RSGB RadCom December 2007 Issue
 

"John Smith" wrote in message
...

And the skills test is, find the missing "not" in the previous post! ;-)

Regards,
JS

RSGB RadCom December 2007 Issue
 

Cecil Moore wrote:
Mike Kaliski wrote:
and that the characteristic impedence will vary along an antennas length.

Well, that's obviously false. The characteristic
impedance of a horizontal wire above ground is
constant at 138*log(4D/d)

The characteristic impedance is not to be confused
with the voltage to current ratio existing on a
standing-wave antenna any more than the characteristic
impedance of a transmission line is to be confused
with the voltage to current radio existing along
its length when the SWR is not 1:1.

Interesting point.

When I use a gamma match on a 1/2 wave vertical with counterpoise, I
have always wondered about the 50ohm impedance point where the gamma
taps the element.

To end feed the antenna, an impedance of thousands of ohms is
encountered, a, seemingly, "strange" distance up the element (in regards
to total element length) and a 50 ohm impedance point is encountered
(needing only a series capacitive reactance to correct for the gamma
rods' inductive reactance.)

It would be interesting if I had a formula which would predict what
impedance would be encountered for all points along the element--know of
any?

I have looked at setting up such a formula, but frankly have been
unsuccessful ... and of course, it is given that antenna length IS
resonate for the frequency in question.

Regards,
JS

RSGB RadCom December 2007 Issue
 

On Wed, 14 Nov 2007 19:41:42 -0800, John Smith
wrote:

A careful argument based on semantics, the authors choice of words, and
standing on the arguments that no mistakes exist in our present
knowledge and that new discoveries in the deep workings of antennas are
yet to be discovered ...

Talk about a mouthful of ****.

Spit it out tell us how your really feel.

73's
Richard Clark, KB7QHC

RSGB RadCom December 2007 Issue
 

Richard Clark wrote:
On Wed, 14 Nov 2007 19:41:42 -0800, John Smith
wrote:

A careful argument based on semantics, the authors choice of words, and
standing on the arguments that no mistakes exist in our present
knowledge and that new discoveries in the deep workings of antennas are
yet to be discovered ...

Talk about a mouthful of ****.

Spit it out tell us how your really feel.

73's
Richard Clark, KB7QHC

Huh? You jest, you have better mental comprehension than that ...

What, you applying for SSI disability and attempting to use your posts
to prove mental incompetence? Mad Cow Disease? ???

Get real ... yawn.

JS

RSGB RadCom December 2007 Issue
 

Michael Black wrote:

Of course, such columns are relatively easy to write, since it's a
filtering of a lot of material down to it's essence.


No, it's such comments that are easy to write.

Now try doing it :-)


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

RSGB RadCom December 2007 Issue
 

"Richard Clark" wrote in message
...
On Thu, 15 Nov 2007 02:47:05 -0000, "Mike Kaliski"
wrote:

It seems that everyone was so busy laughing on this newsgroup,

Hi Mike,

As well crafted a line for trolling as any....

that no one
has actually provided any information as to whether any detailed research
has ever been carried out as to what is going on within the radiating
elements of an antenna.

This, as the lawyers would say, argues a fact not yet in evidence.
Your statement appears to be one that can only be satisfied by meeting
a string of conditions:
1. The actuality of "actually," who is the arbiter of this? This
group has long experienced denial by inventors that their theories
have never been "actually" disproved. "Actually" is one of those
rubbery words that fits any argument that lack definition;
2. "detailed research?" Another qualifier that invites the rejection
of any contribution for lacking unspecified requirements;
3. "what is going on?" Now THERE is a technical goal for detailed
research to be provided as information.
4. "within the radiating elements?" Is this to presume there is some
distinct radiation from "within" elements? This would be a remarkable
measurement achievement to tease it out from the rest. [Could we use
a Gaussian sieve?]

There is loads of theory in the text books, but I

If you moved to the fiction shelves would you say there is loads of
drama in them? [More to the matter, what would you expect?]

have yet to see any empirical measurements or results.

Of what? Actual detailed results of what is going on within radiating
elements?

Help us out here. What instrumentation would be used? What units of
measure would be employed? (In "what is going on" are we talking
about Ohms, Volts, Amperes; or swimming, having a party, or getting
laid off?). What qualifies as detail? How would we recognize it
being actual?

I am aware of the
research into small loops carried out by Professor Underhill (also
published
in RadCom) but it seems that even his results have been disputed.

Hmm, tantalizing, but how do small loops relate to "what is actually
going on?" More so, where within the loop did Professor Underhill
make his measurements, and what were they of? [I might point out
here, editorially, that little content was posted by you up until this
point, and it has evaporated following its solitary mention. If you
stripped out everything, and simply fleshed out this sentence into a
paragraph, it might be meaningful.]

I may have submitted the post, tongue in cheek

Then the joviality that your post heralds is merited, isn't it? This
is called leading with your chin.

, to stir things up a bit, but
on reflection there seems to be something of merit in the idea.

As your post seems to be wholly unrelated to the topic, and apparently
a stream of consciousness from another thread, then this idea is
adorned with rather vague suggestions.

73's
Richard Clark, KB7QHC

Hi Richard

Thanks for yor comments and encouragement. I can well understand your
skepticism and accept that this idea is pretty far out. As you rightly point
out, there are a whole host of issues revolving around what is being
defined, measurement methods and interpretation of results.

The small transmitting loop efficiency experiments were carried out using
thermographic imaging to try and identify areas of heating within the loops.
The areas with maximum heating would indicate high current flow or high
resistance. This information was used to try and derive a theory of
operation and efficiency figures for the loops. The idea being to prove that
efficiency was in fact higher than predicted by the Chu theory. The
methodology and results of the experiment were challenged and Chu theory
seems to have won out, at least for the time being.

I don't see that there would be any need to invoke non standard units for
experimental measurements, ohms, amps and volts should suffice. I have not
worked out the best measurement methods or instrumentation to use, but I am
sure that existing equipment and techniques will suffice. Small sampling
coils, hall effect devices, temperature measurement
probes and thermal cameras are all available at prices which an amateur
experimenter can afford, so there is no reason why these experiments could
not be carried out in a domestic environment rather then an industrial one.

The reason for specifying a single radiating element is because directional
and reflecting elements absorb and re-radiate RF energy. Once the properties
of a single element are known, then it is possible to add additional
elements and make further measurements and assessments of performance. Since
it is already known that all the elements of an antenna interact with one
another, it is important to start with the basics and work up from there.

The choice of the word 'within' was unfortunate because I accept that there
is nothing going on actually within an antenna element, skin effect ensuring
that RF travels on the outside of conductors.

So I come back to my assertion that very little detail seems to have been
published about what is happening really close in to antennas i.e. on the
actual elements making up the antenna. Loads of stuff about near field and
far field experiments, but not specific points of radiation from the antenna
elements. It may all be a complete waste of time but at least I will have
fun and hopefully learn some new stuff doing it.

Regards
Mike G0ULI

RSGB RadCom December 2007 Issue
 

"Cecil Moore" wrote in message
...
Mike Kaliski wrote:
and that the characteristic impedence will vary along an antennas length.

Well, that's obviously false. The characteristic
impedance of a horizontal wire above ground is
constant at 138*log(4D/d)

The characteristic impedance is not to be confused
with the voltage to current ratio existing on a
standing-wave antenna any more than the characteristic
impedance of a transmission line is to be confused
with the voltage to current radio existing along
its length when the SWR is not 1:1.
--
73, Cecil http://www.w5dxp.com

Cecil

Are you sure you are not confusing the characteristic impedance of a dipole
antenna with the characteristic impedence of an open feed line? One is
constant, the other appears to vary along its length. A dipole antenna has
low impedence at a centre feed point and high impedence at it's ends.

Reminds me of the tales of old ladies who used to tie knots in electric flex
to stop the electricity leaking out! I actually met one in real life many
years ago.

Mike G0ULI

RSGB RadCom December 2007 Issue
 

Tom Donaly wrote:
Cecil Moore wrote:
The characteristic
impedance of a horizontal wire above ground is
constant at 138*log(4D/d)

The characteristic impedance is not to be confused
with the voltage to current ratio existing on a
standing-wave antenna any more than the characteristic
impedance of a transmission line is to be confused
with the voltage to current radio existing along
its length when the SWR is not 1:1.

Have you verified this experimentally, Cecil? If you did,
how did you do it?

Here's a quote from "Antennas Theory" by Balanis: "The current
and voltage distributions on open-ended wire antennas are similar
to the standing wave patterns on open-ended transmission lines.
.... Standing wave antennas, such as the dipole, can be analyzed
as traveling wave antennas with waves propagating in opposite
directions (forward and backward) and represented by traveling
wave currents If and Ib ..."

As Balanis suggests, the body of technical knowledge
available for "open-ended transmission lines" is applicable
to "open-ended wire antennas", e.g. dipoles, which really
are nothing but lossy *single-wire* transmission lines.

That characteristic impedance equation for a single-wire
transmission lines can be found in numerous publications and
is close to a purely resistive value. A #14 horizontal wire
30 feet above ground is very close to a characteristic
impedance of 600 ohms. (One half of a 1/2 wavelength dipole
is simply a lossy 1/4 wavelength stub with Z0 = ~600 ohms.)

Before he passed, Reg Edwards had some earlier comments on
the characteristic impedance of a 1/2WL dipole above ground.

Like a normal transmission line open stub, a 1/2WL
dipole supports standing waves that can be analyzed. For the
purposes of a voltage and current analysis, I^2*R losses and
radiation losses can be lumped together into total losses
associated with some attenuation factor, similar to analyzing
a 1/4WL lossy normal stub.

In fact, the losses to radiation from
one half of a 1/2WL dipole can be simulated by EZNEC using
resistance wire in a 1/4WL open stub. Using EZNEC with a
resistivity of 2.3 uohm/m for a 1/4WL open stub gives a pretty
good model of what is happening with one half of a 1/2WL dipole
which is only a lossy single-wire transmission line above earth.
--
73, Cecil http://www.w5dxp.com

RSGB RadCom December 2007 Issue
 

Mike Kaliski wrote:
Are you sure you are not confusing the characteristic impedance of a
dipole antenna with the characteristic impedence of an open feed line?
One is constant, the other appears to vary along its length. A dipole
antenna has low impedence at a centre feed point and high impedence at
it's ends.

The feedpoint impedance of a stub is NOT the same thing
as the Z0 of the stub. The feedpoint impedance of an
antenna is NOT the same thing as the Z0 of the antenna.

The characteristic impedance of a #14 wire 30 feet above
the ground is close to constant at 600 ohms. The formula
for a single-wire transmission line is 138*log(4D/d).
A horizontal dipole is nothing more than a single-wire
transmission line which is known to be lossy.

The characteristic impedance of a transmission line is
constant. If the SWR 1, the voltage to current
ratio varies along its length. That varying impedance
(V/I) is NOT the characteristic impedance which is
constant.

The characteristic impedance of a horizontal dipole is
~constant. Since a dipole is a standing wave antenna,
the voltage to current ratio varies along its length.
That varying impedance (V/I) is NOT the characteristic
impedance which is relatively constant for a horizontal
wire.
--
73, Cecil http://www.w5dxp.com

RSGB RadCom December 2007 Issue
 

On Thu, 15 Nov 2007 12:29:08 -0000, "Mike Kaliski"
wrote:

Thanks for yor comments and encouragement. I can well understand your
skepticism and accept that this idea is pretty far out. As you rightly point
out, there are a whole host of issues revolving around what is being
defined, measurement methods and interpretation of results.

Hi Mike,

OK, but this still tells me nothing of what issue you think I am
skeptical about!

The small transmitting loop efficiency experiments were carried out using
thermographic imaging to try and identify areas of heating within the loops.

Good, that is instructive.

The areas with maximum heating would indicate high current flow or high
resistance.

More properly, their product - Watts.

This information was used to try and derive a theory of
operation and efficiency figures for the loops. The idea being to prove that
efficiency was in fact higher than predicted by the Chu theory.

This names only one theory and doesn't actually illustrate any
differences.

The
methodology and results of the experiment were challenged and Chu theory
seems to have won out, at least for the time being.

Again, all of this is suggestive, not informative. Returning to your
earlier complaint of "detailed research" we have no details beyond
heat imaging challenging the establishment.

I don't see that there would be any need to invoke non standard units for
experimental measurements, ohms, amps and volts should suffice.

Too often, this group has to wade through "what it is not" instead of
"what it is." Tell us what specific units would be convincing for
you, as you have introduced a complaint that needs to be satisfied.

I have not
worked out the best measurement methods or instrumentation to use, but I am
sure that existing equipment and techniques will suffice.

I have worked on a world of instruments (more than anyone here).
Believe me, that experience has NOT answered the question of the ages.

Small sampling
coils, hall effect devices, temperature measurement
probes and thermal cameras are all available at prices which an amateur
experimenter can afford, so there is no reason why these experiments could
not be carried out in a domestic environment rather then an industrial one.

OK, by induction, I presume you are harkening back to these thermal
maps or imaging.

Well, in fact they have been done, their results have been posted to
the net and argued here. You didn't get the invitation?

Unfortunately, that contributor was arguing smaller loops, coils
specifically and the mapping was tangential to the rant. He promised
more data when Spring weather would allow him to pursue this line of
inquiry, but that was several Springs ago, and he has in the interval
chosen to -um- till the same ground.

The reason for specifying a single radiating element is because directional
and reflecting elements absorb and re-radiate RF energy. Once the properties
of a single element are known, then it is possible to add additional
elements and make further measurements and assessments of performance. Since
it is already known that all the elements of an antenna interact with one
another, it is important to start with the basics and work up from there.

True, and certainly it stands to improve clarity by reducing
variables.

The choice of the word 'within' was unfortunate because I accept that there
is nothing going on actually within an antenna element, skin effect ensuring
that RF travels on the outside of conductors.

Plus, thermal imaging would be hard pressed to peer inside a
conductor.

So I come back to my assertion that very little detail seems to have been
published about what is happening really close in to antennas i.e. on the
actual elements making up the antenna. Loads of stuff about near field and
far field experiments, but not specific points of radiation from the antenna
elements. It may all be a complete waste of time but at least I will have
fun and hopefully learn some new stuff doing it.

You mean you are unfamiliar with this work. I've posted my own here
to little attention, I don't think this cycle will attract much more,
but here it is:
http://home.comcast.net/~kb7qhc/ante...pole/index.htm

This doesn't actually attend your preference of thermal mapping, but
you are still vague to the point of "what is happening really close in
to antennas" (even qualified by "on the actual elements" - there's
that word actual again which lends nothing to a specification).

There is an entire field of Science devoted to this (beyond the scope
of many here who would anticipate my answer being "Fields"). This
field is called Plasmonics. Books are written about it, pictures are
taken of it, and I've sat through hours of presentations demonstrating
it. Unfortunately, this crowd of investigators, like Arthur, have
re-invented the wheel and they proclaim it is square.

The long and short of it is that you stand to become more confused,
but it could be rewarding if you wear asbestos.

73's
Richard Clark, KB7QHC