Yuri Blanarovich wrote:
Unless someone shows that 7 points I raised are not
valid, I am happy with results of this interesting exercise.

Here's an interesting EZNEC result. I took the 102' loaded dipole
that was resonant on 3.76 MHz and ran it on 14.3 MHz. I repositioned
the loading coils at a current minimum point with a one ohm resistor
on each side so there is 0.03 wavelength between resistors.

--------------R1--coil1--R2-------FP--------R3--coil2--R4--------------

EZNEC sez:
Current through R1 is 0.1618 amps at -156 degrees
Current through coil1 0.09643 amps at -130 degrees
Current through R2 is 0.08098 amps at -70 degrees

In the ten degrees between R1 and R2, the current doubles and shifts
phase by 86 degrees. Can we use these results to prove there is a
phase shift through a lumped inductor? :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:
Yuri Blanarovich wrote:

Unless someone shows that 7 points I raised are not
valid, I am happy with results of this interesting exercise.


Here's an interesting EZNEC result. I took the 102' loaded dipole
that was resonant on 3.76 MHz and ran it on 14.3 MHz. I repositioned
the loading coils at a current minimum point with a one ohm resistor
on each side so there is 0.03 wavelength between resistors.

--------------R1--coil1--R2-------FP--------R3--coil2--R4--------------

EZNEC sez:
Current through R1 is 0.1618 amps at -156 degrees
Current through coil1 0.09643 amps at -130 degrees
Current through R2 is 0.08098 amps at -70 degrees

In the ten degrees between R1 and R2, the current doubles and shifts
phase by 86 degrees. Can we use these results to prove there is a
phase shift through a lumped inductor? :-)

No.

It'll take a lot more than an EZNEC analysis, or back yard measurement
for that matter, to disprove theory that's been verified and used
successfully for more than a century.

Roy Lewallen, W7EL

Roy Lewallen, W7EL, wrote:

No.

It'll take a lot more than an EZNEC analysis, or back yard measurement
for that matter, to disprove theory that's been verified and used
successfully for more than a century


As I followed this topic thread both in this forum and on eHam,
I formed my own opinion about the observed disparity between
currents entering and leaving an antenna loading coil. My
conclusion was that the parasitic capacitances between the coil
turns and ground were responsible for shunting a fraction of this
current away from the coil terminal that connects to the top part
of the antenna (in the present case of a shortened, vertical
monopole - the typical HF mobile antenna).

To confirm this notion, I created the following EZNEC(tm) model
of a 13-foot, inductively loaded monopole fed against a perfect
ground: (1) a 3-ft bottom section containing the RF source, (2)
a set of four inductors connected in series and occupying a
physical length on the antenna of 2 feet, (3) a set of three
"gimmick" wires attached to the internal nodes of the inductor
assembly and extending horizontally for 2 feet that simulate the
parasitic capacitances between the coil turns and ground and (4)
an 8-foot whip on the top to complete the antenna. The operating
frequency was chosen to be 3900 kHz and the inductors were
adjusted in value to resonate the entire antenna at this frequency.

The results are shown below as an EZNEC printout of the load
data for the four inductors (Inductor 1 is the one closest to
the bottom):

EZNEC ver. 3.0

Yuri's Mobile #1 11/7/2003 6:05:04 AM

--------------- LOAD DATA ---------------

Frequency = 3.9 MHz

Load 1 Voltage = 4280 V. at 89.99 deg.
-- Current = 10.24 A. at -0.01 deg.
Impedance = 0 + J 418 ohms
Power = 0 watts

Load 2 Voltage = 4144 V. at 89.98 deg.
-- Current = 9.914 A. at -0.02 deg.
Impedance = 0 + J 418 ohms
Power = 0 watts

Load 3 Voltage = 3756 V. at 89.97 deg.
-- Current = 8.985 A. at -0.03 deg.
Impedance = 0 + J 418 ohms
Power = 0 watts

Load 4 Voltage = 3125 V. at 89.97 deg.
-- Current = 7.476 A. at -0.03 deg.
Impedance = 0 + J 418 ohms
Power = 0 watts

Total applied power = 156.6 watts


As can be seen, there is roughly a 25% reduction in current from
bottom to top on the "loading coil".

Interestingly, most of this current-shunting appears to take
place near the top of the "coil".

This model is admittedly quite crude. The conclusions I reached
were that there was at least a qualitative effect from the parasitic
shunting capacitances on the current flow through a loading coil
and that quantitatively it appears to be fairly significant.

I have included the text description of the model from EZNEC
below:

EZNEC ver. 3.0

Yuri's Mobile #1 11/7/2003 6:24:20 AM

--------------- ANTENNA DESCRIPTION ---------------

Frequency = 3.9 MHz
Wire Loss: Zero

--------------- WIRES ---------------

No. End 1 Coord. (in) End 2 Coord. (in) Dia (in) Segs
Conn. X Y Z Conn. X Y Z
1 GND 0, 0, 0 W2E1 0, 0, 36 0.1 8
2 W1E2 0, 0, 36 W3E1 0, 0, 42 0.1 1
3 W4E1 0, 0, 42 24, 0, 42 0.1 1
4 W2E2 0, 0, 42 W5E1 0, 0, 48 0.1 1
5 W6E1 0, 0, 48 0, 24, 48 0.1 1
6 W4E2 0, 0, 48 W7E1 0, 0, 54 0.1 1
7 W8E1 0, 0, 54 -24, 0, 54 0.1 1
8 W6E2 0, 0, 54 W9E1 0, 0, 60 0.1 1
9 W8E2 0, 0, 60 0, 0, 156 0.1 1

Total Segments: 16

-------------- SOURCES --------------

No. Spec. Pos. Actual Pos. Amplitude Phase Type
Wire # % From E1 % From E1 Seg (V/A (deg.)
1 1 1.00 6.25 1 10 0 I

-------------- LOADS (R + jX Type) --------------

Load Spec. Pos. Actual Pos. R X
Wire # % From E1 % From E1 Seg (ohms) (ohms)
1 2 50.00 50.00 1 0 418
2 4 50.00 50.00 1 0 418
3 6 50.00 50.00 1 0 418
4 8 50.00 50.00 1 0 418

No transmission lines specified

Ground type is Perfect


Just to complete the picture, here is the Source data:

EZNEC ver. 3.0

Yuri's Mobile #1 11/7/2003 6:48:30 AM

--------------- SOURCE DATA ---------------

Frequency = 3.9 MHz

Source 1 Voltage = 16.43 V. at 17.66 deg.
Current = 10 A. at 0.0 deg.
Impedance = 1.566 + J 0.4984 ohms
Power = 156.6 watts
SWR (50 ohm system) = 31.937

I will be happy to send out the .EZ file for this
to any interested parties. Splice together the
e-mail address below to contact me.

73,

Jim Bromley, K7JEB

k7jeb (at) qsl (dot) net

K7JEB wrote:
I will be happy to send out the .EZ file for this
to any interested parties. Splice together the
e-mail address below to contact me.

Good stuff, as usual, Jim. It comes as no surprise to me that a three
dimensional component with distributed resistance, distributed inductance,
and distributed capacitance changes the voltages and currents at each end
of the component. The changes are accentuated in a standing-wave environment.

And to improve on your model a tad, make the capacitive wires equal on
each side of the installation point, i.e. instead of a 2 foot wire sticking
out horizontally, make it one foot of wire sticking out in two opposite
directions. That will minimize radiation from those wires.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil, W5DXP, wrote:

And to improve on your model a tad, make the capacitive wires equal on
each side of the installation point, i.e. instead of a 2 foot wire sticking
out horizontally, make it one foot of wire sticking out in two opposite
directions. That will minimize radiation from those wires.

Good suggestion, Cecil. I had planned to make the capacitive
wires into little square-shaped contraptions having about the
same size as a turn of wire on the loading coil and then
duplicate them up and down in the Z direction. I may still
do this, but I wanted to publish the preliminary results as
soon as I saw an effect, however imperfectly perceived.

Jim, K7JEB

Roy Lewallen wrote:
It'll take a lot more than an EZNEC analysis, or back yard measurement
for that matter, to disprove theory that's been verified and used
successfully for more than a century.

Nobody is out to disprove theory. But it seems apparent that the lumped
inductor conceptual model and a real-world inductor have little in common.
For the same reason, one cannot use a model of a lossless transmission
line to determine real-world efficiency. Models do not dictate reality.
It is supposed to be the other way around.
--
73, Cecil http://www.qsl.net/w5dxp



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