On Apr 23, 10:10*pm, Roy Lewallen wrote:

Some of your questions can be answered by doing a google groups search
of this newsgroup for the topic "Current in antenna coils controversy"
in 2003.

Roy, I've glanced at some of those references and it looks like
there's years of "catch-up" reading for me

It seems like the starting point for one of the earliest discussions
was whether or not there is a variation in current amplitude along the
length of a loading coil, with some pretty strong opinion saying that
there isn't. I don't want to go over old ground, but perhaps you can
give me a simple answer to this one question:

When I use EZNEC to model a 6ft whip above a loading coil (40T, 6"
diameter, 12" long), and look at the current distribution across the
coil at the resonant frequency of the antenna (3.79 MHz), I see 1A at
the base of the coil increasing to 1.07A at the centre of the coil and
then dropping to 0.69A at the top of the coil. My question is: "Can I
believe that I would see a similar current variation in the 'real
world', or is this some failing of EZNEC to model the antenna
properly?"

Regards,
Steve G3TXQ

steveeh131047 wrote:

Roy, I've glanced at some of those references and it looks like
there's years of "catch-up" reading for me

It seems like the starting point for one of the earliest discussions
was whether or not there is a variation in current amplitude along the
length of a loading coil, with some pretty strong opinion saying that
there isn't. I don't want to go over old ground, but perhaps you can
give me a simple answer to this one question:

When I use EZNEC to model a 6ft whip above a loading coil (40T, 6"
diameter, 12" long), and look at the current distribution across the
coil at the resonant frequency of the antenna (3.79 MHz), I see 1A at
the base of the coil increasing to 1.07A at the centre of the coil and
then dropping to 0.69A at the top of the coil. My question is: "Can I
believe that I would see a similar current variation in the 'real
world', or is this some failing of EZNEC to model the antenna
properly?"

Regards,
Steve G3TXQ

Yes, you would see this in the real world. EZNEC does a very good job of
modeling a wire antenna with a loading coil, provided that you model the
coil as a wire helix rather than lumped "load", and you can trust the
results. As I've implied, a lumped load is quite a good model for a
physically small, essentially non-radiating loading coil like a toroid
on a magnetic core.

Roy Lewallen, W7EL

On Apr 23, 10:44*pm, Roy Lewallen wrote:

Yes, you would see this in the real world. EZNEC does a very good job of
modeling a wire antenna with a loading coil, provided that you model the
coil as a wire helix rather than lumped "load", and you can trust the
results. As I've implied, a lumped load is quite a good model for a
physically small, essentially non-radiating loading coil like a toroid
on a magnetic core.

Roy: thanks for the unequivocal and clear answer.

Steve G3TXQ

Roy Lewallen wrote:


Regards,
Steve G3TXQ

Yes, you would see this in the real world. EZNEC does a very good job of
modeling a wire antenna with a loading coil, provided that you model the
coil as a wire helix rather than lumped "load", and you can trust the
results. As I've implied, a lumped load is quite a good model for a
physically small, essentially non-radiating loading coil like a toroid
on a magnetic core.

Roy Lewallen, W7EL

which makes perfect sense...
NEC is a MoM code and is ideally suited to calculating the current
induced in one wire by the currents in other wires. I should think it
would do an excellent job modeling a air core solenoid, especially if
the wire diameter is small compared to the spacing between turns,etc,
assuming that you don't get into numerical precision problems.

On Apr 23, 7:40*pm, Jim Lux wrote:
Roy Lewallen wrote:

Regards,
Steve G3TXQ

Yes, you would see this in the real world. EZNEC does a very good job of
modeling a wire antenna with a loading coil, provided that you model the
coil as a wire helix rather than lumped "load", and you can trust the
results. As I've implied, a lumped load is quite a good model for a
physically small, essentially non-radiating loading coil like a toroid
on a magnetic core.

Roy Lewallen, W7EL

which makes perfect sense...
NEC is a MoM code and is ideally suited to calculating the current
induced in one wire by the currents in other wires. I should think it
would do an excellent job modeling a air core solenoid, especially if
the wire diameter is small compared to the spacing between turns,etc,
assuming that you don't get into numerical precision problems.

If eznec does not take into account dielectric loading then the
application is not in equilibrium and thus Maxwells laws are not
applicable. Maxwells laws are based solely on the presence of
equilibrium or accountability of all loads applied which when all are
added equals zero per Newtons laws.
Regards
Art

steveeh131047 wrote:
I see 1A at
the base of the coil increasing to 1.07A at the centre of the coil and
then dropping to 0.69A at the top of the coil.

FYI Steve, five years ago I showed Roy how to estimate
the phase shift through the coil using ARCSIN(0.69) =
~46 degrees. To this day, he refuses to acknowledge
what EZNEC is telling him about current on a standing
wave antenna which is: A current phase measurement
on a standing wave antenna is meaningless. Here's a
couple of graphic that illustrate what I am saying:

http://www.w5dxp.com/coil.gif

http://www.w5dxp.com/phasor.gif

These graphs are very close to your measurements
above.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

On Apr 23, 4:36*pm, steveeh131047 wrote:
On Apr 23, 10:10*pm, Roy Lewallen wrote:



Some of your questions can be answered by doing a google groups search
of this newsgroup for the topic "Current in antenna coils controversy"
in 2003.

Roy, I've glanced at some of those references and it looks like
there's years of "catch-up" reading for me

It seems like the starting point for one of the earliest discussions
was whether or not there is a variation in current amplitude along the
length of a loading coil, with some pretty strong opinion saying that
there isn't. I don't want to go over old ground, but perhaps you can
give me a simple answer to this one question:

When I use EZNEC to model a 6ft whip above a loading coil (40T, 6"
diameter, 12" long), and look at the current distribution across the
coil at the resonant frequency of the antenna (3.79 MHz), I see 1A at
the base of the coil increasing to 1.07A at the centre of the coil and
then dropping to 0.69A at the top of the coil. My question is: "Can I
believe that I would see a similar current variation in the 'real
world', or is this some failing of EZNEC to model the antenna
properly?"

Regards,
Steve G3TXQ

Steve.
To determine the accuracy of Eznec first requires the use of a program
with the ability to change input so that it relates to the
requirements of Maxwell' radiation laws This means a program with an
optimiser function which adheres strictly with Maxwells laws and its
applicability produced which means all forces are accounted for. You
have then established a datum line for a radiator where all forces
are accounted for per Maxwell. When that final configuration per
Maxwell' laws emerges one should be able to insert this same
configuration into Eznec to check to see if all relative factors are
the same as that provided by the program with optimizer abilities. Any
differences that come about is a measurement of deviation from
Maxwell's laws and thus its applicability. There are other programs
that are available that are useable only for
predetermined planar forms such as the Yagi where all forces are not
accounted for
such as the Corriollis effect i.e. that force is ignored thus Maxwells
laws are not applicable.
Regards
Art
Art