From NEC2 to the real world with accuracy
 

Hi,

So I've spent months, rather years, carefully designing a new 5 band
cubical quad for myself. I've always known that I would use #12 solid
copper wire (not stranded), so that is what I used when running NEC2
to optimize this touchy antenna design (over millions of iterations).

Well, real world things are starting to happen. For wire, I've decided
what I would like to use is an enameled coated copperweld wire. I'll
buy the plain copperweld wire and coat it myself.

So my question is, what is the most accurate way to make sure when I
build the quad that I account for the velocity factor (unknown) of the
wire I use? Should I grid dip the elements and make sure they agree
with my NEC2 model? Can I build a simple loop on a higher frequency
with the wire and then somehow use that information to rescale my wire
lengths? What is the "right" way to do this? I wonder how consistent
velocity factor will be if I do my own coating on the wire....maybe
hand coating is a bad idea for this reason....

I spent a lot of time designing a Yagi with NEC2. I used Leeson's
correction for taper elements and to calculate the effect of the
element to boom mounts. All that attention paid off - I thought my
Yagi lived up to the NEC2 predictions very well.

-Scott, WU2X

From NEC2 to the real world with accuracy
 

On Tue, 11 Mar 2008 22:47:57 -0700 (PDT), wrote:

So my question is, what is the most accurate way to make sure when I
build the quad that I account for the velocity factor (unknown) of the
wire I use? Should I grid dip the elements and make sure they agree
with my NEC2 model?

Hi Scott,

This sounds like a good solution, but you don't state the limits of
accuracy you've painfully sought to achieve. I'm not sure about the
reference to a million iterations (which would certainly suggest the
erosion of accuracy through accumulating rounding errors).

However, GDOs don't suggest precision to me. Yes, you can measure the
frequency to a jillion places, but can you find the null to the same
resolution? Meters are not all that resolving unless you've got them
in a bridge.

Can I build a simple loop on a higher frequency
with the wire and then somehow use that information to rescale my wire
lengths?

Sure, but you seem to inform yourself about the difficulty with the
prescient questions that follow:

What is the "right" way to do this? I wonder how consistent
velocity factor will be if I do my own coating on the wire....maybe
hand coating is a bad idea for this reason....

I would first ask why you are coating them at all?.

If I might anticipate because the copper oxidizes and presents a high
resistance to current, I would point out that enamel is even more
resistive and the current isn't going to travel through it either (the
current will travel through the proverbial path of least resistance -
under the coating of resistive layer covering no matter what it is
composed of).

73's
Richard Clark, KB7QHC

From NEC2 to the real world with accuracy
 

wrote:
Should I grid dip the elements and make sure they agree
with my NEC2 model?

I use my MFJ-259B a lot more than I use my grid dip
meter. In any case, cutting and trying is usually
required to achieve the desired gain and F/B ratio
at the frequency of interest.
--
73, Cecil http://www.w5dxp.com

From NEC2 to the real world with accuracy
 

wrote in message
...
Hi,

So I've spent months, rather years, carefully designing a new 5 band
cubical quad for myself. I've always known that I would use #12 solid
copper wire (not stranded), so that is what I used when running NEC2
to optimize this touchy antenna design (over millions of iterations).

Well, real world things are starting to happen. For wire, I've decided
what I would like to use is an enameled coated copperweld wire. I'll
buy the plain copperweld wire and coat it myself.

I think I would spend the extra money and buy copper wire. One nick in your
coating and the copper surface and the wire will disappear. If you must use
copperweld, try The Wireman or The RF Connection for copperweld that has a
high density black polyethylene jacket.

I would hate to spend all the time to design and build a quad and then have
the wire be the weakest link.

Dale W4OP

From NEC2 to the real world with accuracy
 

If I might anticipate because the copper oxidizes and presents a high
resistance to current, I would point out that enamel is even more
resistive and the current isn't going to travel through it either (the
current will travel through the proverbial path of least resistance -
under the coating of resistive layer covering no matter what it is
composed of).

(I am addressing more than one post with this response)

Basically I want to use copperweld for durability. Its not a matter of
saving money over hard drawn copper. I have no experience with (bare)
copperweld, but I have read that if you get a nick in the copper
layer, basically the steel will start rusting away at that point (very
quickly). So I don't have problem using some enamel to protect it (and
have done this in the past with hard drawn). I am using copperweld/
insulated wire for my low band antennas - but anyone who has actually
built a quad knows insulated wire is much too heavy, esp. when you are
dealing with 5 bands.

I have used hard drawn copper with enamel on it on 10 meters and never
had a problem with a wire breaking in 10 years. So, I am not really
sure if I need copperweld, but I have no expierence with larger quad
loops. The goal is to have this thing be reliable.

Regardless still - whatever I wire I use - even if it was bare #12
solid copper wire, I still want to go through the exercise of getting
the wire I actually used in sync with my model. So, I'd rather focus
the conversation on that topic.

With respect to manually tuning the quad (reflector) after its up,
yes, that seems to be the conventional wisdom. How practical and
possible is that for me? Mine will sit on 72' US Tower crankup/tilt
over - short of renting some huge bucket/boom, I can't see myself
manually tuning it when its up. The best I will do is take some type
of field measurements and see if it displays anything close to the
pattern NEC2 predicts - or better yet, just see if I am happy with it
as is. I did not have to make any adjustments to the monoband yagi
that went right from NEC2 to the tower, so, I am hoping for the same
good fortune.


-Scott, WU2X

From NEC2 to the real world with accuracy
 

On Mar 12, 9:50 am, wrote:
If I might anticipate because the copper oxidizes and presents a high
resistance to current, I would point out that enamel is even more
resistive and the current isn't going to travel through it either (the
current will travel through the proverbial path of least resistance -
under the coating of resistive layer covering no matter what it is
composed of).

(I am addressing more than one post with this response)

Basically I want to use copperweld for durability. Its not a matter of
saving money over hard drawn copper. I have no experience with (bare)
copperweld, but I have read that if you get a nick in the copper
layer, basically the steel will start rusting away at that point (very
quickly). So I don't have problem using some enamel to protect it (and
have done this in the past with hard drawn). I am using copperweld/
insulated wire for my low band antennas - but anyone who has actually
built a quad knows insulated wire is much too heavy, esp. when you are
dealing with 5 bands.

I have used hard drawn copper with enamel on it on 10 meters and never
had a problem with a wire breaking in 10 years. So, I am not really
sure if I need copperweld, but I have no expierence with larger quad
loops. The goal is to have this thing be reliable.

Regardless still - whatever I wire I use - even if it was bare #12
solid copper wire, I still want to go through the exercise of getting
the wire I actually used in sync with my model. So, I'd rather focus
the conversation on that topic.

With respect to manually tuning the quad (reflector) after its up,
yes, that seems to be the conventional wisdom. How practical and
possible is that for me? Mine will sit on 72' US Tower crankup/tilt
over - short of renting some huge bucket/boom, I can't see myself
manually tuning it when its up. The best I will do is take some type
of field measurements and see if it displays anything close to the
pattern NEC2 predicts - or better yet, just see if I am happy with it
as is. I did not have to make any adjustments to the monoband yagi
that went right from NEC2 to the tower, so, I am hoping for the same
good fortune.

-Scott, WU2X

Scott, you are introducing sharp corners to your new antenna so NEC
will stray from accuracy.
Art

From NEC2 to the real world with accuracy
 

On Mar 12, 11:01 am, Art Unwin wrote:
Scott, you are introducing sharp corners to your new antenna so NEC
will stray from accuracy.

Is NEC4 better in this regard?

Here is the NEC2 reported performance of my current design. Its a 24
foot boom, with 5 bands. 4 elements on 15-10 and 3 elements on 20-17.
Optimization is for F/R around mid-band and bandwidth (under 2.5:1 at
edges).

http://remote.wu2x.com:8888/WU2X/

Click each band.html file to see the graphs on each band. The non-
active driven elements are shorted.

Here is the stock Cubex 4 element quad, which is 4 elements on all
bands (on a 24' boom).

http://remote.wu2x.com:8888/Cubex/

-Scott, WU2X

From NEC2 to the real world with accuracy
 

On Mar 12, 10:22 am, wrote:
On Mar 12, 11:01 am, Art Unwin wrote:

Scott, you are introducing sharp corners to your new antenna so NEC
will stray from accuracy.

Is NEC4 better in this regard?

Here is the NEC2 reported performance of my current design. Its a 24
foot boom, with 5 bands. 4 elements on 15-10 and 3 elements on 20-17.
Optimization is for F/R around mid-band and bandwidth (under 2.5:1 at
edges).

http://remote.wu2x.com:8888/WU2X/

Click each band.html file to see the graphs on each band. The non-
active driven elements are shorted.

Here is the stock Cubex 4 element quad, which is 4 elements on all
bands (on a 24' boom).

http://remote.wu2x.com:8888/Cubex/

-Scott, WU2X

I would suggest that you check with what Cebik says about it.
At the same time you are also now dealing with vertcal polarisation
which also has a lot of characteristics that are different from planar
yagis where the elements are not in equilibrrium as compared to a quad
design.
One can discharge corona where the other doesn't soto use the same
calculations
for designs that behave differently raises a lot of questions besides
the sharp corners.
Niether of the programs are perfect but better than shooting in the
dark.
Art

From NEC2 to the real world with accuracy
 

On Wed, 12 Mar 2008 07:50:08 -0700 (PDT), wrote:

With respect to manually tuning the quad (reflector) after its up,
yes, that seems to be the conventional wisdom. How practical and
possible is that for me? Mine will sit on 72' US Tower crankup/tilt
over - short of renting some huge bucket/boom, I can't see myself
manually tuning it when its up. The best I will do is take some type
of field measurements and see if it displays anything close to the
pattern NEC2 predicts - or better yet, just see if I am happy with it
as is. I did not have to make any adjustments to the monoband yagi
that went right from NEC2 to the tower, so, I am hoping for the same
good fortune.

Hi Scott,

For tuning, one established technique is to get it up high enough off
the ground, pointed up, so that it is not affected by ground too much,
but still accessible by a ladder.

As for checking actual performance, note that in all practicality you
lack the means to measure the full 3 dimensional performance. Further,
even monitoring out 10 miles still puts you below the horizon, and for
HF that is barely more than a correlative, as nearly every NEC tool
shows performance above the horizon when it comes to the radiation
lobe characteristics. Otherwise you would need a helicopter....

You can measure against beacons, but now you toss in the variable of
propagation and you would have to marry the NEC output to WINCAP and
perform several dozen tests each day over the course of a month or
two. IF YOU ARE TALKING PRECISION AND ACCURACY.

On the other hand, you've already validated your testing, modeling,
and performance to your efforts for one band - Trust your tools and
data to be able to extrapolate it.

73's
Richard Clark, KB7QHC

From NEC2 to the real world with accuracy
 

wrote:
On Mar 12, 11:01 am, Art Unwin wrote:
Scott, you are introducing sharp corners to your new antenna so NEC
will stray from accuracy.

Is NEC4 better in this regard?


Neither NEC-2 nor NEC-4 has any problem in this regard. Art's statement
is incorrect as quoted.

Roy Lewallen, W7EL