In article <pgg3r2lsoqpqruu0p68b10o1m3t0farhc6@4ax.com>,
Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
>adykes@panix.com (Al Dykes) hath wroth:
>
>>What's so hard. Put the AP in a table, put a laptop with netstumbler
>>on a table far enough away to get a middle reading and then go back
>>and put the plastic box over the AP. Don't move anything. walk back to
>>the laptop. look at the graph.
>
>Have you actually tried it? I have. Let's try something simple.
>Setup your laptop on the table with Netstumbler and have it probe your
>own access point. Never mind the pretty graphs, just look at the
>signal strength and SNR numbers. I'll assume you have the typical
>rubber ducky antennas on your access point.
>
>Now, take a 6" or so piece of PVC or ABS pipe and slide it over one or
>both antennas on the access point. Record the measurements before and
>after inserting the pipes. Go away and get some coffee or tea. Record
>the before and after measurements again. Go away and watch a TV show.
>Record the measurements before and after. Open or close a door or
>window. Do it again. If you're really lucky, you'll have a +/- 3dB
>spread in values of signal strength, and about twice that for SNR.
>
>>I agree that, in general antenna measurements are a PITA.
>
>Yep, especially indoors where uncontrolled measurements are the norm.
>
>Incidentally, if you have access to a spectrum analyzer that does NOT
>have a digital readout, put a spread spectrum signal on the screen
>from a controlled source (signal generator or directly connected
>access point), and ask your available friends and accomplices to read
>the indicated level off the screen. My guess is about +/- 2dB
>variation depending on the focus. Incidentally, tall people tend to
>produce low readings, while short people produce high readings, both
>due to parallax.
>
>So, have you figured out the spectrum analyzer quiz question?


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

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.




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a d y k e s @ p a n i x . c o m
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