Roy Lewallen wrote:

Richard Harrison wrote:

Cecil, W5DXP wrote:
"Assuming the source signal is a pure sine wave, if the standing wave
current "isn`t in general sinusoidally shaped (as Roy said)", then the
antenna would have to be introducing harmonic radiation that doesn`t
exist in the source signal."

Either Cecil is misquoting me, or Richard is misquoting Cecil.

Richard quoted me correctly. I did *NOT* quote you. I merely
stated what I thought you said.

Cecil calls the total current the "standing wave current".

That is absolutely false. Total current equals standing wave
current plus traveling wave current. Or standing wave current
equals total current minus traveling wave current. Subtract
out the traveling wave component and a pure standing wave
component is left.

Note that you did not quote me. You merely stated what you
thought I said and you were mistaken.

I never said
that the standing wave current isn't sinusoidally shaped. I said that
the *envelope* of the standing wave -- that is, a graph of the magnitude
of the current on a transmission line as a function of position along
the line -- is not sinusoidally shaped except in the special case of a
complete reflection.

The envelope of the standing wave current is the same whether
reflection is complete or not since the traveling wave current
has been subtracted from the total current.

Seems you should have said the total current envelope is not
sinusoidal. The standing wave current envelope is obviously
sinusoidal since the traveling wave has been subtracted.

This isn't a personal theory, but a very well
established fact which can easily be derived from fundamental equations.

Please provide a reference that says after the traveling wave
current has been subtracted from the total current, the resulting
standing wave current envelope is not sinusoidal.

(Or it can even be found clearly stated in texts for those unable to
understand the derivation.) On antennas, the current distribution
(magnitude of current vs position) is generally not sinusoidal either,
although it's approximately so on thin wire antennas.

Just because the scale of the position axis changes with VF doesn't
mean things become non-sinusoidal.

Assuming that the transmission line is driven with a pure sine wave, the
forward, reverse, and total currents as a function of *time* will be
sinusoidal and consequently no harmonics will be generated.

This statement contradicts what I thought you said before. Seems
we are now in agreement.
--
73, Cecil http://www.qsl.net/w5dxp