half-baked

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The wavelength of a 2 KHz sound wave and a 2 GHz radio wave are almost
the same. If I set up a small speaker as a sound source and go running
around the house with a sound level meter, can I get an idea of where
the radio waves will go? This may not work well for absorbtion by
walls, etc. (perhaps a conversion formula can be applied) but it might
work ok for diffraction around corners and at the edges of objects in
the signal path. A speaker wouldn't be an isotropic radiator but
perhaps there's a way to make it approximate one.

Bruce

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Isn't it just as easy to place an AP and run around with a laptop and
netstumbler or similar? :)

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wrote:

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Yes, that probably makes more sense. By the way, do you know of other
applications similar to Netstumbler?

Thanks,
Bruce

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Kismet, Wellenreiter, Boingo client and if you want to go spend a whole
load of money...Airmagnet.

David.

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Here's a propagation calculator that takes diffraction from rounded
surfaces and other parameters into account:

http://www.cjseymour.plus.com/software.htm

It's the second program listed.


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ping me an email and i'll demo what airmagnet does.

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bseiler @ xspampatmedia.net
without spaces and xspam


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Well, let's see.
Sound:
  330 meters/sec / 2000 cycles/sec  = 16.5cm wavelength
RF:
  3E8 meters/sec / 2.4E9 cycles/sec = 12.5cm wavelength
Yep, close enough.

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Interesting idea.  The sound level meter may not be sensitive enough
to operate at the same unobstructed distance that Wi-Fi will run at
(100 meters) unless you really crank up the volume on the sound
source.  

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It won't work at all through walls.  Sound is propogated through walls
by re-radiation of the sound.  A wall moves slightly with the sound
and causes the other side of the wall to move at the same rate.  This
re-radiates the sound.  Wireless goes through some materials, but not
others.  Fiberglass insulation will block sound, but not wireless.
Lots of other differences.

Another problem is reflection.  Much of wireless propogation is by
reflection.  Different materials of reflecting surfaces simply don't
reflect sound the same way they reflect RF.  Interestingly, if they
did, then the interference patterns would be similar for both sound
and RF.  For example, glass will reflect sound and pass RF.

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It's not possible to simulate an isotropica radiator with RF either.
Instead I suggest simulating a dipole using a conical reflector
directly above a speaker pointed upward.  The reflected sound will
form roughly a donut shaped pattern.

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--
Jeff Liebermann     jeffl@comix.santa-cruz.ca.us
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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You're right. There are many differences. Also, sound waves aren't
polarized like radio waves. Guess I'll have to call it a thought
experiment only :)


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