On Fri, 15 Aug 2003 09:40:12 -0500, "William E. Sabin"
sabinw@mwci-news wrote:
The problem remains:

How is the *real* part of the antenna input
impedance, regardless of how it is fed and
regardless of what kind of antenna it is, get
"transformed" to the *real* 377 ohms of free space?


Hi Bill,

Transformation, as a term, seems to be problematic without any more
care for the preferred term of transduction (ignoring the historical
usage it clashes with). How words could have any bearing on the
process itself is more a calmative to the user than a need for the
group.

So, if we were to simply ignore ALL the terms, how many show up at the
table to discuss the PROCESS (I hope that's the right word...)?

If we simply cast off the electrical aspect of it (seeing how
difficult it is to conduct discussion for this topic in that
vernacular), the correlative of the organ pipe would be useful. It
too creates a standing wave at the drive point; and it employs a
resonant structure wherein the wave stands. It conforms to the
transmission line principles of termination in that a close or open at
the end is meaningful, and harmonically related to wavelength in a
media. If this seems an outrage (because the former kidnapping of
terms is ignored) consider the following quote from Reference Data for
Radio Engineers:
"...Maxwell's initial work on electrical networks
was based on the previous work of Lagrange
in dynamic systems."
This reference then tumbles into the discussion of "Acoustic and
Mechanical Networks and their Electrical Analogs"

It can be seen that the structure imposes critical significance in the
harmonic component, but is wholly inert without excitation. In other
words, it is not the causative agent, nor is it the agent of
transmission. The pressure excess would cause air flow with or
without it. Of course, there is an efficiency problem in that lax
attitude and that necessarily brings us back to structure and fields
(pressure in this case).

What has this to do with near field and far field? For the organ
pipe, what is the near field, what is the far field? Here, we get
into issues as we formerly did by looking at dimension and wavelength.
There are two classes of Acoustic Impedance that bear to this
intimately.

Those two classes compute for a spherical wave front, and for a planar
wave front:
"...the acoustic impedance for a spherical
wave has an equivalent electrical circuit
comprising a resistance shunted by an inductance.
In this form, it is obvious that a small spherical
source (r is small) cannot radiate efficiently since
the radiation resistance [formula] is shunted by a small
inductance [formula]."

The plane wave Acoustic Impedance formula does not exhibit this
inductive shunt. The difference between the two cases is simply a
matter of scale, and is as arbitrarily chosen as with the abandoned
antenna. That is to say, the definition of antenna far field being
expressed as residing 10 wavelengths away also finds the correlative
in this difference of Acoustic Impedance.

What is this shunt? The compressibility of the medium which is the
mechanical analog of storage.

What is the difference between the case of the organ pipe and the
antenna? For the pipe, the medium is lossy (and employing a vacuum
brings its own obvious issues for the organ) and we find the loss
expressed in phonons (the heat of jostling material). For the antenna
(especially in the void of a vacuum, a useful medium) we find no such
issue and consequently no related phonons (loss to heat within the
medium). Some would note this also encompasses the traditional
demarcation between transducer and transformer.

Irrespective of the difference, both exhibit a region wherein the
MEDIA supports the transition (and perhaps we should call these
structures transitioners --- only kidding :-).

As I stated in the past, it is absurd to crop the picture such that
the description demands that an antenna ends at the literal tips of
its structure as if virtual clips connect it to the æther.

73's
Richard Clark, KB7QHC