Information Technology Reference
In-Depth Information
the light decreases almost to darkness. If the light passes through a window screen
or curtains, some of the light gets through, but it is much dimmer. It is just as if you
had increased the distance. That simulates the attenuation of ultrahigh-frequency
signals, except that real radio waves can go right through objects, such as plaster-
board, that are quite opaque to light.
While this method is very useful in WLAN planning, please don't tell anybody
else you are doing this, and do try to keep it to a minimum. We wouldn't want you
running around acting as if radio waves are real.
Outdoor Operation
Outdoor operation of a WLAN has two requirements that differ from the indoor
counterparts. Those are the use of weatherproof wireless antennas (see Fig. 13.4),
and the concept of LAN-to-LAN bridges. The first requirement is really rather triv-
ial, as it exactly mimics the indoor operation, except that a waterproof antenna and
cable are used, lightning protection must be provided, and special antenna mount-
ing hardware and structures are required.
As with any outdoor mountings, you must make a stable mechanical mount-
ing, and allow for the effects of wind, rain, sun, snow, and ice.
The outdoor Yagi antennas for 2.5 GHz and above are often mounted with plas-
tic radome coverings that protect the antenna from many of the effects of weather and
corrosion. You should use highest-quality connectors on the connecting coaxial cable,
and protect them from the elements with a clear silicone rubber material that is
designed for this purpose. The sealant is available in most stores that sell TV antennas.
While national and local codes provide the exact specifications for lightning
protection of outdoor antenna systems, common sense should insist that you pro-
vide the very best protection for the sensitive networking equipment that you can.
Run the drain wires to appropriate ground rods or approved structures. Lightning
happens … don't let it be your problem.
Outdoor operation can be also multipoint, with an omnidirectional antenna,
and you could certainly connect to laptop computers outside. This would techni-
cally be an outdoor application.
The LAN-to-LAN bridge, however, is generally what most vendors mean when
they refer to “outdoor” operation. Point-to-point or point-to-multipoint operation
often requires special operating software for the bridges, in addition to the same
weatherproof antennas and mounts.
If you are connecting from a multiple-station LAN on one side of the link to a
multiple-station LAN on the other side, you will need two bridges with the special
inter-LAN connection software. Some bridges actually have two wireless transceiver
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