Antenna Selection - Nokia RoofTop R240 User Manual

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Radio line of sight
A radio wave is not like a laser with a narrow, pointed beam. RF waves
fan out from a single source and are diffracted or absorbed by objects that
are near the visual line of sight. This area is called the Fresnel Zone. Clear
radio line of sight exists when there are no physical obstructions in the
Fresnel Zone. It is therefore essential that there is a clear radio path by
raising the antenna as high as possible and away from objects near the
radio path.
An example of the Fresnel Zone dimensions is, for a one quarter
NOTE:
mile link, the Fresnel Zone is approximately 7
the line of site. Therefore the height of the antenna must clear the Fresnel
Zone. For very short distances, wooden structures and non metallic
objects have little effect on the RF signal. For long distance paths, there
should be no obstacles close to the RF path.
3.1.1.2 To determine line of sight
1.
Access the rooftop using a safe ladder, either tied or held by another
surveyor.
2.
Scan the other rooftops in the location. Ensure line of sight ensuring
that other routers can be seen from the selected vantage point.
The router being installed may be the first in the area. If this is the
NOTE:
case, ensure that the other rooftops in the area can be seen from the
selected vantage point.
3.
If it is not possible to see other routers/ rooftops, it may be necessary
to install the router on an adjoining tall structure, or to install a mast.

3.1.2 Antenna selection

3.1.2.1 General
In most installations, it is not necessary to be concerned about antenna
selection. The Nokia Wireless Router is supplied with an omnidirectional
antenna which is good for most installations.
Nokia RoofTop™ Wireless Router Installation Guide
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/ feet above and below
2