Short Period Variations in Radio Reception

Continuous records of electric field intensity at distances of from 11 to 2,600 kilometers (6.9 to 1,650 miles) from various broadcasting stations are made by amplifying and rectifying the received current from an open antenna, and recording galvanometer deflections produced by this rectified current. These records show a complex curve containing periodicities ranging from seconds to tens of minutes, the relative amplitude of the short and long period elements varying with the distance. The transition from day to night conditions is shown, and well-marked short period variations ("fading") in night-time reception from a station only 11 kilometers (6.9 miles) distant are found. Simultaneous records at separated receiving points are found to be dissimilar, even with separations as small as 550 meters (1,680 feet), and simultaneous records of different distant stations taken at the same receiving point are also shown to be entirely unlike. A tentative hypothesis for these fluctuations is advanced by the author, in which verying local absorption plays the principal part, but with marked interference effects produced by plural path transmission.