Measurements of Path Intermodulation Distortion over Five Tropospheric Scatter Paths

Path intermodulation (IM) data was derived from noise power ratio measurements taken over five tropospheric scatter paths during system acceptance tests. Path lengths of the five links range from 176 to 515 miles, and the links are operated at frequencies of 600 MHz, 900 MHz, or 2 GHz. Path locations vary from a subtropical environment to overland paths near the Arctic circle. The data is presented in the form of scatter plots of path IM versus transmission loss, with a linear least squares fit to each set of data. A regression of path IM on transmission loss is shown for each individual path, and the regression of path IM on transmission loss is shown for all paths as a function of path geometry. A comparison of measured data with prediction indicates that for long paths the magnitude of path IM is usually underestimated.