Jim Kelley wrote:
It seems that the phase shift you
described earlier would have to cause a change in the standing wave
pattern along the radiator.

It does and that is why it is so difficult to write an equation for
it. There are reflections in both directions at the top and bottom of
the coil in addition to the 100% reflection at the tip of the antenna.
My solution is to get Reg to write a new program. :-)

If the loading coil was at the feedpoint,
then the maximum current would appear only at the feedpoint.

I hesitate to introduce secondary effects before most have understood
the primary effects, but that is not a true statement. Some percentage
of what the other side is saying is true. However, the other side
considers those effects to be supreme when they are only secondary -
but they are NOT negligible secondary effects. The maximum current
in the base-loaded system does not appear at the feedpoint. The
maximum current in a base-loaded system appears inside the coil and
that current is of greater magnitude than the feedpoint current. I'm
sorry to muddy the waters even farther with that tidbit.
--
73, Cecil http://www.qsl.net/w5dxp


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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

Reg Says:

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.

WROOOONG!

Have you ever tried antenna shootouts? Cecil can enlighten you about the
difference in efficiency and signal levels radiated by various configurations
(bottom, center, top loading).
The efficiency is proportional to the AREA under the current curve on the
loaded radiator. That is dependent on the position of the loading element
within the radiator. That also depends on the current distribution (drop :-)
across the coil. Use that in the loaded parasitic element beams and the effect
is magnified.
So obvious, but hard to swallow for Rauchians?

Viva Bush!!! Sayonara sKerry botoxed flipflopping lying girlie man.

Yuri, K3BU.us

Yuri Blanarovich wrote:
Reg Says:

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.


WROOOONG!

Have you ever tried antenna shootouts? Cecil can enlighten you about the
difference in efficiency and signal levels radiated by various configurations
(bottom, center, top loading).
The efficiency is proportional to the AREA under the current curve on the
loaded radiator. That is dependent on the position of the loading element
within the radiator. That also depends on the current distribution (drop :-)
across the coil. Use that in the loaded parasitic element beams and the effect
is magnified.
So obvious, but hard to swallow for Rauchians?

Viva Bush!!! Sayonara sKerry botoxed flipflopping lying girlie man.

Yuri, K3BU.us

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

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

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

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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On 03 Nov 2004 15:01:47 GMT, oUsama (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.

When someone posts the results of a "shootout" where the *same*
vehicle, in the *same* location, with the test antenna located at the
*same* position on the vehicle, fed with the *same* transmitter and
where the *same* receiver is used for field strength then *maybe* I'll
give some credence to the results. Otherwise, it's all hogwash.

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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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).