Loading Coils; was : Vincent antenna
 

Jim Kelley wrote:
Honestly, Cecil, it's pretty hard to know what you mean considering the
reckless way you throw around the term 'phase'. I'll grant that you
might know what you mean, but I don't see how you can expect anyone else
to.

Jim, if you have trouble understanding the word "phase",
look it up in a technical dictionary. I don't have time
to waste my time teaching everyone the principles of AC
waves in EE201.

But assuming some others are having the same problem as
you: From the IEEE Dictionary:

"phase - The fractional part t/P of the period P through
which t has advanced relative to an arbitrary origin."

FYI: For a signal proportional to cos(x)*cos(wt), the
phase doesn't change with 'x'. That's why standing wave
current cannot be used to measure delay.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
Tom Donaly wrote:
The lack of technical content of your post is duly noted.

The lack of technical content of your post is duly noted.

Not as noted as the lack of technical content in your post noting
the lack of technical content of my post noting the lack of technical
content in your original post.
73,
Tom Donaly, KA6RUH

Loading Coils; was : Vincent antenna
 

Tom Donaly wrote:

The lack of technical content of your post is duly noted.
73,
Tom Donaly, KA6RUH

Hmmm, we are noting "duly noted" "technical minds" ok, duly noted here
.... thanks for the heads up, from this example--others will be easy to
recognize! Thanks! Now don't change on me ...

JS

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
K7ITM wrote:
Cecil, I posed two very specific examples for you to work out to show
us that you can actually correctly find the phase shift for travelling
waves, as you promised you could and would.

Sorry, Tom, when I came to the word "superconductor", I
stopped reading your posting. Please try to stick to
the real world of amateur radio next time. Anyone at
anytime can come up with some impossible esoteric
example that defies solution. Such examples are a
"vexations of the spirit" and I don't waste the
little time I have left on such nonsense. Please go
find another victim for your tarbaby.

In other words, you can't do it. Why don't you just say so?
73,
Tom Donaly, KA6RUH

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
Gene Fuller wrote:
So you think an EM wave cannot travel 10 inches in 3 ns? Try again.

Nice attempt at a diversion, Gene. What I said is that a
4 MHz EM wave cannot travel 10 inches in 3 ns through a
2" dia, 100 turn loading coil. If you disagree, please
feel free to prove me wrong.

Cecil insists that an 80 meter loading coil behaves nearly the same as
one of Corum's quarter-wave resonators. Others believe the coil
behavior is closer to a lumped circuit model.

The entire rest of the antenna is ten degrees. Why wouldn't
a 75m loading coil operate nearly the same as Corum's 1/4WL
resonators??? Are Maxwell's laws different for loaded mobile
antennas or for Corum's coils?

What diversion?

I was responding directly to a statement from Dan. This issue is at the
crux of the controversy. The entire question is whether waves can leap
tall buildings with a single bound or whether they must climb the
stairs. Have you forgotten everything????

The detailed technical content in "Why wouldn't" is noted. That debate
technique generally solves lots of issues.

8-)

73,
Gene
W4SZ

Loading Coils; was : Vincent antenna
 

Richard Clark wrote:
On Mon, 03 Dec 2007 22:08:42 GMT, Gene Fuller
wrote:

Go ahead, try any configuration you want. See if you agree with that web
calculator.

C'mon Gene,

Drop the shoe. What is the result? I've lost track of the URL and
would like to hear the punchline. Cecil won't understand it anyway,
so what difference would it make?

73's
Richard Clark, KB7QHC

The calculator is at

http://hamwaves.com/antennas/inductance.html

I believe that Owen first mentioned that website, but I could be wrong.

I am looking at the calculation for beta, the axial propagation factor.
It appears to be unchanged for any length of coil from very short to
much longer than a quarter-wave resonant length. I cannot change the
frequency any more, since Cecil thinks that is a diversion. However, the
calculator does not seem to respond correctly in that case either.

The calculator notes state that it uses the "n=0 sheath helix waveguide
mode", which is what Corum's Telsiks paper was all about. In that paper
he indicated various conditions for validity, such as the fact that the
coil must be near a quarter wave resonance for some of the mathematical
approximations to be valid.

I am not arguing with the "n=0 sheath helix waveguide mode". I am merely
pointing out that the calculator web page seems to be a "one size fits
all" situation that may not be appropriate when required conditions that
are not met.

73,
Gene
W4SZ

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
Gene Fuller wrote:
Are you so blinded by the battle that you cannot see anything else? I
was not talking about 80 meter loading coils. I was talking about the
overly broad application of the Corum model on that web page.

Well, since the context is 80 meter bugcatcher loading coils,
I guess that's why I was confused.

Actually, the context has been the loading coil measured by W8JI.
Perhaps that is why there is so much confusion.

8-)

73,
Gene
W4SZ

Loading Coils; was : Vincent antenna
 

On Dec 3, 5:49 pm, "Tom Donaly" wrote:
Cecil Moore wrote:
K7ITM wrote:
Cecil, I posed two very specific examples for you to work out to show
us that you can actually correctly find the phase shift for travelling
waves, as you promised you could and would.

Sorry, Tom, when I came to the word "superconductor", I
stopped reading your posting. Please try to stick to
the real world of amateur radio next time. Anyone at
anytime can come up with some impossible esoteric
example that defies solution. Such examples are a
"vexations of the spirit" and I don't waste the
little time I have left on such nonsense. Please go
find another victim for your tarbaby.

In other words, you can't do it. Why don't you just say so?
73,
Tom Donaly, KA6RUH

It's his tarbaby, not mine. My description was just for an
inductively loaded antenna, and a capacitively loaded antenna. I was
simply describing a method by which I could make a very small high-Q
coil; the small capacitor can be had from DigiKey. The obvious
question is, does the size of the reactive loading component matter?
Then, if so, why, and to what degree?

What is it that loads (tunes) the antenna? Is it primarily the
inductance of the coil, or is it parasitic effects such as the coil's
capacitance to the outside world? Would the antenna be properly
loaded with pure inductance, or does it _require_ the parasitic
capacitance of the coil to the outside world?

By the way, there's another way I can place an inductive reactance at
a point in the antenna, in a way that it's not coupled to the outside
world: I can make the antenna conductor be the outside of a piece of
coaxial cable, and use the coaxial inside as a shorted stub which
reflects a pretty good (fairly high Q) inductive reactance back to a
particular point such as a quarter of the antenna length back from
each end, where the stub connects across a gap in the outer
conductor. Can I use such an inductive reactance to tune the
antenna? Will there then be a difference in current at each end of
the gap across which that reactance connects? If there is not, and
we're dealing with a standing-wave antenna, how do we account for all
the "electrical degrees" we need to--or do we really even need to be
counting "electrical degrees"?

(Joseph Boyer's wonderful article, "The Antenna-Transmission Line
Analog," is highly recommended here...)

Others are welcome to ponder all that while Cecil tries to unstick
himself from his tarbaby.

Cheers,
Tom

Vincent antenna
 

"art" wrote in message
...
On 27 Nov, 06:18, Cecil Moore wrote:
John Smith wrote:
1/2 wave monopoles
have little dependence of a full counterpoise or ground for, at least,
acceptable performance.

The Zepp antenna is a 1/2WL monopole with no
counterpoise.
--
73, Cecil http://www.w5dxp.com

That makes sense. Physically it is half wave
but electrically it is a full wave antenna.
It is able to radiate on its surface and is unable to radiate
as it returns down the center of the wire.
(assuming the antenna is not tubular)
The path on the outside is helical which promotes a slow wave
so the physical wavelength has to be increased slightly to
compensate.When JS made his Vincent model the physical
length was slightly longer than a electrical half wave length
because of this so it still was not quite balanced.
To bring the antenna into balance there must be a contrawound
widing put into place such that the radiating current on the
return path is exposed and not enclosed. Doing this will not
correct the slow wave phenomina but will neutralise the
increased inductance created by the windings and at the same time
bring the radiator back to equilibrium where the correct LC ratio
is maintained and the radiator is a full electrical wavelength in
equilibrium and of variable shape and elevation.
Sound familiar?
Art Unwin.....KB9MZ...xg
Note the wire center contains no inductive or capacitive
properties, only resistive. Thus radiation will be slightly
over 50% of a full wave radiator.



To put it mildly:
The biggest crock of sheeeet yet!

bada BUm

Vincent antenna
 

Yuri Blanarovich wrote:
...
Yuri K3BU.us



WOW! What a work of art, what did you title this one, "Yuri Sucks Again?"

JS

Vincent antenna
 

Yuri Blanarovich wrote:

...
To put it mildly:
The biggest crock of sheeeet yet!

bada BUm



Could you possibly lighten up on the intellectual content of your
posts--some of are "Yuri Challenged" yanno?

JS

Vincent antenna
 

Yuri Blanarovich wrote:

...
Yuri K3BU.us



Frankly, I DON'T think diversity is a good thing, any chance of
convincing you we are all idiots and you would be better off returning
to your country of birth? Well hell, just a thought ... :-D

JS

Loading Coils; was : Vincent antenna
 

Tom Donaly wrote:
In other words, you can't do it. Why don't you just say so?

In other words, I don't take stupid paths down the
primrose lane. Here's one for you: If electrons
were in the nucleus and protons orbited the nucleus,
would RF waves still propagate the same way?
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Looks like I didn't miss much by being out of town for a few days. The
same arguments and hand-waving are still raging. But I'll try to add one
constructive bit of information:

NEC calculates field interactions by means of very fundamental and very
well established electromagnetic principles. As a result, it does a very
good job of predicting currents in an inductor which is modeled as a
helix. There are some caveats as there always are with any modeling
process, particularly:

1. The spacing between the outsides of the wires in adjacent turns
should be at least one wire diameter, and ideally several. NEC does not
account for uneven distribution of current around a wire (proximity
effect). This mainly impacts effective resistance.

2. The whole model must do some radiating, although even very
inefficient radiating structures are analyzed with good accuracy. A
check of the average gain usually reveals if there's a problem with the
overall calculation. I've gotten quite good results with a model
consisting of a fairly small coil with a wire through the center
connecting the coil ends, and a source at the middle of the wire.

To the extent that the program is providing accurate results, it can be
used as a verification or refutation of measurements, and to test
whatever alternate theories one wants to propose. Cecil likes to split
currents into sets of traveling waves, which in itself is fine. However,
when all the waves are added together to produce the actual current, the
result should agree with measurement and with analysis by established
theory. This means that, again to the extent that the model calculations
are being done correctly, the solution using traveling waves should
agree with NEC modeling results.

One huge advantage of using NEC results is that they're not limited by
lumped constant, traveling wave, waveguide mode, or other approximations
which hold only over some range of conditions. Results should transition
from one to another smoothly since the same fundamental laws apply
regardless of the regime. (One additional caveat, though, when doing
analysis at extremely high frequencies: the wire circumference has to be
no more than a small fraction of a wavelength, because as mentioned
earlier the program does assume equal current distribution around the wire.)

Of course, comparison of rigorous numerical measurements or modeling
results with vague, hand-waving theories with no supporting equations or
other mathematical tools is a total waste of the reader's time, and
that's pretty much all that seems to be happening here. But if anyone is
actually seriously interested in investigating alternative theories or
analytical methods, NEC or derivative programs such as EZNEC can provide
powerful assistance in confirming or refuting them. Unless, of course,
the objective is an attempt to refute the validity of Maxwell's
equations, in which case disagreement with NEC should be expected.

Both NEC and EZNEC provide simple ways of generating a helical model.

Roy Lewallen, W7EL

Loading Coils; was : Vincent antenna
 

Gene Fuller wrote:
In that paper
he indicated various conditions for validity, such as the fact that the
coil must be near a quarter wave resonance for some of the mathematical
approximations to be valid.

What he *didn't* say is that if that same coil is cut
in half and used at the same frequency, the Z0 and VF
change.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Gene Fuller wrote:
Actually, the context has been the loading coil measured by W8JI.

Actually, W8JI himself says the coil he used is similar
to a 75m mobile loading coil.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

K7ITM wrote:
Others are welcome to ponder all that while Cecil tries to unstick
himself from his tarbaby.

It's your tarbaby, Tom, not mine. When you can tell me
what's the difference between a duck, I will tackle your
equally ridiculous questions.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:

...
Roy Lewallen, W7EL

Oh gawd, the voice of recon' and ruin returns!

Don't question NEC/EZNEC, they are gods! Etc. ...

Why not tear 'em open, maybe if we see the equations which these
applications utilize we can make much better arguments? ... however, a
childish belief in "magic" is cute, huh?

As always,
JS

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
Tom Donaly wrote:
In other words, you can't do it. Why don't you just say so?

In other words, I don't take stupid paths down the
primrose lane. Here's one for you: If electrons
were in the nucleus and protons orbited the nucleus,
would RF waves still propagate the same way?

Why can't I stick photographic film between the windings in a large coil
in HF range and get clouding of the film--apparently these photons are
"different" and don't react with the emulsion?

Sorry, I have a religious belief in EM radiation which does NOT involve
photons ... :-(

Now don't throw stones, I am just "reaching",
JS

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:
But if anyone is
actually seriously interested in investigating alternative theories or
analytical methods, NEC or derivative programs such as EZNEC can provide
powerful assistance in confirming or refuting them.

Here is an email response from Roy, W7EL, when I used
EZNEC to disprove his invalid coil current measurements.
He apparently didn't like the EZNEC results from this file:

http://www.w5dxp.ez/coil512.EZ

Roy Lewallen wrote on May 12, 2007:
I resent your trying to use EZNEC support as a surreptitious
way to continue pushing your junk science on me. If you send
me one more non-support related email, I'll put you on my spam
list so your messages won't even make it to my ISP and I won't
have to waste any more of my time on you. That'll mean no more
EZNEC support, and I'll refund your EZNEC purchase price. So go
ahead, send me one more non-support email and make an easy $149.00.

Roy previously posted my private email without my permission
so turn about is fair play.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
http://www.w5dxp.ez/coil512.EZ

Sorry, obviously should have been:

http://www.w5dxp.com/coil512.EZ

Look at the "Load Dat" to see the actual phase shift
through that coil.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:

Roy previously posted my private email without my permission
so turn about is fair play.

One thing we are ALL are in agreement with, and I say this with complete
confidence, well I think, anyway, we'd all show up to KILL spammers!

Ya'd think they'd be ashamed ...

Regards,
JS

Vincent antenna
 

On 3 Dec, 19:13, John Smith wrote:
Yuri Blanarovich wrote:
...
Yuri K3BU.us

WOW! What a work of art, what did you title this one, "Yuri Sucks Again?"

JS
Re
Yuri K3BU. "us"
He is implying that he is a US citizen and is not visiting from
Canada.
That is really hard to believe. I heard he only comes to the States
to work as Santa Claus at the american malls.
The language he probably uses is ....Ho, Ho, Ho, Santa's full of
"sheet"!
There is no way that Yuri could possibly be nice or clean mouthed,
even to children,no matter what the season .

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:

Cecil:

You are one of the few here which has my respect ... tread carefully ...
love your arguments ...

Why can't we all just get along? ;-)

Warm regards,
JS

Loading Coils; was : Vincent antenna
 

Cecil, W5DXP wrote:
"A 1/4WL monopole over ground is known to be 90 degrees long. The phase
of the current changes by only a few degrees from feedpoint to tip. How
much phase shift (delay) in the current would we measure in 30 degrees
of a monopole? Answer: Only one or two degrees. Why is there only a
small number of degrees of phase shift (delay) in the current in 30
degrees of monopole? Because it is "standing-wave current" that is being
used for the measurement and the phase barely changes over the entire
monopole length."

The current distribution and phase along a 1/2-wave dipole have the same
characteristics except that the monopole`s image exists in the other
half of the dipole. Figure 14-2 on page 464 of the 3rd edition of Kraus`
"Antennas" shows the absence of significant phase change just as Cecil
describes above.

Then, if you examine Figure 14-12 on page 474, you`ll notice the solid
lines of the traveling wave progressing in opposite directions versus
the stair step dashed lines representing the standing wave abruptly
shifting its phase by 180 degrees at 1/2-wave intervals. This is
standard transmission line-antenna knowledge and supports Cecil`s
statement above.

You can take Kraus to the bank. I don`t know what all the fuss is about.

Best regards, Richard Harrison, KB5WZI

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
K7ITM wrote:
Others are welcome to ponder all that while Cecil tries to unstick
himself from his tarbaby.

It's your tarbaby, Tom, not mine. When you can tell me
what's the difference between a duck, I will tackle your
equally ridiculous questions.

Perhaps, said in olde' english it would gain more of your
interest/attention--"Shakespearian terms?" rofol

Cecil, don't take the whole world seriously, where would be the fun?

JS

Loading Coils; was : Vincent antenna
 

Correction:

Roy Lewallen wrote:
. . .
Both NEC and EZNEC provide simple ways of generating a helical model.
. . .

NEC-4 has a built-in method for generating a helix (the GH 'card'), but
NEC-2 doesn't. I wouldn't be surprised, though, if the feature hasn't
been added to some versions of NEC-2 floating around, since the basic
programming for that function isn't difficult to do.

Roy Lewallen, W7EL

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote in
:

....
as a helix. There are some caveats as there always are with any
modeling process, particularly:
....

Roy,

Aren't limitations on segment size an issue, especially with small diameter
coils?

Can NEC model a typical HF helically loaded mobile whip reasonably, sy 16mm
diameter, 1.2m long with variable pitch progressing to close spaced turns
on the top 30% or so?

I suspect NEC is not a magic bullet either.

Owen

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:
Correction:

Roy Lewallen wrote:
. . .
Both NEC and EZNEC provide simple ways of generating a helical model.
. . .

NEC-4 has a built-in method for generating a helix (the GH 'card'), but
NEC-2 doesn't. I wouldn't be surprised, though, if the feature hasn't
...
Roy Lewallen, W7EL

The "paid" versions contain this, in a usable fashion, and,
begrudgingly, are worth it ... nuff said.

Regards,
JS

Loading Coils; was : Vincent antenna
 

Owen Duffy wrote:

[pretty good stuff] (if you can see the above, find out how to subscribe
to a free news server)

And, good/free software written by amateurs for amateurs, and in the
free spirit of "elmering":

http://mmhamsoft.amateur-radio.ca/mmana/index.htm

Try it, you'll like it (mikee did! :-D )

Regards,
JS

Loading Coils; was : Vincent antenna
 

Sal M. Onella wrote:

...
Well, well, well! Two men who would otherwise be generating admiration are
in a hair-salon slap fight. Nobody cares but I'm putting this group on
hiatus. Phooey!

Well, well, Mr. Samonella, shame ta' see ya' go, and yer sorry donkey
will be missed ... bye ... gesus, if we begged, would ya' stay? :-O

JS

Loading Coils; was : Vincent antenna
 

I've always regarded email as being private and confidential, and I'm
sorry to see that Cecil doesn't give it the same respect. My email to
Cecil was correctly quoted. However, as so often seems to happen, the
context wasn't accurately reported. I provide support for all EZNEC
customers, including Cecil, as I always have. And I choose not to engage
Cecil in pointless and endless argument about his alternative theories,
either in this newsgroup or by email.

Roy Lewallen, W7EL

Sal M. Onella wrote:
"-------------" ---------------.com wrote in message
. net...
-----------------wrote:
But if anyone is
actually seriously interested in investigating alternative theories or
analytical methods, NEC or derivative programs such as EZNEC can provide
powerful assistance in confirming or refuting them.
Here is an email response from -------------, when I used
EZNEC to disprove his invalid coil current measurements.
He apparently didn't like the EZNEC results from this file:

http://www.-------------/coil512.EZ

---------------------wrote on May 12, 2007:
I resent your trying to use EZNEC support as a surreptitious
way to continue pushing your junk science on me. If you send
me one more non-support related email, I'll put you on my spam
list so your messages won't even make it to my ISP and I won't
have to waste any more of my time on you. That'll mean no more
EZNEC support, and I'll refund your EZNEC purchase price. So go
ahead, send me one more non-support email and make an easy $149.00.
----- previously posted my private email without my permission
so turn about is fair play.
--
73, ------ http://www.---------.com

Well, well, well! Two men who would otherwise be generating admiration are
in a hair-salon slap fight. Nobody cares but I'm putting this group on
hiatus. Phooey!

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:

...
Well, well, well! Two men who would otherwise be generating
admiration are
in a hair-salon slap fight. Nobody cares but I'm putting this group on
hiatus. Phooey!



When I was younger, I read articles by Roy--seriously.

"His program" EZNEC is a noteworthy contribution to "antenna
builders"/amateurs--I find, concretely, this cannot be debated ...

Simply the end of the story ... now, many other things exist too ... if
"things seem differently", so be it.

Nuff' said ... I'd go further even, Roy got me my extra--while not
directy, maybe, he did!

Regards,
JS

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
Ian White GM3SEK wrote:
However, any valid explanation of practical loading coils must
predict zero phase shift for the boundary condition where the coil
displays no other properties except pure inductance.

Translation: A model must accommodate conditions that
are impossible to achieve in reality. I'm sorry, Ian,
but that is pathological thinking not uncommon on this
newsgroup.

No, Cecil, that is a complete MIStranslation of what a boundary
condition is.

A software model that blows up when R=0 is perfectly
acceptable in the real world. It is a software bug,
not a statement on reality.

It's only your model that blows up. If your model sees lumped-component
behavior as an impossible singularity, that cannot be correct.

Other people's models of antenna loading do not have this problem. They
recognise that lumped inductance is often a good approximation to
reality, so they very sensibly use that as their starting-point. Then
they can progressively apply corrections for the distributed properties
of a real-life inductors. The smaller those corrections are, the simpler
the model becomes.

In practical terms, a lumped-inductance model will take you straight to
a buildable prototype. The necessary corrections can then be applied by
mechanical adjustment, without needing to model the distributed
properties of the loading coil in detail. Such models are to be found in
G4FGQ's MIDLOAD program, ON4UN's 'Antennas for Low Band DXing' and other
handbooks.

There was also an excellent theoretical treatment by Boyer in 'Ham
Radio', which shows in detail how the model of an antenna as an
unterminated transmission line is COMPLETELY capable of incorporating
lumped inductance:
The Antenna-Transmission Line Analog, 'Ham Radio', April and May 1977.



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Loading Coils; was : Vincent antenna
 

"-------------" ---------------.com wrote in message
. net...
-----------------wrote:
But if anyone is
actually seriously interested in investigating alternative theories or
analytical methods, NEC or derivative programs such as EZNEC can provide
powerful assistance in confirming or refuting them.

Here is an email response from -------------, when I used
EZNEC to disprove his invalid coil current measurements.
He apparently didn't like the EZNEC results from this file:

http://www.-------------/coil512.EZ

---------------------wrote on May 12, 2007:
I resent your trying to use EZNEC support as a surreptitious
way to continue pushing your junk science on me. If you send
me one more non-support related email, I'll put you on my spam
list so your messages won't even make it to my ISP and I won't
have to waste any more of my time on you. That'll mean no more
EZNEC support, and I'll refund your EZNEC purchase price. So go
ahead, send me one more non-support email and make an easy $149.00.

----- previously posted my private email without my permission
so turn about is fair play.
--
73, ------ http://www.---------.com

Well, well, well! Two men who would otherwise be generating admiration are
in a hair-salon slap fight. Nobody cares but I'm putting this group on
hiatus. Phooey!

Loading Coils; was : Vincent antenna
 

Owen Duffy wrote:

Roy,

Aren't limitations on segment size an issue, especially with small diameter
coils?

Although NEC has recommended limits on both minimum and maximum segment
length, my experience is that the minimum can often be disregarded with
no apparent degradation of the result. A good test is a small
single-turn loop, for which the theoretical result is well known. There
is a limit to NEC's ability to model a single turn loop for reasons
other than segment length, but the result holds very well for very short
segments. A more important criterion is the segment length to wire
diameter (or radius) ratio. Results begin getting poor when the segment
starts looking like a coin, that is, with a segment length considerably
smaller than the wire diameter. EZNEC spots these conditions and issues
appropriate warnings via its guideline check. Most errors caused by
segmentation problems show up in a poor average gain.

Can NEC model a typical HF helically loaded mobile whip reasonably, sy 16mm
diameter, 1.2m long with variable pitch progressing to close spaced turns
on the top 30% or so?

There's no provision in either NEC or EZNEC to automatically generate a
helix with variable pitch, but you could make a stepped approximation
with several tandem helices. However, if by "close spaced turns" you
mean wires which touch or nearly touch except for the insulation, this
violates the rule I stated earlier, that the distance between outsides
of wires should be at least one wire diameter, and preferably several.
So the coil as you describe it can't be accurately modeled. As long at
the rule is followed, though, NEC or EZNEC should be able to do a good
job of modeling a fairly typical whip loading coil.

I suspect NEC is not a magic bullet either.

Because EZNEC uses NEC for calculations, they both have nearly the same
limitations. I say "nearly" because EZNEC does have some added
protection against very small or large intermediate values in some
calculations, fixes for a few special cases, and minor changes from NEC
for various reasons. Most users are unlikely to see the effects of any
of these, however.

No modeling program, regardless of what's being modeled or how, is a
"magic bullet". Every last one has limitations and requires knowledge,
skill, and often a bit of art to utilize effectively and without a good
probability of serious error. I spend a lot of time and effort here, via
customer support, in the EZNEC manual, and in other venues, bringing
attention to EZNEC's limitations in the hope that it will save users
from getting results which are thought to be valid but aren't.

Side note: I had forgotten that at least one of the copies of NEC-2 I
have includes a GH 'card' provision, so the modification is apparently
quite common. It's not mentioned in the NEC-2 manual I have, however.

Roy Lewallen, W7EL

Loading Coils; was : Vincent antenna
 

John Smith wrote:

...
Nuff' said ... I'd go further even, Roy got me my extra--while not
directy, maybe, he did!

Regards,
JS

directy = directly, but then, ya already knew that ...

Well, ya' know what I mean, hard to argue with a personality that was
there (well, in spirit) when ya' built yer' first CPO (Code Practice
Oscillator--fer' all ya' newbies.)

Thinkin' about it, Roy is a REAL amateur ... and again, nuff' said. I
wish I'd have saved all those magazines.

When I "argue" with/idead/him, it is in the fondest of ways ... but
then, yas' already knew that ... good night Roy.

Real men have strange ways and they don't need explained ...

....

Warm regards,
JS

Loading Coils; was : Vincent antenna
 

Roy,

Thanks for the exhaustive answer.

I appreciate your opinion on the short segment issue. I must admit
playing with it and not noticing things go pear shaped as frequency was
reduced (so that segment length become relatively short).

To those of us that haven't dived into the internals, the warnings are a
concern and prima facie, I would be reluctant to accept and use results
from a model with unresolved warnings.

The helical problem I posed is not unusual, many if not most low HF
helicals wind up with close spaced turns at the top, and the absence of
model accuracy in that part of the antenna renders any model of very
limited value. (I am not suggesting that the Corum approach can deal with
a variable pitch helical with close spaced turns at the top either.) It
is just a real implementation that seems a problem to model.

So, NEC can model your helical so long as your helical is one that NEC
can model!

I am familiar with the GH card, Arie's 4NEC2 has it. I think my version
of EZNEC can generate a helix, but I know that it cannot save a NEC
compatible deck.

I have tried a NEC-2 model of the coil that Tom described with 8
segments/turn (warning: segment length = 0.00013wl). The inductive
reactance is a little different to the Hamwave Corum based calculator,
the R is very different, the self resonance is different (understandably,
likely to be affected by the coil terminations) and we don't know a
measured value for Tom's coil anyway or the true stand alone self
resonance.

Owen

Loading Coils; was : Vincent antenna
 

Owen Duffy wrote:
. . .
The helical problem I posed is not unusual, many if not most low HF
helicals wind up with close spaced turns at the top. . .

Out of curiosity, why?

Roy Lewallen, W7EL

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:

...
Roy Lewallen, W7EL

Great little piece of software, but, want something free without the
restrictions?

http://mmhamsoft.amateur-radio.ca/mmana/index.htm

By amateurs, for amateurs--wouldn't be surprised it it used the same
engine a EZNEC--or, that EZNECS' gui used the same engine!

Regards,
JS