On 11/22/2014 10:19 AM, John S wrote:
A special purpose antenna for maybe just below the 6M band. For railroad
cars (a large metal ground plane). The antenna must be short enough to
pass through tunnels and have a 50 ohm feed impedance.

I saw this antenna in a book but I can no longer remember which book
and, although I've searched, I can't seem to find a reference. It was
probably from the 1950's. Anyway...

Imagine a folded unipole over a large sheet of metal. It will probably
have a high feed resistance of 100 or so ohms. But, if it is bent over
90 degrees starting a short distance above the ground plane, it can be
adjusted to match a 50 ohm feed and with no imaginary component. This
will satisfy not only the feed impedance but also the short height
requirement.

Other than the really nice ground plane of a railroad car's roof and
using a frequency proportional to the plane, there is no obvious reason
this cannot be use in other situations.

Is that not really cool? Comments welcome, of course.

No, Guys, nothing that I have read so far is the thing I have in mind.

Picture this...

A folded unipole on a large sheet of conductive material. Let one of the
vertical elements be connected to the sheet. The other is insulated from
the sheet and has the generator attached.

Now, this configuration has a high feed impedance, even when resonant.
However, if you now bend the antenna at an appropriate point vertically
so that the top portion leans horizontally to the sheet, the antenna
gets lower to the sheet and the impedance lowers.

I have an EZNEC file that I can share if anyone is interested. I will
also continue to search my books for the example.