Re: Cool Temperature Ranges Affecting USB Wireless Adapters Reception

On 25 Nov 2005 10:38:49 -0800, "frankdowling1@xxxxxxxxx"
<frankdowling1@xxxxxxxxx> wrote:

>I have been having trouble with USB adapters in colder temperature
>ranges.
>The manufacturers list a functional temperature range with low around
>35 degrees fahrenheit.
>You would not think with solid state electronics that temperature would
>have a great effect.
>At around that temperature ( 35 of so) the adapters power up fine. the
>computer knows it is there but there is no reception of any type.
>I have tried shorter usb cords and added a powered hub.
>Any connections are taped in plastic so as to avoid humidity shorting
>out the circuit .
>Anyone have any ideas or experience in this matter.

Sure. The problem is not cold but water. At temperatures just above
freezing or actually near the dew point, water will condense on your
USB adapter circuit board. It will detune antennas, short out
adjacent traces, act as an attenuator to RF radiation, and general
wreak havoc with the circuitry. If you're in a marine atmosphere, the
salt in the condensed water will do an even better job of shorting out
the board. Whatever "taped in plastic" is suppose to do does nothing
for condensation unless your box is hermetically sealed and
desiccated.

Your best bet is a polyurethane or acrylic conformal coating, such as
the various products made by Humiseal.
http://www.humiseal.com/protect/guide.htm
It comes in spray cans. You will need some tape or masking goo:
http://www.humiseal.com/temp.htm
to protect connectors, adjustments, and antenna surfaces. You'll also
need a UV lamp to inspect the results to be sure you've covered
everything. When I used to design marine radios, this was the stuff
we used to protect the boards.

You will have a big problem with circuit board antennas. The
dielectric constant of the conformal coating will probably detune the
antenna. Therefore, I suggest you consider using an external antenna.
This can simply be a half wave long dipole made from two pieces of
stiff wire. Just get the antenna off the board.

Good luck and don't do this in the kitchen.

--
Jeff Liebermann jeffl@xxxxxxxxxxxxxxxxxxxxxx
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
.

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