"Tyas_MT" wrote in message
...
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

I've heard that stainless steel whips disipate a significant amount of
energy ay 50 MHz. If you have several hundred watts, you might want to try
transmitting with the ss whip before finalizing your design. You might be
surprized to find that the whip gets warm quickly.

Jerry