On 11 Nov, 05:19, "Richard Fry" wrote:
"art" wrote

It has been stated on this antenna newsgroup that with
short antennas the current goes up the radiator and then turns back
and goes down. If this is so then it must be radiating all the time,
yes? If a radiator is radiating all the time then the efficiency is the
same as a full leght antenna. Yes? This does not conform with
reality Right?

Wrong, as regards your "reality." Using the classic definition of
efficiency, an antenna of ANY length (including a point source) will radiate
nearly 100% of the power it accepts from the r-f source driving it.

The radiation patterns of those antennas will vary. Some will radiate more
relative field in some directions and less in some directions than others
will. But, disregarding dielectric and conductor I^2R losses, ALL antennas
radiate ALL of the power they accept from their driving source (ie, their
efficiencies are equal).

So is it possible that the circuit (current) returns along
the path down the center of the radiator...

No, it's not possible. No matter the direction of flow along a solid
conductor, alternating current tends to travel on/near its outer surface.
This is due to the greater number of enclosed lines of magnetic flux
generated by current flowing at/near its center, which increases the
inductive reactance of the conductor in those areas. The result is a
redistribution of the current to the parts of the conductor cross-section
having the least reactance, ie, on and near its outer surface. Read
Terman's RADIO ENGINEERS' HANDBOOK, 1943 edition, pp 30-31 for more on this
(or many other sources).

IF it was possible then radiation figures accepted by hams
would coincide with respect to short antennas. Yes?.
Then why do all the "experts" reject the notion of the circuit
continueing down the center of the radiator?

Because it doesn't do that.

RF

To say that an AC current will not flow in copper unless it has clear
axis
access to the copper surface is balderdash. Cover the copper with an
insulator
with any thickness that you desire for safety incase you are in error
and then drill
into the center of the copper. Without a safe guard you will die!
What provides resistance on the outside als skin depth can by the
reverse contain current flow to the inside. You like many use the word
"tends"
with respect to external current flow. The word "tends" does not
make the current passage an undeniable fact. Yet you have hung
your hat on that premise. I repeat...balderdash
Art

On 11 Nov, 07:05, "Richard Fry" wrote:
If it's going to where you want it, and if a usable amount of
'signal' gets there, then it's efficient for that particular situation.
If not... then it isn't very efficient, is it?
- 'Doc

____________

In a pure sense, the radiator itself is.

It just may not be as useful in that application as an antenna of
another configuration that provides the system result being sought.

RF

There you go again, "may" does not affirm fact.
Art

I repeat...balderdash
Art


Artsy,
Finally you summarized your "writings" and your repeating of it.
Balderdash trophy of the year goes to Art da ex G man.

Have you considered fishing or other activities?

bada BUm

"art"
What provides resistance on the outside als skin depth can
by the reverse contain current flow to the inside.

This is another of your beliefs that not supported either by theory
or practice.

The word "tends" does not make the current passage
an undeniable fact.

I wrote "tends" because there is no discrete boundary near the outer surface
of a conductor where ALL of the alternating current flowing near its surface
is confined. But almost all of that current flows within several "skin
depths."

The 1.8 MHz skin depth in a round, copper conductor is about 0.06 mm, which
means that a tubular conductor with a wall thickness at least 3 times that
can be used in place of a solid conductor of the same outer diameter, with
no practical change in performance at that frequency.

RF

"art"
There you go again, "may" does not affirm fact.
_________

OK, then.

A 1/2-wave dipole absolutely HAS more directivity than an isotropic radiator
(and so does every other practical antenna).

But when any/all of them accept the same amount of power from an r-f source,
then they ALL will radiate the same total amount of power.

So they are all equally efficient, by the classic definition of total power
in vs. total power out.

Antenna directivity/gain is not a measure of efficiency.

RF

Richard Fry wrote:
"Read Terman`s RADIO ENGINEERS` HANDBOOK, 1943 edition, pp 30-31 for
more on this (or many other sources)."

Amen. Terman doesn`t say different things in different places. He is
consistent. In Terman`s 1955 edition of "Electronic and Radio
Engineering" he writes on page 21:
"It is to be noted that some of this (magnetic) flux exists within the
conductor and therefore links with, i.e., encircles, current near the
center of the conductor while not linking current flowing near the
surface. The result is that inductance of the central part of the
conductor is greater than the part of the conductor nesr the surface;
this is because of the greater number of flux linkages existing in the
central region.

That`s why we have skin effect and why hollow pipes carry HF current as
effectively as solid rods with the same external surface area in most
cases. The pipe`s interior doesn`t carry current unless its diameter is
at least 1/2 wavelength (its cutoff as a waveguide).

Best regards, Richard Harrison, KB5WZI

Art wrote:
"But nobody will question the fact that all computer programs support my
addition to Gaussian law to those of maxwell."

That`s an I dare you.

Roy may tell us if EZNEC needs Art`s embellishment for accuracy.

Art did not answer my question of Nov 8, 10:27am in the "An instructive
trick" thread. It was: "why would we use the time constant without the
angular frequency?"

On page 904 0f the 3rd edition of Kraus` "Antennas" is found:
"The availability of computers in the 1960s provided antenna designers
with an alternative. They could develop software to simulate the
performance of antennas. In general, these techniques either numerically
solve Maxwell`s equations by descretizing the problem using integral
techniques, such as Moment Methods (MoM) as discussed in Sec. 14-11, or
differential techniques, such as finite elements or finite
difference-time domain."

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Richard Fry wrote:
"Read Terman`s RADIO ENGINEERS` HANDBOOK, 1943 edition, pp 30-31 for
more on this (or many other sources)."

Amen. Terman doesn`t say different things in different places. He is
consistent. In Terman`s 1955 edition of "Electronic and Radio
Engineering" he writes on page 21: "It is to be noted that some of this
(magnetic) flux exists within the conductor and therefore links with,
i.e., encircles, current near the center of the conductor while not
linking current flowing near the surface. The result is that inductance
of the central part of the conductor is greater than the part of the
conductor nesr the surface; this is because of the greater number of
flux linkages existing in the central region.


What Terman says is true, for the particular example that he chooses.
But it may leave an incorrect impression that the conductor needs to be
completely encircled by flux linkages.

In fact the skin effect will develop on the surface of any conducting
material of any shape, wherever there is RF current flowing.

Here is a link to a detailed mathematical proof, from 'Transmission
Lines for Communications' by C W Davidson (Macmillan Press, 1978, ISBN 0
333 32738 1): http://www.ifwtech.co.uk/g3sek/misc/skin.htm

Davidson's analysis starts with the most general assumption possible:
that RF current is flowing over any small patch of a conductor's
surface. No assumption is required about the reason for the RF current
to be present, only that it is. Likewise no assumption is required about
the cross-section of the conductor, only that it has an exposed surface
(and by implication, that there are no constraints due to a small radius
or insufficient depth). Davidson then derives all the usual equations
for the skin effect. The only drawback of this derivation is that it is
highly mathematical, and difficult to put into words; but it's still
physically correct.

To repeat, I am not saying that Terman's explanation is incorrect; only
that the skin effect is a far more general phenomenon than his
particular examples imply.

This is important because, by taking the existence of the skin effect as
a guaranteed starting-point, the explanations for the behaviour of
coaxial cables, 'bazooka' baluns, 'shielded' loops and many other
devices will all fall neatly into place.


--

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

"Richard Harrison" wrote in message
...
Art wrote:
"But nobody will question the fact that all computer programs support my
addition to Gaussian law to those of maxwell."

That`s an I dare you.

Gauss's law IS one of Maxwell's equations. In fact both Ramo Whinnery and
Van Duzer's "Fields and Waves in Communications Electronics" (pg 237 in the
1st edition) and Jackson's "Classical Electrodynamics" (compare pg 2 and 33
in the 2nd edition). So every time art makes that assertion he is just
showing his ignorance of the facts.

Dave wrote:
"Gauss`s law IS one of Maxwell`s equations."

Yes. I`ve suggested Kraus to Art but he seems not to have pored through
Kraus yet. On page 395 of the 3rd edition of Antennas is a table of
Maxwell`s equations in integral form. One column is from Ampere, another
from Faraday, and the last two are from Gauss.

Best regards, Richard Harrison, KB5WZI