Whats a Fresnel radius?
Fresnel (pronounced Freh-nel) noticed that objects placed on some ellipsoids with the transmitter and reciever at their foci, would strongly affect the signal strength received. Briefly, this is due to the slightly longer paths of reflected signals causing near-exact cancellation or doubling of the signal at the receiver. Therefore, objects in or near the signal path can improve or degrade the signal, depending on where it is. In general we want to keep the signal path clear. The Fresnel radius is the width of the 1st Fresnel zone, found half way between the sender and receiver. You should make sure that this radius is clear of obstacles.
