Dr. Slick wrote:
Roy Lewallen wrote in message ...

Y'see, if you really, really want an antenna to be a kind of automobile,
you can cook up a bunch of reasons to convince yourself that it is. The
same method works for astrology and fortune telling, too.



Shall i call this a Straw man argument? Or putting words in
someone's mouth?

Feel free to call it what you want. I believe I've made as valid an
argument for an antenna being an automobile as you did for it being a
transformer, and based on the same criteria.




Well, if you agree that two antennas/transducers in close
proximity will make a transformer (albeit a somewhat inefficient
one!), then i don't think i was that far off base.

I agree.




The optimization of an antenna depends on many factors, only one of
which is the nature of the medium in which it's immersed. And among the
medium's important properties are its permeability, permittivity, and
the velocity of a wave propagating in it. The phase velocity and
characteristic impedance can both be calculated from the permeability
and permittivity, so you can't really say any one of these is more
important than the other.

It doesn't make any sense to throw out the concept of free space
impedance just because it confuses people who don't know what it means.
It's an extremely useful and well-understood concept. For example,
reflection of a wave from a plane conductor or the ground can easily be
found by calculating a reflection coefficient based on the impedance of
the reflecting surface and the impedance of the impinging wave. (The
impedance of a wave can be quite different close to an antenna than it
is after it's traveled some distance.) If you look in some of those
texts I recommended, you'll find the impedance of free space cropping up
all over the place.

What needs to be thrown away is the belief that all impedances are the
ratio of a voltage to a current, along with the notion that only
resistors can have resistance.

Roy Lewallen, W7EL



You have convinced me that you are correct about both of these
points.

Good. Then the effort was worthwhile.


But i don't think that an antennas impedance will not be affected
by the permeability of the medium that surrounds it. An antennas
input impedance will be different in free space as opposed to being
immersed in water, for example.

Indeed it will.


This indicates to me that the antenna is indeed "matching" 50
Ohms to the impedance of free space, even if it is a different type of
impedance.

That's a leap I'm unable to make or to follow.

Do you think that the characteristics of a transformer of a
specific turns ratio, gauge wire, and core geometry, will NOT depend
on the core material? I would say definitely it WILL depend on the
material.

Actually, an adequate core shouldn't appear as a significant factor in
transformer performance. Naturally, an inadequate core will adversely
affect it. But I just don't accept that as evidence, let alone "proof"
that an antenna is fundamentally an impedance matching device.

I see that you won't be swayed from your visualization. But hopefully
some of the other readers can see the fallacy of the concept. I think
I've done all I can, so I'll leave this topic now.

*Chuckle* I was just reminded of something that happened years ago, when
my son was a small boy. He learned that I was an engineer, so he
couldn't wait to see the train I drove. After a great deal of repeated,
patient, explanation, I finally got across (I thought) a description of
what I did, and that it had nothing to do with trains. Well, he had
occasion to visit me at work quite a long time later. He kept wandering
off. When I asked why, he explained that he was trying to find where the
train was kept. Yeah, I might not drive trains, but I must have
*something* to do with trains.

Slick, you've got the right concepts now, but you're still looking for
that train.

Roy Lewallen, W7EL