User's Manual

Trees and other foliage contain a lot of water and therefore also attenuate the RF
signal.
So the easiest approach to making good quality radio links is to have an
unobstructed line of sight between the transmitter and receiver, as illustrated in
Figure 10-5.
LOS
NLOS
X
NLOS
X
Figure 10-5: Line of Sight (LOS) and Non-LOS.
This does not mean that RF cannot penetrate buildings, or that it cannot bounce
off buildings and work its way to the receiver. It just means that such
arrangements require a lot of RF skill and experience to make them work.
It has also become popular in the wireless industry to talk of Near-Line-of-Sight
(NLOS). Again, radio waves do funny things when they pass over the edge of an
obstruction, but it takes a lot of experience with RF to predict the results.
One rule of thumb is to clear such objects by some extra room. Good
communications links clear objects in the middle of the link by 10-15 feet at this 5
GHz band. This is called the Fresnel Zone clearance, as illustrated in Figure 10-
6.
ARCXtend manual, August 2003 10-5