Jeff Duntemanns Drive-By Wi-Fi Guide
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An Enclosure Example
Figure 16.6 is a photo of a workable 30 caliber ammo can installation for a D-Link DWL-900AP+. There was plenty of room in the can for everything. The can is mounted upside down atop a length of 1/2' water pipe. A 1/2' galvanized pipe floor flange is bolted to the lid of the can with four º-20 flat-head bolts. A 5/8" hole is drilled through the lid beneath the center of the floor flange. The CAT 5 Ethernet cable, carrying power for the access point, is run up the water pipe and through the 5/8" hole into the can.
A female bulkhead N connector passes through the lid of the can. On the inside of the enclosure, a 19" pigtail connects the access point antenna connector to the N bulkhead connector. Outside the can, the parabolic grid antenna is bolted to the pipe mast close enough to the enclosure that the antenna's built-in pigtail reaches the bulkhead N connector directly, making more connectors and coax (with their attendant losses) unnecessary. Ordinarily I'd like to leave a little more room between the enclosure and the antenna, but in our tests the signal doesn't appear to suffer.
In my ammo can unit I mounted the D-Link AP to a piece of scrap aluminum sheet metal to keep it from rattling around inside the can. There are bolt slots in the base of the DWL-900AP+ that made this easy. Drilling into the AP's case was unnecessary. The sheet metal to which the AP is mounted is in turn bolted to a piece of scrap aluminum angle stock that attaches to the ammo can lid under the hex nuts holding the lid to the pipe floor flange.
The D-Link PoE tap has no holes with which to mount it, so I bent a clip out of scrap sheet metal to hold the tap, and bolted the tap bracket to the vertical sheet metal piece with small machine screws. A closer-in view of the assembly from above is shown in Figure 16.7.
Figure 16.8 shows the assembly up on the roof during final testing, with the can closed and everything running. I have some concerns as to the ability of a setup like this to survive an Arizona summer. D-Link indicates that the DWL-900AP+ is rated for operation from 32 º F to 131 º (0º-55 º C) but I have no idea how hot it will get inside the can in July; we'll just have to wait and see. Painting it white will certainly help. An associate asked how an enclosure might be constructed to allow a bridging AP to survive a Maine winter. Personally, I don't do winter, but as D-Link only rates the DWL-900AP+ down to 32º, I'm far from sure it would survive a Maine summer.
Don't forget to weatherproof your enclosure before committing it to the outdoors. (The photos in this chapter show the unit during testing, before weatherproofing.) A liberal coating of exterior silicone caulk on the face of the floor flange before bolting the flange to the lid of the ammo can is essential, as is tape-wrapping or shrink-wrapping the N connector on the underside the assembly. Do whatever you must to keep water out of the N connector between the enclosure and the antenna; water and microwave transmission do not mix!
An enclosure like this doesn't necessarily have to be used for bridging. If you have to serve a sizeable open area, it can help to put an AP up in the air on a pole, working into an omnidirectional or sector antenna instead of the highly directional antenna used for bridging.
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