"John S" wrote in message
...
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.

Sounds like a (much) larger version of the antenna in your mobile phone