Archived from groups: alt.internet.wireless (
More info?)
"Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> wrote in message
news:imi3g0prhidorkqetkfikmm4i0cfc37b9m@4ax.com...
> On Fri, 23 Jul 2004 21:02:08 -0500, "Bob Alston" <bobalston AT aol
> DOT com> wrote:
>
> >OK Thanks. And YEs, I did mean cheap. I was thinking Rubermaid type
boxes.
>
> Groan.
>
> >1) Do I need any kind of vent - for condensation or heat elimination? I
> >would guess there is not much heat in a WAP.
>
> In a previous life, I designed marine radios and some marine telemetry
> (SCADA) hardware. Environmental packaging is an art.
>
> >2) What about cold weather? This unit would be installed in Michigan.
> >Clearly having weather below the 32 degrees F. that is the lower end of
the
> >WRT54G unit's operating spec?
>
> It's difficult to say what is adequate without knowing all the
> environmental issues. I seriously doubt that the WRT54G will work
> properly below 0C. The problem is not the cold temperatures, but the
> condensation that comes with cold temperatures. Water under
> components can easily crack the components or delaminate the circuit
> board traces. Most access points are designed with fairly high
> impedances, with little consideration for condensation or water
> incursion. At 2.4GHz, water is a dead short, so water in the RF
> portions of the board, in the coax connectors, and in the coax cables
> is fatal.
>
> Basically, you need to protect the board from water. The easiest way
> is to coat it with some kind of waterproof coating. Clear acrylic
> paint works well, but not at 2.4GHz as it's slightly hydroscopic.
> Polyurathane works well, but can make a horrible mess.
>
http://www.humiseal.com
> Wax coatings work really well, but don't complain about what it looks
> like after it gets a good dusting. Download and read all about it:
>
http://www.humiseal.com/protect/guide.htm
> Be sure to mask of any electrical and RF connectors (with masking
> tape) before spraying. You don't need an insulating layer in a
> connector. Don't ask me what to do inside the PCMCIA radios found in
> most wireless bridges/routers. I guess you tear it apart and spray
> it.
>
> One really big help is to mount all the electronics vertically. The
> idea is that if there is any water that condenses on the board, it
> will eventually run down to the lower board edge and drip off.
> Horizontal boards make puddle collectors.
>
> The next step is to prevent condensation. You can do it by either
> keeping the internal temperature above the dew point, or by
> hermetically sealing the box and filling it with dry air (or dry
> nitrogen). Most outdoor access points have some kind of heater that
> kicks at about +10C. If you have power to spare, I suggest a
> thermostat and a heater in the box. You might wanna look at how Dlink
> does it with their outdoor radios.
>
> I'm partial to the hermetically sealed approach for both the box and
> any Heliax coax cable. However, finding pressure tight connectors is
> difficult, especially for RJ45 connectors. If you don't mind
> overpriced military grade pressurize connectors, it can be made to
> work. You'll need a sturdy, waterproof, NEMA something enclosure,
> with a bicycle valve seal and a pressure gauge/alarm. A bottle of dry
> air will keep the pressure above ambient. If the box is going up a
> tower, don't bother as the bottle will need to be fairly close to the
> enclosure.
>
> At the other end of the environmental hassle is dissipating the heat.
> Most access points burn about 5-10 watts. The larger units (Soekris)
> burn over 15 watts. If you build the box as an insulated enclosure,
> the heat will build up and eventually cook the electronics. A clear
> case will act like an automobile in the sun, where UV going through
> the clear glass converts to infra-red and gets trapped inside.
> Instant oven. So, some effort should be made to keep solar heating at
> a minimum. I guess the impressive looking clear case is out.
> Something white to reflect the heat might be nice. Any large heat
> sinks on power regulators should be bolted to the case to help radiate
> the heat to the outside air.
>
> Notice I haven't just handed you an answer. I don't think I can
> design an enclosure for the WRT54G that would work without some
> careful calculations and measurements. I certainly don't think it can
> be done with a Rubbermaid box, no conformal coating, no heater, and a
> general lack of waterproofing. Forget about doing it cheap and get a
> real NEMA enclosure.
>
>
> --
> # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
> # 831.336.2558 voice
http://www.LearnByDestroying.com
> # jeffl@comix.santa-cruz.ca.us
> # 831.421.6491 digital_pager jeffl@cruzio.com AE6KS
Thanks. I think I am convinced. No outdoor mounting of the WRT54G.
--
Bob Alston
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