From: weare@bostech.COM
Newsgroups: rec.radio.amateur.misc
Subject: Re: Vertical Colinear
Date: 2 Sep 1992 09:24:23 -0700
Organization: UCSD Usenet Gateway
NNTP-Posting-Host: ucsd.edu

I built a 2M vertical colinear out of copper water pipe (1/2"), and it
works great.  I got the design from one of the ARRL books, probably
an old edition of the Antenna Handbook, but it might have been the ARRL
Handbook.  There isn't anything tricky about the design, so I can describe
it here.

I used two half-waves, though it can be extended by adding more half-wave
sections.  Cut two pieces of pipe to a half-wave, then join the ends with
a quarter-wave matching stub (to get the correct phasing).  The quarter
wave section was also made from pipe, with Cu elbows to join everything.
That is, cut two lengths of pipe to a quarter wave, solder elbows on both
ends of both pipes (facing opposite ways).  Use a short piece of pipe to
join the two halves of the stub into a U-shape (I used a spacing of about
two inches).  Then solder the half-waves to the two remaining elbows of
the matching stub.  It looks like this:

	===================E    E=================
	                   ||   ||
	                   ||   ||
	                   ||   ||
	                   ||   ||
	                   E====E

The long horizontals are the half-waves, the `E`s are the elbows.  The
verticals are the stub.  The whole thing is soldered together.  You can
add sections (can be an odd number) by putting another stub at the end
of a half-wave, then another half-wave.  Thus, three sections looks like:

	=================E    E================E    E=================
	                 ||  ||                ||  ||
	                 ||  ||                ||  ||
	                 ||  ||                ||  ||
	                 ||  ||                ||  ||
	                 E====E                E====E

And so on, for a lot of sections, if you wish.

To feed the beast, I used a coaxial-cable balun (I used RG-8X); the design
can be found many places, and I don't remember it exactly, anyway.  The
balun output (i.e., away from the transmitter) is connected to one of
the stubs, one connection to each leg of the stub, equidistant from
the shorted end of the stub.  Find the exact position for the connections
by trial and error (minimum SWR).  I used hose clamps temporarily
while doing this, then drilled holes for screws (SS) for permanent
connections.  If I recall correctly, the best match occurred about
a third of the way from the shorted end of the stub, and wasn't very
critical.  If you use more than two sections (more than one stub), you
only need to feed it at one stub, preferably near the middle of the
array.  You may be able to avoid the balun, but I haven't tried this
It would probably distort the pattern.

To mount it, the best position is probably at the base of the stub (low
impedance point).  Plumbing supply places have clamps (straps? don't
remember the exact name), designed for anchoring pipe to beams, that are
just bent strips of metal; these would work great for fixing it to
a wooden mast (two by two or something). Using wood near the antenna
would also minimize distortion of the pattern. I actually mounted it by
the end of an half-wave section, through stand-off insulators, to a
metal mast, for some reason I no longer remember.  I works fine like
that, though I haven't done any measurements of the pattern.

How does it work?  Very well.  I actually have an 11-element beam for
2M, but prefer the colinear, because it is omnidirectional, and has
better bandwidth.  The gain seems to be not much less than the beam,
which probably means the beam is broken :-).  It's simple to build,
will last for years and years, and you can't beat the price,
either.

You can probably use Al, instead of Cu, but why pay more?  The antenna
is pretty light with copper.  There's no reason I can think of to feed
the coax through the tubing.

Hope this helps.
----
Jed Weare, NF1Z / G3VVH        weare@bostech.com
Boston Technology              (617) 246-9000 x3519
100 Quannapowitt Parkway
Wakefield, MA 01880.