TP-Link CPE220 CPE520 V1.1 Installation Guide - Page 18

Q2. How to calculate the minimum mounting height of the devices? In order to maximize the received signal strength of the devices, installers need to minimize the effect of the out-of-phase signals, which is caused by obstacles in the path between the transmitter and the receiver. Fresnel Zone is a usual method to calculate this path, as shown in the formula and the figure below. d2 H h+r*(1 40%) (H is the height of the CPE) d1 r h = the height of obstacle at this point r = d1 × d2 ⋅ c d1 + d2 f where, r = Fresnel zone radius in meters c = 3x108 m/s, speed of light f = operating frequency of the devices in Hz d1 & d2 = the distances between the point and the devices in meters For example, assume d1 is 2km, d2 is 8km, and f is 2.4GHz, then r would be 14.142m. Considering a toleration of 40%, allowable radius would be 8.485m. Assume h is 10m, then the result of the minimum mounting height based on this point would be 18.485m. Similarly, calculate the results based on all the points where there are obstacles, and the maximum value would be the final result. For more information, please refer to: http://en.wikipedia.org/wiki/Fresnel_zone 15