FCC type contours / Simple field strength contours

The FCC Contours display in EDX tools (these could also be called Simple Contours) are simple concentric polygons. Each polygon is composed of the loci of a particular Field Strength at Remote value as radiated by a transmitter. These values are calculated by a propagation model which assumes that the signal monotonically decreases as distance from the transmit antenna increases. The FCC models are of this type of model as are Okamura-Hata, Cost-231, IEEE SUI, and ITU-R 370. 

The defining feature of these models is that for each azimuthal transmitter radial a single value for the antenna height above average terrain (AHAAT) is assumed/used for all locations along the radial. All other propagation models consider that each point along a radial can represent a unique elevation difference with respect to the transmitter/receiver antenna. This implies that in many situations the signal level can rise and fall as one moves out along the radial. If this type of prediction is plotted as contours there can be more than one polygon plotted that represents a particular signal level. In EDX products this type of contour display is called Composite Contours. 

Also, note that EDX also offers forms of the monotonic models described above that add varying terrain elevation as a propagation condition. The ITU-R 370+RMD, Hata-Extended, and SUI with Use Terrain active will produce composite contours. Over the years, customers have asked EDX if the ITU-1546 or ITU-1812 models can be used for simple coverage contours. Since these models are not of the monotonically decreasing type they cannot be used for simple contours. However, the ITU-370 is the fundamental basis for ITU-1546 and could be used in its place if simple contours are required.