<OT> Wireless Access Point

[Colin McGregor]

"Peter L. Peres" <plp-ysDPMY98cNQDDBjDh4tngg at public.gmane.org> on Wednesday, October 01, 2003 1:24 PM
wrote:

> On Tue, 30 Sep 2003, Wil McGilvery wrote:
>
> > What I am wondering is if anyone on the list knows of a better way to
> > pinpoint the location of a wireless access point.
>
> There would be the trick of making the antenna directive and taking a
> bearing or two. You can do this using yourself (your body) as movable
> attenuator screen. Put the laptop on a non-metallic desk and slowly walk
> around the desk while keeping fairly close to the laptop. When the
> fieldstrength indicator dips you are cutting the main vector that ties the
> laptop to the transmitter. Keep in mind that there will be reflected paths
> too so there will be several dips. The biggest one is the one you are
> looking for.

A directional antenna would likely be the easiest route in this sort of
case, it isn't the only way to attack the problem. There is what is known as
time domain direction finding, where one has several non-directional
antennas and then one compares when the signal arrives at the different
antennas (i.e.: the first antenna to get the signal is the closest and which
antenna gets the signal second will help refine the direction, etc...). The
good thing about time domain direction finding is that it is fast, it can
determine the position of a transmitter in effectively no time since it
doesn't have to shift a directional antenna around. The bad news is time
domain direction finding is a complex pain to set-up (not an issue for hams
who have made direction finding part of their hobby, nor is it an issue for
the military, where speed in locating of a transmitter can be an issue of
life and death...).

Colin McGregor - VE3ZAA

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