Radio wave propagation is a very complex process. It is impossible to precisely predict how waves will spread and what values we will measure at some particular point. Therefore we have some mathematical models to approximate radio propagation and to calculate field strength values according to predefined probability.
The propagation model, which is based on electromagnetic theory and on statistical analysis of both terrain features and radio measurements, predicts the median attenuation of the radio signal as a function of distance and the variability of the signal in time and in space. Propagation models define curves and formulas. With such model we can predict propagation in arbitrary distance from the transmitter.
Using curves and mathematical formulas manually is a very tough task. In order to automate and speed up such calculations many software tools were developed. Normally, radio planning software packages are used by broadcasters, mobile operators and radio frequency authorities. Because of complexity and small number of potential customers, the price of such software package can be pretty high. But there is one exception to this rule.
Radio Mobile is a software tool for radio propagation calculation. The author has decided to publish it under the “freeware” license which means that the software is freely available on the web. This software is primarily dedicated to amateur radio, however, it can be also used in other areas including broadcasting and professional mobile communications.
Calculations are based on the Longley-Rice propagation model. This is a general purpose radio propagation model for frequencies between 20 MHz and 20 Ghz. In order to use the software you also need terrain model data. This data is needed for calculations of effective heights which are needed to perform propagation calculations. You can find some terrain model data sources on the web. They offer free DTM (Digital Terrain Model) data which is enough to start working with the Radio Mobile.
Radio Mobile supports many fancy features like possibility to use DTM in various formats (DTED, SRTM), also in many layers with different resolution, possibility to add map pictures in raster format (BMP, JPEG, GIF, TIFF, PNG), possibility to calculate interference between radio stations and lots of functions to customize the view.
Basic way of use consists of entering radio stations with all parameters (if they are not entered yet) and calculation of the coverage. Here you have a lot of options to customize the calculation and view. Results can be saved for later use. It is also possible to define calculation step for coarse calculations to save some time.
For result display it is usually not enough to display it on the gray scale DTM. You would probably like to see it on some map. For this purpose you can use any map picture with known coordinates. The software allows you to enter coordinates for each picture in order to display it correctly over the DTM.
A very useful function is the calculation of interference between radio stations. You define protection ratio and minimum field strength for calculation and the software marks interference area with predefined color.
The software is also very useful for microwave link planning. It allows you to display terrain profile between two points, display of optical visibility from any point and calculation of link parameters. Although this software is free and dedicated for amateur radio it can be very useful tool for daily radio communication tasks.