Examples
Outdoor Antenna Installation Guide
3-17
NOTE:
In this example we will only demonstrate the calculation for
the link between building
a
and
c
. However as different
clearance factors may apply for each of these links, you
are advised to calculate the actual range for each link
individually when designing a “real” outdoor antenna link.
For the purpose of this example we presume that:
■
The antenna installation will be installed in a dense urban
area, where the distance between building
a
and building
c
is
1.6 Km.(1.0 mi.).
■
The actual clearance is 3m. (9.9ft.), being the height of the
antennas on the mast
2
.
Now let’s calculate the probable range for this example using the
formula introduced on page 3-2:
Range = Maximum Range x Cable Factor x Clearance Factor
1.
Looking at Table 3-2 on page 3-5, we learn that a High Speed
link between a 7 dBi Omni-Directional Antenna and a 14 dBi
Directional Antenna may cover a maximum distance of 1.8 Km.
(3.4 mi.), provided that the signal path clearance is 4.1m. (13.5
ft.) or better.
2.
Using a calculator we can easily determine that the actual
clearance of 3m. (9.9ft.) is about 75% of the required 4.1m.
(13.5 ft.) which equals a Clearance Factor of 75%.
3.
The Cable Factor is 65%, since all sites have been connected
via 22m.(75ft.) antenna cables (see Table 3-3 on page 3-8 and
the Cable Factor Diagram pictured in Figure 3-1 on page 3-9.
2
According to the information about dense urban areas described on page
3-11, we use the height of the antennas above the roof-tops of both
buildings to determine the level of actual clearance.
