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Re: OT: wifi antennas



Les wrote:

> Antenna's are more complex than they appear.  Think of how a bell
> sounds.  If you change the shape of the bell a bit, its sound changes,
> and the area over which it can be heard also changes.  Antenna's are
> like that.  Moreover a bell has one dominant mode or tone.  Antenna's do
> that too.  But WiFi is not antenna friendly.  It is comprised of many
> tones, spread over a wide range, kind of like a piano keyboard.  So the
> antenna needt to match that frequency, and work for all the associated
> tones.  In addition there are requirements for the area over which it
> can be heard.  RF engineers call that the radiation pattern.  Some
> antenna's radiate in a donut pattern.  This is the basic type of
> antenna, called a dipole.  BUT the radiation that is above and below the
> desired places where receivers might be is wasted, so good WiFi antennas
> are designed to squish the donut, and that squishing causes more
> radiation in the desired areas and less radiation in undesired areas,
> which the antenna manufacturers call "gain".  In other words the signal
> travels farther in the desired direction.  So for a good wifi device
> antenna, the radiation pattern should be flat (gain of 3-5 db), and the
> graphic of the radiation should be a sort of wheel laying on its side.
> 
> To make this work, the antenna needs to match the transmitter for
> efficient power transfer, and it needs to be mounted away from
> interfering objects at least 3 wavelengths (about 1yard or 1meter from
> walls or objects as tall or taller than the antenna).
> 
> Hope this gives you some background and some idea of how to get the best
> from your antenna purchase.

I wonder if this is true?
My impression is that the most important factor is the number of walls
and ceilings that the signal has to pass through,
and particularly the material these are made from.
I don't think the position of the antenna in the room is that significant.
I suspect it is almost impossible to work out how the wireless waves
are reflected from walls and other objects.

Incidentally, I have one very good external antenna, from Avaya.
It attaches to the back of an Orinoco gold card,
which in this case is in a PCI adaptor.

I see that Linksys (Cisco) sell quite a cheap WiFi extender.
I don't have one, but as far as I could see it is designed
to re-broadcast the signal.





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