Computer prediction of field strength in the planning of radio systems

The application of a method of predicting the field strengths from mobile radio base station transmitters and in radio links is presented, and the extension of the method to facilitate frequency assignment is outlined. The topographic data for a country are stored in a computer and programs are provided which predict the signal levels produced by a specific transmitter at points spaced 0.5 km apart. A further program enables a plotter to be used to derive signal level contours which can be overlaid on a map. The field strength prediction method is proving valuable in the siting of VHF base stations, in the reduction of field testing required for mobile systems, and in the study of possible areas of cochannel interference. It has also been extended to effect path calculations for point-to-point radio links. An extension of the cochannel interference study in which channel assignments are made by a logical procedure so as to maintain co-channel interference below some chosen level while making the minimum demands on the spectrum is outlined. The method described has potential applications in national frequency planning.