Proper AP Mounting
There are endless
ways to mount APs. Some APs come with versatile mounting brackets that provide
many options (see Figure 12-8a and 12-8b); others might offer only a simple
keyhole mounting option (see Figure
12-8c), in which case mounting possibilities are limited unless you
fabricate some type of bracket.
For antenna mounting, the style of antenna dictates the
available methods. You may need to purchase different antenna mounting brackets
for your particular site. Antenna mounting hardware is available from many
different vendors, or even the local two-way radio shop or hardware.
The reliability of the mounting (of both the APs and the
antennas) is a primary concern. The last thing that a customer wants is to have
something fall from the ceiling or wall and cause injury (or cause damage to the
WLAN devices) because of improper installation.
Some mounting methods are as simple as placing the AP on top of
a cabinet, desktop, cubicle wall, and so on, as shown in Figure 12-9. Such simple methods are common for small
sites that just require one or two APs.
Note
Make sure the antenna is not located next to the metal portion
of a cabinet or desk. In Figure 12-9, the
antenna sticks up vertically above any metal objects, so this is not an
issue.
Other mounting options include wall mounting and ceiling
mounting, as described in the next sections.
Wall Mounting
Wall mounting of APs is very simple, particularly when using
the standard type of antennas. Here you can use the small keyhole-type mounts if
the AP does not need to be mounted more securely. In some cases, the installer
will have a standard electrical box placed in the wall, with the Ethernet cable
run through the wall to the box. In such a case, a mounting bracket can be
screwed to the box and the AP mounted to the bracket (and secured, if
necessary). The AP covers the mounting screws and provides a bit more
security.
Figure 12-10 shows two
mounting examples. In both cases, the AP is mounted to a junction box in the
wall, where the Ethernet cable exits and attaches to the AP without being
seen.
When mounting to a wall, you generally place the AP as high as
possible. However, you need to be aware of a few issues when wall mounting an
AP. First, if the AP is using an omnidirectional antenna, as is the case with
both APs in Figure 12-10, try to position
the antennas between the wall studs so that there is limited interaction with
the studs (especially if they are metal studs). Second, position the antennas
vertically. If the AP is mounted like the example in Figure 12-10a, one dipole will point up and one will point
down. This positioning provides omnidirectional coverage and diversity
support.
Another issue to investigate is what is behind the wall. If you
install an AP with omni-directional antennas on a wall that has something on the
other side of it that might create multipath signals or interference, AP
coverage and performance might be detrimentally effected.
Finally, when wall mounting an AP, do not place the AP so far
up the wall that the antennas are close to the ceiling. In the case of drop
ceilings, the metal support structure can cause the antenna performance to drop
off. If the ceiling is made of drywall, there might be metal corner beads at the
ceiling and wall junction. It is best to have the antennas at least a few inches
below the ceiling.
Ceiling Mounting
The most
common type of mounting is ceiling mounting, which provides the best overall
coverage for the AP and the easiest access for running cables. If the AP has
self-contained antennas (nonmovable antennas), the product might not radiate
well when placed on the ceiling. The site survey engineer should address this
issue by identifying the mounting orientation in the site survey report. If the
AP uses a standard-type dipole, the antennas should hang straight down from the
ceiling, as shown in Figure 12-11.
In many cases, the APs will be mounted above the ceiling tile
and the antennas below the ceiling. When mounting in this fashion, you need to
attach the AP to some structure, not just place it on top of a ceiling tile
(which is actually quite common). The best method is to mount the AP to the
building structure, such as to an I-beam. You can buy clamps at any
electrical-supply outlet and even some home-improvement centers to securely
attach WLAN products to an I-beam.
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