(7) Step 7 - Connect the dots to establish the required Fresnel zone clearance area for

the radio path between transmit and receive stations.

(8) Step 8 - Find any points of terrain inside the required clearance area.

d. First Fresnel zone exercise. This exercise shows how to determine first Fresnel zone

clearance, given:

d1 = 16 kilometer

d2 = 24 kilometers

f = 4 GHz

D = 40 kilometers

(1) First, multiply d1 by d2 (in this example, multiply 16 by 24, which equals 384).

Next, multiply f by D (multiply 4 by 40 which equals 160). Next, divide 384 by 160, which

equals 2.4. Then, determine the square route of 2.4, which is 1.549 or 1.55. Finally, multiply

1.55 by either 17.5 (determine the Fresnel zone in meters or by 72.1 to determine the Fresnel

zone in feet). 17.5 X 1.55 equals 27.125 or about 27 meters (C = 27 meters). 72.1 X 1.55 equals

111.755 or about 112 feet (C = 112 feet).

(2) Figure 2-10 illustrates plotting the Fresnel zone on nonlinear graph paper, where

d1 = 16 kilometer; d2 = 24 kilometers; f = 4 GHz; and D = 40 kilometers. In the illustration, at

the 16-kilometer distance mark, a line is drawn at a right angle to the straight line drawn between

points A and B (Step 2, LOS procedures for SHF microwave radio systems).

(3) Using the formula, the required Fresnel zone clearance at the 16-kilometer

distance has been determined to be approximately 27 meters (Step 3). Using the elevation scale

on the left margin of the graph paper for reference, a dot is placed on the line signifying the

required Fresnel zone clearance for that distance (Step 4).

e. As in VHF/UHF procedures, if LOS and first Fresnel zone clearance cannot be

obtained, communications could be degraded. To obtain first Fresnel zone clearance, the

required clearance. The alternative is to relocate one or both of the radio sites to achieve the

necessary results.

5.

Summary. In this lesson, you learned about the planning considerations for line-of-sight

(LOS) engineering, to include determining antenna heights for transmit/receive sites and

developing a manual LOS profile.

Integrated Publishing, Inc. |