Q: What is the images/Egli Propagation Model/Egli Propagation Model?
A: The Egli model is described in "Radio Propagation Above 40MC Over Irregular Terrain" (Proceedings of the IRE, Vol. 45, Oct. 1957, pp.1383-1391).
Egli is a greatly simplified model that assumes "gently rolling terrain with average hill heights of approximately 50 feet" (Land Mobile Radio Systems, Edward N. Singer, PTR Prentice Hall, 1994, p. 196). Because of this assumption, no terrain elevation data between the transmit and receive facilities is needed. Instead, the free-space propagation loss is adjusted for the height of the transmit and receive antennas above ground.
As with many other propagation models, Egli is based on measured propagation paths and then reduced to mathematical model. In the case of Egli, the model consists of a single equation for the propagation loss:
Where:
A is the attenuation in dB
D is the path distance in miles
F is the frequency in MegaHertz
HT is the transmitter antenna height above ground level (AGL) in feet
HR is the receiver antenna height above ground level (AGL) in feet
The typical equation used for Free Space loss (in dB) is:
Converting for British units
To isolate the portion of the loss attributable to Egli considerations, subtract the free-space portion from the computed Egli attenuation:
The computed received field at a given location can be found by subtracting this loss value from the computed space field value. (The computed attenuation of the Egli model in SoftWright’s Terrain Analysis Package (TAP)Ô is never allowed to be less than free space attenuation. If the value of AEgli is zero or less, the free space field value is used.
The simplicity of the model makes it one of the fastest for computing field strength values. Obviously, like any model, Egli should be used only in circumstances that fit its assumptions. The Egli model should not be used in areas of rugged terrain, significant obstructions, etc. Egli says it is "limited to those geographical areas which are similar to plane earth, such as relatively short over-water and very flat barren land paths."
