[svlug] Wireless cards and distance and intervening walls etc

Vince Duperron duperron at charter.net
Sun Jul 14 13:17:31 PDT 2002

> The machine that is unreliable has more walls between it and the server, 
> and there is a bathroom between, but the distance in each case is no more 
> than 20 meters (~60feet).
> Has anyone seen this. If I replaced the server's card with one with an 
> external aerial, is that more likely to work?
> Finally, are there any software tool I can use to check signal strength 
> that the cards are seeing?

802.11 uses a microwave signal to transmit data between stations.
At the frequency it uses (about 2.4GHz) walls are semi-opaque.
Opacity varies with material and thickness.  Some things to 
keep in mind when operating at this frequency.  A wavelength 
is about 12cm and a quarter wavelength is about 3cm.
Movements of the transceiver about this much can mean the difference
between good and bad signal.  Items about this large may interact strongly 
with the signal.

You might try moving one, or both of the stations.  An external
antenna might help, especially if the antenna has gain (a tiny 
yagi-uda, for example).  Even a quarter wave antenna may be better
than the antenna built into the card.  A quarter wave antenna is
a piece of wire about 3.1cm long.  Ideally it would be placed
above a metal plane (top of your computer case?)  You might try
placing a 3.1cm long wire into the card antenna connector and
see if it helps.  If the card is inside of your computer case,
try removing the case and see if that helps.  A metal case
would be very effective in blocking radiation from your

To measure the effect of your changes do:
cat /proc/net/wireless

Hope this helps


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