Hi Dan, I tried your program, it runs fine, and I get identical results. I
also learned a couple of things from your code: Setting "GE" = 0 implies no
ground plane present (I would normally set it to "1"), and my "Nec Vu"
function shows the antenna with no ground plane. Running the program,
however, returns the correct result with an average ground.

I also ran the program with no radial loading (code below), and the gain
increased marginally. It seems loading the radials does not help much.

Frank



CM 75 m Vertical 16 ft high
CE
GW 1 11 0 0 7.5342 0 0 2.6 8.13999e-4
GW 2 12 0 0 2.6 1.8288 0 2.6 8.13999e-4
GW 3 12 0 0 2.6 1.47953028 1.07494167 2.6 8.13999e-4
GW 4 12 0 0 2.6 0.56513028 1.73929216 2.6 8.13999e-4
GW 5 12 0 0 2.6 -0.5651303 1.73929216 2.6 8.13999e-4
GW 6 12 0 0 2.6 -1.4795303 1.07494167 2.6 8.13999e-4
GW 7 12 0 0 2.6 -1.8288 2.2396e-16 2.6 8.13999e-4
GW 8 12 0 0 2.6 -1.4795303 -1.0749417 2.6 8.13999e-4
GW 9 12 0 0 2.6 -0.5651303 -1.7392922 2.6 8.13999e-4
GW 10 12 0 0 2.6 0.56513028 -1.7392922 2.6 8.13999e-4
GW 11 12 0 0 2.6 1.47953028 -1.0749417 2.6 8.13999e-4
GE 1
GN 2 0 0 0 13.0000 0.0050
LD 4 1 7 7 3 2100
LD 5 1 1 107 5.8001E7
EX 0 1 11 00 1 0
FR 0 11 0 0 3.5 0.05
RP 0 181 1 1000 -90 90 1.00000 1.00000
EN
"dansawyeror" wrote in message
...
Frank,

Good morning. I had a few minutes and created the following model. It is
shortened and the number of segments in the vertical is increased. I also
set the inductors to 3 Ohms. (That may be optimistic for the antenna,
Reg's program predicts 2 Ohms is achievable for larger coils on the
radials.) (Sorry for the long numbers.) This shows a resonance at 3.9 MHz
and 9.9 Ohms.

4nec2 did not like the GM card, I did not remove it.

Dan

CM 75 m Vertical 16 ft high
CE
GW 1 11 0 0 7.5342 0 0 2.6
8.13999e-4
GW 2 12 0 0 2.6 1.8288 0 2.6
8.13999e-4
GW 3 12 0 0 2.6 1.47953028 1.07494167
2.6 8.13999e-4
GW 4 12 0 0 2.6 0.56513028 1.73929216
2.6 8.13999e-4
GW 5 12 0 0 2.6 -0.5651303 1.73929216
2.6 8.13999e-4
GW 6 12 0 0 2.6 -1.4795303 1.07494167
2.6 8.13999e-4
GW 7 12 0 0 2.6 -1.8288 2.2396e-16
2.6 8.13999e-4
GW 8 12 0 0 2.6 -1.4795303 -1.0749417
2.6 8.13999e-4
GW 9 12 0 0 2.6 -0.5651303 -1.7392922
2.6 8.13999e-4
GW 10 12 0 0 2.6 0.56513028 -1.7392922
2.6 8.13999e-4
GW 11 12 0 0 2.6 1.47953028 -1.0749417
2.6 8.13999e-4
GE 0
LD 5 1 0 0 58001000 0
LD 4 1 7 7 3 2100
LD 4 2 1 1 3 2000
LD 4 3 1 1 3 2000
LD 4 4 1 1 3 2000
LD 4 5 1 1 3 2000
LD 4 6 1 1 3 2000
LD 4 7 1 1 3 2000
LD 4 8 1 1 3 2000
LD 4 9 1 1 3 2000
LD 4 10 1 1 3 2000
LD 4 11 1 1 3 2000
EX 0 1 11 0 1 0
GN 2 0 0 0 13 5.e-3
FR 0 1 0 0 3.5 0
EN



Frank wrote:
Dan,

I find antenna problems very interesting, so do not mind spending time on
running models.

The radials were based on your comments in an earlier post about "2 meter
radials". You have provided me with a lot of information in subsequent
posts, so will use that info to try and construct a more realistic model.
I still have a couple of questions though: how many radials are you
using, and where do you position the radial loading coils?

You are correct about the "GM" problem, and I forgot it produced an error
in 4nec2. The last "ITS" field should be an integer. I have not
completely confirmed it with 4nec2, but the ITS field refers to the tag
to be replicated -- in this case tag 2. GM generates 9 tags rotated by
36 degrees, and saves a ton of GW cards.

I cannot understand why your simulation takes 5 minutes since there are
only 184 segments, and 11 frequencies. I just checked and it takes only
3.9 seconds with my NEC2 program, or 4nec2. Anyway my model will take a
lot of revision to replicate your actual antenna. May get a chance to
look at it later tonight.

73,

Frank


"dansawyeror" wrote in message
...

Frank,

Thanks for the model. I did not expect you to model this or I would have
been more specific. The antenna is about 14 feet. The coil is about 4
feet from the base.

Now the radials: Did you base the radial from Reg's model? Try 3.97 MHz,
1 meter above ground, 3 meter radials, and a 60mm long by 300 mm dia 66.7
uH loading coil. These grounds have to be tuned as well.

I am using 4nec2 and am getting errors from the GM card. Wasn't there an
issue with these being a decimal instead of an integer?

BTW - The simulation on my laptop takes over 5 minutes to run.

Dan

Frank's Basement 2 wrote:

Hi Dan, thanks for the interesting info. You did not specify
dimensions,
but from your comments it appears you are using a vertical about 23 ft
high.
Such a monopole would have a 3.5 ohm input impedance when placed above a
perfectly conducting ground, and gain about +4.5 dBi. Adding a center
loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi.
Base loading provides an input impedance of 5.5 ohms with almost the
same
gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above
an
average ground, the input impedance increases to 40 ohms, and gain -6.3
dBi.

Adding lumped element loading coils, (75 uH, Q = 400) in each radial
(antenna base end) drops the input impedance to 37 ohms, and gain -6.4
dBi.
Don't know why this does not agree with Reg's program. Probably I made
some
fundamental error with the NEC model. Included the code below, so you
may
see an error I missed.

73,

Frank

CM 75 m Vertical 23 ft high
CE
GW 1 64 0 0 23 0 0 0.25 0.0026706
GW 2 12 0 0 0.25 6 0 0.25 0.0026706
GM 1 9 0 0 36 0 0 0 002.002
GS 0 0 .3048
GE 1
GN 2 0 0 0 13.0000 0.0050
EX 0 1 64 0 1.00000 0.00000
LD 5 1 1 184 5.8001E7
LD 4 1 33 33 4 1600
LD 4 2 1 1 4 1750
LD 4 3 1 1 4 1750
LD 4 4 1 1 4 1750
LD 4 5 1 1 4 1750
LD 4 6 1 1 4 1750
LD 4 7 1 1 4 1750
LD 4 8 1 1 4 1750
LD 4 9 1 1 4 1750
LD 4 10 1 1 4 1750
LD 4 11 1 1 4 1750
FR 0 11 0 0 3.5 0.05
RP 0 181 1 1000 -90 0 1.00000 1.00000
EN






Frank,

Good morning. Let me start at the beginning. I have a loaded vertical
on

75


meters. The combination of the antenna and ground measure about 40 Ohms
at

the


antenna. The models all show such an antenna over a perfect ground
should

have a


radiation resistance of between 3 and 4 Ohms. That says the antenna
system

is


less the 10% efficient.

This then is a journey to reduce ground resistance. Attempts to add

radials and


wire mesh to the ground have had very little if no effect. This leads
to

Reg's


c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned
to

a 2


meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms

range.


Together this should result is a 8 Ohm system. The ratio can be
directly
inferred as an performance improvement of 5 to 1 or 7 db. This is worth

some


effort.

To answer your question the first step will be one coil and one radial.

The


objective is the get the antenna system close to 10 Ohms. From there I

will


experiment with adding radials and coils. I am not sure what to expect.

Thanks - Dan





Frank wrote:


Not sure I understand what is going on Dan. Are you planning on
loading
each radial element?

Frank


"dansawyeror" wrote in message
...



These results were from Reg's c_poise program. The band is 75 meters
and
the coils were about 70 uH. The coils were a relatively large
diameter,

on


the order of a meter. The wire lengths were about 20 meters. By
varying
the length the coil, the coil wire may be varies from 1mm to 12mm.

Richard Clark wrote:



On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror
wrote:





The devil is in the details. Modeling shows large coils with 1 mm
wire
have a Q in the range of a few hundred. On the other hand a coil
with

12


mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6

Ohms


while the 12 mm coil is on the order of 1 Ohm.

Given these model results it says there is a significant difference
between 1 mm and 12 mm coils.


Hi Dan,

In the details, indeed. What is the LENGTH of wire in this 6 Ohm
resistor? What is the LENGTH
of wire in this 1 Ohm resistor? How many turns are in these "large
coils?" What is their diameter? What is their solenoid length?

Without these details, there is nothing said that is significant.

73's
Richard Clark, KB7QHC