"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)?

No. Not enough to notice.

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.)

Not much...You may have to trim the antenna, but you won't know for
sure until you actually try it.

Also is there going to be any effect from the capacitance between the shield
braid of my coax and the antenna segment surrounding it?


Dunno.. I doubt 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.

Yep, that antenna will need feedline decoupling. A 2nd lower 1/4 wave
copper tube, closed at the top and grounded to the shield, and open at
the bottom like a bell, would be even better. I'd at least use a coax
choke. MK

--

"Mark Keith" wrote in message
m...
"Tyas_MT" wrote in message
...

Dunno.. I doubt 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.

Yep, that antenna will need feedline decoupling. A 2nd lower 1/4 wave
copper tube, closed at the top and grounded to the shield, and open at
the bottom like a bell, would be even better. I'd at least use a coax
choke. MK

I am considering trying to make a feed point balun at the center insulator,
but I won't have much room. I've got it laid out horizontally and it tunes
up pretty good as is, but I have not gotten with the guy to make my little
center insulator.

I'm mounting this above my 6m quad as an omni-vertical... I figure I can
stick it on top of a PVC pipe and it will interfere less with the quad than
a 1/4 ground plane would (and it looks better).

Thanks for the responses... I don't think heating the whip will be a
problem, though loss might... I'm only running 5 watts key down.

I'm really shooting for the occasional cross polarized weak signal
contact... though I think that the difference in gain between the dipole and
the (horizontal polarized) quad will end up meaning that vertical signals
are about the same... but it's worth a shot.

73
KD4COX
Eric