adykes@panix.com (Al Dykes) hath wroth:

>In article <pgg3r2lsoqpqruu0p68b10o1m3t0farhc6@4ax.com>,
>Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
>>So, have you figured out the spectrum analyzer quiz question?

>I'm not sure what the quiz is, but it's an interesting effect.

Naw, I goofed. I was running two threads involving spectrum analyzer
issues and managed to get them muddled. If you're curious, see:
<http://groups.google.com/group/alt.internet.wireless/msg/fef4de0f08c81ddf>
for the actual question under "Quiz Time".

>I agree that the table-top test is crude but for controlled
>environment (which my big room is if I don't change anything) I'm not
>sure why the reading would wonder around by 6dB, all on it's own.

It will wander around about 6dB without much effort and 10dB if you
start to move things around. Ever notice those nifty looking
Netstumbler signal strength and SNR graphs? Ever notice that they're
NOT flat top lines, but are rather ragged on the top? Those are the
variations I'm mumbling about. For example, look at Netstumbler
screen at:
<http://seattlewireless.net/index.cgi/WAP54G>
Notice the variations over 8 minutes (total) run. If I ignore the
total dropouts, my guess from the two parts of the graph are 12dB
variation on the left and about 10dB on the right.

Try it. Place a laptop somewhere that it's not going to move, and
probe an access point (preferably your own) that also isn't going to
move. Start it running and then go away for a while (to avoid having
your body affect the readings). As long as you don't cheat and use an
ultra strong saturating signal, you'll see variations similar to the
above URL. The numbers are real and you'll also see them with a
spectrum analyzer, on an antenna range, and in any highly reflective
environment. You might not see it in an RF anechoic chamber, but I
currently don't have access to one of those to try it.

Hmmmm.... I just fired up Netstumbler and checked the neighbors access
point (mine is too close and too strong). I'm seeing over 10dB
variations over about 3 minutes if I ignore the dropouts.


--
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