Yuri Blanarovich wrote:

Now someone is going to come right back at me, talking about "real life"
this and "practical" that. But if someone does not understand how an
inductor is even *meant* to behave, all their practical knowledge is
built on sand - they may know lots of stuff, but they don't truly
understand it.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek


Here we go again!

Where have you been Ian? Applying DC current behaviour in the inductor to
standing wave RF current situation in the antenna, Eh?

No.

Step 1: I am starting from the fundamental AC current behaviour of an
ideal inductor. The phases of the voltages at its opposite ends are
different; but at every given instant, the currents at its opposite ends
are equal and in phase.

2. I am expecting that ideal inductor to behave in exactly the same way
when used as a loading device in an antenna - which in fact it does,
because exactly the same laws of physics apply.

3. Then I'm in a good place to start to think how that behaviour will
change for a real inductor that has both physical size and capacitive
coupling to the rest of the antenna.


In case you missed previous exchanges
http://www.k3bu.us/loadingcoils.htm

That is in practice and (right) theory. Cecil showed (hairpinned) model in
EZNEC. And that ain't no lie!

73 and keep your readers informed properly :-)


Oh, I shall, I shall...

I'll begin by pointing out the obvious: an ideal inductor, a honkin'
great length of Airdux and a shorted parallel stub are three physically
different objects. Each one is a different kind of loading device, with
different effects when inserted into an antenna - and none of those
loading devices is the same as the length of real antenna that it's
claimed to "replace".

The flaw in your viewpoint is that you are expecting a loading device to
"replace" too many of the properties of a genuine piece of antenna. It
actually replaces very few of them, and each different loading device
does it in a different way.

Cecil's stub behaves exactly as expected - for a stub. But a shorted
transmission line is not an inductor - it has some of the properties of
an inductor, but not all of them. In particular, the currents at its two
terminals can be unequal, because a stub can carry common-mode current
and radiate and EM field, which an inductor cannot. Therefore the stub
example is irrelevant to a discussion that is trying to compare various
inductors.

The same is true of different types of inductors. The ideal inductor and
the Airdux are both loading devices - they do not completely replace the
missing piece of the antenna. They replace it in one respect only
(making the feedpoint reactance equal to zero) but all other things
about the loaded antenna are *different* from the full-sized antenna. In
particular, the current and voltage distributions above and below the
load are different from full size, and so of course is the feedpoint
resistance.

I cannot explain every detail of Barry Boothe's measurements, but I know
for certain that the true explanation is the one that obeys all the laws
of physics and circuit theory, down to the last detail.

What you have, Yuri, is an "explanation" that uses those laws in some
parts, but twists or ignores them in others. That cannot possibly be
correct.



--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek