Current in antenna loading coils controversy
Yuri Blanarovich
Here is the good one for you on eHam.net
http://www.eham.net/articles/6512
between yours truly (right) and Tom, W8JI (wrong).
It centers around the argument that the RF current in the antenna loading coils
is (or not) equal. Classic case of "theory" (wrongly applied) to real life
measurements and facts. There is referenced previous article that started it
all and on my budding web site www.K3BU.us full text with pictures at
http://www.k3bu.us/loadingcoils.htm
It looks like this factor is not properly accommodated in modeling programs
using loading inductors in antenna elements. In view of the above, time
permitting, I will try to do some work and try to shed some more light on the
subject.
Any experiences out there, rather than more "reasons" why it ain't so?
Proper accommodation in modeling programs can give substantial improvement in
loaded elements modeling.
Let the games begin :-)
Yuri, K3BU
Reg Edwards
to the controversy.
" . . . loading coil current . . . is (or is not) equal to what
????????? ".
Please state unambiguously and explicitly what it is you wish to know.
---
Reg.
Wes Stewart
set up a tar baby:
|
|Let the games begin :-)
You say (at least I think you said): "Roy Lewallen, W7EL, author of
EZNEC and Wes Stewart, N7WS recommend workarounds to replace the coil
with cylinder of similar size or breaking the coil to number of
physical segments with appropriate inductances."
I'll admit to forgetting more things as I get older but I'll be damned
if I remember making any such statement.
Can you post a link to this so I know what it is that you think I
said, or what I said that I don't remember saying?
Wes Stewart N7WS
Yuri Blanarovich
>????????? ".
>
>Please state unambiguously and explicitly what it is you wish to know.
>---
>Reg.
Look at the article(s), it refers to current being equal (or not) at both ends
of the loading coil in the antenna elemnt.
In a nutshell, I (and W9UCW, etc.) found that current diminishes accross the
coil. W8JI using Kirchoff and Ohm says it can't.
I am curious if anyone else made measurements (never mind "theory") and what
they found.
Yuri
Yuri Blanarovich
>Can you post a link to this so I know what it is that you think I
>said, or what I said that I don't remember saying?
>
>Wes Stewart N7WS
>
>
Without going the route of providing "evidence" I posted the question about the
modeling loading coils here, and Roy and you provided suggestions of the
described workaround (if my memory doesn't fail me :-)
Yuri
w4jle
"Yuri Blanarovich" <k3...@aol.comnoSaddam> wrote in message
news:20031029135840...@mb-m04.aol.com...
> Howdy perpetual arguers!
Wes Stewart
wrote:
In other words, I didn't say it.
|
|Yuri
Reg Edwards
> I (and W9UCW, etc.) found that current diminishes across the
> coil. W8JI using Kirchoff and Ohm says it can't.
>
> I am curious if anyone else made measurements (never mind "theory") and
what
> they found.
=============================
If you mean the current distribution along the length of the coil was not
uniform but tapering then it is not surprising.
The important thing is by how much did it taper and in what direction? Up
or down?
Please describe clearly the type of instruments used and how you made your
measurements.
By how much did the current measuring instrument affect the strength of
current flowing, for example by detuning the antenna?
What was the length and diameter of the coil, and the number of turns?
What were the lengths of the antenna above and below the coil?
At what frequencies were the measurement made?
What was the current in amps in the coil wire at the bottom, at the centre
and at the top of the coil?
What does the current distribution in the coil affect, AND BY HOW MUCH?
----
Reg
Jim Kelley
Reg Edwards wrote:
> If you mean the current distribution along the length of the coil was not
> uniform but tapering then it is not surprising.
>
> The important thing is by how much did it taper and in what direction? Up
> or down?
>
> Please describe clearly the type of instruments used and how you made your
> measurements.
>
> By how much did the current measuring instrument affect the strength of
> current flowing, for example by detuning the antenna?
>
> What was the length and diameter of the coil, and the number of turns?
>
> What were the lengths of the antenna above and below the coil?
>
> At what frequencies were the measurement made?
>
> What was the current in amps in the coil wire at the bottom, at the centre
> and at the top of the coil?
>
> What does the current distribution in the coil affect, AND BY HOW MUCH?
> ----
> Reg
Gee, Reg. Until now I've always gotten the impression that you already
learned everything there was to know about this stuff. :-)
73, AC6XG
Yuri Blanarovich
>Another stiff dick contest between you and Tom?
>
Yep,
I post fact of life, Tom pompously chimes in that it can't be so with some
added ridicule, and I won't budge to a bully that is barking up the wrong tree.
This is about 5th time. Watch him to become expert in few moths "he said it all
along" :-) and will become a guru.
All in the good spirit of learning :-)
Yuri
Yuri Blanarovich
>What does the current distribution in the coil affect, AND BY HOW MUCH?
>----
>Reg
>
>
Reg it is all there in my article and references I posted in my post. Can you
look up those links or is there a problem? I hate to go over the stuff again.
If you can't look up the links, perhaps I could post the text here, but article
has details, measurements, pictures of meters and facts of life.
Yuri
www.K3BU.us
Reg Edwards
> learned everything there was to know about this stuff. :-)
>
> 73, AC6XG
=============================
Jim, if you promise, cross-your-heart, not to tell anybody I'll let you into
a long-hidden secret.
When it comes to the the distribution of current along a loading coil on a
vehicle-mounted whip I am severely handicapped in that I have never been
mobile in a motor car with a radio transmitter, never owned a motor car,
never even held a driver's licence.
Otherwise I am quite a normal person who takes an interest in electric
currents flowing along wires, rods, through coils and around the surfaces of
such things as vehicle bodies. Normallity extends to world-wide objections
against being choked by petrol fumes and the now common practice of
financing pirate expeditions to obtain the diminishing raw material from
which the poisonous liquid is refined.
It seems Yuri is interested in modelling short, coil loaded antennas. He
refers to controversy. I can set his mind at rest and assure him there is
none.
When the length of a loading coil is short in comparison with the overall
height of the antenna, certainly in comparison with a wavelength, the
current into one end can be assumed, with negligible error, to be equal to
that which comes out of the other end as with any other coil in an L,C,R
network analysis. Its stray capacitance can be ignored except for
investigating its self-resonant frequency.
It is a lump of inductance effectively concentrated at its midpoint. For
estimating antenna behaviour and performance it is necessary only to add
half the length of the coil to the length of the lower portion of the
antenna, and to do likewise to the upper length. The antenna's distributed
radiation and wire loss resistance can be sufficiently accurately estimated
from these dimensions, all being transformed to the feedpoint according to
the normal transforming action of the lengths of transmission line (the
antenna parts) involved.
================================
When coil length is nearly as long as the antenna, ie., a close-wound
helical for the lower frequencies, in which coil loss for a high inductance
is minimised by using thick wire rather than an inconvenient, very large
diameter coil, the antenna is best considered as a continuously loaded
1/4-wavelength transmission line in which its uniformly-distributed
capacitance, loss resistance and radiation resistance per unit length is
taken into account.
================================
For practical purpose, these different-proportioned sorts of short vertical
antennas all have the same, simple, well known radiation pattern. Any slight
differences are overwhelmed by variations, entirely out-of-human-control, in
the local environment and along the propagation path. What matters is
radiating efficiency. The standard of radiating efficiency is that of a very
high 1/2-wave dipole of any orientation and there's no need to be concerned
here where the radiation disappears to.
There is only one question of consequence. At what height up a short
vertical is a coil of given intrinsic Q to be located to maximise radiating
efficiency? It is never at or very near the top! As coil height increases
the required inductance and number of turns increases rapidly. Coil loss
resistance always overtakes the improvement in radiation resistance due to
the change in distribution of current along the antenna. A high resistance,
self resonant coil of many turns of fine wire right at the top of the
antenna eventually fails.
================================
There are various special cases which are dealt with by simple programs
available from the website below.
There is one program which covers from helicals, via screwdrivers, to lumped
coils. The coil can slide up and down the antenna to find the location of
maximum efficiency for given coil length and diameter. The number of coil
turns and wire gauge are automatically recalculated to maintain the same
required antenna resonant frequency. Program name is LOADCOIL.exe
Download and run in a few seconds.
----
=======================
Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
=======================
Richard Clark
wrote:
>but article
>has details, measurements, pictures of meters and facts of life.
Hi Yuri,
Then what's left to be said here?
73's
Richard Clark, KB7QHC
Yuri Blanarovich
>
>It seems Yuri is interested in modelling short, coil loaded antennas. He
>refers to controversy. I can set his mind at rest and assure him there is
>none.
>
>When the length of a loading coil is short in comparison with the overall
>height of the antenna, certainly in comparison with a wavelength, the
>current into one end can be assumed, with negligible error, to be equal to
>that which comes out of the other end as with any other coil in an L,C,R
>network analysis. Its stray capacitance can be ignored except for
>investigating its self-resonant frequency.
There is none? You are confirming there is one by your above statements.
The point is that W9UCW measured, that difference in "normal" loading coil
(not long coils or helicals) is in order of 40 to 60% less at the top of the
coil. That is significant in calculating or optimizing the efficiency of loaded
antenna. MEASURE it and don't rely on myth perpetuated since 1955 by Belrose
till today's ARRL Antenna Book. ON4UN has it right in his book.
Resonance is no big deal, efficiency is greatly affected, modeling programs are
way off especially if you include more loaded parasitic elements.
Did you read my article, facts and measurements? You can try to repeat the
measurements to validate the effect. That's what I am looking for, if we are in
error, would like to have it pointed out. Not speculations that it "should be"
like that.
Yuri
Yuri Blanarovich
>Then what's left to be said here?
>
>73's
>Richard Clark, KB7QHC
>
See the comments from the flat earth society, even Reg has and "hasn't" have a
problem.
Significant impact on modeling software. If the stuff is not accomodated
properly, then results (mainly efficiency) are way off.
Mobile antennas, shortened antennas can be made better if we have handle on the
thing.
Yuri, K3BU/m
Cecil Moore
> Any experiences out there, rather than more "reasons" why it ain't so?
> Proper accommodation in modeling programs can give substantial improvement in
> loaded elements modeling.
Assume a transmission line with an SWR of 10:1. Put a series inductor
in series with the transmission line. Assuming negligible losses, the
forward current is the same at each end of the coil and the reflected
current is the same at each end of the coil. The question is: Do the
superposed currents, Ifwd+Iref, remain constant? Of course not, because
of phase shifts. With a large enough coil, one could cause a current
maximum point on one side of the coil and a current minimum point on
the other side.
That same principle holds true for standing wave antennas which are
antennas with (surprise!) standing waves. The current is NOT the same
at each end of the coil (unless a current maximum or current minimum
occurs in the middle of the coil). However, for traveling wave antennas,
the current at each end of a loading coil would be close to equal.
--
73, Cecil http://www.qsl.net/w5dxp
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http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
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Cecil Moore
> In a nutshell, I (and W9UCW, etc.) found that current diminishes accross the
> coil. W8JI using Kirchoff and Ohm says it can't.
If you put a loading coil 1/3 of the way up on an end-fed 1/2WL
vertical, the net current will increase across the coil. The
net current can decrease, or increase, or be the same magnitude
for special cases. Think Ifwd+Iref with the coil causing major
phase shifts.
Open-ended antennas like dipoles are standing wave antennas. The
forward current is relatively constant through the coil and the
reflected current is relatively constant through the coil. But
the phasor sum of those two currents can vary wildly from end
to end in the coil because of phase shifts.
Yuri Blanarovich
the standing waves do it again!
So far the best argument against W8JI's Kirchoffs and Ohms!
With your permission I will post this public posting back at the eHam.net.
Now see what Reg says, hopefuly after reading the article.
Yuri
Yuri Blanarovich
>Open-ended antennas like dipoles are standing wave antennas. The
>forward current is relatively constant through the coil and the
>reflected current is relatively constant through the coil. But
>the phasor sum of those two currents can vary wildly from end
>to end in the coil because of phase shifts.
>--
>73, Cecil http://www.qsl.net/w5dxp
>
Don't we have a case of coil being RF choke to certain extent?
Also I think that behaviour of radiator before and after the coil defines the
magnitude of the current, no?
Yuri, K3BU
Richard Clark
wrote:
>It looks like this factor is not properly accommodated in modeling programs
>using loading inductors in antenna elements. In view of the above, time
>permitting, I will try to do some work and try to shed some more light on the
>subject.
Hi Yuri,
With respect to the data:
>Here are some actual measurements of current below and above loading coils.
> 92" mast, using a HI-Q coil (openwound airdux, 2 1/2"d) with small thermocouple
>type meters mounted on the insulated coil support. First for 40m, moving the coil
>in the mast from base to center to top (with hat) and reresonating.
> Base --100ma below & 66ma above
> Center --100ma below & 45ma above
> Top --100ma below & 37ma above
This speaks more of simple Resistive heat loss supported by your own
direct observation of:
> I fried the loading coil with 600W into Hustler resonator,
>melting heat-shrink tubing and wire at the bottom of the coil.
As you, through personal testimony, offer that the bottom of the coil
was warmer (hotter even) than the top; and further, given that the
measuring device is caloric based (thermocouple) it stands to reason
that the close association to heat inflates the base reading not
through the evidence of higher current, but higher (and demonstrable)
heat. The pictures show the close proximity of the thermocouples to
the heat source/coil and also reveal no readings at greater distances
from the coil.
You go to great lengths to portray the current distribution along the
entire length of the radiator from authoritative sources, and yet you
do nothing to confirm them; except over the small portion that
fascinates you and is prone to just such systematic error as I
describe.
Cecil Moore
> I post fact of life, Tom pompously chimes in that it can't be so with some
> added ridicule, and I won't budge to a bully that is barking up the wrong tree.
> This is about 5th time. Watch him to become expert in few moths "he said it all
> along" :-) and will become a guru.
I don't understand what the fuss is all about. The forward current hits
the end of the dipole and is reflected. There are standing current waves
on a standing wave antenna. A loading coil shifts the phase between Ifwd
and Iref so anything is possible across a coil, increasing currents,
decreasing currents, or equal magnitudes of currents. It all depends on
the phases involved. For dipoles shorter than 1/2WL, the current decreases
across the loading coils. For a 1WL dipole with the loading coils located
1/3 of the way from the feedpoint, the net current through the coils will
actually increase.
--
73, Cecil http://www.qsl.net/w5dxp
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
Cecil Moore
> When the length of a loading coil is short in comparison with the overall
> height of the antenna, certainly in comparison with a wavelength, the
> current into one end can be assumed, with negligible error, to be equal to
> that which comes out of the other end as with any other coil in an L,C,R
> network analysis.
But Reg, why do you think they call it a standing wave antenna? Would
you also assert that the current is equal when a coil is installed in
a transmission line with reflections? If it weren't for reflections
from the open ends of a dipole, the feedpoint impedance would be
hundreds of ohms. It's the reflections that reduces the feedpoint
impedance to ~70 ohms.
Cecil Moore
> The point is that W9UCW measured, that difference in "normal" loading coil
> (not long coils or helicals) is in order of 40 to 60% less at the top of the
> coil.
All explained by the different phasing of the forward and reflected
currents at that point. If you want to blow Tom's mind, measure the current
in and out of a coil placed 1/3 of the distance up in a 1/2WL vertical.
The current will *INCREASE* from the bottom of the coil to the top of
the coil. How many times have we been warned not to use lumped circuit
theory on distributed networks?
Cecil Moore
> Thanks Cecil,
> the standing waves do it again!
See if you can get Tom to assert that the current into and
out of a coil in series with a transmission line with reflections
is also constant. :-) Same principles apply.
> So far the best argument against W8JI's Kirchoffs and Ohms!
You can get a ballpark estimate of those currents by comparing
a 1/2WL dipole to a loading coil dipole. Assuming the following
two dipoles are resonant on the same frequency:
-----y----------x-----FP-----x----------y-----
-----coil-----FP-----coil-----
Assume the feedpoint impedances are the same and the losses in
the coils are negligible. The net current into the coil is close
to the current at 'x'. The net current out of the coil is close
to the current at 'y'.
Cecil Moore
>>Open-ended antennas like dipoles are standing wave antennas. The
>>forward current is relatively constant through the coil and the
>>reflected current is relatively constant through the coil. But
>>the phasor sum of those two currents can vary wildly from end
>>to end in the coil because of phase shifts.
>
> Don't we have a case of coil being RF choke to certain extent?
RF chokes are usually high enough impedance to drop virtually all
the RF voltage across the choke.
> Also I think that behaviour of radiator before and after the coil defines the
> magnitude of the current, no?
It can be thought of as a very lossy transmission line where
the loss is radiation. Please see my other posting comparing
a 1/2WL dipole to a loaded dipole.
--
73, Cecil http://www.qsl.net/w5dxp
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
Mark Keith
>
> Any experiences out there, rather than more "reasons" why it ain't so?
> Proper accommodation in modeling programs can give substantial improvement in
> loaded elements modeling.
>
> Let the games begin :-)
>
> Yuri, K3BU
Dunno, I think it varies. But I sort of agree with Tom, I think it's
fairly constant across the coil. The reason I think so, is because the
electric field across the coil is also constant, and I can easily see
that using a fluorescent bulb across the antenna and coil. Sure, there
may be some decrease, but that could be due to wire resistance loss.
Also, the construction of the antenna itself could vary the current
across the coil. If the whip is top loaded, and the current would be
linear up the whip anyway, I would think it would also be linear
across the coil, no matter where it was. If the coil were base loaded,
with the sharply tapering current distribution up the whip, the taper
across the coil *might* be more. Another reason I think it's fairly
constant is because if I elevate the coil up the whip, I also elevate
and improve the current distribution. The current will be fairly
constant all the way up to the top of the coil, and then start to
taper off as you go up the "stinger" part of the whip. If the
distribution were not fairly linear across the coil, I don't think you
would see this. I'm sure it's not perfectly linear, but I think it is
for all *practical* purposes. And like I said, probably can vary from
antenna to antenna. I haven't read the eham thing yet, but I guess
this is my wishy washy vote... MK
Reg Edwards
radiating - is it the forward or is it the backward wave ?
---
Reg
Yuri Blanarovich
>
>This speaks more of simple Resistive heat loss supported by your own
>direct observation of:
>> I fried the loading coil with 600W into Hustler resonator,
>>melting heat-shrink tubing and wire at the bottom of the coil.
No, it confirms that there is a significant (not negligible) difference in the
current at the bottom vs. top of the coil. Yes, Hustler has small (almost
resistive) wire on 80m resonator. If you trasmit for short period of time (not
enough for heat to equalize) and feel it, or use thermal strips to check
temperature, you would see the taper in the current from bottom to top. It is
in order of 50%, not negligible. Coils in tests are good quality, not
"resistive" wire, current relatively low (100mA) as shown in W9UCW measurements
and pictures.
The point is, if the current was constant or close to it, you would not see the
difference as we see it. Heat rises to the top, if anything the top would be
warmer if the current was constant. If the coil is uniform colenoid, same wire,
diameter (resistance), spacing and it shows difference in heat produced accross
the coil, then we can, using I2R formula, deduct that that current at the
bottom is greater than on the top. W9UCW measurements confirm that, Cecil
explains. Speculations that Earth must be flat might satisfy those reading the
(wrong) books, but will not jive with reality.
Simple way to test it, transmit 100W to 80m Hustler resonator, and feel the
coil. Even insensitive people can feel the significant difference in
temperatures. Put 500W to it for longer period and watch the heatshrink tubing
shrivel from the bottom up. This eliminates all the "errors" with meters to
prove the point.
Yuri, K3BU/m
Yuri Blanarovich
>
>Dunno, I think it varies. But I sort of agree with Tom, I think it's
>fairly constant across the coil.
MEASURE or FEEL it! Or disprove what W5DXP is saying.
It appears that current drop is proportional to the current drop in the section
of the antenna that is "missing" - replaced by the coil. You can express it in
electrical degrees and it appears to correspond to cosine distribution.
Yuri, K3BU
Cecil Moore
> Can any of you guys tell me which of the waves on the antenna does the
> radiating - is it the forward or is it the backward wave ?
An electron experiences the sum of those two waves and emits a
photon when it is energized enough. So the answer is both.
Cecil Moore
> MEASURE or FEEL it! Or disprove what W5DXP is saying.
This is easy to see using EZNEC. Model a 102' G5RV on 20m
and look at the current distribution. There are three
current maximums and four current minimums. If you install
a loading coil at a current maximum or current minimum, the
current magnitude will be the same on both sides of the coil.
If you install a loading coil at a point where the slope of
the current is negative (decreasing), the current at the bottom
of the coil will be greater than the current at the top of the
coil. This is the usual case for mobile antennas.
If you install a loading coil at a point where the slope of
the current is positive (increasing), the current at the bottom
of the coil will be less than the current at the top of the
coil.
Note: 'Top' of coil is the end closest to the the ends of the
antenna. 'Bottom' of coil is the end closest to the feedpoint.
Richard Harrison
"Can any of you guys tell me which of the waves on the antenna does the
radiating - is it the forward or is it the backward wave?"
I agree with Cecil, "So the answer is both."
Think of a traveling wave antenna, the rhombic. When it is properly
terminated, there is no backward wave and the radiation pattern is
unidirectional. Eliminate the termination resistance and a total
reflection occurs at the antenna`s far end. Now the rhombic is a
bidirectional antenna.
Best regards, Richard Harrison, KB5WZI
Richard Clark
wrote:
>Richard KB7QHC wrote:
>>
>>This speaks more of simple Resistive heat loss supported by your own
>>direct observation of:
>>> I fried the loading coil with 600W into Hustler resonator,
>>>melting heat-shrink tubing and wire at the bottom of the coil.
>
>The point is, if the current was constant or close to it, you would not see the
>difference as we see it. Heat rises to the top, if anything the top would be
>warmer if the current was constant.
Hi Yuri,
Your testimony contradicts your sentiments. You offer
incontrovertible evidence of heat at the bottom of the coil explicitly
in your statement above, and this below:
>Simple way to test it, transmit 100W to 80m Hustler resonator, and feel the
>coil. Even insensitive people can feel the significant difference in
>temperatures. Put 500W to it for longer period and watch the heatshrink tubing
>shrivel from the bottom up. This eliminates all the "errors" with meters to
>prove the point.
>
You are using a thermocouple which is sensitive to heat, the heat of
coil loss will inflate the reading. You have twice offered heat at
the bottom of the coils that correlate strongly with inflated current
values from a caloric sensor. You have no other thermocouple data
supporting the nature of the current distribution, just the isolated
section you find attractive. Put simply, your measurements have no
reference (readings from the entire length of the radiator).
You went to some trouble to offer testimonial from reference sources
on the nature of that distribution, but you did not measure it confirm
your testing. Two readings in isolation do not prove you have 100mA
into the bottom when there is only one reading below the coil.
If you are not interested in obtaining those remaining readings of
that current distribution, then you have a poor case.
Richard Harrison
"I ordered 19th edition of ARRL Antenna Book and followed chain of
references that led to information on page 16-7 and Fig. 9 and 10."
Excellent purchase. A series circuit tends to have the same current
throughout except when its length is significant with respect to
wavelength. A standing wave antenna has a reflected wave which makes
impedance a function of location along the antenna. So, a certain power,
incident and reflected, combine to produce voltage and current
variations on an antenna which are related to those on a transmission
line. Since radiation from an antenna occurs, power in each direction is
not constant as it tends to be on a transmission line because radiation
is taking a toll in each direction, and that`s a good thing. It`s the
purpose of the antenna.
Coil Q is important to efficiency if any part of the XL/R is loss
resistance and not radiation resistance. Radiation resistance is the
purpose of the antenna.
My ON4UN Figures are the same as Yuri`s but appear as Fig 9-22 on page
9-15. These show the current decline across a loading coil including the
obvious case of a solenoid used as an antenna where the entire current
distribution is within the continuous loading coil.
The ARRL Antenna Book has been exposed to scrutiny for many years. By
the 19th edition it`s a safe bet that moat of it is correct (without
consideration of "strings", 5 dimensions, or 11 parallel universes).
From what I`ve seen of ON4UN`s book, he got it right too.
Mark Keith
> NM5K
> >
> >Dunno, I think it varies. But I sort of agree with Tom, I think it's
> >fairly constant across the coil.
>
> MEASURE or FEEL it! Or disprove what W5DXP is saying.
Dunno, he seems to be saying about the same thing. It depends where
the coil is mounted.
>
> It appears that current drop is proportional to the current drop in the section
> of the antenna that is "missing" - replaced by the coil. You can express it in
> electrical degrees and it appears to correspond to cosine distribution.
I could buy that to an extent I guess. But say if you had a top loaded
vertical, with linear current distribution, the current across the
coil should be appx equal no matter where the coil is placed. But if
no top loading, maybe so.. MK
Yuri Blanarovich
>Incorrect. HEAT does not rise at all, however hot gas or hot liquid
>will rise in response to gravity. This has nothing to do with a loading
>coil made from solid parts.
>
>--
>Bill, W7TI
Incorrect, incorrect.
If we suppose the loading coil is heating up equally (the flat earth society
argument), it heats air immediately surrounding it. Air is heating up, rises up
as you say, as it rises it picks up the other air that is heating up and they
rise together. As they progress, they heat up rest of the coil on the way up,
with the result being that the top should be warmer (hotter) than the bottom.
If we have quarter wave whip with loading coil, and the bottom contrary to the
above mechanism is warmer, thet ergo ipso there must be more current flowing in
the bottom part of the coil, confirming what we say.
Yuri, K3BU/m
Yuri Blanarovich
>You are using a thermocouple which is sensitive to heat, the heat of
>coil loss will inflate the reading. You have twice offered heat at
>the bottom of the coils that correlate strongly with inflated current
>values from a caloric sensor. You have no other thermocouple data
>supporting the nature of the current distribution, just the isolated
>section you find attractive. Put simply, your measurements have no
>reference (readings from the entire length of the radiator).
>
The bottom meter is below the coil, so there is no heat heating up the
thermocoupled meter. If you insert the meters some distance away from the coil,
you would see the corresponding readings showing the difference between the top
and bottom. Arguments that heat or magnetic field affect the thermocouple RF
ammeters are just not realistic.
>You went to some trouble to offer testimonial from reference sources
>on the nature of that distribution, but you did not measure it confirm
>your testing. Two readings in isolation do not prove you have 100mA
>into the bottom when there is only one reading below the coil.
>
I did just rough test with one of my meters (has 8 A), flipping the coil and I
can see some deflection at the bottom and none at the top with 100 W into the
antenna. W9UCW et al did hundreds of measurements and showed just some
examples.
>If you are not interested in obtaining those remaining readings of
>that current distribution, then you have a poor case.
>
My "case" is to bring this to attention of those who are still "knowing" that
the current in loading coils is the same at both ends. If they doubt, they can
do their own measurements and see what it is, or show us where we are wrong.
Again, ON4UN in his Low Band DXing book has it right, ARRL Antenna Book has it
wrong and is perpetuating 50 year old misconception.
Just MEASURE or FEEL it!
>73's
>Richard Clark, KB7QHC
Yuri, K3BU/m
Yuri Blanarovich
>I could buy that to an extent I guess. But say if you had a top loaded
>vertical, with linear current distribution, the current across the
>coil should be appx equal no matter where the coil is placed. But if
>no top loading, maybe so.. MK
>
Top loaded vertical does not have LINEAR current distribution, that is another
simplification, fallacy. Current in the radiator has cosine distribution. At
the base, there is not much difference, just like in cosine of the angle
corresponding to the electrical length of radiator at that point.
Again, this subject of current distribution is important in optimizing the
antenna design by fine tuning the position of the loading coil in the antenna,
combination with top loading etc. Morew current flowing in the radiating part
of the antenna - the stronger the field and louder signal.
The "linear" current distribution mentioned in ARRL Compendium and Antenna Book
is the simplification propagated from Belrose's 1955 QST article. It is close,
but not exact and introduces confusion as it is demonstrated by the flat earth
society.
Yuri, K3BU/m
Tdonaly
>
>Again, this subject of current distribution is important in optimizing the
>antenna design by fine tuning the position of the loading coil in the
>antenna,
>combination with top loading etc. Morew current flowing in the radiating part
>of the antenna - the stronger the field and louder signal.
What is "the radiating part of the antenna," Yuri?
73,
Tom Donaly, KA6RUH
Richard Clark
wrote:
>>
>>You are using a thermocouple which is sensitive to heat, the heat of
>>coil loss will inflate the reading. You have twice offered heat at
>>the bottom of the coils that correlate strongly with inflated current
>>values from a caloric sensor. You have no other thermocouple data
>>supporting the nature of the current distribution, just the isolated
>>section you find attractive. Put simply, your measurements have no
>>reference (readings from the entire length of the radiator).
>>
>
>The bottom meter is below the coil, so there is no heat heating up the
>thermocoupled meter
...
>Just MEASURE or FEEL it!
>
Hi Yuri,
As I said, your testimony contradicts your sentiments (for the third
time now). As you offer no inclination to provide more data (a
complete survey along the entire length of the radiator using the
thermocouple devices), this is not much in the way of proof.
Richard Clark
wrote:
>If we suppose the loading coil is heating up equally
Hi Yuri,
You have already testified twice that it does not - so why IF it
around?
1.)
>>If you trasmit for short period of time (not
>>enough for heat to equalize) and feel it, or use thermal strips to check
>>temperature, you would see the taper in the current from bottom to top. It is
>>in order of 50%, not negligible.
2.)
>>Put 500W to it for longer period and watch the heatshrink tubing
>>shrivel from the bottom up.
73's
Richard Clark, KB7QHC
Cecil Moore
> My "case" is to bring this to attention of those who are still "knowing" that
> the current in loading coils is the same at both ends.
The current can be the same at both ends if the coil is positioned at a
current minimum or current maximum point which is NOT the case with
mobile antennas.
The key to understanding is to recognize that the coil causes the
opposite phase change in the forward current as it does in the reflected
current so they *cannot* track each other through the coil.
Cecil Moore
> What is "the radiating part of the antenna," Yuri?
The part of the antenna under the ideal top hat.
Reg Edwards
---
Reg.
Yuri Blanarovich
>What happens when the coil is a flat pancake ?
>---
>Reg.
>
>
>
It tastes good :-)
Wouldn't make a difference. W9UCW used toroid and got the same results. Have
you read the article?
Yuri
Mark Keith
> >
> >I could buy that to an extent I guess. But say if you had a top loaded
> >vertical, with linear current distribution, the current across the
> >coil should be appx equal no matter where the coil is placed. But if
> >no top loading, maybe so.. MK
> >
>
> Top loaded vertical does not have LINEAR current distribution, that is another
> simplification, fallacy. Current in the radiator has cosine distribution.
It's still fairly constant. But the degree would depend on the height
of the vertical vs the length of the top hat wires. If the hat is too
small, I doubt you would see as steady a distribution up the radiator.
At
> the base, there is not much difference, just like in cosine of the angle
> corresponding to the electrical length of radiator at that point.
I'm not sure what you mean by this. Do you mean the current across the
coil would be more steady than if the coil were higher? Does this
include using the top loading wires?
>
> Again, this subject of current distribution is important in optimizing the
> antenna design by fine tuning the position of the loading coil in the antenna,
> combination with top loading etc. Morew current flowing in the radiating part
> of the antenna - the stronger the field and louder signal.
Sure. But this is old news. I beat Reg's vertload program to death
finding the best overall coil height for my mobile antenna. Basically
I ended up putting it as high as I could. Which ended up a center load
at 5 ft up, with a 10 ft whip. Or 8 ft up on a 13 ft whip when parked,
and using the "Super" mode...:)
>
> The "linear" current distribution mentioned in ARRL Compendium and Antenna Book
> is the simplification propagated from Belrose's 1955 QST article. It is close,
> but not exact and introduces confusion as it is demonstrated by the flat earth
> society.
Dunno, I've never read it. Maybe calling the distribution as "linear"
is the wrong term, but the current is still fairly steady along the
radiator in the case of the vertical with the large top hat. I'm
looking at a model of one now. The current distribution is almost like
a twin tower standing next to the vertical. There is a slight decrease
from bottom to top, but it's very small. It's still my view that the
difference in current at each end of the coil used in such a case is
fairly small. No matter where the coil was mounted.
I've never said they would be exactly the same. Seems to me I started
off by saying they could vary a bit depending on the antenna. So if
you are saying they would be close, but not exact, you seem to be
saying the same thing I said to begin with, which seems to be the same
thing Cecil is saying. ??? Crap, I'm becoming confused.... I'm not
good at playing these type games. That's why I didn't even bother
reading the "current war" over on e-ham. *Sounds* like a 598 thread
nit pick contest just judging from what I've heard... It's not "that"
important to me, being I don't see what it would do for me, even if I
found there to be a fairly large difference from each end. If you have
pertinent info which shows the current is not even close to being
constant across the coil, please enlighten us. "I guess you are
attempting to" But at this point, I think everyone is starting to
chase their tales and bark at the moon.
I'm not really seeing the point, being the art of improving current
distribution in short verticals using coil placement is old news. MK
Cecil Moore
> What happens when the coil is a flat pancake ?
Don't you have a program for predicting the electrical
characteristics of a flat pancake coil? :-) Seriously,
what are those characteristics? Is there a formula?
Yuri Blanarovich
> At
>> the base, there is not much difference, just like in cosine of the angle
>> corresponding to the electrical length of radiator at that point.
>
>I'm not sure what you mean by this. Do you mean the current across the
>coil would be more steady than if the coil were higher? Does this
>include using the top loading wires?
>>
It is roughly like this: Consider quarter wave vertical (90 degree radiator),
no coils or loading, you will get current max at the base and then diminishing
towards the end to zero. Distribution is in the form of cosine function, nice
cosine curve. Now if you would insert the coil anywhere in that radiator and
shorten it and tune it back to resonance, the current distribution accross the
coil would correspond to the "missing" portion of the radiator that coil
replaces. Efficiency of the antenna is roughly proportional to the area under
the curve. ON4UN pictures show that. Appears that the best compromise position
for the loading coil is about 2/3 from the base. Having top loading, it
"stretches" the high current carrying portion of the radiator. The lower the
loading coil is, the less difference in current drop accross the coil (cosine
function) but shortening of the more current carrying radiator - less
efficiency.
>> Again, this subject of current distribution is important in optimizing the
>> antenna design by fine tuning the position of the loading coil in the
>antenna,
>> combination with top loading etc. Morew current flowing in the radiating
>part
>> of the antenna - the stronger the field and louder signal.
>
>Sure. But this is old news. I beat Reg's vertload program to death
>finding the best overall coil height for my mobile antenna. Basically
>I ended up putting it as high as I could. Which ended up a center load
>at 5 ft up, with a 10 ft whip. Or 8 ft up on a 13 ft whip when parked,
>and using the "Super" mode...:)
>>
That perhaps points to some error in validity of the formula, and confirms our
findings. Experience and W5DXP reported shootout results point to reverse
dimensions, 10 feet mast and 5 ft whip, coil about 2/3 up the antenna. You want
to have as much as possible the mast length and then best compromise between
the coil inductance (properties) and remaining whip (and hat).
Well, looking at fairly simple example of typical 40m loaded mobile model
antenna, as W9UCW used, having current vary 40 to 60% is significant, measured
differences in field strength are in order of 10 dB and that is significant. I
guess it must be like religion, you believe what you want and if the reality
doesn't matter, than let everybody be happy. But this has tremendous impact on
modeling especially in loaded parasitic arrays. If W8JI showed that Eznec
calculated current to be different by fractions and the measurements show
around 50% difference, then we have huge discrepancy and warning not to rely on
results like that.
There is too much reliance now going on modeling program results, ignoring some
realities. Some people are becoming "experts" on antennas based on modeling
results, without building one. But, even lightbulb can radiate and make some
people happy, but it is not my intention to argue with those. My goal is to
maximize the performance of the antenna and take advantage of propagation modes
for maximum results in the contests, where every fraction of dB counts.
It just amazes me that some people go to great length to speculate, calculate,
rather than go and verify the measurements and see what it REALY is. You can
see that in the threads after the articles.
What I was looking for is to see 1. if anyone else MEASURED the current in
loading coils, and what results they arrived at (and if we are wrong, then
where did we go wrong). 2. If this is right than to have modeling software
implement it with least error. I would like to use that for optimizing, say,
loaded elements for receiving arrays on low bands, optimizing mobile antennas,
loaded multielement beams, etc.
Yuri, K3BU/m
Cecil Moore
> I've never said they would be exactly the same. Seems to me I started
> off by saying they could vary a bit depending on the antenna. So if
> you are saying they would be close, but not exact, you seem to be
> saying the same thing I said to begin with, which seems to be the same
> thing Cecil is saying. ???
Nope, not what I am saying at all. I'm saying the magnitude of the forward
current doesn't change much through the coil and the magnitude of the
reflected current doesn't change much through the coil. That satisfies
Kirchhoff. But the net current, which is the superposition of those two
currents, can change drastically because of the relative phase differences
on each side of the coil.
w4jle
If we feed an antenna at the current point, the current decreases as the
voltage increases along the antenna element from feed point to end..
That being said, a coil replacing a segment of an antenna (in order to
physically shorten it) will exhibit the same properties (relating to
currents) as the segment it replaced.
"Richard Clark" <kb7...@comcast.net> wrote in message
news:e9c3qvce8s6345551...@4ax.com...
Cecil Moore
> Re: Current through a coil in an antenna.
>
> If we feed an antenna at the current point, the current decreases as the
> voltage increases along the antenna element from feed point to end..
>
> That being said, a coil replacing a segment of an antenna (in order to
> physically shorten it) will exhibit the same properties (relating to
> currents) as the segment it replaced.
Yep, if the feedpoint impedances are the same and both are lossless,
that has to be true.
Here's a repeat of a diagram I drew earlier.
-----y----------x-----FP-----x----------y----- 1/2WL dipole
-----coil-----FP-----coil----- loaded dipole
Assume the physical length of the loaded dipole is 1/4WL.
Each coil replaces the section between 'x' and 'y'. The currents
at 'x' and 'y' are quite different, being 1/8WL apart.
Consider an 8 foot center-loaded 75m mobile antenna. 87% of the
electrical length of the antenna is in the coil.
Cecil Moore
> What I was looking for is to see 1. if anyone else MEASURED the current in
> loading coils, and what results they arrived at (and if we are wrong, then
> where did we go wrong). 2. If this is right than to have modeling software
> implement it with least error. I would like to use that for optimizing, say,
> loaded elements for receiving arrays on low bands, optimizing mobile antennas,
> loaded multielement beams, etc.
Hi Yuri, try this out for your argument in the other group. Using EZNEC:
Example 1: 102' CF dipole with loading coils in the center of each arm
to cause the antenna to resonate on 3.76 MHz. I get XL=j335 ohms.
Example 2: Replace the above loading coils with series inductive stubs
hanging down. Ten foot stubs with six inch spacing between the wires is
what I used. What happens to the current across that six inch gap is obvious
from the current plot using EZNEC. Hint: There is a step function across
that six inch gap just as there will be with a six inch coil.
Then ask: Why doesn't EZNEC treat these two cases the same way?
Cecil Moore
> There is too much reliance now going on modeling program results, ignoring some
> realities.
Yuri, here is a modeling result that you might like. :-) I took a 102' dipole
and loaded it in the center of each leg with an inductive stub that made the
dipole resonant on 3.76 MHz. I added a one ohm series 'load' to each side of
the stub. Drawing one leg of the dipole, it looks like this:
----------R2-+ +-R1----------FP--- ... other half
| |
| | inductive
| | stub
+-+
EZNEC reports 0.85 amps through R1 and 0.57 amps through R2, a difference
of 33%. If one could model the inductive loading reactance as an actual
physical coil instead of a lumped single point impedance, results would
be similar to the above.
Now here is something that might blow some minds. The inductive stub
above is ten feet long. That's about 1/8WL on 20m. A 1/8WL shorted stub
equals +jZ0. The results of running the above antenna on 20m is that the
current through R1 is 185 degrees out of phase with the current through R2.
At the time when the current through R2 is flowing toward the end of the
antenna, the current through R1 is flowing toward the feedpoint. Wonder
what Kirchhoff would say about that. If you replace the stub with a coil
of the same reactance, not much changes.
Tell W8JI to stop using lumped circuit analysis when he should be using
distributed circuit analysis. :-)
Yuri Blanarovich
(Where is Roy? We could use expert guidance in modeling the case.)
I will post your comments on eHam.net.
The analogy using stubs is excellent. That brings the question of using nice
coils, vs. stubs, vs. toroids in shortened antennas. But we will save that for
another thread with proper name.
Now watch for W8JI twisting into: "I said that all along" see him changing his
web page and become a guru who "discovered" that current accross the loading
coil in the antenna is significantly different and Yuri (et al) will remain the
idiot who can't get the things right :-)....
Happened many times before :-(
Thanks again!
Yuri, K3BU/m
As Ken, K7GCO keeps saying: "Don't they get tired of being wrong?"
Cecil Moore
> Thank you Cecil and Fred!
> (Where is Roy? We could use expert guidance in modeling the case.)
I sent Roy a copy of the EZNEC file that I sent to you. Anyone else
who wants a copy of those files, send me an email.
> I will post your comments on eHam.net.
Which forum/topic?
--
73, Cecil, W5DXP
Tdonaly
>
>Tell W8JI to stop using lumped circuit analysis when he should be using
>distributed circuit analysis. :-)
>--
>73, Cecil http://www.qsl.net/w5dxp
>
You know, it's against the law to kill people, Cecil. I
almost choked to death on my morning cup of
Bo Lee when I read that. :-)
73,
Tom Donaly, KA6RUH
Mark Keith
> >NM5K:
>
> > At
> >> the base, there is not much difference, just like in cosine of the angle
> >> corresponding to the electrical length of radiator at that point.
> >
> >I'm not sure what you mean by this. Do you mean the current across the
> >coil would be more steady than if the coil were higher? Does this
> >include using the top loading wires?
> >>
>
> It is roughly like this: Consider quarter wave vertical (90 degree radiator),
> no coils or loading, you will get current max at the base and then diminishing
> towards the end to zero. Distribution is in the form of cosine function, nice
> cosine curve. Now if you would insert the coil anywhere in that radiator and
> shorten it and tune it back to resonance, the current distribution accross the
> coil would correspond to the "missing" portion of the radiator that coil
> replaces. Efficiency of the antenna is roughly proportional to the area under
> the curve. ON4UN pictures show that. Appears that the best compromise position
> for the loading coil is about 2/3 from the base. Having top loading, it
> "stretches" the high current carrying portion of the radiator. The lower the
> loading coil is, the less difference in current drop accross the coil (cosine
> function) but shortening of the more current carrying radiator - less
> efficiency.
This would apply to a non top loaded antenna, but I wonder about a top
loaded "large hat" antenna. The current distribution is fairly steady
up the whip, even without using a coil.
>
> >> Again, this subject of current distribution is important in optimizing the
> >> antenna design by fine tuning the position of the loading coil in the
> antenna,
> >> combination with top loading etc. Morew current flowing in the radiating
> part
> >> of the antenna - the stronger the field and louder signal.
> >
> >Sure. But this is old news. I beat Reg's vertload program to death
> >finding the best overall coil height for my mobile antenna. Basically
> >I ended up putting it as high as I could. Which ended up a center load
> >at 5 ft up, with a 10 ft whip. Or 8 ft up on a 13 ft whip when parked,
> >and using the "Super" mode...:)
> >>
>
> That perhaps points to some error in validity of the formula, and confirms our
> findings. Experience and W5DXP reported shootout results point to reverse
> dimensions, 10 feet mast and 5 ft whip, coil about 2/3 up the antenna. You want
> to have as much as possible the mast length and then best compromise between
> the coil inductance (properties) and remaining whip (and hat).
But the coil placement on mine was mechanically limited. Yes, 2/3 up
is the best appx place, but I can't do that, except when parked. With
the 10 ft "stock" version, the upper 5 ft is stinger whip. I don't
have a sturdy support for the coil any higher than 5 ft up. Besides,
I'd hang the coil up on too many tree branches. The base of my antenna
is about 4.5 ft off the ground. My coil is nearly 10 ft in the air as
it is. Thats why I only use the lower extender mast only when parked.
My coil is then nearly 13 ft in the air. And the stinger still 5 ft
higher than that.
This is why I do add a lower 3 ft mast when I'm parked. I then do
approach the 2/3 level. There was no error involved. I just can't do
everything I'd like when it comes to that antenna. If I'm working 75m,
and I'm doing say 10 over 9 to someone with the 10 ft version,
switching to the 13 ft version will usually bump me up to 15 over 9.
Thats the usual difference I see in the real world.
>
> >> The "linear" current distribution mentioned in ARRL Compendium and Antenna
> Book
> >> is the simplification propagated from Belrose's 1955 QST article. It is
> close,
> >> but not exact and introduces confusion as it is demonstrated by the flat
> earth
> >> society.
> >
>
> Well, looking at fairly simple example of typical 40m loaded mobile model
> antenna, as W9UCW used, having current vary 40 to 60% is significant, measured
> differences in field strength are in order of 10 dB and that is significant.
What does this refer to? The comparison of current at each end of the
coil, or the overall antenna performance changes due to varying the
height of the coil?
If this is total performance increase from raising the coil, I don't
doubt it.
But thats not what this is really about. We are talking about the
differences in current at each end of the coil, and the ramifications
IF it's proven that the current drops off a good bit at the upper end
of the coil, compared to the lower end. I contend that even if you
prove that there is a major current difference at each end of the
coil, it will have no real impact on the design of short verticals. We
are already using the optimum coil heights, whether the current
difference is large, or not.
I
> guess it must be like religion, you believe what you want and if the reality
> doesn't matter, than let everybody be happy. But this has tremendous impact on
> modeling especially in loaded parasitic arrays.
Yes, maybe modeling, but not the design of the antennas as I use them.
I don't use modeling to design short verticals in general. I never do
for mobile antennas. I prefer to calculate using a program like
vertload. I don't consider vertload as "modeling". I consider it a
calculator program. The only time I model short verticals is if I'm
adding a top hat, and this would usually be something like a large
160m antenna for home use. I like to model it to get an idea of the
current distribution. But I don't rely on that model to calculate
efficiency.
If W8JI showed that Eznec
> calculated current to be different by fractions and the measurements show
> around 50% difference, then we have huge discrepancy and warning not to rely on
> results like that.
Well, that is fine. I hope the "correct" answer is known sooner or
later. But I don't rely on modeling when designing short verticals, so
I really doubt the "correct" answer will effect me much one way or the
other. It's not really an issue to me, being I already know the best
appx coil placement heights to use. And this was determined quite a
few years ago, before modeling was even common.
>
> There is too much reliance now going on modeling program results, ignoring some
> realities. Some people are becoming "experts" on antennas based on modeling
> results, without building one.
I've built all mine. "different coil heights" And like I said, I
don't use modeling for mobile antennas. I use "calculator" programs.
But, even lightbulb can radiate and make some
> people happy, but it is not my intention to argue with those. My goal is to
> maximize the performance of the antenna and take advantage of propagation modes
> for maximum results in the contests, where every fraction of dB counts.
I agree, and do the same thing. I wouldn't bother totally rebuilding
my mobile antenna if this were not the case. My old coil was only 2 ft
up..:(
>
> It just amazes me that some people go to great length to speculate, calculate,
> rather than go and verify the measurements and see what it REALY is. You can
> see that in the threads after the articles.
I'm not really set up to measure this accurately. I'd have to rig up
some gear/couplers, whatever, to do that. Besides, I've never really
worried about it much. I don't think it would have any effect on how I
build my short verticals.
>
> What I was looking for is to see 1. if anyone else MEASURED the current in
> loading coils, and what results they arrived at (and if we are wrong, then
> where did we go wrong).
I haven't done that. I'm just going by other related real world
observations I see.
2. If this is right than to have modeling software
> implement it with least error. I would like to use that for optimizing, say,
> loaded elements for receiving arrays on low bands, optimizing mobile antennas,
> loaded multielement beams, etc.
I have no problems with that, if indeed it does cause a modeling
error.
MK
Cecil Moore
> Cecil wrote,
>>Tell W8JI to stop using lumped circuit analysis when he should be using
>>distributed circuit analysis. :-)
>
> You know, it's against the law to kill people, Cecil. I
> almost choked to death on my morning cup of
> Bo Lee when I read that. :-)
I apologize for that, Tom. If you had choked to death, would
there have been enough evidence to convict me? :-)
--
73, Cecil, W5DXP
Tdonaly
>
>I apologize for that, Tom. If you had choked to death, would
>there have been enough evidence to convict me? :-)
>--
>73, Cecil, W5DXP
>
Not in California, Cecil. It would have been the
perfect crime.
73,
Tom Donaly, KA6RUH
Reg Edwards
"Mark Keith" < wrote
> I beat Reg's vertload program to death
> finding the best overall coil height for my mobile antenna. Basically
> I ended up putting it as high as I could. Which ended up a center load
> at 5 ft up, with a 10 ft whip.
===============================
There are 3 losses - coil loss resistance, ground loss resistance and
radiation resistance.
To calculate and maximise efficiency all 3 values must be transformed to a
common point - the base feedpoint.
The length of radiator between coil and base behaves is a transmission line
transformer which transforms the coil loss resistance (XL/Q) to another
value at the base. Would-be modellers should take this into account.
The Cosine current distribution along the radiator is a direct consequence
of its behaviour as a lossy line. (Actually, it is not an exact cosine shape
because of end-effect)
Efficiency = Rrad / ( Rrad+Rcoil+Rground ).
Rground is constant. For short antennas Rrad is the smallest of the 3
resistances.
As the coil is moved further up the antenna both Rrad and Rcoil increase.
But even if the coil is located at the extreme top of the antenna, radiation
resistance cannot increase to more than 4 times the radiation resistance
when the coil is located at the base feedpoint. Usually it is considerably
less than 4.
So the rapidly increasing coil loss resistance very soon overtakes the
increase in radiation resistance. Even if coil Q remains constant, coil
loss resistance increases just by virtue of its necessary increase in
inductive reactance.
To maintain resonance coil inductance increases inversely proportional to
the length of the whip above it. So when the coil is located 95% of the way
to the top of the antenna its loss resistance is TWENTY times greater than
that of a base loading coil even when Q is unchanged. In practice, a coil
having 20 times the inductance but with the same overall dimensions will
very likely have a lower Q and an even higher resistance.
Its easy to see the fixed value of Rground in the above efficiency formula
has the following effects -
When coil loss is less than ground loss, higher radiating efficiency is
achieved by placing the coil nearer to the top of the antenna.
And vice-versa.
When ground loss is very small (zero if antenna is a pair of two
back-to-back radiators to form a dipole) efficiency is relatively high
anyway, maximumum efficiency perhaps occurring with the coil located in the
lower half of the antenna. The slight improvement relative to base loading
(as part of a tuner) may not then be worth the mechanical inconvience of
fitting a coil in the antenna anyway.
An important factor, not considered quantitatively by anybody, is that a
mobile antenna is not just a loaded vertical - the vehicle body, just by
looking at it, obviously forms the major portion of the antenna and is
floating above ground. The vehicle body plus loaded whip should be
considered to be an off-centre-fed, short, 1/2-wave resonant vertical dipole
and modelled as such.
---------------------------------------------------------
Regarding antenna modelling - program LOADCOIL considers all 3 parts parts
of the antenna, the mast, loading coil and whip, as consecutive lengths of
transmission line each with its own Zo and loss resistance. It is obliged to
do this because it covers actual antenna heights approaching 1/4-wavelength
as may be erected in your backyard.
And it continues to do this for very short antennas with very short loading
coils even where there would be negligible error by assuming the current
going into one end of the coil is the as what comes out of the other.
There's a companion program TOPHAT2. There's no coil in it.
----
=======================
Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
=======================
Yuri Blanarovich
> Besides, I've never really
>worried about it much. I don't think it would have any effect on how I
>build my short verticals.
Good for you :-)
Granted, we are close to optimum with mobile verticals.
If I understand how and why things work, I can do better job on optimizing and
maximizing the performance of the antennas, especially when it comes to more
element loaded arrays. You would see significant difference in
designing/optimizing say 3 element loaded beam. Modeling software uses currents
in elements and calculates mutual interaction between the elements. If the
current distribution and magnitude are off by 50% then we have major problem.
Yuri
Yuri Blanarovich
>I sent Roy a copy of the EZNEC file that I sent to you. Anyone else
>who wants a copy of those files, send me an email.
>
I didn't get it, for direct mail take noSaddam out :-)
>> I will post your comments on eHam.net.
>
>Which forum/topic?
>--
>73, Cecil, W5DXP
The article and follow up comments are at:
http://www.eham.net/articles/6512
Yuri, www.K3BU.us
Yuri Blanarovich
>When ground loss is very small (zero if antenna is a pair of two
>back-to-back radiators to form a dipole) efficiency is relatively high
>anyway, maximumum efficiency perhaps occurring with the coil located in the
>lower half of the antenna. The slight improvement relative to base loading
>(as part of a tuner) may not then be worth the mechanical inconvience of
>fitting a coil in the antenna anyway.
>
But not in the far field, affecting low angle radiation. Practical results and
measurements show that it is worth the mechanical inconvinience to place the
coils where they belong. Just ask Cecil about results of mobile antenna
shootouts.
>An important factor, not considered quantitatively by anybody, is that a
>mobile antenna is not just a loaded vertical - the vehicle body, just by
>looking at it, obviously forms the major portion of the antenna and is
>floating above ground.
At this time it is "bad" enough to look at this one aspect of loaded antennas.
Of course in mobile antennas, the vehicle plays important role. W9UCW excluded
that, used "perfect" radial field ground to eliminate other variables in order
to have a closer look at the current distribution.
Another interesting finding was that there was almost negligible difference in
Q of coils. When they compared "perfect" loading coil (Bugcatcher type) with
"poor" coil of Webster Bandspanner, thay saw fractions of dB difference.
Yuri, K3BU/m
Cecil Moore
> Practical results and
> measurements show that it is worth the mechanical inconvinience to place the
> coils where they belong. Just ask Cecil about results of mobile antenna
> shootouts.
I feel the same way, Yuri, but at a shootout, +2dB is worth it's weight in
tachyons. +2dB may or may not be noticeable during normal operation. I use
a screwdriver even though I know how to do better.
--
73, Cecil http://www.qsl.net/w5dxp
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
Cecil Moore
> The article and follow up comments are at:
>
> http://www.eham.net/articles/6512
Egads, did I get the last word? (so far) That's proof of action
at a distance. I'm a thorn in the side of hams who are not even
on the same newsgroup as I. :-)
Mark Keith
> Yuri Blanarovich wrote:
> > The article and follow up comments are at:
> >
> > http://www.eham.net/articles/6512
>
> Egads, did I get the last word? (so far) That's proof of action
> at a distance. I'm a thorn in the side of hams who are not even
> on the same newsgroup as I. :-)
Dunno...I finally got up enuff courage to wade thru a bunch of that
myself. Both had some decent points..But....Just using my built in
"BS" filter only, which rarely seems to fails me, and ignoring all
other influences, I still have to side with Tom. I still think the
current is fairly constant. But not perfectly so, and can vary due to
the antenna and it's mount, etc. I guess I'll just wait until the
smoke clears to see how far off I am. This will be a good test of my
filter unit. :) As far as who wins, I could care less. Nothing
personal either way...But I have learned never to ignore my BS filter,
so I'm going with it. :) MK
Yuri Blanarovich
"BS" filter only, which rarely seems to fails me, and ignoring all
other influences, I still have to side with Tom. I still think the
current is fairly constant.<<
>Nothing
>personal either way...But I have learned never to ignore my BS filter,
>so I'm going with it. :) MK
>
Same here,
did your filter filtered out W5DXP pudding? The "theoretical" proof is right
there. Or are you drinking the same coolaide as Tom? :-)
Yuri
Reality vs. Speculations? Duuuh?
Cecil Moore
> Dunno...I finally got up enuff courage to wade thru a bunch of that
> myself. Both had some decent points..But....Just using my built in
> "BS" filter only, which rarely seems to fails me, and ignoring all
> other influences, I still have to side with Tom. I still think the
> current is fairly constant.
The key to understanding is to realize that the net current is the
phasor sum of the forward current and reflected current (on a standing-
wave antenna). Assume a 10 degree phase delay through the coil on the
frequency of operation. Ifwd-in and Iref-out are on the same side of
the coil. Ifwd-out and Iref-out are on the other side of the coil.
Ifwd-in--> coil Ifwd-out-->
-----------------------////////////-------------------------
<--Iref-out <--Iref-in
Assume that |Ifwd-in| = |Ifwd-out| which satisfies Kirchhoff
Assume that |Iref-in| = |Iref-out| which satisfies Kirchhoff
Ifwd-in + Iref-out = net current on left side of the coil
Ifwd-out + Iref-in = net current on right side of the coil
Ifwd-out lags Ifwd-in by 10 degrees
Iref-out lags Iref-in by 10 degrees (Iref-in leads Iref-out)
Now let's assume that Ifwd-in and Iref-out are in phase. So current
on the left side of the coil equals Ifwd-in at zero degrees plus
Iref-out at zero degrees which is a current maximum point.
Ask yourself: Can we have a current maximum point on both sides of
the coil? I trust that answer is obvious.
Ifwd-out lags Ifwd-in by 10 degrees. Iref-in leads Iref-out by 10 degrees.
So current on the right side of the coil equals Ifwd-out at -10 degrees
plus Iref-in at +10 degrees, NOT a current maximum point.
Therefore, in this example, net current on the left side of the coil
cannot possibly be equal to net current on the right side of the coil.
Cecil Moore
> Same here,
> did your filter filtered out W5DXP pudding? The "theoretical" proof is right
> there. Or are you drinking the same coolaide as Tom? :-)
Yuri, my latest posting sheds more light. Apparently, W8JI doesn't
realize that there are two superposing currents phasor-adding together
to get the net current and the phase distribution between those two
current waves are opposite because they are traveling in opposite
directions. This is a characteristic of standing-wave antennas.
See what happens when one tries to ignore the component waves?
Because the two currents are traveling in opposite directions, any phase
delay through the coil shifts the phase of the two currents IN OPPOSITE
DIRECTIONS. Thus the total relative phase shift effect through a 10 degree
coil is 20 degrees.
Yuri Blanarovich
>Therefore, in this example, net current on the left side of the coil
>cannot possibly be equal to net current on the right side of the coil.
>--
>73, Cecil http://www.qsl.net/w5dxp
>
>
Thanks for another gem,
I apologize to Reflected Waves, for they are important and I will treat them
with greater respect. I still don't like them in the feedlines, but I love them
in the radiators :-)
Yuri, www.K3BU.us
Cecil Moore
> I apologize to Reflected Waves, for they are important and I will treat them
> with greater respect. I still don't like them in the feedlines, but I love them
> in the radiators :-)
Yuri, to be perfectly consistent, you would need to change all your
standing-wave antennas to traveling-wave antennas. I've got some
non-inductive terminating resistors for sale at the right price. :-)
--
73, Cecil http://www.qsl.net/w5dxp
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
Yuri Blanarovich
>Yuri, to be perfectly consistent, you would need to change all your
>standing-wave antennas to traveling-wave antennas. I've got some
>non-inductive terminating resistors for sale at the right price. :-)
>--
>73, Cecil http://www.qsl.net/w5dxp
>
>
Well, I've been thinking on those sleepless nights, how to turn standing wave
Yagis or Quads into traveling wave ones, with no back lobes. Got recipe? I've
got resistors.
Yuri
Mark Keith
Oh, purely speculation on my part. I have no easy way of really
knowing the reality. There is a small part that keeps bugging me, but
I'd have to see for sure where he is measuring the currents. I missed
the pix on the site. I'll assume for now he measured at each end of
the coil, pretty much at the connection to the mast or whip. The part
the bugs me is a possible stunting of the current at the top of the
coil due to the capacitance it is looking at, at the end of the coil.
To my thinking, once you leave the coil, even right at the end, you
should see a reduction of current, compared to say even a turn or two
from the top of the coil. I'm just wondering if this may be giving a
false indication of the true currents within the coil,if he is
measuring slightly outside of the coil. I'd be more satisfied if he
could measure a few turns from each end "using a large, many turns,
coil for 80 or 160" to get a general view within the windings
themselves. But I realize this could be very difficult. You all may be
totally correct. I'd just like to be a little better convinced before
I totally agree. I expect a slight decrease in current at the top vs
bottom. But I don't expect it to be large. I also don't expect the
bottom of the coil to be "hot", with a radical current taper on the
upper windings. The main thing I see to causing a reduction of
current , is the stinger on top of the coil. "capacitance" I wonder if
he is seeing the effects of that capacitance in his lower measurement?
Only the shadow knows for sure....:/
As far as the reverse currents Cecil mentions, I'd have to ponder that
a while.
Seems to me that could wildly vary from antenna to antenna depending
on height, coil positions, any top loading, etc..Although it looks
good on paper, I smell a hook. So I'd have to think about that more.
BTW, this amount of current in the coil, is something I've also
thought about myself. I've just come to the "different" conclusion
it's fairly constant through the coil. I could always be wrong.
Wouldn't be the first time.. But I need to see/hear a bit more to be
convinced. MK
Mark Keith
I found this comment interesting. Note this is from one that actually
has tried measuring the current in coils. This was from the site you
mention...
>>>>>>>>>quote>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
I once had an occasion where the bottom of a coil did get warm, while
the top did not. Yet my RF ammeters showed the same current on both
ends. What was going on?
I ultimately determined that the soldered connection from the coil to
the lower antenna mast (for experimentation, it was copper) was adding
some undesireable resistance. Solder is not a particularly good
conductor of electricity. I copper-plated over the solder joint. Not
only did the bottom section of the coil no longer get warm, but the
two RF ammeters both showed about 20% more current flowing in the
antenna. And my far-field instruments showed a 1.5dB increase in field
strength.
>>>>>>>>>>>>unquote>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
This is one example of being fooled....If you took coil temp at face
value, you would think the current taper was quite steep, judging from
the temp's of the windings. But nope...A resistive connection seemed
to be the culprit. Note that his meters showed the same current on
both ends. :/ You can see why I'm afraid of that "hook" that usually
is lurking ready to bite at a moments notice.
Don't worry, if you are right, it will come out in the end. But that
hook...Ouch.. MK
Reg Edwards
accuracy where RF measurements are concerned.
Especially HF current and power measurememts.
Far too much importance is attached to names like GR and HP and Fluke rather
than their own abilitity to assess and sum the accumulation of measuring
errors.
--
=======================
Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
=======================
"Mark Keith" <nm...@wt.net> wrote in message
news:25eb70d7.03110...@posting.google.com...
Cecil Moore
> As far as the reverse currents Cecil mentions, I'd have to ponder that
> a while.
While you are pondering, here is a quote from _Antenna_Theory_, by Balanis.
"Standing wave antennas, such as the dipole, can be analyzed as traveling
wave antennas with waves propagating in opposite directions (forward and
backward) and represented by traveling wave currents 'If' and 'Ib' in
Figure 10.1(a)."
Standing wave antennas necessarily have standing waves caused by forward
waves and reflected waves. Analyze any coil subjected to forward current
and reflected current and you will be forced to agree that the current
at one end of the coil is not the same as the current at the other end
of the coil. W8JI is thinking lumped circuits when he should be thinking
distributed networks. The phase shift through the coil changes the
phase relationship between the forward current and reflected current, so
of course, their superposed value will be different at each end of the coil.
--
73, Cecil http://www.qsl.net/w5dxp
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
Yuri Blanarovich
>
>Radio amateurs and just as many professionals suffer from delusions of
>accuracy where RF measurements are concerned.
>
>Especially HF current and power measurememts.
>
>Far too much importance is attached to names like GR and HP and Fluke rather
>than their own abilitity to assess and sum the accumulation of measuring
>errors.
Thank goodness we have your formulas, failproof programs and variety of
speculations. Gentlemen, case is solved, closed. We can't measure it, we are
all bunch of dumb delusional morons with faulty instruments who don't know how
to use them. Current must be the same in the coil according to Rauch, Kirchoff,
Ohm, Reg. So now make your antennas out of coils, you will have constant
current radiator tip to tip with 300% efficiency and you can throw your
instruments away. Reg has the formula for it, use it!
Seriously, I thank you Cecil, Fred and few others who enlightened our case,
that's what I was hoping for and found it here. It will be the springboard for
further development, it already gave me some ideas how to improve efficiency of
loaded aerials. The others from the flat earth society showed their colors and
they ain't pretty. Just like democRATs, when they are deficient in arguments
they triviliarize and ridicule.
We are planning mobile antenna shootout here on east coast in the spring, so
get your wares ready and see who is da king koil.
Yuri, da BU/m
Yuri Blanarovich
>I once had an occasion where the bottom of a coil did get warm, while
>the top did not. Yet my RF ammeters showed the same current on both
>ends. What was going on?
>
What was he measuring, where was the coil?
W9UCW used 100 mA at the bottom, I doubt that this would "cook" the coil. You
see the pictures, they are good quality coils and he use two meters and
flippped the coil to eliminate possible error as described here.
>I ultimately determined that the soldered connection from the coil to
>the lower antenna mast (for experimentation, it was copper) was adding
>some undesireable resistance. Solder is not a particularly good
>conductor of electricity. I copper-plated over the solder joint. Not
>only did the bottom section of the coil no longer get warm, but the
>two RF ammeters both showed about 20% more current flowing in the
>antenna. And my far-field instruments showed a 1.5dB increase in field
>strength.
>
Again, put on the fricken Hustler 80m resonator, feed it 100W and feel it! No
meters, no hokus pokus, just "naked" antenna.
>
>This is one example of being fooled....If you took coil temp at face
>value, you would think the current taper was quite steep, judging from
>the temp's of the windings. But nope...A resistive connection seemed
>to be the culprit. Note that his meters showed the same current on
>both ends. :/ You can see why I'm afraid of that "hook" that usually
>is lurking ready to bite at a moments notice.
>Don't worry, if you are right, it will come out in the end. But that
>hook...Ouch.. MK
>
One insufficiently described measurement is enough to throw rest out of the
window? W9UCW has shown data from various measurements and positions of the
coil (pictures how it was done) and W5DXP backed it up with explanation of
reflected wave and simulation and comparison with loading stub. It came out,
this is the ned. If you choose not to believe, its a free country :-)
Yuri
Yuri Blanarovich
I added picture of current distribution when using inductance in the form of
loading stub as described earlier and from Eznec file supplied by Cecil. It is
at the end of the article at
http://www.k3bu.us/loadingcoils.htm
It shows the jump accross the stub, but when replaced by lumped inductor, the
Eznec shows constant current accross the coil.
Yuri
Cecil Moore
> Current must be the same in the coil according to Rauch, Kirchoff,
> Ohm, Reg.
Kirchhoff and Ohm were not wrong. For a lossless coil, the forward current
magnitude must be the same in the coil and the reflected current magnitude
must be the same in the coil. But the net current is the sum of those two
component waves which have phase angles rotating in opposite directions.
The basic problem is using lumped circuit calculations for a distributed
network problem, a well known no-no.
Roy Lewallen
looks pretty silly. Of course EZNEC shows no current difference across a
load. The EZNEC model of a load has zero length, so the current at both
terminals has to be the same. You will see a current change over the
length of a model of a conductor, because it does have length. The coil
in the web site pictures certainly has length, so why should you be
surprised to find a current change over its length? Did the experimenter
perhaps do the same test with the meters placed the same distance apart
with just a conductor in between? Would there be some great revelation
in finding that the current was different at the two points?
I was intrigued by the claim that a toroid measured significantly
different from one end to the other. I wonder if the tester tried
reversing the meters to verify that he got the same reading in both
cases. If he did, I'd be interested in learning more details.
Unfortunately, the main objective of the web site seems to be to insult
Tom, W8JI, rather than to be objective. So in my mind that leaves the
possibility open that the experimenter is more interested in finding
evidence that would disprove Tom than in presenting carefully measured
and objective data.
Roy Lewallen, W7EL
Cecil Moore
> I haven't had the time to participate in this, but in a brief look, it
> looks pretty silly. Of course EZNEC shows no current difference across a
> load. The EZNEC model of a load has zero length, so the current at both
> terminals has to be the same.
It appears that EZNEC also doesn't account for phase shifts across
a zero length coil.
Mark Keith
> >I once had an occasion where the bottom of a coil did get warm, while
> >the top did not. Yet my RF ammeters showed the same current on both
> >ends. What was going on?
> >
>
> What was he measuring, where was the coil?
> W9UCW used 100 mA at the bottom, I doubt that this would "cook" the coil. You
> see the pictures, they are good quality coils and he use two meters and
> flippped the coil to eliminate possible error as described here.
NO , I didn't see the pictures. Like I said, they didn't load on that
site. All the pix load except his.
>
> >I ultimately determined that the soldered connection from the coil to
> >the lower antenna mast (for experimentation, it was copper) was adding
> >some undesireable resistance. Solder is not a particularly good
> >conductor of electricity. I copper-plated over the solder joint. Not
> >only did the bottom section of the coil no longer get warm, but the
> >two RF ammeters both showed about 20% more current flowing in the
> >antenna. And my far-field instruments showed a 1.5dB increase in field
> >strength.
> >
>
> Again, put on the fricken Hustler 80m resonator, feed it 100W and feel it! No
> meters, no hokus pokus, just "naked" antenna.
What would that mean? The hustler coil is known to be flawed, and
makes a poor coil to be tested in this manner. The effects of it's
metal end caps, and overall design problems are fairly well known. I
refuse to use such a lousy coil. You can feed my homebrew coil 100w
all day long, and you won't feel anything except the finger on the
mike button hand start to go numb from holding the key down.
>
> >
> >This is one example of being fooled....If you took coil temp at face
> >value, you would think the current taper was quite steep, judging from
> >the temp's of the windings. But nope...A resistive connection seemed
> >to be the culprit. Note that his meters showed the same current on
> >both ends. :/ You can see why I'm afraid of that "hook" that usually
> >is lurking ready to bite at a moments notice.
> >Don't worry, if you are right, it will come out in the end. But that
> >hook...Ouch.. MK
> >
>
> One insufficiently described measurement is enough to throw rest out of the
> window?
No, it's just a good example of why you have to watch out for that
"hook" when doing measurments like this.
W9UCW has shown data from various measurements and positions of the
> coil (pictures how it was done) and W5DXP backed it up with explanation of
> reflected wave and simulation and comparison with loading stub. It came out,
> this is the ned. If you choose not to believe, its a free country :-)
Yep, it sure is. I sure as hell won't have anything shoved down my
throat. I'm sorry, but you all haven't convinced me yet that your
measurements are any more accurate than the one I quoted on that same
web page. And the one I quoted did give a fairly good description of
how he went about it. The guy I quoted said he saw constant current
across the coil. How do you explain that? Should I automatically
dismiss his findings just because you all have a web page and a bunch
of pictures? How do I know who did the more accurate test? I DON'T!!!
So I will trust neither of you until I have further info. Thats life
in the big city, and like I said before, nothing personal. I'd subject
anyone else to the same rigid standards. Go ask the poor suckers
building EH antennas if I cut them any slack...:/ I imagine they hate
my guts the way I talk about their antenna.
I can take all the time I want to decide who is right. I'm in no big
hurry. You can't rush something like this when only a few even have
the gear set up to properly measure this. Like I said before, you all
may be perfectly correct. I have no problem with that. But I'm not
totally convinced yet that you may not be seeing the effects of some
measurement error. I just don't have enough info on the "hooks"
involved in doing a test like that. I've never done them. Obviously,
judging from the other guys results,and many other comments, there are
a few hooks lurking. He said he saw constant current across the coil,
and explained why he saw hot lower windings. And his explaination made
perfect sense to me. I give his test just as much weight as I do
yours at this point. Either one of you could be correct, and I have no
way of telling who is at this point. MK
Mark Keith
> Mark Keith wrote:
> > As far as the reverse currents Cecil mentions, I'd have to ponder that
> > a while.
>
> While you are pondering, here is a quote from _Antenna_Theory_, by Balanis.
>
> "Standing wave antennas, such as the dipole, can be analyzed as traveling
> wave antennas with waves propagating in opposite directions (forward and
> backward) and represented by traveling wave currents 'If' and 'Ib' in
> Figure 10.1(a)."
>
> Standing wave antennas necessarily have standing waves caused by forward
> waves and reflected waves. Analyze any coil subjected to forward current
> and reflected current and you will be forced to agree that the current
> at one end of the coil is not the same as the current at the other end
> of the coil. W8JI is thinking lumped circuits when he should be thinking
> distributed networks. The phase shift through the coil changes the
> phase relationship between the forward current and reflected current, so
> of course, their superposed value will be different at each end of the coil.
How much though? What would be an average ratio difference you would
be likely to see on a 8 ft center loaded whip? Or lets go one
better...What would be a likely "worse case" scenario? Will this vary
from antenna to antenna? I would think so. I've never said there would
not be a difference. I actually expect a small difference. But I still
don't think it would be a large amount. Will this change in value be
enough to cause large errors in modeling these antennas? It's already
obvious to me that any info I may gleen from these tests will have no
impact on the position of my loading coils, being I already use them
at the optimum heights. Or as close as physically possible anyway. So
any info gleaned from these tests would only be useful from a modeling
aspect. And I'm not in a position to really comment on that too much.
I don't design modeling engines. Is it your opinion that the modeling
we now see with these antennas and coils is quite flawed? It's obvious
Yuri seems to think so. Myself, I really don't know at this point.
I've never worried about it too much. I don't model shorter than 1/4
wave verticals. MK
Yuri Blanarovich
>I haven't had the time to participate in this, but in a brief look, it
>looks pretty silly. Of course EZNEC shows no current difference across a
>load. The EZNEC model of a load has zero length, so the current at both
>terminals has to be the same. You will see a current change over the
>length of a model of a conductor, because it does have length. The coil
>in the web site pictures certainly has length, so why should you be
>surprised to find a current change over its length?
W8JI used it as a "proof" that current in the loading coil is virtually the
same at both ends. We were not surprised, but W8JI was insisting that it is,
used Eznec to prove it (go see his web site) and ridiculed us.
>Did the experimenter
>perhaps do the same test with the meters placed the same distance apart
>with just a conductor in between? Would there be some great revelation
>in finding that the current was different at the two points?
Not to us, but see W8JI arguments speculating and "knowing" that current must
be the same.
>I was intrigued by the claim that a toroid measured significantly
>different from one end to the other. I wonder if the tester tried
>reversing the meters to verify that he got the same reading in both
>cases. If he did, I'd be interested in learning more details.
I believe he did use the same method, and W9UCW can answer that. Looks like you
are also not getting the main point of the argument. Appears that the rule is:
"loading inductance (whatever form) inserted in the radiating element exhibits
current magnitudes at its ends corresponding to the current in the length of
radiator in electrical degrees that it replaces." Replacing inductance with
piece of wire won't do the simulation, it has to have properties of inductor
(replacing radiator's segment in degrees, inductance). Toroid, loading stub,
and lumped inductors do the same thing.
>Unfortunately, the main objective of the web site seems to be to insult
>Tom, W8JI, rather than to be objective. So in my mind that leaves the
>possibility open that the experimenter is more interested in finding
>evidence that would disprove Tom than in presenting carefully measured
>and objective data.
Not so, first I posted on eHam.net fact that current is different at the ends
of loading coil. To which W8JI rode in with his "answers" and ridiculed me in
public (I don't know the laws, didn't read the books, etc.) to which I
responded in kind, provided proof and defended my (and others) position.
Because this has happened about fifth time (he did it to others too) I simply
will not take the crap and bite back. He is parading as a knowitall guru and
pontificating with sometimes erroneous information. If anyone questions or
challenges that, he does his routine. If you read the trail from the start you
would get the picture. If he discussed the matters in a civil manner, there
would be no problem, we can exchange arguments, learn something and mainly give
a credit where is due. That's what professionals do. He first argues wrong,
then goes away for a while and then emerges with change as a guru or inventor.
That does not give hams good name and is poor example for those no-coders
coming into ham radio.
From the past postings, you could probably see that I can discuss the subjects
in a civil manner, but when someone who is wrong starts pulling out smart ass
remarks and ridicule, the gloves are off and I will defend the truth to the
end. It is not just proving Tom wrong, it is to set the record straight, to
bring aspect of antenna engineering to light (after 50 years of perpetuation of
wrong in some antenna books), to alert software designers to the problem so
they can accommodate the proper procedure or workarounds. I hope you can see
how inaccurate results will EZnec produce if you simply inserted 0 size
inductors in elements of 3 el. 80m shortened parasitic beam. Magnitudes and
current distribution will be off, producing skewed results. Optimizing programs
will be chasing wrong tail.
Again, I apologize for the tone, but I will not give in to the bully. If he
doesn't learn and shape up, I will be at his case, pointing out the wrongs that
he is disseminating (he has some more on his web site).
We were hoping that you were around, following the discussions, helping to
point where we are wrong, suggest workarounds or proper procedure for modeling
and we are willing to help with testing and verifications. Cecil brought some
insight from the theoretical side, I (and W9UCW?) can do measurements and all
this can bring greater understanding of the phenomena, rather than propagating
misconceptions and wrong ideas.
I found a lot more help and expertise on this NG than on eHam.net no-code flat
earth society, for which I am grateful.
Can we now look at the modeling problems? Seems that Cecil's way of
substituting the lumped inductance with loading stubs allows closer
approximation of configuration for the modeling programs. But this can still
distort the true picture. I would like to point out, that W6?? replaced loading
stubs in 3 el. 80m KLM beam with coils and the performance of the beam,
especially pattern improved tremendously. So it looks like loading wires and
radiation from them (folded along the element) upset the current distribution
and resulting deterioration of performance. (So much for nice, low loss
loading.) This was done, tested, measured and verified, no speculations. Is
there better way of modeling the case, can we use cosine of degree of
electrical length of wire that coil replaces?
>Roy Lewallen, W7EL
Yuri, K3BU
Wes Stewart
wrote:
|I haven't had the time to participate in this, but in a brief look, it
|looks pretty silly. Of course EZNEC shows no current difference across a
|load. The EZNEC model of a load has zero length, so the current at both
|terminals has to be the same. You will see a current change over the
|length of a model of a conductor, because it does have length. The coil
|in the web site pictures certainly has length, so why should you be
|surprised to find a current change over its length? Did the experimenter
|perhaps do the same test with the meters placed the same distance apart
|with just a conductor in between? Would there be some great revelation
|in finding that the current was different at the two points?
I too have been lurking and while I didn't spend any time reading the
eham stuff what was going on here got me looking at a model of this
situation.
I used MultiNEC to invoke EZNEC for all calculations. I modeled a
shorter-than-quarter-wavelength vertical, loaded with an inductor, all
of this over perfect ground. Using MultiNEC, I used equations to
change the length of the radiator, the position of the inductor, keep
the segment length as short as guidelines allow and resonate the
result after each change.
Nothing I did solved this argument but I did make a couple of slightly
related observations. Unless I'm mistaken (always a distinct
possibility):
1) When the radiator is electrically very short and near resonant the
current does not follow the classic patterns shown in most of the ham
literature, i.e. nearly constant below the inductor and close to a
straight line taper above. The current actually peaks at the inductor;
in other words, the highest current point on the structure is at the
inductor.
Hanson's paper (Robert C. Hanson, "Optimum Inductive Loading of Short
Whip Antennas", IEEE Transactions On Vehicular Technology, Vol VT-24,
No. 2, May 1975, pp 21-29) shows this, although his graphs show a
steady decrease in current from the feedpoint to where the peaking
begins. I did not see that, but instead a steadly increasing current
from the feedpoint to the current peak.
Not only that, the peaking is almost independent of inductor Q.
"Almost" meaning that my model shows that the current is actually
slightly higher in a lower Q inductor.
2) The structure Q, defined as the change in reactance with respect
to frequency, is independent of inductor Q.
3) For a give length radiator, gain is unaffected by where the
inductor is located along the length of the radiator and by inductor
Q.
If 3 is correct then I can remove the inductor from the radiator
without effecting the gain and place it before the feedpoint to
resonate the structure. Once out of the radiator, the current through
the inductor is constant. Just like it is in the antenna if it has
zero length.
By now you're all saying, "Huh?" But remember, this is for an antenna
over perfect (zero loss) ground.
So instead of worrying about perfecting our antennas, we should be
trying to perfect ground and/or zero length loading coils.
|
|I was intrigued by the claim that a toroid measured significantly
|different from one end to the other. I wonder if the tester tried
|reversing the meters to verify that he got the same reading in both
|cases. If he did, I'd be interested in learning more details.
Considering that *anything* inserted in the structure upsets the
current distribution, as Roy says above, why wouldn't the answer be
different. Even the toroid, or the distance between the insertion
points, have *some* length.
|
|Unfortunately, the main objective of the web site seems to be to insult
|Tom, W8JI, rather than to be objective. So in my mind that leaves the
|possibility open that the experimenter is more interested in finding
|evidence that would disprove Tom than in presenting carefully measured
|and objective data.
Eureka!
Wes Stewart N7WS
Yuri Blanarovich
the differences in current are in order of 40 - 60%, that is significant.
The lower the band, the shorter the antenna, the bigger the effect, the more
important where the coil is. It will vary from antenna to antenna, depending on
the coil "shortening" factor. If the coil is closer to the feedpoint, the
current difference is lees, but efficiency suffers most. As you move coil up
the radiator, turns increase, current difference increases and effciency goes
up. If you replace (part of) coil with top loading, current differences
decrease (0 difference at 0 deg. long coil) and your efficiency goes up.
Efficiency or radiated power of loaded antenna is roughly proportional to the
area under the corresponding current curve of the remaining (straight)
radiator. Coil "eats" part of the radiator and its current carrying (radiating)
capabilities, this is why the current will be significantly different at the
ends of the coil. I hope this illustrates the situation?
As Cecil showed, modeling is not accounting for the effect and now that Roy is
on, we hope to sort things out and come up with ways to best implement the
phenomena in modeling programs. Right now, it appears that the best way to
approximate the effect is to use loading stubs of the same inductance as
intended coil.
Barry and Cecil agreed to cooperate on the article describing in detail (and in
civil manner :-) this subject and we hope that Roy will join us adding the
modeling aspect to it.
Yuri, K3BU/m
Yuri Blanarovich
>NO , I didn't see the pictures. Like I said, they didn't load on that
>site. All the pix load except his.
>>
Then you are missing a lot.
I don't know what the problem with eHam.net site is, I uploaded all the
pictures the same way, some showed, some not. This is why I posted link to my
page
http://www.k3bu.us/loadingcoils.htm
which has the pictures, also RIGHT drawings from ON4UN book, latest modeling of
W5DXP stub loaded G5RV and some selected comments explaining the phenomena.
Check it out.
>> Again, put on the fricken Hustler 80m resonator, feed it 100W and feel it!
>>No meters, no hokus pokus, just "naked" antenna.
>
>What would that mean? The hustler coil is known to be flawed, and
>makes a poor coil to be tested in this manner. The effects of it's
>metal end caps, and overall design problems are fairly well known. I
>refuse to use such a lousy coil. You can feed my homebrew coil 100w
>all day long, and you won't feel anything except the finger on the
>mike button hand start to go numb from holding the key down.
>
Another "very well known fact" from W8JI's teachings? Metal caps are at both
ends, top would feel the same then, it doesn't. Hustler coil is "lousy" because
uses aluminum wire to achieve "match" through some loss and that is additional
loss. But from the point of view as inductor, it is uniformly wound solenoid,
same wire and diameter, so according to I2R law, the heat developed in it is
proportional to the square of current. If there is more heat at the bottom,
then irrefutably there is more current flowing at the bottom.
Here is the shocker:
When W9UCW bunch was measuring various coils, they also compared that perfect
coil as you and I have (heavy wire, proper form factor, good connections) to
"lousy" Webster Banspanner sliding coil (aka cheap screwdriver) they found
negligible difference in measured signal strength. They rechecked everything
scratched their heads, but that was it. So another myth about the quality of
coil (resistance of course applies, but is minuscule) importance. Now when we
look at it from the point of view of effect of the coil on the efficiency of
antenna, it is explanatory. Coil replaces portion of radiator that is not there
anymore, so the significance of its quality is not as important as the position
of the coil on the radiator (area under current curve). Of course the ohmic
losses are a factor, but that is minuscule (ohms or two) versus reduction in
current flowing in remaining radiator. I like and have big fat coils, but looks
like they can be optimized better, perhaps heavier wire in first few turns,
slimmer construction, less wind load, but placed higher up on the mast. So
there is another one you don't have to believe, I sure was surprised.
Measure it!!!
>Yep, it sure is. I sure as hell won't have anything shoved down my
>throat. I'm sorry, but you all haven't convinced me yet that your
>measurements are any more accurate than the one I quoted on that same
>web page. And the one I quoted did give a fairly good description of
>how he went about it. The guy I quoted said he saw constant current
>across the coil. How do you explain that? Should I automatically
>dismiss his findings just because you all have a web page and a bunch
>of pictures? How do I know who did the more accurate test? I DON'T!!!
I am not a salesman, I will not try to convince you of anything. I can
elaborate and answer some questions and it is up to you to believe it or not.
You can believe engineers with education, their experience and results, or you
can believe some "technical impostor" as K7GCO phrased it.
You could see almost constant current across the coil if the coil is at the
base of quarter wave radiator, has heavy windings and is replacing relatively
short electrical length of the radiator. Did he mention what coil, where was
the coil placed? We have methods and pictures of W9UCW tests on various bands
at different positions, we have yet to get objections or pointed out errors in
his setup. We don't know much about the other one. W8JI said that he measured
thousands of loading coils, modeled them and found no difference. He is
obviously lying. He has yet to tell us about ONE measurement I asked him to do.
You believe what you want. As I mentioned we will write concise article on the
subject and you can take it from there or stick with Rauchians.
I sure enjoyed this exercise, learned from it a thing or two and I am looking
forward to implement some of the stuff (measure it too) in the design of new
loaded mobile and low band antennas. As they say on FreeRepublic.com, this is
series and hugh :-)
Yuri, K3BU
Yuri Blanarovich
>
>I used MultiNEC to invoke EZNEC for all calculations. I modeled a
>shorter-than-quarter-wavelength vertical, loaded with an inductor, all
>of this over perfect ground.
How did you model inductor, as physical zero length inductance?
Did you try substituting (coil) inductor with equal inductance loading stub?
Did you try one of the situations (band, antenna/coil size) that W9UCW
describes in his measurements?
He used almost "perfect" ground of 60 radials for measurement. Results will be
offest by some amount due to varying ground conditions (at very low angles),
but in the same way and this is not the subject of the argument.
>>The current actually peaks at the inductor;
in other words, the highest current point on the structure is at the
inductor.<<
That's what W8JI calculated in EZnec, does it make sense? Like 2+2 is 4.5? Why
would inductor "suck" the current up? We should then use "those" inductors to
suck the current all the way to the top of the whip - perfect antenna?
Cecil, can you 'splain that?
>>3) For a give length radiator, gain is unaffected by where the
inductor is located along the length of the radiator and by inductor
Q. <<
(If the inductor is zero length?)
This should be huge screaming flag that there is something drastically wrong
with your whole approach. Look at any mobile shootout results and you will see
10 - 20 dB differences, ask Cecil, he wittnessed them.
Looks like we exhausted reasoning, facts, measurements, found what we wanted,
unless there is breakthrough in capturing the effect in modeling software we
are at the end of the rope.
Yea, Eureka!
Thanks!
Yuri, K3BU/m
Mark Keith
> >I once had an occasion where the bottom of a coil did get warm, while
> >the top did not. Yet my RF ammeters showed the same current on both
> >ends. What was going on?
> >
>
> What was he measuring, where was the coil?
> W9UCW used 100 mA at the bottom, I doubt that this would "cook" the coil. You
> see the pictures, they are good quality coils and he use two meters and
> flippped the coil to eliminate possible error as described here.
OK, I found the other website and saw the pictures. But this leads me
back to my previous post, which no one has commented on yet. To me,
the upper meter is actually measuring a point above the coil. But it
hard to tell from the pix exactly where the coupler is mounted. The
main question I would like answered is, would the presence of the
capacitive whip above the coil effect the current reading you got,
being you seem to be measuring slightly above the coil? To me, it
seems it would being you are not measuring inside the coil windings
themselves, but slightly above the coil. If this capacitance is the
cause of the decreased reading, then yes, it would be totally normal
to see the same results if you flipped the coil and meters. MK
Cecil Moore
> The guy I quoted said he saw constant current
> across the coil. How do you explain that?
Constant current across the coil is one of the possiblities.
Increasing current across the coil is one of the possibilities.
Decreasing current across the coil is one of the possibilities.
It all depends upon where the coil is inserted in the antenna.
Yuri Blanarovich
>back to my previous post, which no one has commented on yet. To me,
>the upper meter is actually measuring a point above the coil. But it
>hard to tell from the pix exactly where the coupler is mounted. The
>main question I would like answered is, would the presence of the
>capacitive whip above the coil effect the current reading you got,
>being you seem to be measuring slightly above the coil? To me, it
>seems it would being you are not measuring inside the coil windings
>themselves, but slightly above the coil. If this capacitance is the
>cause of the decreased reading, then yes, it would be totally normal
>to see the same results if you flipped the coil and meters. MK
>
There is no coupler involved. Meter is inserted between the end of the coil and
remaining mast or whip. Thermocouple meters have negligible insertion effect,
they act as perhaps an inch of wire inserted in the circuit, which is easily
compensated for by retuning either the antenna or moving the frequency. Their
meter mechanism is virtually immune to any RF field distortion. They are
specially designed to measure the RF current with minimum impact on the
measured circuit and to be interfered with. If you can grab one at the flea
market get it!
You could measure current on each turn if you managed to cut it and insert the
ammeter. It would show cosine curve decrease across the coil. Measuring it at
the first turn, end of the coil or inch or two above or below the coil produces
virtually the same results, difference in the current there is really
minuscule.
Another close way of measuring the current is to fashion the current
probe/coupler made of (split) ferrite ring, have few turns of pickup wire,
rectifier and small meter. (There is a description on one of G something web
pages.) You could slide this contraption up and down the radiator and measure
the current. Of course you have to back off and not to touch anything in
vicinity, otherwise you will detune the antenna setup and get erroneous
results. The most accurate and practical way is the way W9UCW did it, he read
the meters with binoculars from the distance.
Yet another way is to use thermal effect, use thermal strips, paste it along
the coil, put some power to it and watch the colors change. Not terribly
accurate, but proof that meters do not disturb the circuit or distort the
measurements.
You can't use probes, scopes or anything with wires attached to it, it detunes
the antenna and gives useless results
Yuri, K3BU.us
Cecil Moore
> How much though? What would be an average ratio difference you would
> be likely to see on a 8 ft center loaded whip?
A lot on 75m. Not much on 12m.
> Or lets go one
> better...What would be a likely "worse case" scenario?
The worse case I can think of is a short center-loaded whip
on 160m. :-) The coil is almost all of the necessary 1/4WL.
> Will this vary from antenna to antenna? I would think so.
Of course. It is all capable of being calculated.
> Is it your opinion that the modeling
> we now see with these antennas and coils is quite flawed?
The antenna current reported by EZNEC is inaccurate because of
simplified assumptions. EZNEC assumes that the current doesn't
change through the single point inductive load. Therefore, EZNEC
cannot be used to prove that the current doesn't change.
Cecil Moore
> in other words, the highest current point on the structure is at the
> inductor.<<
>
> That's what W8JI calculated in EZnec, does it make sense? Like 2+2 is 4.5? Why
> would inductor "suck" the current up? We should then use "those" inductors to
> suck the current all the way to the top of the whip - perfect antenna?
> Cecil, can you 'splain that?
Again, the current can either stay the same, increase, or decrease through
an inductor depending upon where it is located. Has that statement sunk
in on anyone? If you install a coil 1/8WL up on a 1/2WL vertical, the
current through the coil will *INCREASE*. If you install it in the center,
the current magnitude will be the same in and out of the coil and opposite
in phase. If you install it 1/8WL from the top, the current will decrease
through the coil like it does on a 1/4WL mobile antenna.
Yuri Blanarovich
>Again, the current can either stay the same, increase, or decrease through
>an inductor depending upon where it is located. Has that statement sunk
>in on anyone?
Yes,
to be more precise, we are actualy arguing about the case of resonant quarter
wave vertical, as a typical mobile antenna.
Other losses, such as ground conditions, poor contacts, color of eyes are not
considered here.
Yuri
Roy Lewallen
aren't any. It does account for voltage phase shift. It uses the same
equations I learned in freshman circuits class. Perhaps they taught
those same equations in Texas, too, but I can't be sure.
Roy Lewallen, W7EL
Wes Stewart
wrote:
|>N7WS:
|>
|>I used MultiNEC to invoke EZNEC for all calculations. I modeled a
|>shorter-than-quarter-wavelength vertical, loaded with an inductor, all
|>of this over perfect ground.
|
|How did you model inductor, as physical zero length inductance?
Yes.
|Did you try substituting (coil) inductor with equal inductance loading stub?
Yes. No difference.
|Did you try one of the situations (band, antenna/coil size) that W9UCW
|describes in his measurements?
No. I only skimmed the other web sites. Didn't see anything there to
make me change my mind. A couple of ammeters separated by 10% of the
radiator length doesn't work for me. Might as well put one at the
bottom and one at the top.
|He used almost "perfect" ground of 60 radials for measurement. Results will be
|offest by some amount due to varying ground conditions (at very low angles),
|but in the same way and this is not the subject of the argument.
Perfect ground is perfect. Any number of radials doesn't approach
perfect ground.
|
|>>The current actually peaks at the inductor;
|in other words, the highest current point on the structure is at the
|inductor.<<
|
|That's what W8JI calculated in EZnec, does it make sense?
Yes.
|Like 2+2 is 4.5? Why
|would inductor "suck" the current up?
It doesn't "suck it up." Haven't you ever hear of circulating
current?
|We should then use "those" inductors to
|suck the current all the way to the top of the whip - perfect antenna?
|Cecil, can you 'splain that?
|
|>>3) For a give length radiator, gain is unaffected by where the
|inductor is located along the length of the radiator and by inductor
|Q. <<
|
|(If the inductor is zero length?)
Yes
|This should be huge screaming flag that there is something drastically wrong
|with your whole approach. Look at any mobile shootout results and you will see
|10 - 20 dB differences, ask Cecil, he wittnessed them.
Remember...perfect ground. Mobile antennas have almost no ground.
|
|Looks like we exhausted reasoning, facts, measurements, found what we wanted,
|unless there is breakthrough in capturing the effect in modeling software we
|are at the end of the rope.
My results compare more closely with Hansen's than anything else I've
seen put forward. I rest my case.
Wes Stewart N7WS
Later, I'm back to NASCAR at PIR.
Mark Keith
> >NM5K:
>
> >NO , I didn't see the pictures. Like I said, they didn't load on that
> >site. All the pix load except his.
> >>
>
> Then you are missing a lot.
> I don't know what the problem with eHam.net site is, I uploaded all the
> pictures the same way, some showed, some not. This is why I posted link to my
> page
> http://www.k3bu.us/loadingcoils.htm
> which has the pictures, also RIGHT drawings from ON4UN book, latest modeling of
> W5DXP stub loaded G5RV and some selected comments explaining the phenomena.
> Check it out.
I found them earlier...
>
> >> Again, put on the fricken Hustler 80m resonator, feed it 100W and feel it!
> >>No meters, no hokus pokus, just "naked" antenna.
> >
> >What would that mean? The hustler coil is known to be flawed, and
> >makes a poor coil to be tested in this manner. The effects of it's
> >metal end caps, and overall design problems are fairly well known. I
> >refuse to use such a lousy coil. You can feed my homebrew coil 100w
> >all day long, and you won't feel anything except the finger on the
> >mike button hand start to go numb from holding the key down.
> >
>
> Another "very well known fact" from W8JI's teachings?
No, just personal experiences. But I never had a heat issue with a
hustler. I never used one long enough to develop any heat...:/
Metal caps are at both
> ends, top would feel the same then, it doesn't. Hustler coil is "lousy" because
> uses aluminum wire to achieve "match" through some loss and that is additional
> loss.
Well that also. But I think the windings are also overly tight.
But from the point of view as inductor, it is uniformly wound
solenoid,
> same wire and diameter, so according to I2R law, the heat developed in it is
> proportional to the square of current. If there is more heat at the bottom,
> then irrefutably there is more current flowing at the bottom.
Well, not irrefutably. Obviously the other guy that tested had a case
that was excess resistence at the base of the coil. I'm not saying
this was a problem in your case, but he seemed to have no more heating
issues after he fixed the connection.
>
> Here is the shocker:
> When W9UCW bunch was measuring various coils, they also compared that perfect
> coil as you and I have (heavy wire, proper form factor, good connections) to
> "lousy" Webster Banspanner sliding coil (aka cheap screwdriver) they found
> negligible difference in measured signal strength. They rechecked everything
> scratched their heads, but that was it.
Actually, thats fairly old news. I had heard of that test months ago.
Maybe from more than one person. I think others have found the same
thing. And it doesn't surprise me one bit when mobiles are involved.
Ground losses almost always overshadow coil losses on a mobile.
So another myth about the quality of
> coil (resistance of course applies, but is minuscule) importance.
Well, it's not totally a myth. Coil losses can eat your lunch if you
want first rate performance. The hustler coils are a case in point.
They are pathetic compared to my coils. The difference on the air is
like night and day. But! If you have so much ground loss that it
overshadows the coil loss, even in that case, a better coil won't help
much.
In other words, the better the ground system, the more any coil
deficiencies will show up.
Now when we
> look at it from the point of view of effect of the coil on the efficiency of
> antenna, it is explanatory. Coil replaces portion of radiator that is not there
> anymore, so the significance of its quality is not as important as the position
> of the coil on the radiator (area under current curve). Of course the ohmic
> losses are a factor, but that is minuscule (ohms or two) versus reduction in
> current flowing in remaining radiator. I like and have big fat coils, but looks
> like they can be optimized better, perhaps heavier wire in first few turns,
> slimmer construction, less wind load, but placed higher up on the mast. So
> there is another one you don't have to believe, I sure was surprised.
> Measure it!!!
I have. I've been building different homemade mobile coils for about
13 years. I've come to the conclusion wire size is generally not very
important at all, AS LONG as the proper pitch/winding ratio is used.
Don't wind them too close together. My current coil uses thinner wire
than my old one. I much prefer a lighter coil. But I'm fairly sure it
actually works as well if not better than the heavier old one. It is
wider than the old one. "3 inch vs 2 inch"
>
>
>
> I am not a salesman, I will not try to convince you of anything. I can
> elaborate and answer some questions and it is up to you to believe it or not.
> You can believe engineers with education, their experience and results, or you
> can believe some "technical impostor" as K7GCO phrased it.
I'm not believing anyone. I'm going by my own experiences, and my own
gut hunches. "BS filter" :) W8JI has very little to do with any of my
ideas. His was just one viewpoint out of many.
>
> You could see almost constant current across the coil if the coil is at the
> base of quarter wave radiator, has heavy windings and is replacing relatively
> short electrical length of the radiator. Did he mention what coil, where was
> the coil placed? We have methods and pictures of W9UCW tests on various bands
> at different positions, we have yet to get objections or pointed out errors in
> his setup.
I think a lot of that is only a few lurking on there actually know
how, or have the equipment to make an accurate measurement. So most
wouldn't know if the setup could cause problems or not. I don't say
this lightly, as it appears to be quite a "hook" prone undertaking. I
sure don't have the setup to do it, or have even tried something like
that. I do know from messing around with fluorescent tubes and the
mobile antennas, that the electric field around the coil seems to be
very steady across, and abruptly decreases once the stinger begins.
This while quite possibly an erroneous assumption, led me to believe
the current across the coil is also fairly constant in direct relation
to that.
> You believe what you want. As I mentioned we will write concise article on the
> subject and you can take it from there or stick with Rauchians.
Why do you keep involving Tom in this? I have nothing to do with him.
Frankly, I find comments like "Raunchians" and "Flat Earthers" etc,
kind of tacky. So far I haven't accused you all of any "voodoo"
antenna magic, like I do say the EH bunch. I just want to make sure
all the bases are covered as far as the accuracy of the measurments,
and also the exact locations of the couplers. I still question the
accuracy of hooking the top coupler on the lower end of the stinger.
No matter how close the coil is....
>
> I sure enjoyed this exercise, learned from it a thing or two and I am looking
> forward to implement some of the stuff (measure it too) in the design of new
> loaded mobile and low band antennas. As they say on FreeRepublic.com, this is
> series and hugh :-)
There is no doubt that elevating the coil on a low band antenna
improves the current distribution. I've tested it many times, over and
over again. BUT! This will not model worth a hoot if you look at gain
numbers alone. Note Wes's recent post. If I remember right, most
programs will leave the gain pretty much the same, as you vary coil
height. They sure don't show the real world increases anyway...But you
want to include top loading if you want the best of the best. Omit
that, and it'll never happen. BTW, to my thinking, the capacitance is
what draws the current through the coil. And I haven't tested it, but
I bet the current taper above the coil is much more abrupt with a
short stinger, than a longer one. There is no doubt a short stinger
does a poor job of drawing current through the coil. Thats what kills
the average ham sticks with the short stubby stingers. There is little
capacitance to draw current through the coil. A large enough top hat
will give you a fairly steady current distribution up the whip,
regardless of the coil placement. Raising the coil in addition to the
hat helps a bit more. But I think less so than with a non hatted
antenna. Coil placement is critical if you run the low bands, and
don't use a top hat. But thats nothing really new to people that fart
with mobile antennas all the time. I think what you are doing is a
good thing, and worthwhile. But I'd chill as far as Tom is concerned.
You seem to be taking his criticisms a bit personal, and respond in
kind. This all distracts greatly from the original point of the
excercise. It's like the parasitic thing with the amps between him and
Measures. Even after all the bickering, I'm still not totally sure
what to believe as far as parasitic bangs in tube amps. The best
answers seemed to get bogged down in the quagmire of constant
bickering. :/ If I'm doing something I *think* is right, and someone
disagrees, I'll assess it, and if I still think I'm right, I just
ignore them. I think that would be your best course. It's his right to
disagree with you. Nothing you can really do about it, and no point
wasting energy, or stirring discontent over it. MK
Cecil Moore
> Of course it doesn't account for phase shifts of current, since there
> aren't any. It does account for voltage phase shift. It uses the same
> equations I learned in freshman circuits class. Perhaps they taught
> those same equations in Texas, too, but I can't be sure.
Roy,
We are talking about distributed networks. Of course, there is a phase
shift in the current as well as the voltage. You and W8JI seem to be
using lumped circuit analysis when you should be using distributed
network analysis. The center loading coil for a 75m mobile antenna
is an appreciable percentage of an electrical wavelength so you cannot
use your lumped circuit analysis without introducing errors.
Art Unwin KB9MZ
This term of reactance "sucking" or "drawing"
current up the antenna,
I have never heard of reactances described
like this before.
Has an article been written lately with these terms
since I saw another poster use the same terminology?
Regards
Art
nm...@wt.net (Mark Keith) wrote in message news:<25eb70d7.03110...@posting.google.com>...