OT: wifi antennas

[Les]

On Wed, 2009-01-28 at 21:14 +0000, Paul Smith wrote:
> On Wed, Jan 28, 2009 at 12:18 PM, Anne Wilson <annew at kde.org> wrote:
> >> >>> Could someone please advise me regarding USB antennas to improve the
> >> >>> reception wifi Internet signal?
> >> >>
> >> >> A wifi antenna doesn't normally connect via USB, but via a screw-on
> >> >> coaxial connector (a smaller version of what you find on cable TV
> >> >> boxes).
> >> >>
> >> >> Hawking makes a number of different external antennas which seem
> >> >> to work fairly nicely.  Make sure you get one compatible with your
> >> >> wifi setup (e.g. 802.11A and 802.11B/G use different frequencies).
> >> >
> >> > Also, I believe that some really only work with matching hardware.  I
> >> > added an Edimax antenna to my router, and it actually gave slightly less
> >> > signal than the router's own antenna.
> >>
> >> Most of the add-ons are highly directional (mine are, but I want them
> >> that way).  That may also play a part.
> >
> > I did know that, but no matter what I did, I couldn't get a good result.  I
> > think it was a mis-match, somewhere along the line.  I have a couple of Edimax
> > PCI cards.  Maybe when I have time to play I'll experiment and see if they get
> > a better result.
> 
> I would like to thank all respondents for your help.
> 
> Paul
> 
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.

Regards,
Les H