How high should
I place my outdoor wireless Access Point antennas?
This depends upon a lot of factors. If you have a building
with roof access, this is usually the best option, since the
feedline losses may be minimized if the equipment can be placed
near the antennas. A minimum height is usually around 75 feet.
This places the antennas above most trees. This height will
also give a radio horizon of approximately 12 miles, assuming
flat terrain. If you have taller trees, or tall buildings
nearby, you may wish to use an antenna height of 200 feet
or more. This gives a radio horizon of 14 miles. As towers
may fall under local zoning ordinances, you may also wish
to consider water towers, grain elevators or utility poles
as other options. Placing Aceess Point antennas higher than
100 feet exposes them to greater amounts of interference,
more feedline losses, zoning restrictions, FAA lighting requirements,
and larger cell areas. Existing towers may be located using
these sites - TelecomSiteSource, FCC Antenna Structure Registration
and Wireless Radio Tower Locator. Grain elevators may be located
using this site - Grain Elevator Locator.
What are the advantages
of using sector antennas instead of an omni?
There are several good reasons to use sector antennas:
More capacity - By using 3 sector antennas on DSSS channels
1, 6 and 11 with 3 AP's, you can triple the number of clients
in a given area.
Better signal levels - Sector antennas usually have more gain
than omni's and can be mechanically downtilted to focus where
the users are. This results in fewer retries and less packets
lost. A WIPOP sector antenna will pay for itself if just one
customer did not need an amplifier.
Channel Re-Use - Because the sector antenna can be downtilted,
the signals are not thrown out to the horizon. This allows
that channel to be re-used several miles away at a different
Eliminate interference - Because a sector antenna is directive
and usually has good front-to-back (F/B), it can reduce or
eliminate interference from sources that are behind the sector
Example of channel reuse
do I hook up four 90 degree sector antennas on one tower?
Conventional thought says that there aren't enough non-overlapping
2.4 GHz DSSS channels to put 4 channels on one tower. Usually,
panel antennas with high F/B are selected, and channel 1 antennas
are placed on opposite sides (e.g. North & South) and
channel 11 antennas are also placed on opposite sides (e.g.
East & West). If separate access-points are used for all
4 antennas, the isolation may need to be increased between
antennas on the same channel by spacing them farther from
the tower face or on opposite corners of a building. FHSS
systems may use separate frequency sets on each panel without
However, there is new evidence that supports
the use of DSSS channels 1,4,8 and 11 on the same tower. A
white paper from Cirond Networks discusses this possibility.
Also, check out this article from ExtremeTech. Isolation will
need to be increased between antennas in this case by spacing
them farther from the tower face, or by vertical separation
of 10 feet or more.
What wireless antenna
should I use to cover a small campus area of a few buildings?
If your coverage area is small with distance to the hub of
less than a mile (1.6 km), a small omnidirectional antenna
such as our 2426AA (5 dBi gain) or 2437AA (7.5 dBi gain) may
be used. If the AP will be located on the edge of the campus,
a 120 degree sector antenna such as our 2443AA 12 dBi panel
antenna may be used.