frequency stability of quartz and atomic oscillators over averaging intervals of varying duration.  To show that ADEV may also be useful for the analysis of radio path stability, this presentation will apply ADEV analysis to WWV Doppler Shift measurements recorded with the Grape 1 receiver designed by N8OBJ.  This analysis greatly benefits from the fact that the WWV broadcasts are referenced to an ensemble of atomic oscillators continuously adjusted to agree with Coordinated Universal Time (UTC), and the Grape 1 receiver is referenced to a GPS disciplined oscillator (GPSDO) referenced to atomic oscillators aboard the satellites, that are also in step with UTC.  Therefore, atomic clock accuracy is always present at both ends of the radio path. This presentation will first describe how ADEV is defined and computed, including a discussion of free software tools that are readily available.  It will then discuss how everything necessary to compute ADEV can be obtained from the Grape 1 data files.  It will demonstrate that the small instabilities present in the GPSDO that Grape 1 uses for its reference should be indiscernible in the WWV measurements.  Finally, the presentation will show annotated ADEV graphs generated from the collected data.  The presented measurements are predominantly groundwave observations of WWV, recorded at a distance of about 15 km from the station by W0DAS in Fort Collins, Colorado, and at a distance of about 81 km by K0WWX in Broomfield, Colorado.  However, the same ADEV analysis described here is easily applicable to both groundwave and skywave data.