Current in Loading Coils
 

A loading coil thread is climaxing over on qrz.com. I have
used EZNEC to generate a graphic which shows a 3/4WL vertical
and a similar 1/2WL vertical with a ~1/4WL loading coil. The
loading coil is a wire helical coil containing (surprise)
roughly 1/4WL of wire. The coil does a good (not perfect)
job of replacing 1/4WL of wire. Many things can be gathered
from observation of the current reported by EZNEC for the
two antennas. The coil occupies roughly the same number
of degrees of the antenna as the wire it replaces. The
current at the top and bottom of the coil is roughly the
same as the current at the two ends of the wire it replaces.
Is the coil an exact replacement? Of course not.

EZNEC says the current flowing into the bottom of the coil
is 0.1168 amps and the current flowing out of the top of
the coil is 0.748 amps. Say what? How can more current
flow out of a coil than is flowing in? Aren't those two
currents supposed to be equal? What gives?

Some gurus have mistakenly treated the net current on a standing
wave antenna as a lumped circuit current. The lumped circuit
analysis falls apart in the presence of standing waves and
the myth of equal net current in and out of a coil has been
created as a result. Hint: A typical mobile antenna is a
standing wave antenna and the net standing wave current reported
by EZNEC doesn't much flow at all. It just, well, stands there
like good little standing waves are supposed to. That
standing wave pattern is illustrated in the graphic at:

http://www.qsl.net/w5dxp/qrzgif35.gif

The two EZNEC files used to generate that graphic are available
from me upon request.
--
73, Cecil http://www.qsl.net/w5dxp

Current in Loading Coils
 

Cecil Moore wrote:
Is the coil an exact replacement? Of course not.

Just got an email that prompted me to expand this statement.
The worst thing about replacing a piece of wire antenna with
a coil is of course, the wire radiates well and the coil
radiates hardly at all. But that's a compromise we are forced
to live with for 75m mobile antennas.
--
73, Cecil http://www.qsl.net/w5dxp

Current in Loading Coils
 

Okay, I will take the bait and demonstrate my ignorance:

EZNEC says the current flowing into the bottom of the coil
is 0.1168 amps and the current flowing out of the top of
the coil is 0.748 amps. Say what? How can more current
flow out of a coil than is flowing in? Aren't those two
currents supposed to be equal? What gives?

I thought the power was constant, not the current. If that is the
case, then IE must be constant and therefore the current must go up
where the volts go down.

I would appreciate the EZNEC copies because I learn easiest by
examples and I am interested in how you put the comparison together.

John Ferrell W8CCW