On Fri, 9 Apr 2004 14:13:07 -0500, "Tyas_MT"
wrote:

I'm planning on making a 6m vertical dipole, using a tube lower element
(shield side) to run the coax to the center point.
I have an almost perfectly sized stainless steel whip (old CB antenna), and
already have a slightly longer section of copper pipe to use for the bottom
that I can easily cut down. A friend that makes custom plastic stuff says if
he has the proper sized scrap he'll bore and cut a plastic insulator/whip
support for me... if not he'll get the stuff at cost.

Mounted sideways it would look something like this:
- Steel Whip
+ Feedpoint/section insulator/whip support
= Copper pipe with feedline (coax) running through it to feed point
------------------------+===============
Left side connected to center conductor at feedpoint
Right side connected to shield at feedpoint

What I'd like to know is if it is going to have a major effect on my
dimensions/bandwidth/anything else if I use different materials for the two
sections of the dipole (steel for the whip, copper for the pipe)? And what
kind of effect is having the two different element sizes going to have as
well? (I know increasing element sizes tends to raise overall bandwidth, but
not sure how only one element will effect the antenna as a whole.)

Also is there going to be any effect from the capacitance between the shield
braid of my coax and the antenna segment surrounding it? The website I read
this from didn't mention that, though they did say you may want to coil the
feedline about 4-6 turns about another quarter wavelength from the end of
the antenna.

Thanks in advance
73
KD4COX, Eric

Eric,
You've essentially described a 'sleeve dipole', dont sweat it about
interaction between the copper pipe and the coax inside - though you
may wish to secure the lower end as well so it doesn't rattle around
inside the pipe. As to the use of different materials affecting
performance, shouldn't be an issue. Make sure though that you cut the
elements on the long side so you can trim to optimum length. You may
wish to do a Google search on 'sleeve dipole' and see if you find any
info that will help.

Good luck,
Howard
KE6something or other