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Old October 16th 04, 09:59 PM
Yuri Blanarovich
 
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Default Current in loading coil, EZNEC - helix

Howdy Antenna NGers,

I took the time to check out the Helix feature in EZNEC 4.08 and modeled the
"worst" case - CB whip or 10 m whip with loading coil - helix half way up and
then the same helix moved up to 3/4 way up. Things will get more pronounced
when more turn, more inductance coil is used and frequencies are lower. Yes,
Virginia there is a CURRENT DROP across the loading coil, unless you have more
"appropriate" or "scientwific" term for it.

Rough dimensions: 1m mast (5 mm copper wire/tubing), 20 cm long coil/helix with
5 cm diameter turns, 5mm wire diameter, 10 turns, spacing 2 cm followed by 1 m
whip
Resonated at 27.05 MHz
With base current 1 A, at the end of mast/start of coil the current is 0.87457
A
at the end of coil/start of whip the current is 0.66884 A - a decent drop of
0.20573 A or 20.5 % - not an "EQUAL" (you DC coil believer types!!!)

Then I moved the same coil up 50 cm, so the mast was 1.5 m, same coil, followed
by .5 m of whip.
Again with base current of 1 A, the bottom of the coil had current this time
was 0.65479 A, while top of the coil 0.37127 with larger drop of 0.28352 A or
28.3 % - even bigger not "EQUAL" with resonant frequency moving up to 28.7 MHz,
which corresponds to REALITY measured, experienced and finally properly (close
enough) modeled. Even M0RON (with apologies if there is call like that issued
:-) can see the nice current drop across the coil displayed in the VIEW.

Thank you Roy (now you believe it?), Cecil, Richard. Now the unbelievers can
even model this case themselves and SEE it properly. So ON4UN, K3BU, W9UCW,
W5DXP, KB5WZI were and are right. W8JI, G3SEK et al are sooooo wrong :-) Some
still persist, some are converted and many will be enlightened.

Now if Roy can incorporate elegant way of modeling real life coil/inductance by
inputing Inductance L and its physical size and have it calculate things
without modeling turns, that would be a winner and a segment saver.

So after all, those "dumb" hams pointed out 50 years of misinformation in even
ARRL "bibles" like Antenna and Handbooks :-(yep, latest 2005 "revision" still
has it in it)

Just watch W8JI to massage his web page and twist out of this one (yet another
egg in the face :-)

Yuri Blanarovich, www.K3BU.us
www.computeradio.us
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Old October 17th 04, 02:54 AM
Tom Donaly
 
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Default

Yuri Blanarovich wrote:
Howdy Antenna NGers,

I took the time to check out the Helix feature in EZNEC 4.08 and modeled the
"worst" case - CB whip or 10 m whip with loading coil - helix half way up and
then the same helix moved up to 3/4 way up. Things will get more pronounced
when more turn, more inductance coil is used and frequencies are lower. Yes,
Virginia there is a CURRENT DROP across the loading coil, unless you have more
"appropriate" or "scientwific" term for it.

Rough dimensions: 1m mast (5 mm copper wire/tubing), 20 cm long coil/helix with
5 cm diameter turns, 5mm wire diameter, 10 turns, spacing 2 cm followed by 1 m
whip
Resonated at 27.05 MHz
With base current 1 A, at the end of mast/start of coil the current is 0.87457
A
at the end of coil/start of whip the current is 0.66884 A - a decent drop of
0.20573 A or 20.5 % - not an "EQUAL" (you DC coil believer types!!!)

Then I moved the same coil up 50 cm, so the mast was 1.5 m, same coil, followed
by .5 m of whip.
Again with base current of 1 A, the bottom of the coil had current this time
was 0.65479 A, while top of the coil 0.37127 with larger drop of 0.28352 A or
28.3 % - even bigger not "EQUAL" with resonant frequency moving up to 28.7 MHz,
which corresponds to REALITY measured, experienced and finally properly (close
enough) modeled. Even M0RON (with apologies if there is call like that issued
:-) can see the nice current drop across the coil displayed in the VIEW.

Thank you Roy (now you believe it?), Cecil, Richard. Now the unbelievers can
even model this case themselves and SEE it properly. So ON4UN, K3BU, W9UCW,
W5DXP, KB5WZI were and are right. W8JI, G3SEK et al are sooooo wrong :-) Some
still persist, some are converted and many will be enlightened.

Now if Roy can incorporate elegant way of modeling real life coil/inductance by
inputing Inductance L and its physical size and have it calculate things
without modeling turns, that would be a winner and a segment saver.

So after all, those "dumb" hams pointed out 50 years of misinformation in even
ARRL "bibles" like Antenna and Handbooks :-(yep, latest 2005 "revision" still
has it in it)

Just watch W8JI to massage his web page and twist out of this one (yet another
egg in the face :-)

Yuri Blanarovich, www.K3BU.us
www.computeradio.us


There may be a difference in current along the coil, but it isn't a
current drop. There is no such thing as a current drop in the sense
people use when they say "voltage drop." By the way, Yuri, since you
are such an unsung genius of electromagnetic analysis, here's a
challenge: design a loading coil for a short vertical radiator that
doesn't have, or has only very little, current variation along its length.
73,
Tom Donaly, KA6RUH
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Old October 17th 04, 03:49 AM
Yuri Blanarovich
 
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Default


There may be a difference in current along the coil, but it isn't a
current drop. There is no such thing as a current drop in the sense
people use when they say "voltage drop."


So what you call decrease of current from one to the other?

By the way, Yuri, since you
are such an unsung genius of electromagnetic analysis,


Where is this coming from?

here's a
challenge: design a loading coil for a short vertical radiator that
doesn't have, or has only very little, current variation along its length.
73,
Tom Donaly, KA6RUH


No need for that, W8JI has plenty of them, go ask him.
Are you trying to bu funny or play trolling Chipster here?

73 Yuri
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Old October 17th 04, 04:12 PM
John Smith
 
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Default


"Yuri Blanarovich" wrote in message
...
Howdy Antenna NGers,


(snip)


So after all, those "dumb" hams pointed out 50 years of misinformation in
even
ARRL "bibles" like Antenna and Handbooks :-(yep, latest 2005 "revision"
still
has it in it)



I think you are taking what ARRL says out of context. I will quote from page
16-7 in The ARRL Antenna Book, 20th edition...

"The loading coil acts as the lumped constant that it is, and disregarding
losses and coil radiation, maintains the same current flow throughout. As a
result, the current at the top of a high-Q coil is essentially the same as
at the bottom of the coil. This is easily verified by installing RF ammeters
immediately above and below the loading coil in a test antenna."

Don't overlook the part about disregarding losses and coil radiation. And,
don't overlook the part about verifying the current with ammeters. Have you
done that?

The ARRL book doesn't even recommend using a loading coil with an 8 foot
whip on the 10 meter band. Read the whole chapter. Note that your "coil" is
7.4% (6.7 degrees) of the antenna system length. It is no longer the lumped
device which is assumed in the book. Please repeat your experiment on an
8-foot whip at 40 meters and then verify with current meters.

If you can still make the same assertions for 40 meters, submit your
findings to the ARRL for publication. If they find them worthwhile, I'm sure
they will publish them.

John


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Old October 17th 04, 10:13 PM
Yuri Blanarovich
 
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Don't overlook the part about disregarding losses and coil radiation. And,
don't overlook the part about verifying the current with ammeters. Have you
done that?

The ARRL book doesn't even recommend using a loading coil with an 8 foot
whip on the 10 meter band. Read the whole chapter. Note that your "coil" is
7.4% (6.7 degrees) of the antenna system length. It is no longer the lumped
device which is assumed in the book. Please repeat your experiment on an
8-foot whip at 40 meters and then verify with current meters.

If you can still make the same assertions for 40 meters, submit your
findings to the ARRL for publication. If they find them worthwhile, I'm sure
they will publish them.

John


Been there, done it. Check for more story on the subject
http://www.k3bu.us/loadingcoils.htm

Yuri, K3BU.us


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Old October 18th 04, 01:53 AM
John Smith
 
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Default


"Yuri Blanarovich" wrote in message
...
Don't overlook the part about disregarding losses and coil radiation.
And,
don't overlook the part about verifying the current with ammeters. Have
you
done that?

The ARRL book doesn't even recommend using a loading coil with an 8 foot
whip on the 10 meter band. Read the whole chapter. Note that your "coil"
is
7.4% (6.7 degrees) of the antenna system length. It is no longer the
lumped
device which is assumed in the book. Please repeat your experiment on an
8-foot whip at 40 meters and then verify with current meters.

If you can still make the same assertions for 40 meters, submit your
findings to the ARRL for publication. If they find them worthwhile, I'm
sure
they will publish them.

John


Been there, done it. Check for more story on the subject
http://www.k3bu.us/loadingcoils.htm

Yuri, K3BU.us




And in which ARRL publication might I find this information?

John


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Old October 18th 04, 03:06 AM
Yuri Blanarovich
 
Posts: n/a
Default



And in which ARRL publication might I find this information?

John



Since 1953 Belrose article in QST, in all ARRL Antenna Books and Handbooks it
is shown that current across the loading coil (mobile or loaded antennas) is
uniform, while ON4UN Low Band DXing shows and explains it right.

I will have some more samples modeled with EZNEC and one of these days
comprehensive article on the subject. Jus' need some free time.

Yuri
  #8   Report Post  
Old October 18th 04, 04:40 AM
John Smith
 
Posts: n/a
Default

"Yuri Blanarovich" wrote in message
...


And in which ARRL publication might I find this information?

John



Since 1953 Belrose article in QST, in all ARRL Antenna Books and Handbooks
it
is shown that current across the loading coil (mobile or loaded antennas)
is
uniform, while ON4UN Low Band DXing shows and explains it right.

I will have some more samples modeled with EZNEC and one of these days
comprehensive article on the subject. Jus' need some free time.

Yuri



No, I meant in which ARRL publication can I find either ON4UN's or your
article correcting the last 50 years of "misinformation?"

John


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Old October 18th 04, 05:34 PM
Yuri Blanarovich
 
Posts: n/a
Default



No, I meant in which ARRL publication can I find either ON4UN's or your
article correcting the last 50 years of "misinformation?"

John




So far the stuff is on my and W5DXP web site, more coming soon as soon as
weather and QRL gets more friendly.

Stay tuned or do your own measurements.

Yuri
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Old October 18th 04, 11:46 PM
Richard Harrison
 
Posts: n/a
Default

Tom Donaly, KA6RUH wrote:
"There may be a difference in current along the coil, but it isn`t a
current drop."

Call it a decline if you don`t like the word drop.

A wave traveling along an antenna induces current in the wire. This
current causes radiation from the wire.

A current traveling from "a" to "b" in the wire loses energy to
radiation. The energy at "b" is less than the energy at "a" if the
source is at "a".

If the impedance at "a" is the same as the impedance at "b", the voltage
and the current at "a" are larger than the voltage and current at "b".

We don`t need energy to decline from "a" to "b" to have a current drop.
We only need current to decline between "a" and "b". Yuri has
demonstrated a "current drop" with r-f ammeters inserted at both ends of
the loading coil. Analysis of the cause is not necessary to demonstrate
a current drop.

As straight wires are usually better radiators than the same wire in
coils, I speculate that the current drop measured by Yuri is mostly due
to the high impedance (High voltage, low current) on the output of the
loading coil.

Best regards, Richard Harrison, KB5WZI

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