Wideband Measurements of Medium-Frequency Atmospheric Radio Noise

Abstract

Wideband measurements of radio noise in the medium frequency (400-500 KHz) band have been made in the southwestern USA at. a remote site well removed from sources of man-made interference. To perform these measurements, a sophisticated noise recording system was designed and built to simultaneously record radio noise from two independent antennas in 100 kHz bandwidth, and the software required for processing and analysis of the data was developed. Three successful field missions in Nevada yielded a data, base consisting of approximately 575 high density tape recordings and 1800 magnetic computer tapes containing the transcribed noise data. Computeraided analysis of the tape-recorded noise provides new information regarding the characteristics of wideband atmospheric noise and the effects of bandwidth on them. First-order statistics (average power; amplitude probability distribution; Vd) are calculated and compared with CCIR 322 values. Higher order statistics (autocorrelation function; pulse duration and pulse spacing distributions; average positive crossing rates) are also derived. I t is found that increasing the bandwidth increases Vd far less than would be anticipated by CCIR 322. Also, characteristic changes are introduced into the pulse statistics by varying the bandwidth. The results of 4 weeks of daytime and nighttime measurements in early autumn will be discussed, and a brief description of the wideband noise recording equipment and analysis technique will be given.