Ok Dan, glad you have gotten in working. Will try and get my program to
sweep. As for the coil you can enter a helix by clicking on "Run", then
"Geometry builder". I have not done anything with this feature, but it
looks interesting.

Frank

"dansawyeror" wrote in message
...
Frank,

I have now been able to get this to work. Thank you. Open the main window,
and then the calculate button, and then select the first option. This
causes my system to perform a sweep. It shows a resonance sweep for this
model.

I am currently stuck performing a successful update of the input file. I
would like to use the windows feature to change the coil spec for
instance.

Dan

Frank wrote:
Dan, here is the code I copied and pasted it directly from 4nec2 nec edit
page. I have not yet figured out how to have swept frequency data, as
the program only seems to recognize the first frequency of 135 MHz.

Frank

CM Loaded 2 m monopole
CE
GW 1 15 0.4 0 5.6 0.4 0 1.6 0.025
GH 2 50 .32 1.6 .4 .4 .4 .4 0.025
GM 100 0 0 0 0 0 0 4 0
GW 3 15 0.4 0 4 0.4 0 0 0.025
GS 0 0 0.025400
GE 1
GN 1
EX 0 3 15 00 1 0
LD 5 101 1 15 5.8001E7
LD 5 102 1 50 5.8001E7
LD 5 3 1 15 5.8001E7
FR 0 41 0 0 135 2
RP 0 181 1 1000 -90 90 1.00000 1.00000
EN


"dansawyeror" wrote in message
...

Frank,

Umm. I tried to set the GM ITS field to 0 and that did not make any
difference. Can you forward the nec file that does not produce the error?

Thanks - Dan

Frank wrote:

Ok Dan, figured where the problem was. It is just necessary to set the
ITS field to zero, and the code runs ok.

Frank

"Frank" wrote in message
news:eXpCf.199081$OU5.8916@clgrps13...


Dan, I am running NEC-Win Pro from Nittany Scientific. I do not have
any experience with 4nec2, but have taken a quick look at the NEC
manual to figure out what the error is.
The "GH" card generates a helix with the base positioned at z = 0. My
first "GW" card positions a wire from the top of the helix with a
length of 4". Since the GH card position is fixed it must be followed
by a coordinate transformation "GM" to position the helix, and the GW
1, card to the desired position. For some reason the last field (ITS
field) was filled with a decimal number indicating the range of "Tags"
to be moved (000.051 which means all tags from zero to 51, but there
are only 2 tags prior to the GM card, so don't know why this happened).
In any case this worked on my model. The default entry for the ITS
field is zero, or just leave blank. This works fine for me, and just
moves the GW 1, and GH card positions as desired.

Experimenting with 4nec2 indicates if the only geometry card is a GH,
followed by a GM card, then the transformation appears to work. It is
only when there are other geometry cards present that the GM function
fails.

More study of the help menu in 4nec2 is required to figure out the
correct structure for the ITS field.

Frank


"dansawyeror" wrote in message
...


I tried to run the nec in 4nec2. It produces and error"

"ITS GM card (x,y) not supported in nec2 engine"

Which model are you using? Do you know the source of this error?

Thanks - Dan




Frank wrote:


Dan,

Be interested to see what the exact dimensions of the coil are.
Anyway, it seems we have some agreement on the 600 nH value, although
my physical NEC helix models do not agree based on my estimate of
your coil dimensions. I understand that EZNec uses a "Minninec"
ground, which allows antenna contact with a perfect ground, but uses
actual ground parameters to analyze the reflections. I am not sure
about this, but would assume from the point of view of the input
impedance, that the ground would be considered perfect; and therefore
lossless. I also noticed I had some borderline NEC warnings when
attempting to construct a coil with #10 AWG, so sometimes had to
resort to a much thinner conductor.

My models showed about 17 ohms at resonance when connected to a
perfect ground. The only time I observed impedances as low as 6 ohms
was far

from resonance when the antenna was highly capacitive. Ideally I

should construct a ground screen, but for the time being will
consider a perfect ground.

A free space dipole might be easier to model, but I am curious to
understand why there are discrepancies in the monopole modeling.

Frank

PS, be interested in any comments on my NEC code:

CM Loaded 2 m monopole
CE
GW 1 15 0.4 0 5.6 0.4 0 1.6 0.025
GH 2 50 .32 1.6 .4 .4 .4 .4 0.025
GM 100 0 0 0 0 0 0 4 000.051
GW 3 15 0.4 0 4 0.4 0 0 0.025
GS 0 0 0.025400
GE 1
GN 1
EX 0 3 15 00 1 0
LD 5 101 1 15 5.8001E7
LD 5 102 1 50 5.8001E7
LD 5 3 1 15 5.8001E7
FR 0 41 0 0 135 2
RP 0 181 1 1000 -90 90 1.00000 1.00000
EN
"dansawyeror" wrote in message
...



Frank,

I will re-measure the coil dimensions. The recall the coil measured
600nH. That is the value I used when I modeled this antenna using
EZNec. It showed resonance at about 145 MHz and 12 Ohms. (That was
using an average real ground.)

If I assume the antenna measurements are correct then is it the
ground that accounts for the difference between 6 Ohms and the
modeled 12 Ohms?

Now I am on to model and measure a center loaded dipole.

Dan

Frank wrote:



"dansawyeror" wrote in message
...




Frank,

The antenna I am trying to model is a center 'loaded vertical'. It
is a 4 inch base, 5 turns at 40 percent spacing on a .8 diameter
inch form and a 4 inch tip. The material is Num 10 solid copper. I
adjust the frequency by stretching or compressing the coil.
Currently it is resonant at about 141.7 Mhz. The 8405a shows a
phase shift of 1 degree per 30 kc change in frequency.

I have used both the vertload model and the EZNEC model. Both
predict an antenna R of about 5 Ohms. The 25 Ohm load shows a 12
db power difference between forward and reverse. The antenna shows
a 10 db power difference between forward and reverse.

Thanks - Dan


Dan, I have modelled a 5 turn inductor, 0.8" diameter, varying in
length from 0.8" to 1.6". The inductance values are 380 - 490 nH.
An, approximately 9" long monopole, with a 5 turn helix appears to
be resonant at about 190 MHz, with a highly reactive 6 ohm input
impedance at 141 MHz. Using a lumped element simulation the
required load inductance, for 141 MHz, is about 600 nH.

The only way to resolve these discrepancies is to do a standard
single port network analyzer calibration and measure the actual
input impedance of the antenna.

Frank