8405a working and measuring resonance?
 

Well, After many trials and much learning I believe the 8405a is currently
working and actually making measurements. The breakthrough was a web article
showing Tau ranging from -1 to +1. This finally made sense of the comments
posted here.

Now to the setup and the measurements. I have built a loaded vertical for 2
meters and placed it over a 3 foot by 5 foot ground screen. The exact frequency
of the antenna is unknown. This is assembly moved into another room and
connected via an unknown length of 50 Ohm cable. The technique is labor
intensive, but in the end produces consistent results.

The 8405a is connected to a dual directional coupler. The connector lengths are
tuned to produce zero phase. The coupler is driven by a signal generator and
connected to the antenna assembly.

Now the tuning process: It involves tuning the antenna for a zero phase return
and then temporally replacing the antenna with a 25 Ohm terminator. The 8405a is
set to zero phase adjusted to he terminator. The antenna is then re-substituted
for the terminator and the frequency is adjusted to produce the next zero phase.
The cycle is the frequency is adjusted to the antenna and the meter zeroed phase
adjusted to the terminator. This is repeated.

The first attempt did not resolve. That is it the values did not trend toward a
common frequency and phase. However the second attempt, which was just a few MHz
away did. The result was a measurement that was consistent and repeatable. The
meter was set to the 6 degree scale and the measurements were sensitive to 5 kc
differences in frequency. The results were consistent to 1/5 a degree.

The Smith Chart shows for a purely resistive load that the return phase from a
fixed cable and frequency is independent of R. That is the return phase is
constant for a frequency, fixed cable, and pure resistive load. That would imply
that when the phase return is the same for a resistive load and an unknown then
the unknown is a pure resistive load. This is a way to normalize the effects of
an unknown cable to determine resonance.

I think this actually works. Is there a better way to do this?

Thanks - Dan

8405a working and measuring resonance?
 

"dansawyeror" wrote in message
...
Well, After many trials and much learning I believe the 8405a is currently
working and actually making measurements. The breakthrough was a web
article showing Tau ranging from -1 to +1. This finally made sense of the
comments posted here.

Now to the setup and the measurements. I have built a loaded vertical for
2 meters and placed it over a 3 foot by 5 foot ground screen. The exact
frequency of the antenna is unknown. This is assembly moved into another
room and connected via an unknown length of 50 Ohm cable. The technique is
labor intensive, but in the end produces consistent results.

The 8405a is connected to a dual directional coupler. The connector
lengths are tuned to produce zero phase. The coupler is driven by a signal
generator and connected to the antenna assembly.

Now the tuning process: It involves tuning the antenna for a zero phase
return and then temporally replacing the antenna with a 25 Ohm terminator.
The 8405a is set to zero phase adjusted to he terminator. The antenna is
then re-substituted for the terminator and the frequency is adjusted to
produce the next zero phase. The cycle is the frequency is adjusted to the
antenna and the meter zeroed phase adjusted to the terminator. This is
repeated.

The first attempt did not resolve. That is it the values did not trend
toward a common frequency and phase. However the second attempt, which was
just a few MHz away did. The result was a measurement that was consistent
and repeatable. The meter was set to the 6 degree scale and the
measurements were sensitive to 5 kc differences in frequency. The results
were consistent to 1/5 a degree.

The Smith Chart shows for a purely resistive load that the return phase
from a fixed cable and frequency is independent of R. That is the return
phase is constant for a frequency, fixed cable, and pure resistive load.
That would imply that when the phase return is the same for a resistive
load and an unknown then the unknown is a pure resistive load. This is a
way to normalize the effects of an unknown cable to determine resonance.

I think this actually works. Is there a better way to do this?

Thanks - Dan

Why are you using a 25 ohm termination? The procedure for calibration
requires a short, open, and 50 ohm load. It is also important that you know
the coupler directivity at the test frequency. There is nothing wrong with
calibrating the test fixture at the end of an unknown length of coax;
although you will experience some degradation in the dynamic range of the
return loss.

Regards,

Frank

8405a working and measuring resonance?
 

Frank,

The Smith Chart shows that a termination value other then 50 Ohms is required to
calibrate the 8405a to zero phase for the frequency and cable. That said there
are two zero points, I will have to think about the effect of these on the
measurements.

Frank wrote:
"dansawyeror" wrote in message
...

Well, After many trials and much learning I believe the 8405a is currently
working and actually making measurements. The breakthrough was a web
article showing Tau ranging from -1 to +1. This finally made sense of the
comments posted here.

Now to the setup and the measurements. I have built a loaded vertical for
2 meters and placed it over a 3 foot by 5 foot ground screen. The exact
frequency of the antenna is unknown. This is assembly moved into another
room and connected via an unknown length of 50 Ohm cable. The technique is
labor intensive, but in the end produces consistent results.

The 8405a is connected to a dual directional coupler. The connector
lengths are tuned to produce zero phase. The coupler is driven by a signal
generator and connected to the antenna assembly.

Now the tuning process: It involves tuning the antenna for a zero phase
return and then temporally replacing the antenna with a 25 Ohm terminator.
The 8405a is set to zero phase adjusted to he terminator. The antenna is
then re-substituted for the terminator and the frequency is adjusted to
produce the next zero phase. The cycle is the frequency is adjusted to the
antenna and the meter zeroed phase adjusted to the terminator. This is
repeated.

The first attempt did not resolve. That is it the values did not trend
toward a common frequency and phase. However the second attempt, which was
just a few MHz away did. The result was a measurement that was consistent
and repeatable. The meter was set to the 6 degree scale and the
measurements were sensitive to 5 kc differences in frequency. The results
were consistent to 1/5 a degree.

The Smith Chart shows for a purely resistive load that the return phase
from a fixed cable and frequency is independent of R. That is the return
phase is constant for a frequency, fixed cable, and pure resistive load.
That would imply that when the phase return is the same for a resistive
load and an unknown then the unknown is a pure resistive load. This is a
way to normalize the effects of an unknown cable to determine resonance.

I think this actually works. Is there a better way to do this?

Thanks - Dan


Why are you using a 25 ohm termination? The procedure for calibration
requires a short, open, and 50 ohm load. It is also important that you know
the coupler directivity at the test frequency. There is nothing wrong with
calibrating the test fixture at the end of an unknown length of coax;
although you will experience some degradation in the dynamic range of the
return loss.

Regards,

Frank

8405a working and measuring resonance?
 

"dansawyeror" wrote in message
...
Frank,

The Smith Chart shows that a termination value other then 50 Ohms is
required to calibrate the 8405a to zero phase for the frequency and cable.
That said there are two zero points, I will have to think about the effect
of these on the measurements.

Dan,

I am not sure how you arrived at the above conclusion. The procedure should
be as follows: Short the end of the coax at the antenna location, then
adjust the line stretcher for a 180 degrees phase shift. This is your
reference reflection coefficient of -1 (i.e. 1 180). Remove the short and
verify the reflection coefficient is 1 0. Connect a known 50 ohm load,
which should provide a return loss of 30 dB. The angle of the reflection
coefficient is irrelevant. If the return loss of the 50 ohm load is
significantly less than 30 dB, then either your load is not very good, or
you have poor coupler directivity. Attach the antenna, measure, and record,
the magnitude and angle of the reflection coefficient. Repeat the procedure
for all frequencies of interest. You will then be able to plot the result
on the Smith Chart. At the frequencies you are working, which I believe is
in the 100 to 200 MHz range, it is doubtful that the non-ideal short/load
standards parasitics will effect the results significantly.

I have done such measurements countless times, although with HP VNAs, which
makes the procedure far less tedious.

Hope this helps,

Frank

8405a working and measuring resonance?
 

Frank,

Your comment about my post is correct upon analysis it is not relevant.

I am trying to identify the resonance frequency of an antenna. When that point
is found I am trying to measure the input impedance (should be R + 0j).

Assuming 50 Ohm source and cable, the smith chart shows for lengths of cable
terminated in values other the 50 Ohms, say 25R 0j, those points will plot of a
constant SWR = 2 circle. I am using that circle below:

I am assuming that for a frequency where the antenna is resonant that the phase
read from the antenna and the phase read from non 50 Ohm 0j load will be the
same. If that is true then 'zeroing' the meter by adjusting the phase offset
will not effect the frequency of resonance. It is simply a convenience.

This method should yield a direct resonant frequency reading.

Dan

Frank wrote:
"dansawyeror" wrote in message
...

Frank,

The Smith Chart shows that a termination value other then 50 Ohms is
required to calibrate the 8405a to zero phase for the frequency and cable.
That said there are two zero points, I will have to think about the effect
of these on the measurements.


Dan,

I am not sure how you arrived at the above conclusion. The procedure should
be as follows: Short the end of the coax at the antenna location, then
adjust the line stretcher for a 180 degrees phase shift. This is your
reference reflection coefficient of -1 (i.e. 1 180). Remove the short and
verify the reflection coefficient is 1 0. Connect a known 50 ohm load,
which should provide a return loss of 30 dB. The angle of the reflection
coefficient is irrelevant. If the return loss of the 50 ohm load is
significantly less than 30 dB, then either your load is not very good, or
you have poor coupler directivity. Attach the antenna, measure, and record,
the magnitude and angle of the reflection coefficient. Repeat the procedure
for all frequencies of interest. You will then be able to plot the result
on the Smith Chart. At the frequencies you are working, which I believe is
in the 100 to 200 MHz range, it is doubtful that the non-ideal short/load
standards parasitics will effect the results significantly.

I have done such measurements countless times, although with HP VNAs, which
makes the procedure far less tedious.

Hope this helps,

Frank

8405a working and measuring resonance?
 

On Sun, 22 Jan 2006 09:29:38 -0800, dansawyeror
wrote:

Frank,

Your comment about my post is correct upon analysis it is not relevant.

I am trying to identify the resonance frequency of an antenna. When that point
is found I am trying to measure the input impedance (should be R + 0j).

Assuming 50 Ohm source and cable, the smith chart shows for lengths of cable
terminated in values other the 50 Ohms, say 25R 0j, those points will plot of a
constant SWR = 2 circle.

Only when the cable Zo = 50 +j0.

8405a working and measuring resonance?
 

"dansawyeror" wrote in message
...
Frank,

Your comment about my post is correct upon analysis it is not relevant.

I am trying to identify the resonance frequency of an antenna. When that
point is found I am trying to measure the input impedance (should be R +
0j).

Assuming 50 Ohm source and cable, the smith chart shows for lengths of
cable terminated in values other the 50 Ohms, say 25R 0j, those points
will plot of a constant SWR = 2 circle. I am using that circle below:

I am assuming that for a frequency where the antenna is resonant that the
phase read from the antenna and the phase read from non 50 Ohm 0j load
will be the same. If that is true then 'zeroing' the meter by adjusting
the phase offset will not effect the frequency of resonance. It is simply
a convenience.

This method should yield a direct resonant frequency reading.

Dan

Dan, The reflection coefficient of 25 ohms is 0.333 180, so if you do trim
the line stretcher for 180 degrees, then attaching the antenna will
determine how close you are to nominal R + j0. You need to reset your line
stretcher at each frequency until you obtain a 180 degree phase shift on the
return loss from the antenna. It is reasonable to assume that your antenna
has an impedance in the region of 37 ohms, so the 180 phase shift is
probably correct. For the reflection coefficient at 0.333 0 the input
impedance is 100 ohms. For such an antenna it is probably easer to just
tune the antenna for minimum reflection coefficient and forget the phase
angle.

Frank

8405a working and measuring resonance?
 

I am assuming the reflection angle of 0j terminations would all be the same (you
said 180), this includes both resistive loads and an antenna at resonance. The
method I am using relies on that.

I am confused about one thing in the smith chart program. Cables identified as
stubs create a circle that goes through infinity and do not exhibit a constant
SWR, while simple cables create a constant SWR circle with the center and 50 Ohm
0j.

I believe the setup I am testing exhibits the constant SWR characteristic.

Dan

Frank wrote:
"dansawyeror" wrote in message
...

Frank,

Your comment about my post is correct upon analysis it is not relevant.

I am trying to identify the resonance frequency of an antenna. When that
point is found I am trying to measure the input impedance (should be R +
0j).

Assuming 50 Ohm source and cable, the smith chart shows for lengths of
cable terminated in values other the 50 Ohms, say 25R 0j, those points
will plot of a constant SWR = 2 circle. I am using that circle below:

I am assuming that for a frequency where the antenna is resonant that the
phase read from the antenna and the phase read from non 50 Ohm 0j load
will be the same. If that is true then 'zeroing' the meter by adjusting
the phase offset will not effect the frequency of resonance. It is simply
a convenience.

This method should yield a direct resonant frequency reading.

Dan


Dan, The reflection coefficient of 25 ohms is 0.333 180, so if you do trim
the line stretcher for 180 degrees, then attaching the antenna will
determine how close you are to nominal R + j0. You need to reset your line
stretcher at each frequency until you obtain a 180 degree phase shift on the
return loss from the antenna. It is reasonable to assume that your antenna
has an impedance in the region of 37 ohms, so the 180 phase shift is
probably correct. For the reflection coefficient at 0.333 0 the input
impedance is 100 ohms. For such an antenna it is probably easer to just
tune the antenna for minimum reflection coefficient and forget the phase
angle.

Frank

8405a working and measuring resonance?
 

dansawyeror wrote:
I am assuming the reflection angle of 0j terminations would all be the
same (you said 180), this includes both resistive loads and an antenna
at resonance. The method I am using relies on that.

I am confused about one thing in the smith chart program. Cables
identified as stubs create a circle that goes through infinity and do
not exhibit a constant SWR, while simple cables create a constant SWR
circle with the center and 50 Ohm 0j.

I believe the setup I am testing exhibits the constant SWR characteristic.

No real-world transmission line exhibits a constant SWR since
no real-world transmission line is lossless. Constant SWR
circles are approximations. The actual SWR curve is a spiral
from a point on that constant SWR circle that, in the limit,
spirals down to the Z0 of the line.

For instance, using Owen's feedline calculator, the SWR at a
500 ohm antenna fed with 100 feet of RG-58A is 10:1 and the
SWR at the other (source) end is 1.42:1 for 146 MHz.
--
73, Cecil http://www.qsl.net/w5dxp

8405a working and measuring resonance?
 

I am assuming the reflection angle of 0j terminations would all be the same
(you said 180), this includes both resistive loads and an antenna at
resonance. The method I am using relies on that.

I am confused about one thing in the smith chart program. Cables
identified as stubs create a circle that goes through infinity and do not
exhibit a constant SWR, while simple cables create a constant SWR circle
with the center and 50 Ohm 0j.

I believe the setup I am testing exhibits the constant SWR characteristic.

Dan

Dan, if the load is resistive, and less than 50 ohms (assuming the center of
the Smith Chart is considered to be 50 ohms), then the angle of the
reflection coefficient is 180 degrees. If the load is resistive, and
greater than 50 ohms, then the reflection coefficient angle is 0 degrees.
As you approach the center of the Smith Chart the angle becomes less and
less relevant.

Shunt stubs - either open or shorted - always pass through "zero" (And
infinity - which you will not see since it is in parallel with the load
impedance) and the selected impedance on the Smith Chart. This is based on
the effect that an open stub, at quarter wave multiples, will exhibit
successive open and short circuits; as will a shorted stub.

Your method will exhibit a constant reflection coefficient circle (and
VSWR), with the angle varying from 180 degrees through zero degrees and then
back, through negative angles, to 180 degrees.

Frank

8405a working and measuring resonance?
 

Frank, this is consistent with what I am observing. The claim is for a given
frequency when a 0j load (in the range of 10 to 40 Ohms) and an unknown load
(assumed to be in the range of 10 to 40 Ohms) show the same phase shift then the
unknown is 0j also. It is not necessary that the loads be the same value, only
within the range. (I will have to experiment with loads over 60.)

So far nothing has surfaced to contradict this.

Thanks - Dan

Your method will exhibit a constant reflection coefficient circle (and
VSWR), with the angle varying from 180 degrees through zero degrees and then
back, through negative angles, to 180 degrees.

Frank

8405a working and measuring resonance?
 

"dansawyeror" wrote in message
...
Frank, this is consistent with what I am observing. The claim is for a
given frequency when a 0j load (in the range of 10 to 40 Ohms) and an
unknown load (assumed to be in the range of 10 to 40 Ohms) show the same
phase shift then the unknown is 0j also. It is not necessary that the
loads be the same value, only within the range. (I will have to experiment
with loads over 60.)

So far nothing has surfaced to contradict this.

Thanks - Dan

Dan, essentially your assumptions are correct providing you have no error
terms such as poor directivity.

Frank

8405a working and measuring resonance?
 

Thanks. I have two coupler systems, one with very good directivity and one with
only moderate directivity. The antenna is resonant at about 141.6 MHz. There is
a difference of about a couple of hundred kc between the systems.

Now on the the "R" measurements. Both systems indicate an antenna resistance of
over 30 Ohms. This antenna has been modeled with three different models. They
all indicate a Rr in the range of 5 Ohms. The antenna is grounded by a 3 foot by
5 foot screen mesh. While this is not infinite, it should provide a good ground.
Do you have a suggestion of where to look for the discrepancy?

Dan

Frank wrote:
"dansawyeror" wrote in message
...

Frank, this is consistent with what I am observing. The claim is for a
given frequency when a 0j load (in the range of 10 to 40 Ohms) and an
unknown load (assumed to be in the range of 10 to 40 Ohms) show the same
phase shift then the unknown is 0j also. It is not necessary that the
loads be the same value, only within the range. (I will have to experiment
with loads over 60.)

So far nothing has surfaced to contradict this.

Thanks - Dan


Dan, essentially your assumptions are correct providing you have no error
terms such as poor directivity.

Frank

8405a working and measuring resonance?
 

"dansawyeror" wrote in message
...
Thanks. I have two coupler systems, one with very good directivity and one
with only moderate directivity. The antenna is resonant at about 141.6
MHz. There is a difference of about a couple of hundred kc between the
systems.

Now on the the "R" measurements. Both systems indicate an antenna
resistance of over 30 Ohms. This antenna has been modeled with three
different models. They all indicate a Rr in the range of 5 Ohms. The
antenna is grounded by a 3 foot by 5 foot screen mesh. While this is not
infinite, it should provide a good ground. Do you have a suggestion of
where to look for the discrepancy?

Dan

Dan, the frequency difference is most likely caused by the poor directivity
of one of your couplers, so would not worry about it. Just take the reading
with the better coupler. The forward power coupled into the reverse port
will cause a phase error.

As for your modelling: what program are you using, and how do you describe
the ground screen? I ran a quick model above a perfect ground -- using
NEC2. According to my program the input impedance is 36 ohms at resonance.
The radiation efficiency, with a copper conductor, is 99.6%, so the
radiation resistance is obviously very close to 36 ohms. I can run a model
with a ground screen, but would like to replicate your structure as close as
possible. The actual height of my model monopole is 0.505 m (19.88"), and
is resonant at 141.8 MHz.

Frank

8405a working and measuring resonance?
 

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

Frank wrote:
"dansawyeror" wrote in message
...

Thanks. I have two coupler systems, one with very good directivity and one
with only moderate directivity. The antenna is resonant at about 141.6
MHz. There is a difference of about a couple of hundred kc between the
systems.

Now on the the "R" measurements. Both systems indicate an antenna
resistance of over 30 Ohms. This antenna has been modeled with three
different models. They all indicate a Rr in the range of 5 Ohms. The
antenna is grounded by a 3 foot by 5 foot screen mesh. While this is not
infinite, it should provide a good ground. Do you have a suggestion of
where to look for the discrepancy?

Dan


Dan, the frequency difference is most likely caused by the poor directivity
of one of your couplers, so would not worry about it. Just take the reading
with the better coupler. The forward power coupled into the reverse port
will cause a phase error.

As for your modelling: what program are you using, and how do you describe
the ground screen? I ran a quick model above a perfect ground -- using
NEC2. According to my program the input impedance is 36 ohms at resonance.
The radiation efficiency, with a copper conductor, is 99.6%, so the
radiation resistance is obviously very close to 36 ohms. I can run a model
with a ground screen, but would like to replicate your structure as close as
possible. The actual height of my model monopole is 0.505 m (19.88"), and
is resonant at 141.8 MHz.

Frank

8405a working and measuring resonance?
 

"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

8405a working and measuring resonance?
 

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

8405a working and measuring resonance?
 

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

8405a working and measuring resonance?
 

Frank,

I will take the coil measurements.

Into which model programs can this description be loaded? Is there a 'howto'. I
looked on how to dump my model from EZNec and could not find it.

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

8405a working and measuring resonance?
 

Frank,

I will take the coil measurements.

Into which model programs can this description be loaded? Is there a 'howto'. I
looked on how to dump my model from EZNec and could not find it.

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

8405a working and measuring resonance?
 

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

8405a working and measuring resonance?
 

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

8405a working and measuring resonance?
 

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

8405a working and measuring resonance?
 

What are these "Cards" you guys are referring to ?

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

8405a working and measuring resonance?
 

A card is a line of NEC code. I guess it is a hold over from the old days
when NEC must have been run with FORTRAN punch-cards on a mainframe
computer.

Frank

"David" wrote in message
...
What are these "Cards" you guys are referring to ?

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

8405a working and measuring resonance?
 

Frank,

Thanks for that.

BTW: Does anyone know where I can get the wgnuplot.exe for 4nec2ex ?
The site has a link to the gnuplot only, I tried this link but is brings
up a page error.

Frank wrote:
A card is a line of NEC code. I guess it is a hold over from the old days
when NEC must have been run with FORTRAN punch-cards on a mainframe
computer.

Frank

"David" wrote in message
...
What are these "Cards" you guys are referring to ?

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

8405a working and measuring resonance?
 

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

8405a working and measuring resonance?
 

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

8405a working and measuring resonance?
 

"David" wrote in message
...
Frank,

Thanks for that.

BTW: Does anyone know where I can get the wgnuplot.exe for 4nec2ex ?
The site has a link to the gnuplot only, I tried this link but is brings
up a page error.

Dave, sorry I am not very familiar with 4nec, so have no idea what
wgnuplot.exe is. Most of my NEC experience is with NEC-Win Pro, which is so
straightforward and easy to use. Not that I mean to degrade 4nec2, I think
the guys have done a great job for the free software. I guess your best
approach is to keep bugging Arie as I am sure he knows.

Frank


Frank wrote:
A card is a line of NEC code. I guess it is a hold over from the old
days when NEC must have been run with FORTRAN punch-cards on a mainframe
computer.

Frank

"David" wrote in message
...
What are these "Cards" you guys are referring to ?

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

8405a working and measuring resonance?
 

On Fri, 27 Jan 2006 23:29:38 GMT, David
wrote:

Frank,

Thanks for that.

BTW: Does anyone know where I can get the wgnuplot.exe for 4nec2ex ?
The site has a link to the gnuplot only, I tried this link but is brings
up a page error.

I didn't find it too hard, I followed the links from Arie's page.

Try ftp://ftp.gnuplot.info/pub/gnuplot/ and see if you can identify
the correct binary for your (unstated) needs (presumably one of the
windows versions, probably win32 since you wanted w*.exe).

Owen

Frank wrote:
A card is a line of NEC code. I guess it is a hold over from the old days
when NEC must have been run with FORTRAN punch-cards on a mainframe
computer.

Frank

"David" wrote in message
...
What are these "Cards" you guys are referring to ?

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

--

8405a working and measuring resonance?
 

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

8405a working and measuring resonance?
 

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