On Friday, July 27, 2012 12:50:32 PM UTC-5, Szczepan Bialek wrote:
Are the voltages doubled at the ends?

The voltage doubling at the ends of a dipole is simple to understand. A dipole is a standing wave antenna. When the forward wave from the feedpoint encounters the open-circuit at the end of the dipole wire, a reflection takes place where the reflected voltage is in phase with the forward voltage and the reflected current is 180 degrees out of phase with the forward current..

At the end of the dipole, |Vfor|=|Vref| and |Ifor|=|Iref|. So the total voltage and total current at the ends of a dipole a

Vtot = Vfor + Vref = 2*Vfor = 2*Vref

Itot = Ifor - Iref = 0

And of course, no current is going to flow into the open-circuit at the end of the dipole so the total energy in the magnetic field at that point is zero.

All of the energy in the EM waves migrates to the electric field and that's why we get a standing wave voltage maximum at the ends of a 1/2WL dipole.

However, under certain corona conditions, when the impedance at the end of the dipole conductor is much less than infinite, electrons actually migrate from the antenna into the conductive air, e.g. salty fog on the coast. But this is undesirable non-coherent behavior unless you are building a Tesla coil.

I once saw a mobile antenna emitting a red corona glow in the fog on HWY 1 near Monterrey, CA. A traffic cop stopped him for having a "red light" that could be seen by oncoming traffic.
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73, Cecil, w5dxp.com