On the predictions of atmospheric radio noise levels in the tropics

Abstract

Predictions of world-wide radio noise have been published in revised form and adopted by the International Radio Consultative Committee (C.C.I.R., 1957) for use by radio and communication engineers. The prediction curves show expected median, upper decile and lower decile levels of atmospheric radio noise power for all frequencies from 10 kc/s to 30 Mo/s, during 4-hour time blocks of the day for each season of the year. Even though there has been an increase in the number of places where these predictions have been based on actual measurements, unfortunately there have been only few in tropical areas which are known to be major sources of atmospheric radio noise Measurements of atmospheric noise levels have therefore been made at Ibadan, Nigeria (7°N, 4°E) in a tropical area, between 1958 and 1962. These measured values have been compared with corresponding values interpolated for Ibadan from the C.C.I.R. prediction curves. It is found that, in general, the predicted and measured values are in good agreement but the discrepancies at certain times and frequencies have been assessed and reasons for the disagreements discussed. The adoption of the C.C.I.R. 4-hourly divisions of the day for the prediction of atmospheric noise levels and compilation of noise data is re-examined in the light of available information in a tropical area where local storms are prevalent for most parts of the year. The division is found unsatisfactory at least for certain parts of the day and a division of the day into eight periods i.e. 0000–0400, 0400–0600, 0600–0800, 0800–1200, 1200–1400, 1400–1600, 1600–2000, 2000–2400 hours is suggested, together with the advisability of merging the two night periods 2000–2400 and 0000–0400 hours into one noise period in tropical areas where the compilation of noise records usually presents some difficulty.