Comparison between measured and calculated field strength in undulating terrain at MHz in the Alvsbyn district

Measurements of audibility and field strengths were made during the wintry conditions of March 1972 in the district of Alvsbyn at a frequency of 40 MHz. The object of the trials was to test and improve existing devices for the prediction of transmission losses along paths over hilly country. The spatial variations in the field strength were found to be distributed normally with a standard deviation for close lying points (within a radius of 20 m) of 2 db. For measured points at the same distance from the receiver, but well separated in the area a standard deviation of 7 db was obtained by the same method. The calculating models analyzed in the report show that a model based on empirical engineering which takes into account the actual terrain profile, is the best. When using this model, a standard deviation of 5 db was achieved for measuring points widely separated over the area, i.e. clearly better than for the measured data as a whole.