[Antennas] Variation on coaxial dipole antenna

[C Whitaker]

de WB2CPN                        2005.01.21

In theory, (For The Purists), there is a Catch 22
in the coaxial dipole.  One one hand the INSIDE
cavity between the feed coax and the outer tube
or whatever should be an electrical quarter-wave,
and the propagation velocity in that section
needs to be considered.  Then, the OUTSIDE of the
tube should be an electrical quarter-wave because
it's half a dilole antenna.  These lengths rarely
ever come close unless the ratio of coax diameter
to tube diameter gets to be very very big.  The
engineers try to tweak this by flairing the bottom
end of the tube, like "Isopole TM" did back then.

Generally I've found that a coax folded back on
itself is not the way to go.   Two or three inch
tubing may help handle the SWR better.

73  Clete