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  #211   Report Post  
Old November 5th 03, 03:02 PM
Cecil Moore
 
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Ian White, G3SEK wrote:
I don't know what the full detailed explanation is. But I do know that,
in order to be correct for all possible cases, it *must* include the
feature that as the physical dimensions of the coil tend towards zero,
the difference in current between its two ends falls towards zero also.
Any "explanation" that denies this fundamental physical fact is
guar-an-teed to be wrong.

So let's agree on that, and then we can move forward to find an
explanation.


OK, let's agree on that and take another look at the example I just presented
on another thread involving half a dipole.

wire coil wire
---------------////---------------
22.5 deg ? deg 22.5 deg

Assuming a lumped inductance, presumably the current into the coil will have
the same phase as the current out of the coil. Zero phase shift through the
coil means this antenna has the same current phasing as a 40m dipole used on
75m, i.e. the feedpoint current is at a current minimum point. We know that
is NOT the case in reality. So what's the answer?
--
73, Cecil http://www.qsl.net/w5dxp



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  #212   Report Post  
Old November 5th 03, 03:39 PM
Yuri Blanarovich
 
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G3SEK wrote:


But first we all need to agree that for an ideal lumped loading coil,
the current at the top and bottom terminals will be the same. If the
current is not the same at both ends, then the coil cannot be behaving
as an ideal lumped inductor.



We are back to this line of "reasoning":
......and if we rip all four legs off the frog and say "Frog jump", frog doesn't
jump. The "conclusion" is - Froggie is deaf :-)

Is it a big science secret that coils can cause delay, phase shift?
Can anyone also measure the fricken thing and THEN argue????

We have the effect, W9UCW measured it, ON4UN and W5DXP provided explanations,
what's missing? Being wrong, recognizing it and admitting? (Sorry)
Just because software (for now?) cannot digest it, it can't be?
This is becoming amusing to see how serious this misconception was out there
and who is on the bandwagon.
Let's see "better" explanation. The difference is THERE doesn't matter how
anyone denies it!!!
Knowing about it will help to design and optimize the crippled antennas,
including fricken fracktals (with coils).

I am gathering material for test setup allowing to measure RF current in every
foot of the loaded antenna, I have two 8 amp meters, so I will have to use some
power for full deflection, but it will be just another level of the same thing.
You are all invited to witness! I will document it, take pictures and video.

If there are no answers, pointing wrong to the points I have raised in my other
posting, then I am done, can't do anything more, just will do the measurements
and present the results.

Yuri, K3BU.us
  #213   Report Post  
Old November 5th 03, 04:13 PM
Ian White, G3SEK
 
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Cecil Moore wrote:
OK, let's agree on that and take another look at the example I just presented
on another thread involving half a dipole.

wire coil wire
---------------////---------------
22.5 deg ? deg 22.5 deg

Assuming a lumped inductance, presumably the current into the coil will have
the same phase as the current out of the coil. Zero phase shift through the
coil means



this antenna has the same current phasing as a 40m dipole used on
75m, i.e. the feedpoint current is at a current minimum point.


Sorry, I don't understand that last statement...


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
  #214   Report Post  
Old November 5th 03, 05:13 PM
Cecil Moore
 
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Ian White, G3SEK wrote:

Cecil Moore wrote:
OK, let's agree on that and take another look at the example I just
presented
on another thread involving half a dipole.

wire coil wire
---------------////---------------
22.5 deg ? deg 22.5 deg

Assuming a lumped inductance, presumably the current into the coil
will have the same phase as the current out of the coil. Zero phase
shift through the coil means this antenna has the same current phasing
as a 40m dipole used on 75m, i.e. the feedpoint current is at a current
minimum point.


Sorry, I don't understand that last statement...


A 40m 1/4WL vertical used on 40m is 90 degrees long.

A 40m 1/4WL vertical used on 80m is 45 degrees long and we know its characteristics.
If the coil above has zero phase shift, the antenna above is also 45 degrees
long and will exhibit the feedpoint characteristics of a 40m 1/4WL vertical
used on 80m but we know it doesn't exhibit those characteristics. ERGO,
the phase shift through the coil is not zero.
--
73, Cecil http://www.qsl.net/w5dxp



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  #215   Report Post  
Old November 5th 03, 05:29 PM
Art Unwin KB9MZ
 
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"Ian White, G3SEK" wrote in message ...
Yuri wrote:

I am just amazed that with all the "theoretical" arguing going on, why
none of the "learned" experts measure, answer or explain the following
REAL effects or show where I (we) are wrong:

[...]

Yuri is making some fair points - those practical observations do need
to be explained.

But first we all need to agree that for an ideal lumped loading coil,
the current at the top and bottom terminals will be the same. If the
current is not the same at both ends, then the coil cannot be behaving
as an ideal lumped inductor.



I believe that Tom took this stance early on when he explained
variances of slight current change by virtue of the capacitive
component of the real world
inductor when wound on a scale that is used on a vertical radiator.
I suspect that if he brought Q into the equation /discussion people
would not of gotten off track so quickly in the first place! People
have become so enamourd with modeling technics they are willing to let
their guard down
and accept what their results show and throw caution to the wind.
I think I will follow Roy and get out of this one
Art


Now the vainess of man does not allow one to admit error,
so the hole digging continues with faces pointed down
despite pleas from the faces above
Art


That tells us that the explanation has to involve the non-zero physical
dimensions of the coil. In other words, the coil is no longer just a
pure inductor - it also has some antenna-like distributed properties,
which do allow (and indeed require) a current variation along the
length.

I don't know what the full detailed explanation is. But I do know that,
in order to be correct for all possible cases, it *must* include the
feature that as the physical dimensions of the coil tend towards zero,
the difference in current between its two ends falls towards zero also.
Any "explanation" that denies this fundamental physical fact is
guar-an-teed to be wrong.

So let's agree on that, and then we can move forward to find an
explanation.



  #216   Report Post  
Old November 5th 03, 08:30 PM
Ian White, G3SEK
 
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Cecil Moore wrote:
Ian White, G3SEK wrote:

Cecil Moore wrote:
OK, let's agree on that and take another look at the example I just
presented
on another thread involving half a dipole.

wire coil wire
---------------////---------------
22.5 deg ? deg 22.5 deg

Assuming a lumped inductance, presumably the current into the coil
will have the same phase as the current out of the coil. Zero phase
shift through the coil means this antenna has the same current
phasing
as a 40m dipole used on 75m, i.e. the feedpoint current is at a current
minimum point.

Sorry, I don't understand that last statement...


A 40m 1/4WL vertical used on 40m is 90 degrees long.

A 40m 1/4WL vertical used on 80m is 45 degrees long and we know its
characteristics.
If the coil above has zero phase shift, the antenna above is also 45 degrees
long and will exhibit the feedpoint characteristics of a 40m 1/4WL vertical
used on 80m but we know it doesn't exhibit those characteristics. ERGO,
the phase shift through the coil is not zero.


OK, I see what you're getting at, but by changing the frequency you are
losing sight of some important points. Let's stay on the *same*
frequency, halve the physical height of the antenna and insert a lumped
loading coil at the midpoint.

Instead of being 90deg tall, our vertical monopole is now only 45deg
tall (physically). Drawn on its side, and fed against ground at one end,
it now looks like:

wire coil wire
---------------////---------------
22.5 deg ? deg 22.5 deg

(just as you drew it)

Where you're going astray (I suspect) is in believing that the coil
literally "replaces" the 45deg of antenna that was lost when we halved
the height. It doesn't - the loading coil drastically changes the
current distribution.

Fed with 1.0A at the base, the original quarter-wave has a roughly
cosine-shaped current distribution, so the current at a point 22.5deg
from the top is 1A * cos(90-22.5) = 0.38A.

Now feed the loaded antenna with 1.0A at the base. The current
distribution is now radically different: in the bottom 22.5deg of the
antenna, the current hardly changes - let's say it's 0.9A at the bottom
of the loading coil.

Since we have assumed a lumped loading coil, the current at the top of
the coil is the same 0.9A. But now the current distribution in the top
22.5deg is very different from the full-size case: it tapers much more
sharply, from 0.9A down to zero at the very top.

This is all standard stuff. My reason for walking through it is to
emphasize that shortening the antenna and loading it changes many things
about the current distribution, both above and below the loading coil.
And here are two other important differences: the feed impedance of the
loaded antenna is much lower than that of the full-size; and the much
sharper reduction in current is associated with a much higher E-field
over the same length of top section.

To sum up, shortening and loading the antenna creates so many important
differences that you're misleading *yourself* if you say that the
loading coil simply "replaces" the missing length of antenna.


Two footnotes:

1. The diagram for current distribution with center loading in 'Low Band
DXing' is based on the same incorrect assumption that loading coil
somehow fully "replaces" the missing 45deg of antenna. (Fortunately the
method later in the same chapter for calculating the inductance of
loading coils is still OK, because it doesn't depend on any assumptions
about current distribution.)

2. I haven't thought about an answer to Cecil's problems of what happens
to the "missing" 45deg, and what happens to the forward and reflected
waves of voltage and current. Since it's Cecil who chooses to think
about antennas in such ways, he'll have to solve his own problems!

My only point is that a correct solution can *not* involve a difference
in the currents at the two ends of an idealized lumped inductor. Such a
difference simply cannot be... so the true solution will be that bit
harder for Cecil to find.



--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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Old November 5th 03, 08:39 PM
Richard Clark
 
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On 05 Nov 2003 14:39:57 GMT, oSaddam (Yuri Blanarovich)
wrote:


We are back to this line of "reasoning":
.....and if we rip all four legs off the frog and say "Frog jump", frog doesn't
jump. The "conclusion" is - Froggie is deaf :-)

....

I am gathering material for test setup allowing to measure RF current in every
foot of the loaded antenna, I have two 8 amp meters, so I will have to use some
power for full deflection, but it will be just another level of the same thing.
You are all invited to witness! I will document it, take pictures and video.


Hi Yuri,

Good engineering starts with a plan. You start with the instruments
you have available. This is the line of "reasoning" where, if you
have only a hammer, all problems are nails.

It took no more than 1 minute to summon up my EZNEC file of your test
set-up (which you have still failed to confirm, deny, amend, or
specify) to observe that your comment:
so I will have to use some power for full deflection

which is rather low on specifics to observe for myself this must mean
100W as the base current for the model comes quite close to the 8
Ampere full scale deflection for 100W drive.

However, we get into issues of your having done work at the 100mA
levels and we thus turn to my earlier comments about accuracy.

100mA on an 8 Ampere full scale 3.5 inch meter is slightly more than
1% deflection (less than the width of the needle). The 100W
excitation current levels near and through the model's solenoid
exhibit values in the 1 Ampere region or at 12% deflection for an
instrument that is arguably as accurate as 10%. This does not bode
well for a compelling exhibition of any conclusive results.

NOW, if I were wrong to presume that 100W is going to be the
excitation - is that MY fault? If we jack up the power applied
(easily within the means of an amateur so empowered, so to speak) then
that region can certainly be forced into readings of vastly improved
accuracy relative to the available metering. HOWEVER, this now
inhibits doing the full length survey because the lower section would
clearly overload the metering. You can't win for losing.

Well, you can win if you are accomplished at the bench (a rare talent
in this ivory tower where merit is weighed by angel population counts)
by modifying your metering through shunts. I will warn you, however,
it is incumbent upon you to reveal how that was accomplished, how it
was confirmed and the data to support that too. You will also have to
measure the surface temperatures and conspire to replicate them to
your metering (something that you have not really responded to) to
observe the systematic error introduced by these ever growing power
applications. This, in a sense, is a turn of "you can't win for
losing, but you can get close, but you still might lose anyway."

I might add that you stand every chance of being slow cooked while
taking readings. Both for safety's sake and accuracy (so as to not
disturb the fields and those readings) use a telescope. We don't want
your video to appear on FOX. I will add for the sake of anticipating
the gowned one's suggestions, remote readings through extended leads
will invalidate everything.

73's
Richard Clark, KB7QHC
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Old November 5th 03, 09:29 PM
Mark Keith
 
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Cecil Moore wrote in message ...
Mark Keith wrote:
This is the way I view it, and why I couldn't automatically endorse
the fairly large difference they saw. Unless the coil is very long,
say as in a helical whip, I see it acting pretty much as a lumped
inductor. Sure, the current may vary some through the coil when it's a
foot or so long bugcatcher coil, but I don't see it being a major
issue. I wouldn't normally expect to see a sharp current taper across
the coil. I see that type of coil acting much as a "one piece" lumped
inductor, not as a many turned rf roller coaster ride. Not a perfect
lumped inductor, but close enuff for average gov work. MK


The round trip current phase shift in an electrical 1/4WL vertical must
total 360 degrees. If the coil doesn't perform part of that phase shift,
what does?


What if it does though? If the coil is still a fairly small portion of
the overall length, I don't see the change as severe. Heck, if current
is supposed to be the same on each end of the coil, it should be the
same going in both directions.. Seems to me it would pretty much
equal out in the overall scheme of things. Even if one ends up with a
bit more current, being the coil is not that large overall, the
difference should not be drastic. Or to my thinking anyway..I think
it's quite possible a coil mounted higher than 1/2 the total length
shows a sharper cutoff of current at it's end. To me , it's because of
the shorter overall length of the stinger above the coil. The current
taper at the top of the coil and above is more abrupt than if the coil
were center loaded. Or thats the way I see it. Whether it's right or
wrong remains to be seen... MK
  #219   Report Post  
Old November 5th 03, 10:28 PM
Yuri Blanarovich
 
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However, we get into issues of your having done work at the 100mA
levels and we thus turn to my earlier comments about accuracy.

100mA on an 8 Ampere full scale 3.5 inch meter is slightly more than
1% deflection (less than the width of the needle).


Richard,
you got the "wires crossed" - mixing two cases.
W9UCW measured data I have been quoting in my article at K3BU.us, he SET the
power for the bottom meter to read full scale on his 100 mA meter. Then he read
the top meter which showed readings in the 40 to 60 % down.
I have not done my measurements besides "hand test" and frying the Hustler
coils. Just brief test to see how much deflection I get with 100W on 8A meter.

I know a thing or two about measurements, done my years at IBM Test Engineering
Dept. I will document my tribulations and if get it, use infrared camera too.
If W9UCW lied, deceived us I will be the first one to choke him :-) So far he
put figures on what I knew and they jive.
Why don't you guys that know pitfalls of measurement do it and report ?????
Hello????

Yuri. K3BU.us

I am not as dumb as Reg portrays me. Got highest IBM Award - Outstanding
Contribution Award signed by then chairman Frank Cary for Design and
Development Excellence. BTW this was doing something that "experts" at IBM
Endicott lab said it couldn't be done. This coil stuff is trivial in
comparison.
  #220   Report Post  
Old November 5th 03, 10:38 PM
Jim Kelley
 
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"Ian White, G3SEK" wrote:
Since we have assumed a lumped loading coil, the current at the top of
the coil is the same 0.9A. But now the current distribution in the top
22.5deg is very different from the full-size case: it tapers much more
sharply, from 0.9A down to zero at the very top.


Right. But the discussion is about whether the lumped loading coil
model is accurate. Any conclusions based upon inaccurate assumptions
would probably also be inaccurate.

73, Jim AC6XG
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