Measurements of fading on HF communication links

Although much is known about the amplitude statistics of fading on ionospheric paths, CCIR preparations in high-frequency broadcasting for the World Administrative Radio Conference (WARC-HFBC) revealed a lack of knowledge, for both within-an-hour and day-to-day variations of: (i) the correlations of signals and noise; (ii) the correlations of fading on adjacent channels; and (iii) the correlations of fading at different receiving sites within the coverage area of a broadcast transmitter. Consequently, fading allowances adopted in planning standards for reliability and compatibility need to be validated or replaced. A programme of measurements, which will consist of a series of campaigns, each of about one month´s duration, involving different receiving sites throughout Europe covering ranges of 400-2500 km, is currently being undertaken by RAL, with assistance from DTI, to meet this need. The paper presents preliminary analyses of data collected during the first campaign which took place during September-November 1988