using coax shield to create a loading coil ?
 

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

using coax shield to create a loading coil ?
 

Dan, even more questions: I don't understand the relationship of radial
length to height. c_poise seems to allow anything. What is the "H" of a
loading coil?

Frank


"dansawyeror" wrote in message
...
Follow up:

One of the not so apparent results of Reg's program is the relationship of
radial length to height. I chose 2 meters because they were only .7 meters
high.

I raised your model to 2 meters, that reduced the R to about 20 Ohms.
Raising it
to 3 meters lowers it to 18 Ohms.

How did you calculate the H of the loading coils? Is that easy to edit? It
would
seem that these values are closer.

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

using coax shield to create a loading coil ?
 

Dan,

The lumped inductance of 4 +j1750 comes from your previous comment about the
inductance range from 60 - 90 uH. I just chose the mid range value of 75 uH
at 3.8 MHz. To be exact 2*PI*f*L = 1791 ohms. The real part of 4 ohms is
based on an approximate Q of 400.

Incidentaly I am working at another location this morning. The computer is
an old 600 MHz machine, with 384 MB of RAM, and Windows ME OS. The NEC code
here takes 17 seconds to run.

73,

Frank
"dansawyeror" wrote in message
...
I see the length is set to 1.8 meters already. A 2 meter elevation minimum
is
needed to lower ground effects.

How is the lumped inductance set of 4 Ohms and 1750 Z? What impedance does
that
translate to? How did you calculate this value? 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

using coax shield to create a loading coil ?
 

Dan, here is a preliminary run on a 12 ft monopole model structured as
follows:
base at 6 ft, 10 x 6ft radials. All #14 AWG. Ground - perfect, frequency
3.8 MHz.

Zin = 0.968 - j1847.55 ohms;
Efficiency = 87.4 % (structure copper loss);
Gain = 4.15 dBi;
Take-off angle = 0 deg;
Gain at 27 deg elevation (expected TOA with real ground) = +3.09 dBi.

I will try successive modifications to approach a practical model. The code
I used, modified so it should run in 4nec2, is shown below.

73,

Frank

CM 75 m Vertical 12 ft high
CM base 6 ft up, 10 X 6 ft radials
CM copper conductivity
CE
GW 1 24 0 0 18 0 0 6 0.0026706
GW 2 12 0 0 6 6 0 6 0.0026706
GM 1 9 0 0 36 0 0 0 2
GS 0 0 .3048
GE 1
GN 1
EX 0 1 24 0 1.00000 0.00000
LD 5 1 1 144 5.8001E7
FR 0 11 0 0 3.5 0.05
RP 0 181 1 1000 -90 0 1.00000 1.00000
EN


"Frank's Basement 2" wrote in message
news:dhmKf.6088$_62.3050@edtnps90...
Dan,

The lumped inductance of 4 +j1750 comes from your previous comment about
the
inductance range from 60 - 90 uH. I just chose the mid range value of 75
uH
at 3.8 MHz. To be exact 2*PI*f*L = 1791 ohms. The real part of 4 ohms is
based on an approximate Q of 400.

Incidentaly I am working at another location this morning. The computer
is
an old 600 MHz machine, with 384 MB of RAM, and Windows ME OS. The NEC
code
here takes 17 seconds to run.

73,

Frank
"dansawyeror" wrote in message
...
I see the length is set to 1.8 meters already. A 2 meter elevation
minimum
is
needed to lower ground effects.

How is the lumped inductance set of 4 Ohms and 1750 Z? What impedance
does
that
translate to? How did you calculate this value? 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

using coax shield to create a loading coil ?
 

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

using coax shield to create a loading coil ?
 

Frank,

I tried the nec below. The result was resonant at 21.9 and about 34 Ohms. I am
not competent at reading nec cards yet, however the model editor does not show
any coil loads. That could explain the frequency?

Dan

Thanks - Dan

Frank's Basement 2 wrote:
Dan, here is a preliminary run on a 12 ft monopole model structured as
follows:
base at 6 ft, 10 x 6ft radials. All #14 AWG. Ground - perfect, frequency
3.8 MHz.

Zin = 0.968 - j1847.55 ohms;
Efficiency = 87.4 % (structure copper loss);
Gain = 4.15 dBi;
Take-off angle = 0 deg;
Gain at 27 deg elevation (expected TOA with real ground) = +3.09 dBi.

I will try successive modifications to approach a practical model. The code
I used, modified so it should run in 4nec2, is shown below.

73,

Frank

CM 75 m Vertical 12 ft high
CM base 6 ft up, 10 X 6 ft radials
CM copper conductivity
CE
GW 1 24 0 0 18 0 0 6 0.0026706
GW 2 12 0 0 6 6 0 6 0.0026706
GM 1 9 0 0 36 0 0 0 2
GS 0 0 .3048
GE 1
GN 1
EX 0 1 24 0 1.00000 0.00000
LD 5 1 1 144 5.8001E7
FR 0 11 0 0 3.5 0.05
RP 0 181 1 1000 -90 0 1.00000 1.00000
EN


"Frank's Basement 2" wrote in message
news:dhmKf.6088$_62.3050@edtnps90...

Dan,

The lumped inductance of 4 +j1750 comes from your previous comment about

the

inductance range from 60 - 90 uH. I just chose the mid range value of 75

uH

at 3.8 MHz. To be exact 2*PI*f*L = 1791 ohms. The real part of 4 ohms is
based on an approximate Q of 400.

Incidentaly I am working at another location this morning. The computer

is

an old 600 MHz machine, with 384 MB of RAM, and Windows ME OS. The NEC

code

here takes 17 seconds to run.

73,

Frank
"dansawyeror" wrote in message
...

I see the length is set to 1.8 meters already. A 2 meter elevation

minimum

is

needed to lower ground effects.

How is the lumped inductance set of 4 Ohms and 1750 Z? What impedance

does

that

translate to? How did you calculate this value? 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

using coax shield to create a loading coil ?
 

I missed this one. About 96 uH.

Frank's Basement 2 wrote:
Dan, even more questions: I don't understand the relationship of radial
length to height. c_poise seems to allow anything. What is the "H" of a
loading coil?

Frank


"dansawyeror" wrote in message
...

Follow up:

One of the not so apparent results of Reg's program is the relationship of
radial length to height. I chose 2 meters because they were only .7 meters

high.

I raised your model to 2 meters, that reduced the R to about 20 Ohms.

Raising it

to 3 meters lowers it to 18 Ohms.

How did you calculate the H of the loading coils? Is that easy to edit? It

would

seem that these values are closer.

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

using coax shield to create a loading coil ?
 

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

using coax shield to create a loading coil ?
 

Reg Edwards wrote:

Roy, you seem to have forgotten proximity effect.
. . .

Forgotten? I just didn't see what relevance it had on the difference in
Q between an inductor made from a braided coax shield and one made from
solid tubing. And I can't see from your posting anything which adds to
that discussion. But maybe I'm missing something?

Roy Lewallen, W7EL

using coax shield to create a loading coil ?
 

That's correct Dan. I just wanted to systematically build up the antenna,
adding a component at a time, to note where the major losses are. This was
the first trial with no loading -- except for copper conductivity.

From the other model you sent me it seems that any other attempts are
redundant. The major losses are due to ground loss, as expected.
Unfortunately this can only be overcome by increasing the length, and
number, of radials -- something that is pretty well known. Also inductive
loading of the radials does not seem to have any effect, except for
marginally decreasing the antenna efficiency.

I have been interested in installing a short monopole for 160m, so am very
interested in your results. I have a fairly large lot (visible on "Google
Earth), so am not so restricted in radial length.

73,

Frank


"dansawyeror" wrote in message
...
Frank,

I tried the nec below. The result was resonant at 21.9 and about 34 Ohms.
I am not competent at reading nec cards yet, however the model editor does
not show any coil loads. That could explain the frequency?

Dan

Thanks - Dan

Frank's Basement 2 wrote:
Dan, here is a preliminary run on a 12 ft monopole model structured as
follows:
base at 6 ft, 10 x 6ft radials. All #14 AWG. Ground - perfect,
frequency
3.8 MHz.

Zin = 0.968 - j1847.55 ohms;
Efficiency = 87.4 % (structure copper loss);
Gain = 4.15 dBi;
Take-off angle = 0 deg;
Gain at 27 deg elevation (expected TOA with real ground) = +3.09 dBi.

I will try successive modifications to approach a practical model. The
code
I used, modified so it should run in 4nec2, is shown below.

73,

Frank

CM 75 m Vertical 12 ft high
CM base 6 ft up, 10 X 6 ft radials
CM copper conductivity
CE
GW 1 24 0 0 18 0 0 6 0.0026706
GW 2 12 0 0 6 6 0 6 0.0026706
GM 1 9 0 0 36 0 0 0 2
GS 0 0 .3048
GE 1
GN 1
EX 0 1 24 0 1.00000 0.00000
LD 5 1 1 144 5.8001E7
FR 0 11 0 0 3.5 0.05
RP 0 181 1 1000 -90 0 1.00000 1.00000
EN


"Frank's Basement 2" wrote in message
news:dhmKf.6088$_62.3050@edtnps90...

Dan,

The lumped inductance of 4 +j1750 comes from your previous comment about

the

inductance range from 60 - 90 uH. I just chose the mid range value of 75

uH

at 3.8 MHz. To be exact 2*PI*f*L = 1791 ohms. The real part of 4 ohms
is
based on an approximate Q of 400.

Incidentaly I am working at another location this morning. The computer

is

an old 600 MHz machine, with 384 MB of RAM, and Windows ME OS. The NEC

code

here takes 17 seconds to run.

73,

Frank
"dansawyeror" wrote in message
...

I see the length is set to 1.8 meters already. A 2 meter elevation

minimum

is

needed to lower ground effects.

How is the lumped inductance set of 4 Ohms and 1750 Z? What impedance

does

that

translate to? How did you calculate this value? 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