On Sep 23, 6:05*am, Szczepan Bia³ek wrote:

The Luxembourg effect is only possible if the both ends of the dipole are
"visible". The mast was on the tip top.

The Luxemburg effect is not produced by a dipole.

It has been ascribed to be produced in the ionosphere when two very
strong EM waves cross-modulate. More likely it occurs when co-
located, high power transmitters cross-modulate in their output stages
due to coupling between their antennas.

Now no vertical LW masts. But everybody has a
horizontal dipole.

A horizontal dipole produces horizontally polarized EM radiation,
which has very high propagation loss for the ground wave.

For this reason vertical polarization is universally used for LW and
MW signals.

RF

Cecil Moore wrote:
tom wrote:
Note that none of these are particularly close to resonance at the
design frequency.

Yagis do have a resonant frequency but that frequency
is not at the design frequency. At the resonant frequency,
the forward gain and F/B ratio are not optimum. At the
optimum forward gain frequency and/or F/B ratio frequency,
the Yagi, sans matching network, is not resonant.

Agreed, although it has become popular to make designs with about 50+j0
driven elements lately. I think it's to make them simpler and lighter
because, as you say, the other characteristics are not optimum if you do.

tom
K0TAR

Szczepan Bia³ek wrote:
In my antenna radiate the end where the voltage is doubled. In your
something alse. What?

Unfortunately, the voltage doubling is accompanied by
transmission line currents at the ends of the antenna
which are known not to radiate. The reason is obvious.

When two currents are equal in magnitude and opposite
in phase, they do not radiate (much) because their fields
engage in destructive interference. These currents
are commonly known as transmission line currents but
also exist at the ends of a dipole as forward and
reflected currents.

When the phases of two currents are equal they engage
in constructive interference and radiate. These currents
are commonly known as antenna currents and exist at
the middle of a dipole that is equal to or less than
0.5WL long.

Unfortunately for your theory, since the standing wave
voltage is ~90 degrees out of phase with the standing
wave current (in standing wave antennas), the higher
the standing wave voltage the greater the destructive
interference between the forward and reverse currents,
i.e. the higher the voltage, the lower the radiation.

Sorry, but that is a simple fact of physics. If you
want the ends of a dipole to radiate, you need to
terminate those ends in the characteristic impedance
of the antenna in order to prevent transmission line
currents on the antenna.

If one models a 1/2WL dipole with the center 1/4WL part
horizontal and the 1/8WL ends vertical, one will get
a magnitude more horizontal radiation from the center
half of the antenna than vertical radiation from the
vertical half of the antenna. That's easy proof that the
center of a 1/2WL dipole radiates more than the ends.
The vertical radiation is 10 dB down from the horizontal
radiation even though equal lengths of horizontal and
vertical wire exists. Is EZNEC wrong?

Running the above dipole at double the frequency
results in equal currents in each 1/8WL of antenna and
indeed, the vertical radiation equals the horizontal
radiation.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

On Sep 23, 6:14*am, Szczepan Bia³ek wrote:

Highest antenna current do not means high enough to radiate. The high
current is in transmissing line of the short antennas.
In 0.05 no currents at all at the feed point.

If there is no current at the feedpoint terminals of a 0.05WL dipole
then there is no current anywhere else in it, and there would be no
radiation. Obviously that is not the reality.

The current distribution in such short dipoles is triangular in form:
highest at the center, and zero at the ends of the dipole arms.

RF

On Tue, 22 Sep 2009 16:59:19 -0700 (PDT), Art Unwin
wrote:

On Sep 22, 5:30*pm, Registered User wrote:
On Tue, 22 Sep 2009 13:24:17 -0700 (PDT), Art Unwin

wrote:

Well look at how salvage yards sort out metals into different
enclosures.
They apply a displacement current *to a conveyor where each piece of
metal is elevated with spin such that it lands in the appropriate
enclosure which is dependent on the resistivity of the metal elevated.

This isn't exactly how such systems work. Abstractly the system is a
metal detector and a sorting table hanging off a CAN. A controller at
the other end of the CAN 'reads' the discriminator and 'writes' to the
sorter. The writes open and close ejector nozzles. These are the magic
devices that cause the material to 'elevate with spin'.

This method of elevating scrap for recovery has been used for years
and it is the same action that is applied to particles for radiation.
Why would you need a citation for a practice that is well known and in
use?

Because you might be wishing your agenda into how you propose things
work. Who'da thunk that!

Interesting. Can you point to an article or something on the web that
describes what you
say. For myself I have only run into articles by special purpose
machine manufacturers
who deal with sorting machines for scrap yards which deals with many
materials including plastics , glass etc as well as different metallic
materials. This sorting aproach that you mention sounds rather
interesting if they are relying on magic or voodoo!

There is no magic or voodoo involved with a controller area network.

There are all manners of industrial separators and practically all are
custom purposed for the user and the particular type of refuse
stream(s) they will be dealing with. It's certainly not a
one-size-fits-all industry. Most use a combination of methodologies.
Magnetic eddy currents are one means and their use in the industry
only goes back a couple of decades.

In a nutshell here is how eddy currents are primarily used in
materials sorting.

As the eddy current roller spins it creates alternating polar fields.
When inert (non-metallic) material enters a field a field of the same
charge is generated around the object. As the roller spins the next
field is of opposite charge to the field of the object and the object
is repulsed. The momentum provided by the conveyor belt added to the
repulsive force changes the trajectory of the object as it leaves the
end of the conveyor belt. As a consequence inert objects travel
further off the end of the belt.

Non-ferrous metals do not benefit from a charged field and fall
straight down due to good old gravity. Ferrous metals are attracted to
the roller and remain on the conveyor belt until they move past the
roller on the underside of the table. Then those materials also fall
straight down but at a different location from the non-ferrous metals.

http://tinyurl.com/meo9py

On Wed, 23 Sep 2009 12:13:33 +0200, Szczepan Bia?ek
wrote:

"Exactly" makes it very, very easy to show how an analogy fails:
Describe the laminar flow in terms of
the Reynolds number for
the interface between RF and a Biconical Antenna
and
the interface between RF and a thin wire Antenna."

We've already determined you don't know how to do this, and that you
don't have the vaguest idea.

My guess is that you don't even understand the few simple terms in the
quote above. Can you tell us what laminar means? How about
interface? Your response is wholly devoid of their discussion, so I
suppose you cannot except to quote someone else - unfortunately that
does not reveal knowledge.

If you cannot give us a Reynolds number (something like any mechanical
engineer like Art can do - well, yes, I admit that is an unwarranted
presumption on my part), then you may as well let your boat drift on.

73's
Richard Clark, KB7QHC

On Wed, 23 Sep 2009 07:16:49 -0500, tom wrote:

Cecil Moore wrote:
tom wrote:
Note that none of these are particularly close to resonance at the
design frequency.

Yagis do have a resonant frequency but that frequency
is not at the design frequency. At the resonant frequency,
the forward gain and F/B ratio are not optimum. At the
optimum forward gain frequency and/or F/B ratio frequency,
the Yagi, sans matching network, is not resonant.

That's about as useful as saying you do not obtain the maximum miles
per gallon in your car when the ashtray is half full or when the
carpets are at their optimal brushed out nap.

73's
Richard Clark, KB7QHC

On Tue, 22 Sep 2009 23:59:59 -0700, Jeff Liebermann
wrote:

For example, the Antenna and Propagation IEEE Transactions for a year
(12 issues) costs $1,200.

Or you can go to the library and read (and copy) them for free.

Oh, and yes, If you have access to an engineering library on campus.

Oh, and yes, if they let you back on campus..... Sorry, some (Art)
have spit on too many professors.

73's
Richard Clark, KB7QHC

On Sep 23, 9:38*am, Registered User wrote:
On Tue, 22 Sep 2009 16:59:19 -0700 (PDT), Art Unwin



wrote:
On Sep 22, 5:30*pm, Registered User wrote:
On Tue, 22 Sep 2009 13:24:17 -0700 (PDT), Art Unwin

wrote:

Well look at how salvage yards sort out metals into different
enclosures.
They apply a displacement current *to a conveyor where each piece of
metal is elevated with spin such that it lands in the appropriate
enclosure which is dependent on the resistivity of the metal elevated..

This isn't exactly how such systems work. Abstractly the system is a
metal detector and a sorting table hanging off a CAN. A controller at
the other end of the CAN 'reads' the discriminator and 'writes' to the
sorter. The writes open and close ejector nozzles. These are the magic
devices that cause the material to 'elevate with spin'.

This method of elevating scrap for recovery has been used for years
and it is the same action that is applied to particles for radiation.
Why would you need a citation for a practice that is well known and in
use?

Because you might be wishing your agenda into how you propose things
work. Who'da thunk that!

Interesting. Can you point to an article or something on the web that
describes what you
say. For myself I have only run into articles by special purpose
machine manufacturers
who deal with sorting machines for scrap yards which deals with many
materials including plastics , glass etc as well as different metallic
materials. This sorting aproach that you mention sounds rather
interesting if they are relying on magic or voodoo!

There is no magic or voodoo involved with a controller area network.

There are all manners of industrial separators and practically all are
custom purposed for the user and the particular type of refuse
stream(s) they will be dealing with. It's certainly not a
one-size-fits-all industry. Most use a combination of methodologies.
Magnetic eddy currents are one means and their use in the industry
only goes back a couple of decades.

In a nutshell here is how eddy currents are primarily used in
materials sorting.

As the eddy current roller spins it creates alternating polar fields.
When inert (non-metallic) material enters a field a field of the same
charge is generated around the object. As the roller spins the next
field is of opposite charge to the field of the object and the object
is repulsed. The momentum provided by the conveyor belt added to the
repulsive force changes the trajectory of the object as it leaves the
end of the conveyor belt. As a consequence inert objects travel
further off the end of the belt.

Non-ferrous metals do not benefit from a charged field and fall
straight down due to good old gravity. Ferrous metals are attracted to
the roller and remain on the conveyor belt until they move past the
roller on the underside of the table. Then those materials also fall
straight down but at a different location from the non-ferrous metals.

http://tinyurl.com/meo9py

Thank you for confirming the use of eddy currents in the elevation and
projection of scrap materials. My understanding is that the special
purpose machinery industry has now advanced to the ability of sorting
plastic and the like.

"Richard Clark" wrote
...
On Wed, 23 Sep 2009 12:13:33 +0200, Szczepan Bia?ek
wrote:

"Exactly" makes it very, very easy to show how an analogy fails:
Describe the laminar flow in terms of
the Reynolds number for
the interface between RF and a Biconical Antenna
and
the interface between RF and a thin wire Antenna."

We've already determined you don't know how to do this, and that you
don't have the vaguest idea.

My guess is that you don't even understand the few simple terms in the
quote above. Can you tell us what laminar means? How about
interface? Your response is wholly devoid of their discussion, so I
suppose you cannot except to quote someone else - unfortunately that
does not reveal knowledge.

If you cannot give us a Reynolds number (something like any mechanical
engineer like Art can do - well, yes, I admit that is an unwarranted
presumption on my part), then you may as well let your boat drift on.

I have onmy shelf the Fluid dynamics by Dr Ludwig Prandtl. Prandtl is a big
name.
S*