(Thanks, Roy - great technical article!)
   73 = Best Regards
   -Jeff KA5THB
   ka5thb@bigfoot.com
1st installment of the;
                Omni-Gain Vertical Collinear for VHF & UHF
This is a rugged antenna, an omnidirectional collinear, which is capable of
surviving some pretty harsh environments.  It's an excellent choice for
repeater installations and it can be easily top or side mounted to any tower.
Bandwidth is normally 10MHz on the 70cm band and 25MHz on 23cm. Gain figures
for this antenna are what you make of it. You can obtain approximately 3 to
10db over a dipole, depending on the number of elements you use.
The main elements are constructed from 1/2-wavelength sections of coaxial
cable.  You can calculate the element length using the formula of; 5904/FMHz 

Velocity Factor of the coaxial cable you use.  In my first attempt to build
this antenna, I used RG-213 with a velocity factor of 0.66. You might want to
use RG-11 for high power (250+ watts) or RG-6 for low power.
To begin construction, remove the jacket and shield from each element and 
slide
it into hobby brass tubing.  You should select the diameter of the brass tube
to just fit snugly over the dielectric of the coax.  The brass tube provides 

more rigid support for each element and makes it easier to solder them
together.
(If brass tubing is unavailable, leave the shield and jacket of each element
intact.  Cut the shield to the formula length and remove enough of the jacket
to allow soldering. 1/4" max)
Use the above formula to calcualte the lengths of the brass tubes.  I own a
machine shop and can cut these tubes exact. By hand you'll have to get them 
s
close as you can. At UHF and above, dimensions are critical to the overall
performance and SWR.
Cut the coax segment long enough to allow 1/16" of the dielectric and 3/8" of
the center conductor to extend past each end of the tube.  Make as many 1/
2=wave elements as needed for the gain you desire:
 4 elements =  approx.  3.5 dBd gain
 8 elements =  approx.  6.0 dBd gain
18 elements =  approx.  9.0 dBd gain
21 elements =  approx. 10.0 dBd gain
In addition, you will need a 1/4-wave element and a 1/4-wave whip for the top
of the antenna.  The whip is cut to a true one-quarter wavelength (no 
elocity
factor correction) and is made out of number 12 wire or 1/8" brass rod.
The next installment of the Omni-gain vertical collinear will begin the 
cutting
and construction.  Gather your materials now, and don't cut anything until
you've read installment two.
--- FMail 1.02
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