RadioBanter - View Single Post - Current across the antenna loading coil

April 3rd 06, 06:07 PM posted to rec.radio.amateur.antenna

Cecil Moore wrote:

wrote:

In a loading coil with very small distributed capaciatnce to the
outside world compared to termination impedance, current has to be
equal. Phase shift in current at each end has to be nearly zero.

That is a false statement and is at the root of the misconceptions.
Standing wave current does not have to be equal. I have shown how
current at the bottom of the coil can be zero while the current
at the top of the coil is one amp. Do you think the coil is sucking
that one amp sideways from somewhere else through its distributed
capacitance? There's no magic involved, just simple, easy to
understand, distributed network theory. The current at the top
and bottom of a coil depends upon where it is placed in the
standing wave environment. Standing wave current doesn't flow.
It is the underlying forward current and reflected current that
is doing the flowing. Such is obvious from the equations.

Hecht, in "Optics", has the best description of standing waves
that I have ever read. He says: "[Equation (7.30)] is the equation
for a STANDING or STATIONARY WAVE. Its profile does not move
through space. ... [Its phase] doesn't rotate at all, and the
resultant wave it represents doesn't progress through space -
it's a standing wave."

Translating into RF language. Func(kx)*Func(wt) is the equation
for a STANDING or STATIONARY WAVE, i.e. the standing wave is
stationary. Its magnitude does not move through the wire. Its
phase doesn't rotate at all, and the resultant standing wave
it represents doesn't progress through a wire or through a
coil - it's a standing wave.

Until everyone takes time to understand the nature of standing
waves, people will keep making the same tired mistake over and
over.

Hecht was talking about two opposing waves of the same phase and
amplitude interfering with each other. You can't guarantee, in a real
antenna,
that the two waves do have the same phase and magnitude.
73,
Tom Donaly, KA6RUH