> Incidentally, when measuring antenna gain, it's
>considered good form to use a reference antenna with known gain. You
>make the initial measurement with the reference antenna, switch
>antennas, and do it again. The difference in measurements is the
>relative gain.

I sorta considered the Linksys stock WRT-54G antenna to be a reference
of sort. I assume (I know, I know) it is a classic 2dBi omni rubber
duck. I guess you are saying that the terms and statements should be
made as "gain over reference antenna."

> >> You really need all 4 numbers to do a decent job of
> >> determining what's happening. For example, an overpowered transmitter
> >> will yield a much higher signal strength in one direction than in the
> >> other. Any interference might show up only at one end.

Gotcha.

>What you'll find are radical variations over time. It
>can be weather related, reflections from moving objects, or just water
>condensing on the antenna. Lots of sources of errors.

I now understand about the reflection, refraction issues, but apart
from that is the time issue you mentioned. It seems like if one is
not seeing much variation (1-2 db) over the short-term with the
control /reference antenna, then swapping the antennas quickly and
measuring right away should give a decent comparison? That is if
there aren't any moving objects on the scene....??


My biggest question now is about using Netstumbler or Kismet etc. vs
using DD-WRT to measure. Are you saying that DD-WRT is NOT an
acceptable instrument for signal measurement ?

More specifically; "When running DD-WRT-managed devices on both ends
of a wireless link in a controlled environment and then comparing
numbers (dB and SN ratio) reported on the "wireless status" page on
each end's interface as I switch out antennas (on one end only) would
this be an acceptable way to compare antenna gain?"

If not, why? Is DD-WRT's signal level or SN reporting unreliable or
poorly derived? Is Netstumbler's or Kismet's much better?

Also, I still don't see how Netstumbler or anything else running on pc
would work when using a router in client mode. I'm not able to test
it right now, but it seems that Netstumbler would not have any way of
seeing the signal strength if the client router is connecting the
computer via ethernet cable...



This is particularly useful thread, I think. So many people are
buying and building antennas. We all want to be able to tell which
antennas deliver measurable gain. Most folks probably depend on
marketing hype and anecdotal evidence (I put on one of those machV
doodads and it's really humming now, lemme tell 'ya).

And of course we also forget about that four feet of LMR100 and the
TNC adapter that we're using.

And we have no way of judging the accuracy of what tests are
reported. It would be great to have some understanding and agreement
so that various people could be reporting reliable tests with the
antennas they have.


I wish I could do that little test again, but the Linksys is in use
and cannot be pulled. Has anybody else compared the Buffalo HP's
included "hi-gain" rubber duck to the Linksys's included rubber
duck? Is it likely that "hi-gain" to Buffalo means 2dBi? Or that
the RPA to TNC adapter could eat up any difference?

Anyone else done any testing?

Cheers,
Steve