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rooftops.


Measure Twice, Cut Once
Place the access point and PoE adapter into the case and arrange them for best ventilation and
fit. Then add the internal cables and confirm that it still fits. It may be better to replace a sup-
plied cable with a shorter version, especially for stiff Ethernet cables. As shown in Figure 8-16,
lay out all the parts before modifying the case to ensure everything fits. All cables should exit
the case at the bottom to help stop water from entering.
Next, add the pigtail and outside Ethernet cable. The pigtail may be thick and stiff, so antici-
pate carefully where it will run. It is important to have all cables exit from the bottom of the
case. This stops water from running down the cable and into the case.




FIGURE 8-16: Finding the optimal device layout and cable management.
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Chapter 8 ” Build Your Own Outdoor Access Point


When everything is in place and connected, then you can plan where the holes will go.
If the fit is snug enough for everything in the plastic food container, leave the access point and
PoE adapter loose in the enclosure. This will eliminate the need for extra holes and mounting
hardware.

You can remove the access point electronics from its plastic case to reduce the space needed and
enhance cooling. However, this may void the warranty, and you have to be extremely careful
that no metal touches the electronics.


Be sure to plan for the case mounting to the pole or wall as well. If bolts will protrude into the
case, as shown previously in Figure 8-9, make sure the equipment will still fit.
When everything is in place, mark the case carefully to show where holes and mounting points
are located. Then you™re ready to start drilling and cutting.


Modifying the Case
The plastic case is easy to modify using simple tools like a drill and small handsaw.
First drill holes in the case where the cables will pass through (see Figure 8-17). Make sure
your drill bit matches the cable thickness. The cable should be snug, but not pinched. Any
extra gap can be filled with sealant.




FIGURE 8-17: Drill the case first, then cut down to the holes.
194 Part III ” Playing with Access Points


With a plastic case, you can cheat a bit and cut a line down to the holes. The plastic is flexible
enough to bend and allow the cables to pass down to the hole via the cut.
If you™re using a metal or thick molded plastic case, you have a few options:

Make much larger holes to pass the connector through. You can use sealant to fill in the
gaps afterwards.
If you have an Ethernet cable crimper and plugs you can thread the bare cable through
the hole and add your own connector afterwards. This would be more difficult for the
pigtail, but fortunately, pigtail connectors are usually smaller anyway.
Saw a channel down to the hole using two cuts instead of the one shown in Figure 8-17.
You can put the holes closer to the lid to minimize cutting and sealing.

A thin metal file like a rattail file is useful for smoothing out holes or even cutting channels.
When using plastic, bend the plastic to thread the cables through the cut. The cable should be
snugged but not pinched in the hole. (See Figure 8-18.)
If the enclosure is larger than the plastic box shown here, you may need to mount the equip-
ment directly inside the box. The plastic box shown is already snug and there™s no exposed elec-
tronics, so no mounting is needed.
Condensation can form on the inside of a metal case during changing temperatures, so mount
equipment away from the walls to avoid water running onto the electronics. Another reason to




FIGURE 8-18: Cables exit the case without strain or pinching.
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Chapter 8 ” Build Your Own Outdoor Access Point


mount equipment inside the box is to avoid movement and damage in high winds or even dur-
ing installation. Also, connectors may develop poor connections over time if they™re continually
moved or strained.
Make a final check to ensure that everything fits as you expect and that nothing is touching or
rubbing where it shouldn™t be.


Mounting the Case and Antenna
The case is now ready to be mounted on a pole or wall. The steps are:

1. Mount the case on the pole
2. Mount the antenna on the pole
3. Connect the lightning arrestor, antenna, and pigtail
4. Make the connectors watertight
5. Zip tie the cables, leaving drip loops (drip loops give water a place from which to fall)

Mount the case on the pole and then mount the antenna using the instructions that came with
your antenna and its mounting hardware. Add the lightning protector between the antenna
and pigtail and attach the bare copper grounding wire. (See Figure 8-19.)




FIGURE 8-19: Placement of the lightning protector on the pole.
196 Part III ” Playing with Access Points


Screw the lightning protector into your antenna connector and then attach the pigtail to the
other side of the lightning protector. Add the 8 gauge grounding wire to the lightning protec-
tor and run it down the pole with your other cables.
As you work with the cables, be sure to add so-called “drip loops.” These are loops in the cable
where rain will naturally drip off instead of running down the cable and inside connectors or
cases. See Figure 8-20 for an example of a drip loop. This simple cabling trick keeps water
from pouring down onto the connectors.

Anatomy of a drip loop:

Leave a curve in the pigtail as it exits the bottom of your case before it goes back up to
the antenna. Rain will run off the case and down your cable until it gets to the curve and
drips off. If you have the cable so tight that it doesn™t have a curve, then water may run
down the cable from the antenna and into your case.
If your antenna has a short length of cable on it before the connector (rather than a fit-
ting right on the antenna), you may have enough room to put a loop in the antenna cable
before it goes into the lightning protector. Again, this will allow rain to run down the
antenna, down the antenna cable, and then drip from the bottom of the loop”instead of
running down the antenna cable and right into the lightning protector.


To Antenna Connector




Access Point
Connector




Rainwater Runs
Down Cable



Drip Loop




Water Falls
From Drip Loop


FIGURE 8-20: Diagram of a drip loop.
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Chapter 8 ” Build Your Own Outdoor Access Point


Put a complete loop in the Ethernet cable where it exits at the bottom of the box and
fasten it to the pole. This is the least critical cable as it has no outside fittings, but it™s still
good to get water off the cable

Use plastic fasteners, such as plastic zip ties, to hold things in place. However, don™t tighten
them too much on the antenna or Ethernet cables. This dents the cable, which reduces its
effectiveness and decreases your signal.

If you have a choice, buy plastic fasteners labeled “UV resistant.” Otherwise, they may become
brittle and break due to sun exposure.



When all the cables are in the correct places, it is time to waterproof the connectors and install
the final cable ties.
For most installations, standard electrical tape will work great for waterproofing (see Figure 8-21).
Apply the tape liberally by wrapping from the bottom to the top with lots of overlap. You may
need to remove and reinstall some of your cable ties to do this properly.

Applying the electrical tape from bottom to top helps stop rain from creeping under the edges
and loosening the tape over time.




FIGURE 8-21: Wrapping the connectors in electrical tape.
198 Part III ” Playing with Access Points


For extreme weather conditions, there are lots of exotic waterproof solutions, including waxes,
glue-like materials, and layers of different types of tape. Search online for waterproof connector
tape to find a solution that meets your needs and budget.
When you™re all done, stand back and admire the beauty of your creation. (See Figure 8-22.)


Temperature and Water Testing
There are just two steps left before climbing on the roof. Temperature testing ensures that the
access point electronics stay within tolerable limits. If things run too hot, frequent errors and
lockups can occur, and the lifespan of your equipment will be diminished.
Test for water tightness in the optimal working conditions: while it™s dry and sunny. Your
nerves will be rattled enough worrying about the equipment in a rain storm, even if you know
it passed water tests on the ground.

Temperature Testing
Look carefully at your access point. Chances are, there are ventilation slots in its case. These are
designed to encourage a convection flow of air to cool the electronics. Now that it is enclosed
in your outdoor case, it won™t be cooled as originally intended, so you need to see if the box
needs ventilation holes.




FIGURE 8-22: It™s a beautiful thing!
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Chapter 8 ” Build Your Own Outdoor Access Point


Plastic cases tend to get hotter inside than metal cases. The metal walls drain heat from air
inside the case, which keeps it closer to the outside air temperature. For the same reason, it™s
important for the metal case to be a light color. A black case can get very hot and makes it hot
inside. For a great demonstration of this, touch a black car and a white car that have both been
in the sun for a while.
Here™s how to temperature-test your case:

1. Find a suitable thermometer and put it in your case. Use the manufacturer™s stated operat-
ing temperature as a guide for selection. For example, the pictured D-Link has a range of
32 to 131 F (0“55 C), so you can use an oven or BBQ thermometer if it starts around
100 F (37 C).
2. Find a convenient shaded location, plug the Ethernet cable into the PoE adapter and
your home network, and test that everything is working okay.
3. Close the case up as it will be when finally mounted.
4. Stress the access point by copying a large file via wireless from another computer on your
network. This will ensure a high-speed transfer that will heat everything up more than
running at idle.
5. Check the temperature frequently at first, to be sure you don™t fry anything.

If you can read the temperature without removing the thermometer, you™ll see when it reaches a
steady state and you can stop. Otherwise, a few hours should be enough.
If the box gets too hot, then add cooling holes in a way that keeps the box dry inside. You could
start by adding an open hole at the bottom. Then if water does find its way in, it will eventually
drain out.
Another way to cool a plastic box is via the mounting bolts that go through to the mast. Screw
a heat sink to those bolts on the inside of the case. This will transfer heat from inside air to the
outside mast via the metal fittings. The heat sink can be as simple as a piece of scrap metal that
fills the entire bottom of your case. See Figure 8-23 for an example.
When it™s running at a good temperature in the shade, move it to an environment that matches
your final location, such as in the sun. Then repeat the test steps and confirm that it™s still okay.
If the box won™t stay cool enough, some possibilities are:

Add a matching hole near the top, on a side, and at the bottom to encourage convection
cooling. Keeping water out might be hard though.
Find a different mounting case (for example, switch from plastic to metal).
Add a case fan (a simple solar powered fan would be easiest).
Find a cooler location to install the box (such as under an overhang in perpetual shade).
If the case is close to the maximum temperature, install it anyway and plan on replacing
the access point after its run hot for a few days, weeks or months (this might be cheaper
to try than messing around a lot with the case).
200 Part III ” Playing with Access Points




FIGURE 8-23: Diagram of a heat sink installed in a container.



Water Testing
Now the final step, will the box stay dry inside? Grab a bucket of water, dunk it, and find
out”no wait, just kidding!
Seriously, it is useful to see how watertight your box is, but you need to do it the right way. A
garden hose on a gentle spray setting is a good way to start, or under a shower nozzle. Be sure
to simulate rain by holding it above your case and then leave it there for several minutes before
checking. Place toilet paper in your case before testing to provide a fast visual indication that all
is still dry. Leave everything powered off while you™re doing these tests.
Gradually increase the test length until you get to 20 or 30 minutes of gentle spray. Pat yourself
on the back for a job well done when you retrieve your nice dry toilet paper afterwards.
Congratulations!
If the case leaks, find a tube of outdoor sealant at your local hardware store and apply appropri-
ately. Realize that when you seal, it blocks cooling, so it™s prudent to retest your operating
temperature if you need to add a lot of sealant. Repeat until dry.

Make sure that all electrical equipment is completely dry before you apply power. Expect 30 min-
utes or more (depending on the weather) for the slow effects of evaporation to dry out electrical
equipment.
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Chapter 8 ” Build Your Own Outdoor Access Point


Put it On the Roof Already!
After all the assembly and testing, everything is ready to go. Find a nice safe ladder and mount
your new outdoor access point.
Run the Ethernet cable back inside the house, plug it into the PoE adapter and confirm that
everything is working.

Some areas receive frequent lightning strikes. Before mounting your access point outside in such
an area, find some local person who understands grounding and follow his or her advice. Local
amateur radio operators are a great source of information, as are TV or cable installers. Your local
fire department can also provide information and resources.


Last, but not least, find a good ground for the lightning protector grounding cable.
The 8 gauge copper wire should be run via the most direct route possible to a ground
rod. Ground rods should be either solid copper, copper-clad steel, hot-dipped galvanized
steel or stainless steel. They shouldn™t be smaller than 8 feet in length and 1/2 inch in
diameter.
You™ll need fittings designed for grounding to connect everything together. Ground your case
(using the same wire) if it is metal. You may be able to use a metal water pipe in place of a
ground rod. Clean the pipe with a wire brush to expose bare metal and use a fitting designed
for grounding to attach the ground wire to the pipe.
Complete grounding protection advice is beyond the scope of this book. Search online for
“antenna grounding lightning guide” for more information. Some useful starting places are:
www.qsl.net/ccarc/light.html
www.polyphaser.com/ppc_pen_home.asp
With grounding completed and unit powered on, you™re ready to e-mail the neighbors to start a
nightly WLAN party gamefest.




Taking It To The Next Level
Now you™re sharing with the neighbors and surfing from the park, what™s next? So glad you
asked! How™s this for starters:

Traffic plotting ”Track your network usage over time. Maybe it™s time to upgrade your
connection, or block that neighbor downloading movies 24 hours a day.
Do-it-yourself access point ”Why buy something off-the-shelf when you can pay twice as
much to build it all yourself (but have a lot more fun doing it)?

There isn™t enough space to cover these topics in detail, but here are some pointers to get you
started.
202 Part III ” Playing with Access Points


360.0 k
Bits per Second
270.0 k

180.0 k

90.0 k

0.0 k
Week 04 Week 05 Week 06 Week 07 Week 08

FIGURE 8-24: Traffic mapping graph.



Traffic Graphing
Some access points support Simple Network Management Protocol (SNMP) and use it to pro-
vide basic traffic statistics. With the right software, you can retrieve these statistics and log
them over time to produce graphs like the one shown in Figure 8-24. In this residential wire-
less LAN, traffic peaks each evening after work. Business hours are the best times for large
downloads.
The classic free server software for producing graphs is Multi Router Traffic Grapher (MRTG)
at http://people.ee.ethz.ch/˜oetiker/webtools/mrtg/. It™s still popular, though its
more powerful successor RRDtool is gaining ground via add-ons such as Cacti
(www.raxnet.net/products/cacti/).
To use this and similar software, you™ll need a machine running Linux and either some reason-
able Linux skills or a lot of patience to get it running.
Another option is to run the monitoring software directly on your desktop machine. The main
disadvantage is that the machine needs to be on all the time to gather full statistics. Many free
and shareware programs are available.
A good starting point for SNMP monitoring software is the Google directory at:
http://directory.google.com/Top/Computers/Software/Internet/Network_Management/


Do-It-Yourself Access Point
A typical consumer access point consists of a custom-designed computer board running a low
power (though high-speed) Million Instructions Per Second (MIPS) processor, a stripped-down
radio card, and some fancy custom software.
With a little time and exploration, you can build something with much greater capabilities,
including more power, more fine tuning possible, and extra features only limited by your skill
and imagination.
One popular alternative to off-the-shelf access point hardware is the Soekris single board
computer using a mini-PCI wireless card (see Figure 8-25). With some special software,
a little configuration and a PoE adapter, this board becomes a professional-grade access
point.
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Chapter 8 ” Build Your Own Outdoor Access Point




FIGURE 8-25: The Soekris single-board computer configured as a wireless access point.

DIY Hardware
The logical hardware for a homebrew access point is a PC-based architecture. They™re cheap,
plentiful, and well supported with free software. An abandoned 486 computer with a tiny hard
disk will be more than sufficient to make a powerful access point.
However, if you really want bragging rights at your next geek meeting, then take a look at cus-
tom “single-board computers” that strip out all the unnecessary PC parts like video and key-
board support, video display and hard disk drive controllers. Some manufacturers of these and
similar hardware are:

www.soekris.com
www.pcengines.ch
www.mikrotik.com
www.openbrick.org

They use a compact flash card as a hard disk and thus have no moving parts, are very low
power, and run silently.
You™ll need to add a radio card for wireless support. Wireless radio cards previously come pack-

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