2.4GHz signals can go through wooden walls and glass. The signal strength is impacted significantly by brick walls and metal. Trees also have a significant impact on signal strength. As such, 2.4GHz is considered a line-of-sight technology. However, relatively short distances (500m) can be driven through obstacles (none-line-of-sight) either by penetration or multi-path (signals reflecting off other objects) by using higher gain antennas.
2.4GHz signals form cone-shaped invisible regions, called fresnel zones. To determine the height required one must consider the curvature of the Earth, the fresnel zone and any objects in between.
Without doing a sight survey, it is next to impossible to predict signal loss through objects. When designing longer range wireless networks, it is very important to have proper line-of-sight.
The following should provide a rough estimate for determining the required height to achieve proper line-of-sight.
60% of the first fresnel zone should be clear.
The fresnel zone is dependent on the distance between antennas and frequency.
Minimum antenna height = 21.1