[Cu-wireless] I built the 5dBi omni from guerilla.net

[David Young]

Today I built the 5dBi collinear array at guerilla.net. It was a pain
in the ass to build, but while I was building it, I came up with a few
ideas how to build it more easily with higher quality.  I give my ideas
here in case someone else on the list decides to try this antenna.

I cannot test until I've bought some SMA connectors to crimp on LMR400.
If anyone needs any RF components, let me know. I am going to place an
order Monday.

Flux is an idea whose time has come. Too bad I was so late to adopt its
use. Use flux on all the soldered connections, it appears to draw the
solder onto the parts you paint with it. I think the soldered connections
on the decoupler assembly, which were pretty tough for me, would have
been easier using flux.

Buy screws in a few sizes. The ones I bought were too thin, so I was not
able to achieve 6mm-diameter coils. I don't know if it matters too much
the diameter of the coils, but I cannot reason about the trade-offs of
tighter coils when there is NO THEORY WHATSOEVER IN THE ANTENNA PLANS. =)

Build yourself three jigs. The first is to hold the 3/32" brass tubing
parallel with the inner conductor of the SMA connector.  Sadly, the
tubing will not fit snugly over the inner conductor, and it is very hard
to "eyeball" this. I offer this meta-design for your jig: it holds the
tubing and SMA connector in the same vertical axis giving you plenty of
room to apply the soldering iron and solder.

I have a more concrete idea for the second jig, but I have not tried
it myself. To ease the coil-making, take a small piece of plywood and
drill a hole in it 3/64" or larger (the smaller the better). Drive a
screw into the wood near enough the hole so that if you poke a little
bit of the 3/64" brass rod into the hole and twist it around the screw,
the brass rod conforms as closely as possible to the coil except for the
tail poking into the plywood. Lop off the head on the screw. The use of
this jig is that it gives you a big hunk o' wood to hold onto while you
twist the rod around the screw.

Make sure a coil's two tails are collinear.

The third jig holds together the tubes, coils, and decoupler assembly IN
A STRAIGHT LINE with the correct distances between elements while you
solder the antenna together. My collinear antenna came out distinctly
noncollinear because I had no such jig.

If you use a 35,000 RPM Dremel to make adjustments to the length of your
copper tubing, like I did, do your ears a favor and buy a nice set of
ear protectors. That sucker is LOUD.

Dave

-- 
David Young             OJC Technologies
dyoung at onthejob.net     Engineering from the Right Brain
                        Urbana, IL * (217) 278-3933