On Dec 13, 11:16 pm, Cecil Moore wrote:
Keith Dysart wrote:
For convenience assuming the dipole is lossless, it seems
to me that after the transmitter is turned on, some of the
energy is stored in the antenna, but once the antenna
is charged, all the energy entering the antenna is radiated
until the transmitter is turned off, after which the energy
stored in the antenna is radiated until the antenna stores
no energy.

So everything that goes in to the antenna is radiated.

Before steady-state is reached, a considerable amount of
energy is stored in the standing waves following key-down
(your "charging" time). That energy stored in the standing
waves will not radiate until the source is disconnected,
e.g. after key-up.

I follow the principle, but I am not convinced that it is a
"considerable" amount of energy.

A 1/2WL dipole is a standing-wave antenna. The energy
radiated from such an antenna is considerably less than
the energy stored in the standing-waves. The SWR on the
antenna is probably around 20:1.

Consider a quarter wave-length of open circuited line connected
to a 100 W source. After 1/2 cycle it is fully charged. At 4 MHz
it stores 0.125E-6 J of energy. I can not see a mechanism
where a 1/2 wavelength antenna would store more than this
(SWR on the line would be inifinity, much worse than 20:1),
and it will be radiating 100 J/s. 0.125E-6 J is not much in a
system that is moving 100 J/s.

....Keith