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Show Variation of Radio Signal Strengths By MILTON MARSHALL! and THERON LAMBERT2 Since Larmor presented his theory of electronic refraction in 1924, the existence of the ionosphere, i.e the electrical conducting region of the upper .. atmosphere. has been proven. According to this general theory long distance transmission is possible, because of the refraction of radio waves when they enter this ionized region, thus causing the waves to return to the earth. To test the general theories concerning the ionosphere observations of radio fading were made on the signal strength of K. S. L. and K. D. Y. L. A sensitive current galvanomenter, lamp and scale type( Leeds and Northrup), was connected in the a.v.c. circuit of an all-wave Knight super heterodyne receiver. Since the a.v.c. current flowing through the galvan ometer was inversely proportional to the average rectified signal in the de tector, fluctuations in the a.v.c. current were proportional to changes in ampli tude of the radio signa1. Fading of a radio station could easily. be observed by noting the galvanometer deflections. This method does not give absolute values. Noon-day observations (15 min. periods) were made on several different during the period from Feb. 20 to May 1 of this year. In every case the noon-day reading showed a well defined day-to-day variation in signal strength. On the nearby "broadcast" stations, the day-to-day vari ation was so pronounced that most reasonable explanation would be to assume that reflected sky waves were reaching the receiver even during noon-day when ionic densities are near their daily maximum. From the noon-day readings taken over the seventy day period, a sea sonal change in the average signal strength was also observed. That is, as the season changed from Winter to Spring, there was a decrease in the average noon-day signal strength. This effect is to be expected, as the yearly variation in ionosphere densities reaches its lowest value during the Winter months and its highest value in the Summer. The absorption of radio energy increases with increasing ion density. During the months of March and April. a series of sunrise and sunset readings (90 min. periods) were obtained for several radio stations. When ever possible each station was observed at sunrise and at sunset on five con secutive days. The general tendency was for the signal strength to decrease during sunrise and increase during sunset. Fading was very pronounced during those periods, especially during sunset. This effect may be explained by the fact that the ion densities in the lower layers change most rapidly at those periods of the day. The amount and rapidity of the fading increases as the frequency of the radio wave increases. Also the general shape of the fading curve varies considerably with changing local weather conditions. Winds, temperature inversions, and barometric pressure changes effect the density and height of the lowest weakly ionized region of the atmosphere. radio stations 1 2 Professor of Physics and Mathematics, Brigham Young University, Provo, Utah. Graduate Student in Physics Department, Brigham Young Utah. University, Provo, 45 |
