g. LOS profiles also can be determined using linear graph paper, correcting for the
curvature of the Earth and the effects of refraction. The following procedures should be
followed to determine LOS using linear graph paper:
(1) Step 1 - Follow steps 1 through 6 outlined in doing LOS profiles using nonlinear
graph paper (pages 2-4 and 2-5).
(2) Step 2 - Next, select a high or
low point (known as the reference point - X)
that is as near as possible to the mid or
halfway point between the two sites. Use
the conversion chart nomograph in Figure 2-
7 to convert the heights of all prominent
points. Plot the corrected points on linear
graph paper (Figure 2-8, page 2-12).
(3) Step 3 - Connect the points to
determine if a LOS path exists. An example
of a profile done on linear graph paper is
shown in Figure 2-8, page 2-12. The
example shows the initial profile before
correction (dotted line).
Using the
nomograph in Figure 2-7, the heights of all
prominent features are then corrected to take
into account the Earth's curvature and the
effects of refraction on radio transmissions.
The profile after correction is shown by a
solid line.
(4) This paragraph contains an
example of how to use the conversion chart
nomograph in Figure 2-7 with the profile
shown in Figure 2-8, page 2-12.
(a) At the 24-mile/38.6-
kilometer distance in Figure 2-8, page 2-12,
the initial profile prior to any correction is
approximately 150 feet, identified by the
dotted line. The distance from reference
Figure 2-7. Conversion chart nomograph
point X at the 14-mile point is 10 miles.
(b) Go down the right hand column of the nomograph in Figure 2-7 and stop at
the 10-mile point. Read directly across to the left hand column to determine the elevation that
the high point should be corrected (50 feet). Subtract 50 feet from the initial profile of 150 feet
to determine the actual profile after correction of 100 feet. This is identified by the solid line in
Figure 2-8, page 2-12.
2-11
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