Richard,

Thanks for the feedback. No problem with the failing issue, plenty of
that going on.

The way I see it though is that if I can add some knowledge to my
experimentation then at least I can "play" with some hope of moving to a
solution in the right direction.



Richard Clark wrote:
On Sun, 02 Oct 2005 07:16:01 GMT, David wrote:


I need to understand what needs to be used to calculate the length of
Brass tubing sleeve given the tubing diameter is 5/32 and besides air,
the outer sheath of the RG174 is also between the sleeve and Earth
braid. Is the diameter of the tubing critical (will it impact adversely
on SWR looking into this antenna).


Hi David,

The Er of the metal is not something that comes quickly to mind
(especially this late at night). Besides, it sounds like what you are
describing is the radial component which would be fantastically small
(many decimal places, not simply tens of percent).

It also seems like your application is for UHF (you need to be more
specific). This makes such "calculations" little better than SWAGs.
It doesn't take much to be way off. What is even more confounding is
your problem contains a hidden trap.

The sleeve of brass that drops below the feed point is embracing the
jacket of the RG174. THIS constitutes the dielectric constant of
interest and is a material that is different from the insulator of the
inner line. Even more, and as you note above, there is some air mixed
in to really gum up the back of the napkin calculations. This is the
G of the SWAG.

Worst yet, some jacket material is actually quite lossy, or so it has
been reported - another G of the SWAG.

All-in-all, what you need to do is build one and measure it. No doubt
that will lead to another trail of tears. On the other hand, there is
nothing so stimulating to learning than pain. Most of my best
subjects centered on projects I thoroughly screwed up.

As the saying goes:
"If you haven't failed, you aren't trying hard enough."

73's
Richard Clark, KB7QHC