Geographic Correlation Analysis of WWV Ionospheric Propagation: Phase Stability and Fading Statistics for Adaptive HF Radio

We present an analysis of the characteristics of the WWV time signal observed simultaneously at two geographically separated receivers in eastern Massachusetts. Our work has applications in assessing the feasibility of adaptive correction for ionospheric phase distortion in HF communications — analogous to adaptive optics in astronomy. Using KiwiSDR software-defined radio receivers connected to magnetic dipole antennas at Cambridge and Sudbury MA (∼32 km apart), we recorded IQ samples at 2.5, 5.0, 10.0, 15.0, 20.0, and 25.0 MHz over multiple 88-second intervals. The receiver in Cambridge uses a hybrid coupler to extract circular polarization from orthogonal magnetic loops. We measure carrier phase, characterize fading statistics, and compute the phase structure function D(τ ) to quantify phase stability over 20 ms intervals. This time lag corresponds to the round-trip travel time for active compensation of ionospheric variation over a 2000 km path. Results show that 5 MHz exhibits excellent phase stability (RMS ∼0.08–0.20 rad at 20 ms lag) during morning hours, while 25 MHz shows even better stability (RMS ∼0.12 rad at 20 ms lag) during the afternoon when the ionosphere supports skywave propagation at higher frequencies. Fading events are uncorrelated between the two sites, indicating that the RF scintillation pattern on the ground has its dominant structure on spatial scales smaller than 32 km.