Facts
 

Fact 1.

Any loading coil of finite length contributes towards to the total
radiation.

Fact 2.

The input and output currents of a loading coil of finite length are always
different from each other.

Fact 3.

The radiation pattern of a short vertical is fixed and remains independent
of the location/height of the loading coil.

Fact 4.

Computer programs do not tell gospel truths. They are at least as
unreliable as their human programmers.

----
Reg.

As posted in a previous thread go to www.carolyns-creations.com/ve6cb to
view the (modeled) current distribution on an 84" monopole at 21.3 MHz.

Frank


"Reg Edwards" wrote in message
...
Fact 1.

Any loading coil of finite length contributes towards to the total
radiation.

Fact 2.

The input and output currents of a loading coil of finite length are
always
different from each other.

Fact 3.

The radiation pattern of a short vertical is fixed and remains independent
of the location/height of the loading coil.

Fact 4.

Computer programs do not tell gospel truths. They are at least as
unreliable as their human programmers.

----
Reg.

Reg Edwards wrote:
The input and output currents of a loading coil of finite length are always
different from each other.

There's hardly any "input and output currents" for a loading coil in
a standing wave antenna. That concept is why W8JI is in trouble with
his explanations. What is actually being measured is the magnitude
of the standing current wave.

There is forward current flowing into the bottom of the coil and out
the top. There is reflected current flowing into the top of the coil
and out the bottom. The net current is a standing current wave. If we,
as Kraus suggests, assume that the forward current equals the reflected
current (relatively small error in doing so) then there is zero net current
flowing in and out of the coil. The standing wave current is, well, just
standing there and is not "going" anywhere.

The gross error that a lot of people are making is that standing
wave current flows. If the forward and reflected currents are equal,
as Kraus assumes for purpose of discussion, then there is zero net
current flow through the coil. Yet, net current is what everyone
is measuring. What they are actually measuring is the value of
the standing wave current at each end of the coil and it is not
flowing. It is only an artifact of the superposition of the two
waves that are flowing.

The magnitude of the reflected current can be estimated from the
feedpoint impedance. The lower the feedpoint impedance, the closer
in magnitude is the reflected current to the forward current. For
a center-loaded mobile antenna, the reflected current through the
coil appears to be well within 5% of the value of the forward
current.
--
73, Cecil http://www.qsl.net/w5dxp


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"Frank" wrote
As posted in a previous thread go to www.carolyns-creations.com/ve6cb to
view the (modeled) current distribution on an 84" monopole at 21.3 MHz.

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

Frank, I don't know, and it doesn't matter, how you produced the amperes
versus height graph which beautifully displayed itself with a single
mouse-click on my computer screen.

It displays the curve-shape which any properly educated electrical engineer,
or amateur with any intuitive common sense, ought to expect. Thanks!

The many reams of heated arguments which have appeared on this newsgroup
have been a disgrace to the profession. Yes, I know its an amateur mewsgroup
but the (aggressive?) contestents are mostly so-called professionals.

Clearly you have chosen an adequate mathematical demonstration model with
the ability to use it. Most likely without any thoughts about Terman or
theorem-writers Thevenin and Kirchoff, etc., who personally I have hardly
ever heard of.

If you have not already done so, may I suggest you include radiation
resistance in the model for slightly greater accuracy. It may remove the
small kink in your curve which occurs immediately at the bottom end of the
coil. I don't think it should be there. But further elaboration is hardly
worth the effort.

I also think its a good idea to base demonstration models (like actual
experimental measurements) on the lower frequencies. Try the 160 metre band.
They are likely to be more accurate representations.

Frank, if you have the time to spare perhaps you should contribute to this
newsgroup more often. Improve its already good entertainment, even
educational if sometimes confusing, value!

By the way, I'm on Dourthe No.1, Bordeaux 2001, tonight. French politics go
down very well with their excellent wine and British very mature Cheddar
cheese.

Hic!
----
Reg, G4FGQ

Reg Edwards wrote:
By the way, I'm on Dourthe No.1, Bordeaux 2001, tonight.

I hear the French are pi$$ed at us for our small boycott of
French wine, French vacations, French Fries, etc. :-) Ever
notice that us and US mean the same thing for us?
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:

Reg Edwards wrote:

By the way, I'm on Dourthe No.1, Bordeaux 2001, tonight.


I hear the French are pi$$ed at us for our small boycott of
French wine, French vacations, French Fries, etc. :-) Ever
notice that us and US mean the same thing for us?

I'm boycotting Texas. No Texas bugcatchers for me, they're
unamerican.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:
I'm boycotting Texas. No Texas bugcatchers for me, they're
unamerican.

I heard the Texas Bugcatcher guy is an SK so he probably
doesn't care.
--
73, Cecil http://www.qsl.net/w5dxp


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W5DXP wrote:
There is forward current flowing into the bottom of the coil and out
the top. There is reflected current flowing into the top of the coil
and out the bottom. The net current is a standing current wave.

In view of the above, for practical putposes, trying to get maximum performance
out of the loaded radiator, it should be beneficial to have the same diameter
of whip above the coil, rather than tapering whip?
One might deduct that if the current is diminishing towards the top, that the
diameter of the radiator (RF resistance) could be tapered also. But since the
RF current has to flow to the tip and then reflect and go back and interfere
with itself, we should make it uniform, where possible.
We are probably talking about fraction of a peanut, but for the purists and
sake of argument.

Yuri, K3BU.us

"Reg Edwards" wrote in message
...
Fact 1.

Any loading coil of finite length contributes towards to the total
radiation.

NEWSFLASH - there's no such thing as a perfect inductor. Amazing!

Fact 2.

The input and output currents of a loading coil of finite length are always
different from each other.

A natural consequence of fact #1.

Fact 3.

The radiation pattern of a short vertical is fixed and remains independent
of the location/height of the loading coil.

Not so, precisely because said inductor cannot be perfect. HOWEVER, the
difference is neglegible and probably immeasureable.

Fact 4.

Computer programs do not tell gospel truths. They are at least as
unreliable as their human programmers.

Ahh, but at least they are *consistantly* unreliable in predictable ways,
which is more than can be said for humans.

----
Reg.

Reg Edwards wrote:
. . .
Fact 3.

The radiation pattern of a short vertical is fixed and remains independent
of the location/height of the loading coil.


True for practical purposes. People using antenna modeling programs, or
people adept with analytical techniques, will find a small difference in
pattern as the loading coil is moved, due to the changed current
distribution. But it's an inconsequential difference.

Roy Lewallen, W7EL