dansawyeror wrote:
Roy,

Thank you. It is a quick experiment to build a test coax coil and
measure the Q. That should produce enough evidence to test a counterpoise.

In the mean time the research to build a coil out of copper tubing
continues. So far the only alternative I can conceive is to make a
wooden form and wrap the coil on the outside.

Thanks again - Dan

A copper tube will definitely produce an improved Q. If you do make
comparative measurements of ones made from tubing and from coax, please
post the results.

A real problem in maintaining the Q of coils outside in the weather is
keeping water from getting between the turns. Water is very lossy stuff
at HF, and it has a very high dielectric constant. The two combine to
make it a real Q killer if it gets into any region of high electric
field strength. A bit of accumulated dust mixed with the water makes it
worse yet. So if you anticipate leaving the coil on a form and exposed
to the weather, also check the Q when the coil is wet. See
http://www.eznec.com/Amateur/Article...Feed_Lines.pdf for
results of measurements of wet and dry 300 ohm twin lead. It's not quite
the same situation, but the loss mechanism is essentially the same.

I recommend that you do some modeling or just simple calculating, if you
haven't done so already, to see just how high the Q has to be in order
to keep overall loss acceptable.

One final thing to keep in mind -- I've heard reports of poor
performance of elevated verticals being tracked down to badly imbalanced
currents in the radials. Apparently even small physical differences
among the radials can cause one or two to hog all the current. If this
is so, it seems to me that making them more sharply tuned by inductive
loading might make this effect even worse. So when you get the thing up,
I suggest measuring the current in each radial. This is easily done with
a toroid core with a few turns for the secondary and a fairly low R
across the secondary. It's been discussed a number of times on this
newsgroup, the last time quite recently.

Good luck!

Roy Lewallen, W7EL