Ian White, G3SEK wrote:
I want you to stop and think a moment, about how an IDEAL INDUCTANCE
behaves in an antenna. (Sorry to shout, but every time I type "ideal
inductance" quietly, you seem to read something else :-)

Ian, please take your own advice. It's pretty obvious that you are
thinking about an IDEAL INDUCTANCE in terms of a lumped circuit analysis
which is invalid when analyzing a STANDING-WAVE ANTENNA. The equations
governing the behavior of a standing-wave antenna are similar to the
equations governing the behavior of a lossy transmission line with
reflections. In fact, just by looking at the equations, you cannot tell
whether they apply to a transmission line with reflections or to a
standing-wave antenna.

Hint1: Write the equation for the total current on a standing-wave
antenna that includes forward and reflected currents and "loss" due
to radiation.

Hint2: A real-world mobile loading coil acts like a section of transmission
line where Z0=SQRT(L*C). It does NOT act like a lumped circuit inductance.

Hint3: An IDEAL INDUCTANCE doesn't exist in reality. Lumped circuit
inductances are a shortcut that doesn't exist in reality and surely
does NOT apply to distributed networks like a standing-wave antenna.

Hopefully you will agree that an IDEAL INDUCTANCE does not ever have
different currents at its two terminals, and does not radiate either.

Can't agree to that at all. In fact, here's a repeat from another
posting that proves that the superposed forward and reflected
currents at each end of a lossless inductance *cannot* be equal.
Please don't use the copout excuse that an ideal lumped inductance
doesn't have any phase shift through it. *ALL* real-world loading
coils have a phase shift that can easily be measured. If it has
any phase shift at all, the current magnitudes at each end of the
coil *cannot* be equal unless a current min/max occurs in the middle
of the coil which doesn't happen in a typical mobile antenna.

P.S. How about discussing the technical issues instead of the
personalities involved?

There doesn't need to be a current drop through a coil for the
total current to be different at each end. Assume a base-loaded
mobile system. Assume the forward current through the coil is
constant at 1.1 amp. Assume the reflected current through the coil
is constant at 1.0 amp. Assume the phase shift through the coil is
45 degrees.

If the forward current and reflected current are in phase at the
base of the coil (feedpoint) the total current will be

1.1+1.0 = 2.1 amps of total current at the base of the coil.

The total current at the top of the coil will be

1.1 amps at -45 degrees superposed with 1.0 amps at +45 degrees.

1.1*cos(-45) + 1.0*cos(45) = 1.48 amps.

The coil is lossless and the component currents are absolutely
constant through the coil yet the superposed total current at
the top of the coil is only about 71% of the superposed total
current at the bottom of the coil. No "technical jargon" involved.

Using circuit analysis on a distributed network problem simply
demonstrates ignorance of the problem. It's an easy mistake to
make and a hard mistake to admit (especially for gurus :-).
--
73, Cecil http://www.qsl.net/w5dxp


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Richard Clark wrote:
I will agree in this respect, but not all Toms are Rauchs. The term
"Current Drop" is abhorrent to some (a pollution of technical
language), an irritant to others, and inconsequential to many who
simply enjoy the cat fight.

Heh, heh, so you don't believe there is a current drop between the
current maximum point and current minimum point on a transmission
line with reflections? Seems to me going from 2 amps at a current
maximum to 0.1 amps at a current minimum is a measurable drop in
total current.

Would you please provide a proof that going from 2 amps to 0.1 amps
is NOT a drop in total current?

Just one more example of trying to use lumped circuit analysis methods
on distributed network problems. Are you guys ever going to learn?

Hint: With distributed networks involving an appreciable percentage of
a wavelength, there are definitely current drops in the series loop.
This certainly applies to 75m Bugcatcher coils used on standing-wave
mobile antennas.
--
73, Cecil http://www.qsl.net/w5dxp


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Ian, G3SEK wrote:
"Hopefully you will agree that an IDEAL INDUCTANCE does not ever have
different currents at its two terminals and does not radiate either."

Sorry to disappoint you, but adequate demonstration has already shown
different currents in and out of a loading coil. I won`t claim it was an
ideal inductor.

The title: Current in loading coil. EZNEC- helix. This is not about
an ideal inductance.

An inductor, inductance, or retardation coil is used to provide
inductance.

An inductor has a second definition:
"A passive fluidic element which because of fluid inertness, has a
pressure drop that leads flow by essentially 90-degrees." Sounds vaguely
familiar.

Inductance is defined as a "property of a circuit that tends to oppose
any change because of a magnetic field associated with the current
itself. Whenever an electric current changes its value, rises or falls,
in a circuit, its associated magnetic field changes, and when this links
with the conductor itself an emf is induced which tends to oppose the
original current change."

If the purpose is to provide inductance, and the purpose of thiis
inductance is to exhibit Lenz`s law, then an ideal inductor does not
radiate, but I`m not convinced it does not have different currents at
its two ends, as this says nothing about the coil`s quality or
perfection.

After all, self inductance is the production of an oppositely directed
current in reaction to an imposed current.

An ideal coil can very well be arranged not to radiate or couple to the
outside world other than through its terminals. These terminals can face
very different impedances depending on where each is connected in a
circuit with standing waves. That is what confronts the ordinary loading
coil in an antenna circuit.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
An ideal coil can very well be arranged not to radiate or couple to the
outside world other than through its terminals. These terminals can face
very different impedances depending on where each is connected in a
circuit with standing waves. That is what confronts the ordinary loading
coil in an antenna circuit.

Ever wonder why everyone is ignoring the 180 degree phase-reversing
coils described by Kraus in _Antennas_for_all_Applications_? Real-
world coils change the phase of the current from end to end. That
real-world phase shift is all that is required for the total current
at each end of the coil to be different when installed in a standing-wave
antenna undergoing superposition of the forward and reflected currents.

What we seem to have here is a bunch of gurus who are incapable of
admitting that they mistakenly used the lumped circuit model when
they should have used the distributed network model. It's an easy
mistake to make and a hard mistake to admit.
--
73, Cecil http://www.qsl.net/w5dxp


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As straight wires are usually better radiators than the same wire in
coils, I speculate that the current drop measured by Yuri is mostly due
to the high impedance (High voltage, low current) on the output of the
loading coil.
What, Coililng the wire has nothing to do with how well it does or does not
radiate, only with how the radiation is summed into the total field. The
current distribution in a loading coil should be very similar to the current
distribution in the secton of antenna it is replacing.

Jimmie wrote:
What, Coililng the wire has nothing to do with how well it does or does not
radiate, only with how the radiation is summed into the total field. The
current distribution in a loading coil should be very similar to the current
distribution in the secton of antenna it is replacing.

Actually, coiling the wire tends to reduce the far-field radiation
because much of the near-field(s) cancel each other. The currents
on each side of the coil are traveling the opposite direction in
much the same way they do in a transmission line. However, that
doesn't mean the currents at the bottom and top of the coil are
identical. The magnitude of the total current at the bottom and
top of the coil depends in large amount on the phase shift through
the coil.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:
Richard Clark wrote:

I will agree in this respect, but not all Toms are Rauchs. The term
"Current Drop" is abhorrent to some (a pollution of technical
language), an irritant to others, and inconsequential to many who
simply enjoy the cat fight.


Heh, heh, so you don't believe there is a current drop between the
current maximum point and current minimum point on a transmission
line with reflections? Seems to me going from 2 amps at a current
maximum to 0.1 amps at a current minimum is a measurable drop in
total current.

Would you please provide a proof that going from 2 amps to 0.1 amps
is NOT a drop in total current?

Just one more example of trying to use lumped circuit analysis methods
on distributed network problems. Are you guys ever going to learn?

Hint: With distributed networks involving an appreciable percentage of
a wavelength, there are definitely current drops in the series loop.
This certainly applies to 75m Bugcatcher coils used on standing-wave
mobile antennas.
--
73, Cecil http://www.qsl.net/w5dxp


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Next, Cecil, you're going to be talking about a "current gradient"
and a "scalar current field." Here's a question for you, Cecil, and
Richard Harrison, and Yuri, too: how do you take the gradient of
the current at a point on a transmission line, and, if were possible
to do so, what is the physical significance of the result?
73,
Tom Donaly, KA6RUH

Cecil, W5DXP wrote:
"Ever wonder why everyone is ignoring the 180 degree phase reversing
coil described by Kraus in _Antennas_For_All_Applications_?"

TOUCHE`!

(They told me "touche`" was more appropriate than "there goes the SOB".)
In this thread, the foreign word is sure to offennd somebody.

The all-coil phase inverter is another reason to buy Kraus` final book.

Best regards, Richard Harrison, KB5WZI

Jimmie wrote:
"Coiling the wire has nothing to do with how it does or does not
radiate,---."

Good. Just leave your antenna rolled up.

Best regards, Richard Harrison, KB5WZI

Cecil Moore wrote:
I want you to stop and think a moment, about how an IDEAL INDUCTANCE
behaves in an antenna. (Sorry to shout, but every time I type "ideal
inductance" quietly, you seem to read something else :-)

Ian, please take your own advice. It's pretty obvious that you are
thinking about an IDEAL INDUCTANCE in terms of a lumped circuit
analysis
which is invalid when analyzing a STANDING-WAVE ANTENNA.

It makes life easier to compartmentalize your scientific world-view in
that way.... but it is deeply, fundamentally wrong.

In reality, all true scientific knowledge joins up seamlessly - that's
how we *know* it's true! If we can't see how it joins up, that means we
still have work to do. Dividing it into compartments that don't join up
is lazy and will always lead you false.

A fundamental physical property like inductance doesn't change its
behaviour depending on the situation it finds itself in. If you cut the
antenna wire and insert an ideal, lumped inductance, that inductance
will behave in exactly the same way as it does in any other circuit.

If you really looked hard at the math of antennas considered as
transmission lines, you would find there is no problem whatever about
inserting an ideal inductance, with no difference in current between its
two terminals.



--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek