As far as I know is what you wrote incorrect. It is possible to just use the
free space model as a propagation model. Your description is accurate for
the two ray ground model, which is composed of two formulas, first the
same as with the free space model (Friis' transmission equation) and after
the crossover distance another (dating back to Rappaport).
When setting the propagation model to free space you should be able to
derive your settings from the following equation (taken from threshold.cc):
Pt * Gt * Gr * (lambda²)
P = --------------------------
(4*pi * d)² * L
with:
P Recieving Threshold (RXThresh)
Pt Transmission Power
Gr Antenna reciving gain
Gt Antenna transmission gain
lambda wavelength (= 3.0e08 / frequency)
d distance
L System Loss
Best,
-Matt
> First of all I think the the free space model and two ray ground model
> are dependent on antenna height and there is a crossover distance, after
> which the model used is two ray ground. When you say you use free space
> model, you must have the antennas to be very high, to acheive a free space
> loss situation, otherwise two ray ground will take effect after the
> crossover distance.
