Yuri Blanarovich wrote:
Soooo, W8JI and his worshippers were right! Current is just about constant
through the loading coil (for traveling wave) ...
Especially since I modeled the coil with lossless wire. :-)
*Traveling wave current* amplitude is just about constant
at both ends of a loading coil but there's a phase shift
as can be seen at:
http://www.w5dxp.com/current2.htm
In the middle of the coil, the current increases because
of the adjacent coil coupling. There is a little drop off
(unit percents)in amplitude end-to-end because of I^2*R
losses and radiation. But one can consider the coil to be
lossless and non-radiating and still get within a few percent
of reality.
The problem is that W8JI used *standing wave current* for
his measurements. What is flowing through the coil is the
forward current and reflected current, not the standing
wave current. The standing wave current is just standing
there as indicated by the cos(kz) term. The amplitude of the
standing wave current at any point in the coil or on the
antenna has more to do with the phase difference between
the forward and reflected currents than anything else. At
the tip of the antenna, the forward current and reflected
current are equal in magnitude, 180 degrees out of phase,
and thus sum to zero.
I hope Roy approves your use of EZNEC for this demonstration and perhaps
will admit that they were wrong, and indeed the RF current through standing
wave antenna circuit, such a quarter wave resonant vertical monopole, the
loading coil has the current drop along the coil (standing wave circuit).
The current "drop" is an illusion. The current decreases primarily
because of out-of-phase addition of the forward and reflected
current. If one makes the antenna longer and places the loading
coil somewhere else, one can measure a current "rise" through the
coil which is still an illusion created by the in-phase addition
of the forward and reflected currents.
I verified these findings on the bench a couple of months ago
using my 75m Texas Bugcatcher coil loaded with a 3K ohm resistor.
But I wanted to see if EZNEC agrees. It does.
--
73, Cecil
http://www.w5dxp.com