Now I understand the confusion. I am not using EZNEC, and am not familiar
with the program. My analysis is written in NEC code. I do have access to
some graphical results with the use of NEC-Win Pro, but have taken the NEC
output file and imported it to an Excel spread sheet (NEC-Win Pro's
simplified data entry formats do not recognize cards such as 'GH" and "GM"
so am forced to resort to direct code entry). For a constant power input I
therefore have to read the input impedance results, then calculate the
required "Peak" Voltage for the desired power -- note that NEC requires all
voltages and currents to be peak values.

If anybody is interested I have uploaded the models to my wife's business
web site (she will probably kill me when she finds out!). The models show
the current distribution of two 84" monopoles; one of which is loaded with a
6" long, 12 turn helix, of 2.5" diameter. The other is unloaded. The
ground is defined as "Perfect". The input power is set at 100 W. Just
looking at the curves led me to the (mostly) wrong conclusion (verified with
numerical integration of the Excel data) that the Integral of I(z)dz is a
constant. The results are posted at www.carolyns-creations.com/ve6cb

Regards,

Frank


"Roy Lewallen" wrote in message
...
I'd be glad to help clarify any confusion, but I can't for the life of me
figure out what the confusion is about.

Regarding EZNEC's sources, you have the option of using a constant-current
source, constant-voltage source, or having a fixed power applied to the
model. If a fixed power level is chosen, multiple sources will have the
same ratio of voltages and currents as you've specified. For example, if
your model has two sources, one of 1 amp and the other 2 amps, and you
choose a fixed power level, the current from the second source will always
be twice the current from the first (and at the specified relative phase),
but both will be modified as necessary to produce the total power you
specified.

Fixed power is selected in the Options menu. While the relative source
currents (2 amps and 1 amp in the example) are saved with the model, the
Options menu choices aren't. They're applied to all models. Changes you
make in the Options menu remain effective until you end the program. If
you choose "Save as Default" from the Options menu, the current settings
will remain in effect even after you end the program, until you change
them.

I don't personally use a fixed power level very often, since I'm more
often interested in things like currents on wires relative to a source, so
it's convenient for me to set the source to 1 amp. The fixed power level
is useful whenever you need an absolute value of voltage or current,
though, or want to see how the voltage, current, or load power dissipation
changes as you modify the model. It can be helpful in understanding
radiation resistance, by illustrating the relationship among feepoint
power, current, and resistance.

Just what is it that's confusing about radiation resistance and EZNEC
results? Richard's EZNEC results are exactly what I'd expect, and they're
consistent with theory. (I'm talking about established theory found in
textbooks, not ones cooked up by people who don't understand basic
principles or common nomenclature.) The small gain change due to the
ground reflection reaction to altered current distribution was admittedly
a surprise, but it makes perfect sense after a moment's thought. If
someone can summarize what seems to be wrong, I'll do my honest best to
explain it. Is the problem that the gain doesn't go up with Rr? Of course
it doesn't, in the nearly lossless antennas of Richard's models. Why
should it? I tried to explain why in my earlier posting, but I'll try
again if that's what the problem is.

Roy Lewallen, W7EL

Richard Clark wrote:

On Sat, 06 Nov 2004 02:34:32 GMT, "Frank"
wrote:


Regarding Richard's comments "Assuming the same currents". Not sure I
understand, since the feed-point current varies with constant power


Hi Frank,

That is quite simple. The file VERT1.EZ has as a source, a constant
current generator - a fact I pointed out in the summary of my results.
Your presumption of constant power is a natural one for the sake of
common discussion, but it is not even the default source for EZNEC.
[However, having said that, a curiosity of program design has found
that the concept of a "new file" has been orphaned. Any time the
application is opened, it is opened with LAST.EZ and I cannot recall
upon initial acquisition if EZNEC ever started with a blank slate.
Given that you cannot have less than 1 wire nor 1 source, then there
is on way to force a blank file. Hence the concept of a default
resides in the last file opened.]

In other words, each and every iteration of antenna, irrespective of
its presumed or actual Rr or drivepoint Z had the same current applied
to it, 1 Ampere.

Now, if ANY resistance had changed, it then follows that the POWER
would have changed too (which presents us with that puzzle

confused by the expression V=I/R.

that came out of the blue) at a linear rate (1² = 1).

Note, a doubling of drivepoint Z by the addition of a load does not
result in 3dB gain over the former design. I have seen I * I * R
bandied about as an "explanation" and yet at least 3dB is remarkably
absent in the results. What R is this that everyone speaks of?
Certainly not the real component of drivepoint Z. What about the Rr
that must've changed? Copper loss absorb it? Ground loss?

As I offered, I must've done something wrong, taken the wrong turn,
interpreted the modeler in error, -ahem- not read the help file....

I will bet it was that last one - which only reveals no one has. ;-)

[aside]
So, Wes, I will amend my ways and delve into that treasure of
knowledge before returning your work in kind (no point in retread
effort) sometime tomorrow morning. [to the audience]
C'mon folks, this has to be an especially simple resolution - I'm glad
that so many are just as flummoxed (even Reg is uncharacteristically
silent in this regard :-)

73's
Richard Clark, KB7QHC