"Cecil Moore" wrote in message
...
christofire wrote:
The 'loading coil' is distributed throughout the radiating element and,
consequently, throughout the current distribution so it might be possible
to reduce the I^2R loss using the normal-mode helix.

For a fixed length of loaded monopole, a high-Q
center-loading coil (or top-loading coil) will
result in greater efficiency. Helical elements
have been measured in numerous 75m shootouts to
be relatively low-Q and therefore lossier than,
e.g. Texas Bugcatcher Coils.
--
73, Cecil http://www.w5dxp.com


That's interesting. I imagine it would be difficult to support a helix with
a length of many metres whilst keeping the losses low, and of course there
may be a greater total length of conductor in the continuously-loaded case.
Otherwise, I can't think of a fundamental reason why a long normal-mode
helix should have lower Q than a monopole of the same length with a series
inductor somewhere in it.

The Tesla coil brigade appear to have sorted out suitable tube materials in
lengths up to a couple of metres or so with low loss at frequencies up to
the medium wave band or thereabouts.

Chris