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


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

Mark Keith wrote:
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.
--
73, Cecil http://www.qsl.net/w5dxp



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Yuri Blanarovich wrote:
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.
--
73, Cecil http://www.qsl.net/w5dxp



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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

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 Lewallen, W7EL

Cecil Moore wrote:
Roy Lewallen 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.


It appears that EZNEC also doesn't account for phase shifts across
a zero length coil.

On 02 Nov 2003 18:40:25 GMT, oSaddam (Yuri Blanarovich)
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.

oSaddam (Yuri Blanarovich) wrote in message ...
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

Roy Lewallen wrote:
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.
--
73, Cecil http://www.qsl.net/w5dxp



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Mark,
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

(Mark Keith) wrote in message . com...
oSaddam (Yuri Blanarovich) wrote in message ...
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

Roy Lewallen wrote:
Of course it doesn't account for phase shifts of current, since there
aren't any.

You seem to be disagreeing with John Devoldere's "Bible" - "ON4UN's Low
Band DXing", 3rd Edition, on page 9-34 at:

http://www.k3bu.us/loadingcoils.htm

A little thought should prove there is a current phase shift (delay) through
the coil. Let's look at an 8 foot long center-loaded mobile antenna for 75m.
The 4 feet below the coil gives a phase shift of about 5 degrees. Assume zero
phase shift through the coil. The 4 feet above the coil gives a phase shift
of another 5 degrees for a total of 10 degrees at the end reflection point.
It's an open circuit, so a 180 degree phase shift takes place. That puts the
reflected current at 190 degrees. Add the 10 degrees coming back and we see
the reflected current arrives mostly out of phase with the forward current
at the feedpoint. Since the feedpoint impedance is known to be around 15 ohms,
these superposed currents cannot possibly be out of phase and must necessarily
be in phase.

The phase shift (delay) of the current simply cannot be the same with and
without the coil.
--
73, Cecil http://www.qsl.net/w5dxp



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