I could buy that to an extent I guess. But say if you had a top loaded
vertical, with linear current distribution, the current across the
coil should be appx equal no matter where the coil is placed. But if
no top loading, maybe so.. MK


Top loaded vertical does not have LINEAR current distribution, that is another
simplification, fallacy. Current in the radiator has cosine distribution. At
the base, there is not much difference, just like in cosine of the angle
corresponding to the electrical length of radiator at that point.

Again, this subject of current distribution is important in optimizing the
antenna design by fine tuning the position of the loading coil in the antenna,
combination with top loading etc. Morew current flowing in the radiating part
of the antenna - the stronger the field and louder signal.

The "linear" current distribution mentioned in ARRL Compendium and Antenna Book
is the simplification propagated from Belrose's 1955 QST article. It is close,
but not exact and introduces confusion as it is demonstrated by the flat earth
society.

Yuri, K3BU/m

Yuri wrote,

Again, this subject of current distribution is important in optimizing the
antenna design by fine tuning the position of the loading coil in the
antenna,
combination with top loading etc. Morew current flowing in the radiating part
of the antenna - the stronger the field and louder signal.

What is "the radiating part of the antenna," Yuri?
73,
Tom Donaly, KA6RUH

What happens when the coil is a flat pancake ?
---
Reg.

oSaddam (Yuri Blanarovich) wrote in message ...

I could buy that to an extent I guess. But say if you had a top loaded
vertical, with linear current distribution, the current across the
coil should be appx equal no matter where the coil is placed. But if
no top loading, maybe so.. MK


Top loaded vertical does not have LINEAR current distribution, that is another
simplification, fallacy. Current in the radiator has cosine distribution.

It's still fairly constant. But the degree would depend on the height
of the vertical vs the length of the top hat wires. If the hat is too
small, I doubt you would see as steady a distribution up the radiator.

At
the base, there is not much difference, just like in cosine of the angle
corresponding to the electrical length of radiator at that point.

I'm not sure what you mean by this. Do you mean the current across the
coil would be more steady than if the coil were higher? Does this
include using the top loading wires?

Again, this subject of current distribution is important in optimizing the
antenna design by fine tuning the position of the loading coil in the antenna,
combination with top loading etc. Morew current flowing in the radiating part
of the antenna - the stronger the field and louder signal.

Sure. But this is old news. I beat Reg's vertload program to death
finding the best overall coil height for my mobile antenna. Basically
I ended up putting it as high as I could. Which ended up a center load
at 5 ft up, with a 10 ft whip. Or 8 ft up on a 13 ft whip when parked,
and using the "Super" mode...

The "linear" current distribution mentioned in ARRL Compendium and Antenna Book
is the simplification propagated from Belrose's 1955 QST article. It is close,
but not exact and introduces confusion as it is demonstrated by the flat earth
society.

Dunno, I've never read it. Maybe calling the distribution as "linear"
is the wrong term, but the current is still fairly steady along the
radiator in the case of the vertical with the large top hat. I'm
looking at a model of one now. The current distribution is almost like
a twin tower standing next to the vertical. There is a slight decrease
from bottom to top, but it's very small. It's still my view that the
difference in current at each end of the coil used in such a case is
fairly small. No matter where the coil was mounted.
I've never said they would be exactly the same. Seems to me I started
off by saying they could vary a bit depending on the antenna. So if
you are saying they would be close, but not exact, you seem to be
saying the same thing I said to begin with, which seems to be the same
thing Cecil is saying. ??? Crap, I'm becoming confused.... I'm not
good at playing these type games. That's why I didn't even bother
reading the "current war" over on e-ham. *Sounds* like a 598 thread
nit pick contest just judging from what I've heard... It's not "that"
important to me, being I don't see what it would do for me, even if I
found there to be a fairly large difference from each end. If you have
pertinent info which shows the current is not even close to being
constant across the coil, please enlighten us. "I guess you are
attempting to" But at this point, I think everyone is starting to
chase their tales and bark at the moon.
I'm not really seeing the point, being the art of improving current
distribution in short verticals using coil placement is old news. MK

Yuri, K3BU wrote:
"I ordered 19th edition of ARRL Antenna Book and followed chain of
references that led to information on page 16-7 and Fig. 9 and 10."

Excellent purchase. A series circuit tends to have the same current
throughout except when its length is significant with respect to
wavelength. A standing wave antenna has a reflected wave which makes
impedance a function of location along the antenna. So, a certain power,
incident and reflected, combine to produce voltage and current
variations on an antenna which are related to those on a transmission
line. Since radiation from an antenna occurs, power in each direction is
not constant as it tends to be on a transmission line because radiation
is taking a toll in each direction, and that`s a good thing. It`s the
purpose of the antenna.

Coil Q is important to efficiency if any part of the XL/R is loss
resistance and not radiation resistance. Radiation resistance is the
purpose of the antenna.

My ON4UN Figures are the same as Yuri`s but appear as Fig 9-22 on page
9-15. These show the current decline across a loading coil including the
obvious case of a solenoid used as an antenna where the entire current
distribution is within the continuous loading coil.

The ARRL Antenna Book has been exposed to scrutiny for many years. By
the 19th edition it`s a safe bet that moat of it is correct (without
consideration of "strings", 5 dimensions, or 11 parallel universes).

From what I`ve seen of ON4UN`s book, he got it right too.

Best regards, Richard Harrison, KB5WZI

Incorrect. HEAT does not rise at all, however hot gas or hot liquid
will rise in response to gravity. This has nothing to do with a loading
coil made from solid parts.

--
Bill, W7TI

Incorrect, incorrect.
If we suppose the loading coil is heating up equally (the flat earth society
argument), it heats air immediately surrounding it. Air is heating up, rises up
as you say, as it rises it picks up the other air that is heating up and they
rise together. As they progress, they heat up rest of the coil on the way up,
with the result being that the top should be warmer (hotter) than the bottom.

If we have quarter wave whip with loading coil, and the bottom contrary to the
above mechanism is warmer, thet ergo ipso there must be more current flowing in
the bottom part of the coil, confirming what we say.

Yuri, K3BU/m

On 30 Oct 2003 22:59:26 GMT, oSaddam (Yuri Blanarovich)
wrote:

If we suppose the loading coil is heating up equally

Hi Yuri,

You have already testified twice that it does not - so why IF it
around?
1.)
If you trasmit for short period of time (not
enough for heat to equalize) and feel it, or use thermal strips to check
temperature, you would see the taper in the current from bottom to top. It is
in order of 50%, not negligible.
2.)
Put 500W to it for longer period and watch the heatshrink tubing
shrivel from the bottom up.

73's
Richard Clark, KB7QHC

Current through a coil in an antenna.

If we feed an antenna at the current point, the current decreases as the
voltage increases along the antenna element from feed point to end..

That being said, a coil replacing a segment of an antenna (in order to
physically shorten it) will exhibit the same properties (relating to
currents) as the segment it replaced.



"Richard Clark" wrote in message
...
On 30 Oct 2003 22:59:26 GMT, oSaddam (Yuri Blanarovich)
wrote:

If we suppose the loading coil is heating up equally

Hi Yuri,

You have already testified twice that it does not - so why IF it
around?
1.)
If you trasmit for short period of time (not
enough for heat to equalize) and feel it, or use thermal strips to check
temperature, you would see the taper in the current from bottom to top.
It is
in order of 50%, not negligible.
2.)
Put 500W to it for longer period and watch the heatshrink tubing
shrivel from the bottom up.

73's
Richard Clark, KB7QHC

w4jle wrote:
Current through a coil in an antenna.

If we feed an antenna at the current point, the current decreases as the
voltage increases along the antenna element from feed point to end..

That being said, a coil replacing a segment of an antenna (in order to
physically shorten it) will exhibit the same properties (relating to
currents) as the segment it replaced.

Yep, if the feedpoint impedances are the same and both are lossless,
that has to be true.

Here's a repeat of a diagram I drew earlier.

-----y----------x-----FP-----x----------y----- 1/2WL dipole

-----coil-----FP-----coil----- loaded dipole

Assume the physical length of the loaded dipole is 1/4WL.

Each coil replaces the section between 'x' and 'y'. The currents
at 'x' and 'y' are quite different, being 1/8WL apart.

Consider an 8 foot center-loaded 75m mobile antenna. 87% of the
electrical length of the antenna is in the coil.
--
73, Cecil http://www.qsl.net/w5dxp



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If reactance can be seen as a "{missing" part
of a radiator how should we view what a
capacitor represents? Grin
Art


Cecil Moore wrote in message ...
w4jle wrote:
Current through a coil in an antenna.

If we feed an antenna at the current point, the current decreases as the
voltage increases along the antenna element from feed point to end..

That being said, a coil replacing a segment of an antenna (in order to
physically shorten it) will exhibit the same properties (relating to
currents) as the segment it replaced.

Yep, if the feedpoint impedances are the same and both are lossless,
that has to be true.

Here's a repeat of a diagram I drew earlier.

-----y----------x-----FP-----x----------y----- 1/2WL dipole

-----coil-----FP-----coil----- loaded dipole

Assume the physical length of the loaded dipole is 1/4WL.

Each coil replaces the section between 'x' and 'y'. The currents
at 'x' and 'y' are quite different, being 1/8WL apart.

Consider an 8 foot center-loaded 75m mobile antenna. 87% of the
electrical length of the antenna is in the coil.