Reg Edwards wrote:
Cec, I'm not altogether happy about the current coming to a sudden stop at
the ends of a dipole.

It doesn't come to a sudden stop, Reg. It is reflected out of phase such
that the forward current vectorially added to the reflected current equals
zero, i.e. the net current is zero at the ends of the antenna. If appreciable
current flowed through the air, it would first have to ionize the air causing
an arc.

The reflected current from the ends of the dipole is what gives that standing-
wave dipole its low feedpoint impedance. If it weren't for the reflected current
from the ends of the dipole, the feedpoint impedance would be in the hundreds
of ohms and it would be a traveling-wave antenna.

What's that stuff which clearly flows between the plates of a wide-spaced
capacitor?

If current is clearly flowing between the plates, it is called an arc.
Appreciable current doesn't usually flow across the air gap between the
plates. Current flows in the rest of the circuit while charges are stored
on the capacitor plates. Current flowing directly between the plates means
that the air has been ionized and the cap is breaking down. I have one of
those in the horizontal drive section of my TV.
--
73, Cecil http://www.qsl.net/w5dxp



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