vertical antenna loading coil vs toroid
 

On Apr 2, 8:33*am, Cecil Moore wrote:
wrote:
I was wondering if the self shielding properties of the toroid would
have contributed to this conclusion, and because of these properties,
the toroid not have any electrical degrees, so to speak, so when it
come to the radiating element it would need to be slightly longer to
see the electrical degrees for the wavelength or resonance frequency
injected into it. thanks again for the info.

I suspect that the VF of the toroidal loading coil is much
higher than the VF of an air-core loading coil, i.e. the
toroidal loading coil occupies fewer electrical degrees of
the antenna. It makes sense that if the toroidal loading
coil occupies fewer electrical degrees of the antenna that
those degrees must be furnished somewhere else. The toroidal
loading coil seems to be closer to the lumped circuit model
than is the large air-core loading coil which generally
requires analysis using distributed network techniques.

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

There are two things happening with a base loading coil.
The loading coil occupies a certain number of degrees,
e.g. ~36 degrees for a 75m bugcatcher coil. The stinger
occupies maybe ~11 degrees for a total of ~47 degrees.
The other ~43 degrees comes from the phase shift at the
impedance discontinuity between the coil and the stinger.

With a center loading coil, a few degrees are lost at
the impedance discontinuity between the base section and
the coil. That's why a larger coil is needed for a
center-loaded mobile antenna.
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

I am a little confused, you say about the coil and the stinger
occupying a portion of the total 90 degrees, (I can follow this not a
problem), however I thought the purpose of the coil was to add
inductive reactance, due to the shortened length of the radiator, less
than 1/4 wave, therefore having a capacitive reactance overhaul. Let
the shortened vertical be 34-j234 ohms. My understanding is that
depending on on what the reactance is at some freq, I need to offset
this negative reactance with an equal positive reactance. I wasn't
looking at from a degrees point for view. Or is it just 6 of one, half
dozen of the other, both be equal just expressed differently, I like
the degrees point of view for a couple of other arrays I am
experimenting with. (long wires) I think it will simplify things a
whole lot. thanks again for the info and the links, very valuable
info. 73 brett

vertical antenna loading coil vs toroid
 

wrote:
My understanding is that
depending on on what the reactance is at some freq, I need to offset
this negative reactance with an equal positive reactance. I wasn't
looking at from a degrees point for view.

It depends upon which math model is being used and
whether the math model is valid under the existing
conditions. We can neutralize capacitive reactance
with a lumped inductance or with a stub or with a
helical coil. The results are approximately the
same but there are differences.

If the current amplitude changes significantly
between the bottom and top of the loading coil,
the lumped circuit model is not valid because
the coil is an appreciable percentage of a
wavelength more akin to a transmission line
than a lumped circuit.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

vertical antenna loading coil vs toroid
 

On Apr 2, 7:17*pm, Cecil Moore wrote:

It depends upon which math model is being used and
whether the math model is valid under the existing
conditions. We can neutralize capacitive reactance
with a lumped inductance or with a stub or with a
helical coil. The results are approximately the
same but there are differences.

If the current amplitude changes significantly
between the bottom and top of the loading coil,
the lumped circuit model is not valid because
the coil is an appreciable percentage of a
wavelength more akin to a transmission line
than a lumped circuit.
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

Now it is clearer to me. I understand why there is a difference using
lumped circuit analysis as opposed to the the actual coil or stub
analysis. You have provided much valuable info on this subject. Thanks
again. I will load some math program on my pc any do some of the
analzsis of my design and compare it to what I have measured now with
the ones I have built

The reason this came about to me was to use some very short but
extremely strong 1.5" insulators that I have.In order to get the
required inductance with the length of insulators that I have the
losses in the coil would be large, that is why I chose the toroid.

Did you ever try to model a resonator where the coil required is
actually longer than the insulator, so that the vertical part of the
resonator is actually inside the coil , would it somewhat have a
larger inductance then the expected air wound value, similar to a coil
with a ferite inside it (tuning slug) or would the radiator not even
see the amount of the coil that it covered therefore have a lower
inductance. I was thinking, instead of spreading the turns on the
coil to adjust amount of inductance simply move the vertical element
in and out of the coil to adjust it. There discussions before were for
a center loading coil which will be constant, but this last part of
discussion I would like to try for base loaded coil and make it
variable but not tap it conventionally . Hope I described well enough
for you see what I have in mind, Again thanks for the info.73 brett

vertical antenna loading coil vs toroid
 

On Thu, 2 Apr 2009 16:42:32 -0700 (PDT), wrote:

Did you ever try to model a resonator where the coil required is
actually longer than the insulator, so that the vertical part of the
resonator is actually inside the coil

Hi Brett,

After following Cecil's pet theory, and your statement of finding it
useful, your question above becomes a remarkably perplexing
application of that knowledge.

The theory should have answered your question before hand. The
typical shorthand explanation for coils' length equivalency should
have too. The fact of the matter is that for a given height radiator,
there are probably an infinite variety of values for inductance along
the length where the radiator is broken for that coil's insertion. One
inductance value (however it is wound) is not equivalent everywhere -
hence the proposition of a coil having an equivalent length is rather
preposterous.

Most loaded vertical design proceeds along very few lines. The first
consideration is coil placement which is largely dominated with one
consideration: radiation resistance. The optimal point (for an
optimal size of the coil) is somewhere between 40% and 60% the way up
(adding a top hat lends to the variability). Sub-optimal designs
abound and are freely offered everywhere without explanation (but long
on unsupported claims).

Knowing the insertion point, the second consideration is overall
height in relation to wavelength. If the vertical is a loaded one, we
here in the group can well anticipate that it is going to be a very
short one seeking "special sauce" enhancement. Height and wavelength
will dominate the coil inductance at the given insertion point.

Knowing the insertion point and the height/wavelength, the coil's
inductance is fairly well defined. The third consideration is keeping
its loss low. So far I haven't seen that pursued to its logical
conclusion to instead see discussion wander in the poppy fields of
electrical length (that was solved with inductance). Loss drives you
to make the inductor large, with large separations in adjacent
windings. Tightly wound coils, or toroids in the basement band might
be useful at night for an aviation beacon light.

Worry about filling the coil's axis with the radiator is focusing on
the wrong problem, remove the excess, or fold it into the turns of the
coil. This may alter the inductance slightly, but that can be taken
care of with trimming at the top - trivial stuff. Stacked tubing
makes this less than trivial. You go into this expecting that kind of
flexibility because antennas are not designed straight from paper to
elevated tube the first time.

73's
Richard Clark, KB7QHC

vertical antenna loading coil vs toroid
 

wrote:
Did you ever try to model a resonator where the coil required is
actually longer than the insulator, so that the vertical part of the
resonator is actually inside the coil , ...

Never modeled it but have seen its effects during
75m mobile shootouts. One fellow had a hamstick
with the stinger bottom extending down into the
hamstick loading coil. It was a very lossy
condition which improved when he hack-sawed the
excess stinger off.

Do you have EZNEC? If so, I can modify a helical
loading coil to extend the stinger into the middle
of the coil and send the file to you.

Conductors within the loading coil field lower
the effective coil Q. However, I have had good
luck with a 1.25" fiberglass pipe running through
the center of the coil providing mechanical
support. Perhaps you could consider swapping your
insulator for a piece of fiberglass pipe or rod.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

vertical antenna loading coil vs toroid
 

Richard Clark wrote:
One
inductance value (however it is wound) is not equivalent everywhere -
hence the proposition of a coil having an equivalent length is rather
preposterous.

Nobody said one inductance value is equivalent everywhere.
In fact, just the opposite is true. The equivalent length
for different coils with the same inductance depends upon
their physical configurations.

For instance, w8ji's loading coil (100t, 10tpi, 2"dia)
calculates to have a VF of 0.0328 while my 75m Texas
Bugcatcher coil with approximately the same inductance
calculates to have a VF of 0.0198, a 66% difference
proving your above premise to be false.

************************************************** *****
THERE IS NO REQUIREMENT THAT TWO COILS WITH THE SAME
INDUCTANCE OCCUPY THE SAME NUMBER OF DEGREES OF ANTENNA.
************************************************** *****

To understand the details, just compare the following
1/4WL resonant stubs:

---25.3 deg Z0=600 ohm---+---10 deg Z0=50 ohm---open

---70.6 deg Z0=100 ohm---+---10 deg Z0=50 ohm---open

Both stubs are electrically 1/4WL = 90 degrees long.

How can 35.3 physical degrees of stub perform a 90 degree
stub function? Hint: There is a 54.7 degree phase shift
at the '+' junction.

Why does the second example require 80.6 physical degrees
of feedline? Hint: There is only a 9.4 degree phase
shift at the '+' junction.

Why does it take 70.6 degrees of Z0=100 ohm feedline
to perform exactly the same function as 25.3 degrees
of Z0=600 ohm feedline?

Both stub segments, Z0=600 and Z0=100, are providing
the same inductance at the '+' junction point, yet
one is 2.8 times longer than the other.

Is "the proposition of a piece of transmission line
having an equivalent length rather preposterous"?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

vertical antenna loading coil vs toroid
 

Cecil Moore wrote:
wrote:
Did you ever try to model a resonator where the coil required is
actually longer than the insulator, so that the vertical part of the
resonator is actually inside the coil , ...

Never modeled it but have seen its effects during
75m mobile shootouts. One fellow had a hamstick
with the stinger bottom extending down into the
hamstick loading coil. It was a very lossy
condition which improved when he hack-sawed the
excess stinger off.

some times a hack saw *can* be a fine tuning tool.


Do you have EZNEC? If so, I can modify a helical
loading coil to extend the stinger into the middle
of the coil and send the file to you.

Conductors within the loading coil field lower
the effective coil Q. However, I have had good
luck with a 1.25" fiberglass pipe running through
the center of the coil providing mechanical
support. Perhaps you could consider swapping your
insulator for a piece of fiberglass pipe or rod.

Ahh, I had the idea of doing such a thing (add vertical travel) for my
bugcatcher to fine tune swr if it needs tweaked a little. But it looks
like I'll be hopping outside the car a lot after all.

For 75/80 meters, I have like 4 separate taps.

- 73 de Mike N3LI -

vertical antenna loading coil vs toroid
 

On Apr 2, 10:34*pm, Richard Clark wrote:
On Thu, 2 Apr 2009 16:42:32 -0700 (PDT), wrote:
Did you ever try to model a resonator where the coil required is
actually longer than the insulator, so that the vertical part of the
resonator is actually inside the coil

Hi Brett,

After following Cecil's pet theory, and your statement of finding it
useful, your question above becomes a remarkably perplexing
application of that knowledge.

The theory should have answered your question before hand. *

Thanks very much for the information you provided to my posting.
The theory to the question was answered, I was asking the question
once again to the group to see if others have input on the subject I
posted. Knowing me I will probably ask many more questions that I have
already have the answer to, just to raise conversation and debate to
get other views on the subject. Thanks again for the info on the
subject, much appreciated. 73, vo1bbn Brett

vertical antenna loading coil vs toroid
 

On Apr 2, 10:34*pm, Richard Clark wrote:
On Thu, 2 Apr 2009 16:42:32 -0700 (PDT), wrote:
Did you ever try to model a resonator where the coil required is
actually longer than the insulator, so that the vertical part of the
resonator is actually inside the coil

Hi Brett,

After following Cecil's pet theory, and your statement of finding it
useful, your question above becomes a remarkably perplexing
application of that knowledge.

The theory should have answered your question before hand. *

Thanks very much for the information you provided to my posting.
The theory to the question was answered, I was asking the question
once again to the group to see if others have input on the subject I
posted. Knowing me I will probably ask many more questions that I have
already have the answer to, just to raise conversation and debate to
get other views on the subject. Thanks again for the info on the
subject, much appreciated. 73, vo1bbn Brett

vertical antenna loading coil vs toroid
 

On Fri, 03 Apr 2009 10:39:37 -0800, Richard Clark
wrote:

On Fri, 03 Apr 2009 07:34:20 -0500, Cecil Moore
wrote:

Richard Clark wrote:
One
inductance value (however it is wound) is not equivalent everywhere -

Nobody said one inductance value is equivalent everywhere.
Nobody is not very many people which should make this a short list.
But I don't see any names - strange.
In fact, just the opposite is true.
which must mean
Nobody said one inductance value is NOT equivalent everywhere.
or, perhaps:
EVERYBODY said one inductance value is equivalent everywhere.
or, perhaps:
EVERYBODY said one inductance value is NOT equivalent everywhere.
or, perhaps:
Nobody said one inductance value is equivalent NO where.
or, perhaps:
Nobody said NO inductance value is equivalent everywhere.
or, perhaps:
EVERBODY said NO inductance value is equivalent NO where.
...
proving your above premise to be false.
Which apparently nobody (somebody, everbody?) said.

The power of persuasion (Cecil's Degenerative form of the Sub-optimal
Hypothesis of Information Transformation) at its inventive best to be
able to wrestle two contradictory claims together and prove them both
true and false simultaneously!

Cecil must have been posed some very difficult advice as a little
nipper:
"Nobody jumped off the roof because everone did - wouldn't you?"

73's
Richard Clark, KB7QHC

This reminds me of a quote from Yogi Berra (as I recall) about a
retaurant in New York City:

"The place is so crowded, nobody goes there anymore".

W0BF