antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
 

"Roy Lewallen" wrote in message
...
dansawyeror wrote:
Thanks - I will try to figure you how to create a non lumped model for
the inductors. Right now that is 'undiscovered country'.

EZNEC v. 4.0 users should use Wires Window/Create/Create Helix. You'll get
many choices, including position, orientation, various ways of specifying
the pitch and number of turns, twist direction, and so forth. (EZNEC demo
users can create any size helix to see how it works, but won't be able to
run a calculation unless the helix is extremely simple.) In NEC, use a GH
'card'.

There should be at least a wire diameter of air space between turns,
preferably several. (That is, the center-center distance between the wires
in one turn and the wires in adjacent turns should be at least two wire
diameters, preferably more.) If air spacing is less than 2 or 3 wire
diameters, the calculated loss will be somewhat lower than reality because
NEC (or EZNEC) doesn't account for proximity effect.

Roy Lewallen, W7EL

As I understand NEC; large errors can be introduced by junctions of
dissimilar wire diameters, and in particular when the wires are at 90 deg.
Therefore, when you have designed your "GH" inductors, the rest of the
antenna should by constructed of the same diameter wire. This may be
difficult since Dan is using two coils of significantly different Qs. I
guess you could overcome this problem by varying the conductivity of the
inductor to obtain the desired Q. Also, since segmentation tends to be
relatively high in a helix, should segment length tapering be applied to
those segments adjacent to the helix?

Frank, VE6CB

antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
 

Frank wrote:

As I understand NEC; large errors can be introduced by junctions of
dissimilar wire diameters, and in particular when the wires are at 90 deg.
Therefore, when you have designed your "GH" inductors, the rest of the
antenna should by constructed of the same diameter wire. This may be
difficult since Dan is using two coils of significantly different Qs. I
guess you could overcome this problem by varying the conductivity of the
inductor to obtain the desired Q. Also, since segmentation tends to be
relatively high in a helix, should segment length tapering be applied to
those segments adjacent to the helix?

Frank, VE6CB

It's difficult to give an absolute answer to these questions, but some
general comments and guidelines should help.

First, the error introduced by NEC-2 when wires of dissimilar diameter
are connected is generally small, unless the wires are grossly
different. This error can be minimized by making the segments as *long*
as possible adjacent to the junction, which of course is contrary to the
general principle that more segments are better. Even a small error can
cause major changes in the pattern when the dissimilar diameter wires
are in a parasitic element. EZNEC and a number of other programs have a
built-in method of avoiding this problem for certain antenna types, but
plain NEC-2 doesn't. NEC-4 is relatively free of this problem, but it's
quite expensive for hobby use.

The Q of an inductor is determined by the inductance and the loss. The
loss is a function of the dielectric, wire resistance, and radiation
(which isn't really loss, but lowers Q as though it were). NEC type
programs automatically account for the radiation, and it's easy to
include wire loss. So assuming negligible dielectric loss, the programs
should predict Q fairly accurately -- except for proximity affect.
Proximity effect could be modeled in NEC by increasing the resistivity
of the wires in the coil. EZNEC currently allows only a single wire
resistivity for the whole model (although this will probably change in
the next version). However, since the overall loss will be dominated by
the inductors, the higher resistivity could be specified for the whole
model without sacrificing significant accuracy. Alternatively, a number
of resistive loads could be inserted in the inductors.

Segment length tapering usually isn't necessary with NEC based programs,
unless there's a source near a place where the segment length changes.
An average gain check should be run to determine if there's a problem.
If there is, segment length tapering is one tool which can be tried in
improving the average gain.

Roy Lewallen, W7EL

antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
 

"Roy Lewallen" wrote in message
...
Frank wrote:

As I understand NEC; large errors can be introduced by junctions of
dissimilar wire diameters, and in particular when the wires are at 90
deg. Therefore, when you have designed your "GH" inductors, the rest of
the antenna should by constructed of the same diameter wire. This may be
difficult since Dan is using two coils of significantly different Qs. I
guess you could overcome this problem by varying the conductivity of the
inductor to obtain the desired Q. Also, since segmentation tends to be
relatively high in a helix, should segment length tapering be applied to
those segments adjacent to the helix?

Frank, VE6CB

It's difficult to give an absolute answer to these questions, but some
general comments and guidelines should help.

First, the error introduced by NEC-2 when wires of dissimilar diameter are
connected is generally small, unless the wires are grossly different. This
error can be minimized by making the segments as *long* as possible
adjacent to the junction, which of course is contrary to the general
principle that more segments are better. Even a small error can cause
major changes in the pattern when the dissimilar diameter wires are in a
parasitic element. EZNEC and a number of other programs have a built-in
method of avoiding this problem for certain antenna types, but plain NEC-2
doesn't. NEC-4 is relatively free of this problem, but it's quite
expensive for hobby use.

The Q of an inductor is determined by the inductance and the loss. The
loss is a function of the dielectric, wire resistance, and radiation
(which isn't really loss, but lowers Q as though it were). NEC type
programs automatically account for the radiation, and it's easy to include
wire loss. So assuming negligible dielectric loss, the programs should
predict Q fairly accurately -- except for proximity affect. Proximity
effect could be modeled in NEC by increasing the resistivity of the wires
in the coil. EZNEC currently allows only a single wire resistivity for the
whole model (although this will probably change in the next version).
However, since the overall loss will be dominated by the inductors, the
higher resistivity could be specified for the whole model without
sacrificing significant accuracy. Alternatively, a number of resistive
loads could be inserted in the inductors.

Segment length tapering usually isn't necessary with NEC based programs,
unless there's a source near a place where the segment length changes. An
average gain check should be run to determine if there's a problem. If
there is, segment length tapering is one tool which can be tried in
improving the average gain.

Roy Lewallen, W7EL

Thanks for the information Roy, all remarks noted and saved. Will see what
I can do to generate some realistic helical models.

Frank VE6CB

antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
 

Frank,

I observed by playing with the relative inductor values on the vertical segment
and the radial elements that it was possible to move the relative feedpoint.
This supports tuning the antenna by either inductor.

Reg's c_poise program predicts a 75 uH loading coil.

I am excited with prospect of coil models.

Thanks - Dan

Frank's wrote:
"Roy Lewallen" wrote in message
...

Frank wrote:

As I understand NEC; large errors can be introduced by junctions of
dissimilar wire diameters, and in particular when the wires are at 90
deg. Therefore, when you have designed your "GH" inductors, the rest of
the antenna should by constructed of the same diameter wire. This may be
difficult since Dan is using two coils of significantly different Qs. I
guess you could overcome this problem by varying the conductivity of the
inductor to obtain the desired Q. Also, since segmentation tends to be
relatively high in a helix, should segment length tapering be applied to
those segments adjacent to the helix?

Frank, VE6CB

It's difficult to give an absolute answer to these questions, but some
general comments and guidelines should help.

First, the error introduced by NEC-2 when wires of dissimilar diameter are
connected is generally small, unless the wires are grossly different. This
error can be minimized by making the segments as *long* as possible
adjacent to the junction, which of course is contrary to the general
principle that more segments are better. Even a small error can cause
major changes in the pattern when the dissimilar diameter wires are in a
parasitic element. EZNEC and a number of other programs have a built-in
method of avoiding this problem for certain antenna types, but plain NEC-2
doesn't. NEC-4 is relatively free of this problem, but it's quite
expensive for hobby use.

The Q of an inductor is determined by the inductance and the loss. The
loss is a function of the dielectric, wire resistance, and radiation
(which isn't really loss, but lowers Q as though it were). NEC type
programs automatically account for the radiation, and it's easy to include
wire loss. So assuming negligible dielectric loss, the programs should
predict Q fairly accurately -- except for proximity affect. Proximity
effect could be modeled in NEC by increasing the resistivity of the wires
in the coil. EZNEC currently allows only a single wire resistivity for the
whole model (although this will probably change in the next version).
However, since the overall loss will be dominated by the inductors, the
higher resistivity could be specified for the whole model without
sacrificing significant accuracy. Alternatively, a number of resistive
loads could be inserted in the inductors.

Segment length tapering usually isn't necessary with NEC based programs,
unless there's a source near a place where the segment length changes. An
average gain check should be run to determine if there's a problem. If
there is, segment length tapering is one tool which can be tried in
improving the average gain.

Roy Lewallen, W7EL


Thanks for the information Roy, all remarks noted and saved. Will see what
I can do to generate some realistic helical models.

Frank VE6CB

antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
 

Dan, I have been trying to replicate your inductors with NEC. It is a bit
tedious, just guessing wire gauge, coil diameter etc., to obtain the desired
inductance and Q. What are the physical dimensions of your inductors?

Have you had any luck with GH? You may have a problem with 4nec2 since you
must have a GM card along with the GH.

Frank


"dansawyeror" wrote in message
...
Good question. I will play with that. That said, based on Roy's comment at
minimum the load should appear nearly pure resistive.

I just tested the Autek with 6.25, 12.5, and 25 Ohm loads.
25 read 26
12.5 read 12 - 13 - 12 etc.
6.25 read mostly 7 with an occasional 6.

I would say for non-reactive loads it is pretty close.

Tomorrow - will be to experiment with non lumped inductors. That will be a
challenge.

Thanks - Dan


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

Frank,

The Autek is remarkably close. I have used it to checkout 50 and 25 Ohm
loads. For these two values it is very close. (It is battery level
sensitive.)

The couplers are a pair of M-C ZFDC 20-4's.

Dan


Thanks Dan, I had forgotten about Mini-Circuits. Their price is hard to
beat. I may pick up one of the "PDC" series dual directional couplers.
Incidentally your code indicates resonance occurs at 3.54 MHz. I wonder
how the Autek behaves when subjected to a reactive load does it actually
get close to the magnitude?

Frank

antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
 

Frank,

A 'target' coil is 300mm x 300mm of 5/16 copper tubing. It is about 50 feet of
tubing, a .5 pitch, and should be close to 75 uH. This should be close. From
there simulation should show the best performance between varying the coils.

Thanks - Dan


Frank wrote:
Dan, I have been trying to replicate your inductors with NEC. It is a bit
tedious, just guessing wire gauge, coil diameter etc., to obtain the desired
inductance and Q. What are the physical dimensions of your inductors?

Have you had any luck with GH? You may have a problem with 4nec2 since you
must have a GM card along with the GH.

Frank


"dansawyeror" wrote in message
...

Good question. I will play with that. That said, based on Roy's comment at
minimum the load should appear nearly pure resistive.

I just tested the Autek with 6.25, 12.5, and 25 Ohm loads.
25 read 26
12.5 read 12 - 13 - 12 etc.
6.25 read mostly 7 with an occasional 6.

I would say for non-reactive loads it is pretty close.

Tomorrow - will be to experiment with non lumped inductors. That will be a
challenge.

Thanks - Dan


Frank wrote:

"dansawyeror" wrote in message
...


Frank,

The Autek is remarkably close. I have used it to checkout 50 and 25 Ohm
loads. For these two values it is very close. (It is battery level
sensitive.)

The couplers are a pair of M-C ZFDC 20-4's.

Dan


Thanks Dan, I had forgotten about Mini-Circuits. Their price is hard to
beat. I may pick up one of the "PDC" series dual directional couplers.
Incidentally your code indicates resonance occurs at 3.54 MHz. I wonder
how the Autek behaves when subjected to a reactive load does it actually
get close to the magnitude?

Frank

antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
 

"dansawyeror" wrote in message
...
Frank,

A 'target' coil is 300mm x 300mm of 5/16 copper tubing. It is about 50
feet of tubing, a .5 pitch, and should be close to 75 uH. This should be
close. From there simulation should show the best performance between
varying the coils.

Thanks - Dan

Having trouble producing a good model Dan. NEC 2 indicates Qs which are
5000, but no warnings or errors. I can run it in NEC 4.1, single, and
double precision, but I get over 400 warnings in the NEC output file; such
as:

SEGCHK: WARNING - SEGMENTS 1 AND 271 CROSS AT A MIDPOINT WITH SEPARATION
LESS THAN THE SUM OF THEIR RADII

SEGCHK: WARNING - THE CENTER OF SEGMENT 1 IS WITHIN THE VOLUME OF SEGMENT
271

These warnings are particularly strange since, for example, absolute
segments 1 and 271 are almost 12" apart in the model. Will see what I can
do to correct the error.

73,

Frank

The code I am using is as follows:

CM Inductor Q Calculation
CE
GH 1 300 1 12 6 6 6 6 0.3125
GW 2 5 6 0 12 0 0 12 0.3125
GW 3 10 0 0 12 0 0 0 0.3125
GW 4 5 0 0 0 6 0 0 0.3125
GS 0 0 0.025400
GE 0
EX 0 3 5 00 1 0
FR 0 5 0 0 3.7 0.02
LD 5 1 1 320 5.7001E7
RP 0 181 1 1000 -90 90 1.00000 1.00000
EN

antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
 

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

A 'target' coil is 300mm x 300mm of 5/16 copper tubing. It is about 50
feet of tubing, a .5 pitch, and should be close to 75 uH. This should be
close. From there simulation should show the best performance between
varying the coils.

Thanks - Dan

Having trouble producing a good model Dan. NEC 2 indicates Qs which are
5000, but no warnings or errors. I can run it in NEC 4.1, single, and
double precision, but I get over 400 warnings in the NEC output file; such
as:

SEGCHK: WARNING - SEGMENTS 1 AND 271 CROSS AT A MIDPOINT WITH SEPARATION
LESS THAN THE SUM OF THEIR RADII

SEGCHK: WARNING - THE CENTER OF SEGMENT 1 IS WITHIN THE VOLUME OF SEGMENT
271

These warnings are particularly strange since, for example, absolute
segments 1 and 271 are almost 12" apart in the model. Will see what I can
do to correct the error.

73,

Frank

The code I am using is as follows:

CM Inductor Q Calculation
CE
GH 1 300 1 12 6 6 6 6 0.3125
GW 2 5 6 0 12 0 0 12 0.3125
GW 3 10 0 0 12 0 0 0 0.3125
GW 4 5 0 0 0 6 0 0 0.3125
GS 0 0 0.025400
GE 0
EX 0 3 5 00 1 0
FR 0 5 0 0 3.7 0.02
LD 5 1 1 320 5.7001E7
RP 0 181 1 1000 -90 90 1.00000 1.00000
EN

NEC-2 and NEC-4 have different formats for the GH 'card'. This is the
NEC-2 format, which will be interpreted differently by NEC-4. See your
NEC-4 documentation for the correct NEC-4 format.

Roy Lewallen, W7EL

antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
 

NEC-2 and NEC-4 have different formats for the GH 'card'. This is the
NEC-2 format, which will be interpreted differently by NEC-4. See your
NEC-4 documentation for the correct NEC-4 format.

Roy Lewallen, W7EL

Thanks Roy, now you mention it I do remember that there are some
differences. Should have checked with my manual before running it instead
of just cutting and pasting NEC 2 code. Made the appropriate correction and
it is now working with a reasonable correlation with NEC 2. Heck, now I
just noticed I had entered the wire diameter instead of its radius!

Frank, VE6CB

antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
 

Frank,

I observed by playing with the relative inductor values on the vertical
segment and the radial elements that it was possible to move the relative
feedpoint. This supports tuning the antenna by either inductor.

Reg's c_poise program predicts a 75 uH loading coil.

I am excited with prospect of coil models.

Thanks - Dan

Dan, I have done some minor approximations with your coil. I took the
length and diameter to be 12", rather than 300 mm (11.8"). The coil copper
pipe diameter is, as specified, 5/16" (0.3125"). I was a little confused
with your use of the term "Pitch" as 0.5". In the sense of a screw thread
pitch is the distance between adjacent thread peaks, but I took it to mean
the actual distance between the outer walls of the pipe; in which case the
actual pitch is 0.8125". If this is the case the total pipe length is just
over 47 ft. The inductance calculates to 54.2uH, and the Q = 2990. I have
not yet run the program in NEC 4, for greater accuracy, since I would like
to get the model as close as possible in NEC 2.

If I have gotten the pitch definition wrong then the model dimensions will
violate the NEC criteria of the minimum distance between adjacent turns.

The code for this preliminary run is shown below. Some of the odd-ball
dimensions are just to approximately equalize segment lengths.

Despite some of the weirdness of 4nec2, concerning "GH" cards, you should be
able to run it.

Frank

CM Inductor Q Calculation
CE
GH 1 300 0.8125 12 6 6 6 6 0.15625
GW 2 3 0.72322 -5.95625 12 .35542 0 12 0.15625
GW 3 6 .35542 0 12 .35542 0 0 0.15625
GW 4 3 .35542 0 0 6 0 0 0.15625
GS 0 0 0.025400
GE 0
EX 0 3 3 00 1 0
FR 0 5 0 0 3.7 0.02
LD 5 1 1 312 5.7001E7
RP 0 181 1 1000 -90 90 1.00000 1.00000
EN