H. Adam Stevens, NQ5H wrote:

Reg
Your patience is that of a saint.
H.
"Reg Edwards" wrote in message
...

Cec sez,


My solution is to get Reg to write a new program. :-)


=======================================

My patience is wearing thin.

Nevertheless, once more into the breach.

There's no need to write a new program. There's not even any need for an

old

one.

Knowledge of the current distribution along a loading coil has no

practical

use except to assist with drawing pictures of it in books and magazines.

FOR PRESENT PURPOSES THE LENGTH AND IMPEDANCE OF THE ANTENNA BELOW THE

COIL

IS NOT RELEVANT. IT CAN BE CONSIDERED TO BE PART OF THE GENERATOR.

LET THE ANGULAR LENGTH OF THE COIL = THETA DEGREES. OTHERWISE KNOWN AS

THE

PHASE SHIFT. THIS IS A FIXED, IMMUTABLE QUANTITY SET BY THE PROPAGATION
VELOCITY = 1 / SQRT( L * C ).

THE MAGNITUDE OF THE CURRENT DISTRIBUTION ALONG THE COIL IS ALWAYS THE

SAME

COSINE CURVE BUT WHICH IS TRUNCATED (SLICED OFF) AT VARYING ANGULAR

DEGREES

AT EITHER OR BOTH ENDS.

THE ANGLE AT WHICH THE TOP END IS TRUNCATED DEPENDS ON THE INPUT IMPEDANCE
OF THE ANTENNA ABOVE IT. IT IS ALSO RELATED TO Zo OF THE COIL WHICH IS

THE

USUAL SQRT( L / C ).

THE ANGLE AT WHICH THE BOTTOM END IS TRUNCATED IS ALWAYS THE TOP ANGLE

MINUS

THETA. IT CANNOT BE ANYTHING ELSE.

THUS, WHEN THE TOP END IS OPEN CIRCUIT AND THETA = 90 DEGREES WE HAVE A
COMPLETE 1/4-CYCLE OF A COSINE CURVE - A 1/4-WAVE RESONANT HELICAL
ANTENNA.

The foregoing applies to both short, fat coils and long, thin coils,
close-wound or stretched-out.

Coil resistance is the uniformly-distributed radiation resistance plus
conductor resistance.

For useful calculations such as Q, bandwidth, efficiency, etc., you can
forget all about bewildering reflections, standing waves, forward and
reflected power and use the well-known classical transmission line

formulae,

the everyday tools of all good engineers.
The final wanted characteristic, the radiation pattern, can be found with
number-crunching EZNEC-type computer programs which work in an entirely
different manner.
----
Reg, G4FGQ







If patience were money, Reg would be wearing a barrel.
73,
Tom Donaly, KA6RUH

If you're really interested in the "AREA under the current curve,"
you'll have to figure out how to make an efficient, continuously loaded,
short antenna. You'll find, though, that the difference between a
continuously loaded antenna and an antenna with the loading coil,
say, halfway up from the feedpoint won't amount to a hill of beans.
There's still no such thing as a "current drop."
73,
Tom Donaly, KA6RUH


You are flying in a dreamland. Check the results of shootouts comparing
Haasticks and other continuously loaded antennas vs. Bugcatchers or top loaded.
You guys get your noses out of the books and check the reality.

73 Yuri

Reg, G4FGQ wrote:
"For present purposes the length and impedance of the antenna below the
coil is not relevant. It can be part of the generator."

I infer that Reg is saying that at a particular frequency, a loading
coil has a unique voltage across and a unique current through it.

Probably sometimes so, but the simple argument was that the current at
the coil ends can be different. This is caused by superposition of
forward and reflected waves. The same power may have any number of
voltage to current ratios (impedances). The purpose of a loading coil is
to transform an antenna impedance to an impedance more compatible with a
radio. There is a difference in impedance between the ends of a loading
coil so that the current at its ends are different.

The length and impedance of the antenna below the coil participate in
the imbalance seen at opposite ends of the loading coil. The height of
the loading coil on an antenna is thus significant.

The length and impedance of the antenna below the coil participates in
radiation. The function of a transmission line is to convey energy. The
function of an antenna is to radiate energy.

Radiation is a function of unbalanced current and the length through
which it travels (page 864, Terman`s 1955 edition). The current per unit
length below a loading coil is higher than above the coil. More
radiation per unit length results from more current. This affects
impedance at the coil ends.

"For present purposes" we may declare anything so long as we don`t
define our purposes, but Fig 9-22 on page 9-15 of ON4UN`s "Low-Band
DXing" is significant and no one has said his pictures are wrong and
given reasons.

Best regards, Richard Harrison, KB5WZI

Yuri Blanarovich wrote:
If you're really interested in the "AREA under the current curve,"
you'll have to figure out how to make an efficient, continuously loaded,
short antenna. You'll find, though, that the difference between a
continuously loaded antenna and an antenna with the loading coil,
say, halfway up from the feedpoint won't amount to a hill of beans.
There's still no such thing as a "current drop."
73,
Tom Donaly, KA6RUH



You are flying in a dreamland. Check the results of shootouts comparing
Haasticks and other continuously loaded antennas vs. Bugcatchers or top loaded.
You guys get your noses out of the books and check the reality.

73 Yuri

I wrote that you'd have to make an _efficient_, continuously loaded,
short antenna if you want to get the most area under the curve. That's
easier said than done. Certainly, you can't do it.
So a shootout is your idea of a reliable
antenna test. I guess it's no worse than using fish tank
thermometers to measure efficiency.
73,
Tom Donaly, KA6RUH

Reg Edwards wrote:

W5DXP wrote:
My solution is to get Reg to write a new program. :-)

My patience is wearing thin.

Reg, the smiley face means it was a joke. Is you patience
wearing thin concerning my feeble attempts at humor? :-)

THE MAGNITUDE OF THE CURRENT DISTRIBUTION ALONG THE COIL IS ALWAYS THE SAME
COSINE CURVE BUT WHICH IS TRUNCATED (SLICED OFF) AT VARYING ANGULAR DEGREES
AT EITHER OR BOTH ENDS.

Yep, I previously guessed the SQRT(L/C) would be very high for a large coil.
After using your Solonoid program, it seems my guess was much too high. The
Z0 of the coil seems to be more like 1k-2k than the 10k I first guessed.
--
73, Cecil http://www.qsl.net/w5dxp


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Tom Donaly wrote:
You'll find, though, that the difference between a
continuously loaded antenna and an antenna with the loading coil,
say, halfway up from the feedpoint won't amount to a hill of beans.

Wrong! Bragging rights after a 75m shootout are worth a lot more
than a hill of beans. A helical antenna has NEVER beaten a center-
loaded antenna in a 75m shootout. And in fact, my junk box *top-
loaded* antenna beat all the center-loaded bugcatchers in one of
the CA shootouts. The current below the coil is the highest current
in the average 75m mobile antenna. The longer that uninhibited
section is, the stronger the radiated signal, thus my success in
the shootout. My bottom section was about ten feet long, then a
horizontal coil and horizontal top hat. I'm going to refine that
configuration when I get time.

There's still no such thing as a "current drop."

The decrease (drop) in current across a loading coil installed in
a standing-wave antenna does NOT in any way violate Kirchhoff's current
law. One can imply from Kirchhoff's current law that there is no current
decrease (drop) across a point. I don't know anyone who disagrees with
that so any argument is just a straw man. Kirchhoff never said the
current at one point in a network had to equal the current at another
point in the network.

Many patches have been added to the DC circuit model to try to adapt
it to RF networks. Some function after a fashion and some fail utterly.
We all need to be able to recognize the difference. For EM waves, the
E-field and H-field are often affected in the same way. Saying that
the E-field voltage drops but the H-field current doesn't drop is
simply nonsense. Likewise, saying that the H-field current flows and
the E-field voltage doesn't flow is nonsense. The E-field and H-field
are usually inseparable.
--
73, Cecil http://www.qsl.net/w5dxp


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Tom Donaly wrote:
For a guy who is always excoriating people for believing old wives
tales, you've just told a whopper, Reg. It's true, you might get an
answer using the above theory that is "good enough for who it's for,"
but as an expression of what's actually happening in the antenna, it's
hopelessly simplistic.

For this discussion, the magnitude of radiation is irrelevant except
as it relates to "losses" from the system. So please enlighten us as
to "what's actually happening" to the standing-wave current "in the
antenna".
--
73, Cecil http://www.qsl.net/w5dxp


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On Wed, 03 Nov 2004 12:50:53 -0600, Cecil Moore
wrote:
magnitude of radiation is irrelevant
in an antenna forum, this is ludicrous.

On Wed, 03 Nov 2004 12:47:59 -0600, Cecil Moore
wrote:
current across a loading coil installed in a standing-wave antenna does NOT in any way violate Kirchhoff's current
law.
There is no such law of a current into anything but a point (both
dimensionless and componentless).

Yuri Blanarovich wrote:
Check the results of shootouts comparing
Haasticks and other continuously loaded antennas vs. Bugcatchers or top loaded.

Good idea, Yuri. Rename Hamsticks to Hahasticks. :-)
--
73, Cecil http://www.qsl.net/w5dxp


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