Effect of near total solar eclipse on radio propagation of HF, weak-signal propagation reporter (WSPR) transmissions

Background: A North American path of totality granted opportunity to investigate the effects of a solar eclipse on radio propagation. The weak signal propagation reporter (WSPR) modality is acclaimed for detecting low signal-to-noise transmissions and used to study radio propagation. “Spots” are detected WSPR signals originating from a particular transmitter. Methods: The predicted maximum obscuration of the sun at the semi-rural New York field location (Maidenhead FN22, 42°N 74°W) was 97.6%. The Zachtek WSPR Desktop Transmitter outputted 200mW WSPR transmissions cyclically on 80/40/30/20/17/15/12/10M amateur radio bands (“bands”). The EFHW antenna system consisted of a horizontal ~66’ 16awg 20’ high wire in an east-west orientation, 49:1 toroidal impedance transformer, and 25’ RG58c/u coaxial cable. Before, during, and after the eclipse, WSPR transmissions cycled through 80M-10M (minus 60M) bands, transmitting for 105 seconds per band, or 14 minutes through all bands, followed by four minute of rest. Twelve multi-band transmission cycles were completed during the experiment; each complete transmission cycle was considered a “time slot”. Propagated mileage for these spots was obtained from the WSPR Rocks! online repository. For each band, propagation mileage for spots in a given time slot were compared with those of all of the other time slots (Mann-Whitney U for non-parametric, independent data, one- and two- tailed, ρ < 0.05) This was repeated for each band. When identified, significant findings suggest a particular band’s aggregated propagation distances within a given time slot are different (longer or shorter) than those in that band’s remaining time slots. Results: WSPR transmissions at 10.14MHz and 14.09MHz propagated significantly longer distances at the height of the eclipse and afterwards, compared to those preceding maximum sun coverage. This signal path lengthening was not observed in other bands. Solar eclipses may effect 30M and 20M radio wave propagation, causing transmission distances to lengthen at and following maximum solar obscuration.