Analysis of noise measurements at the HF band

The background noise is an important factor for radio systems using the high frequency (HF) band, since performance is often limited by the surrounding noise. ITU has published a recommendation describing sources of radio noise and noise levels for man-made noise in different environments. The recommendation is based on old measurements and more recent measurements have been made, with varying conclusions regarding the validity of the levels for different environments. In this paper, broadband measurements of the HF band were analysed. The measurement campaign consisted of measurements conducted over 36 days during winter conditions with measurements every 13 seconds of the whole HF band. The results showed a large variation of calculated hourly median noise figures in frequency as well as time, for the measurement period. For two specific frequencies, hourly and daily variations were investigated showing that large diurnal variations appear for lower frequencies. In this investigation it was evident that the actual time and length of the measurements on which the median noise figure is based are crucial. The results showed levels of the hourly median noise figure for the remote site between ITU Quiet rural and ITU Rural.