In his recent QEX article, “Ionospheric Disturbances at Dawn, Dusk, and During the 2017 Eclipse,” Steve Cerwin, WA5FRF published his analysis of observations of WWV (5 MHz) and WWVB (60 kHz) transmitters in Ft. Collins, CO as received at his home in San Antonio, TX. Cerwin reports that during the August 21, 2017 eclipse, a definite and measurable enhancement of low frequency (LF) and high frequency (HF) signals from his station. In addition to eclipse observations, Cerwin also examined the dawn and dusk transitions on both frequencies. Notable findings include a propagation null on WWVB that is correlated in time with dusk and dawn, and is consistent with destructive interference from a combination of ionospheric skip and ground-wave multipath propagation. Cerwin also reports on increased frequency jitter at 5 MHz during these times, as well a radical positive frequency swing at dawn and a negative swing at dusk.
