Afar AR24027, Руководство оператора

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AR24027 Operator’s Manual
6-9
4. Following the radio path line on the map, identify all obstructions. Most topographical maps
identify geographic information, such as hills and lakes, only. However, vegetation, buildings or
other structures that will interfere with radio transmissions must also be included.
5. Plot each obstruction on the graph, marking its elevation and distance from the sites. For dense
vegetation such as forests, add 40 to 60 feet (12 to 18 m) to the ground elevation.
6. Add the Earth’s curvature to the height of each obstruction. For each obstruction calculate this
increment by using the following formula:
d
=
d1
×
d2
×
C
K
Where:
(for US units:)
d = additional height increment in feet
d1 = distance of the obstruction from the first site in miles
d2 = distance of the obstruction from the second site in miles
C = .667 for US units
K = refractive index (use a value of 1.33).
(or for metric units:)
d = additional height increment in meters
d1 = distance of the obstruction from the first site in km
d2 = distance of the obstruction from the second site in km
C = .079 for metric units
K = refractive index (use a value of 1.33).
Add the “d” value to the height of each obstruction plotted on the graph.
7. Add the Fresnel Zone clearance to the height of each obstruction (the required increment is 60%
of the first Fresnel zone radius). For each obstruction calculate the increment using the formula:
d
=
C
d1
×
d2
F
×
D
Where:
(for US units:)
d = 60% of the first Fresnel zone radius in feet
d1 = distance of the obstruction from the first site in miles
d2 = distance of the obstruction from the second site in miles
C = 1368 for US units
F = 2400 (frequency in MHz)
D = total path length in miles (d1 + d2).
(or for metric units:)
d = 60% of the first Fresnel zone radius in meters
d1 = distance of the obstruction from the first site in km
d2 = distance of the obstruction from the second site in km
C = 529 for metric units