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<DIV><FONT face=Arial size=2>Well, me and a mate sat down on the weekend to
build some omni's. We used the Collinear <BR>design posted on the
Melbwireless site here (<A
href="http://melbwireless.dyndns.org/pages.php?page=2.4Ghz+Vertical+Colinear">http://melbwireless.dyndns.org/pages.php?page=2.4Ghz+Vertical+Colinear</A>).
Building was reasonably straight forward once we worked out the more than
cryptic documentation and sorted through all the measurements.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>A few points of note... </FONT></DIV>
<DIV><FONT face=Arial size=2>A 6mm screw with 16 threads per inch didn't exist
at our hardware shop. Even if it had, the pitch would be wrong.
There is just no way one could coil a 3/64 brass rod around the scree without
the coils touching.</FONT></DIV>
<DIV><FONT face=Arial size=2>The design looks seriously strange to us.
There is nothing like it in the usual sources, ARRL experimenters guide and the
like. With no maths provided it is almost impossible to verify the
theory.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>We cut all the parts accurately and measured with
verniers. With soldering complete and attached to a SMA connector, we set
about to test it. Initial testing was done with a Compaq WL100 and
pigtail. We were talking to a WAP11 upstairs. We couldn't see any
appreciable results so we figured it would be easier to test if we walked up the
street till we nearly ran out of signal and plugged it in. Once in
position 0m up the street we plugged it in and to our horror saw the SN ratio go
down (- ive scale) about 15db. The card then alternated up and down every
second or so on diversity. The internal antenna presumably doing better
than our "5db" omni.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>We rechecked all our measurements, construction and
integrity of the wiring. Still no go! Just to make sure we weren't
dreaming we plugged in one of the Galaxy antennas I have
previously modified from the same place. After moving the antenna
around a bit we notice a 14-15 db gain on the internal antenna.
Considering we had 5m of RG 213 on the end, one of those terrible Lucent
connectors and the Galaxy antenna isn't really designed for ISM frequencies, we
thought this was pretty good. The score thus far Galaxy 1, homebrew omni's
0.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>We then set to building another design. This
time a 26 element omni. The maths we could understand and the design
involved simply bending the brass... so this time we thought we might be more
successful. We didn't actually use the full 26 elements, more like
7. We felt this antenna couldn't be any worse than the last in any
case. Anyway, back we walked to our original testing place and no joy on
this attempt either although we didn't drop quite so many db's. The score
now Galaxy 2, homebrew omni's 0.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>Having got this far we were a bit discouraged, but
we decided to press on and build a Pringles antenna. This looks promising,
although we haven't finished it yet. The design is a well known ARRL one,
used by hams for quite some time. I'll keep you posted.
</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I'd also be interested in hearing from anyone that
has managed to successfully build an omni with a verifiable
gain....</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>Cheers</FONT></DIV>
<DIV><FONT face=Arial size=2>Richard.</FONT></DIV>
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