Loading Coils; was : Vincent antenna
 

Roger wrote:
Roy is giving good advice to study time domain reflectometry.

That's a good way to find out what is in each of
those black boxes.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

AI4QJ wrote:
"Roy Lewallen" wrote:
Does the new knowledge include a way to tell the
four black boxes apart at one steady state frequency, or how many
"electrical degrees" each one contains?

Where did the extra black box come from and who made the restriction on
frequency? I should be able to use any voltage or frequency I want, don't
you think?

Just raise the stakes, Dan. Challenge Roy to prove the
impedance is -j567 without applying a source signal.

I wonder what is the ulterior motive in arbitrarily
handicapping the person doing the measurements?

Roy mentioned the TDR for the other problem. Seems a TDR
is exactly the instrument needed to find out what is in
each of those black boxes. Or just order the black boxes
already specified with its s22 parameter stamped on the
black box.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Keith Dysart wrote:
When allowed to excite the black boxes with different
signals there are many ways to determine an internal
equivalent circuit. The question here was did the various
ways of making -j567 affect the results for sinusoidal
single frequency excitation.

Yes, it illustrated the two separate and different
IEEE definitions for "impedance", one a cause for
the voltage to current ratio and one a result of a
voltage to current ratio.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Keith Dysart wrote:
When I look at one of those coils, I think it is one big complicated
mess of distributed capacitance and inductance. There is intra and
inter turn capacitance and capacitance to ground. A mess.

Some say such a coil can be adequately modelled using a lumped
inductor.

I'm afraid you have fallen for someone else's mis-statement of that
point of view.

The most recent posting about lumped inductance was probably mine. It
states both the value and the limitations of this approach.

"Lumped inductance is often a good approximation to reality, so [most
models other than Cecil's] very sensibly use that as their
starting-point. Then they can progressively apply corrections for the
distributed properties of a real-life inductors. The smaller those
corrections are, the simpler the model becomes.

In practical terms, a lumped-inductance model will take you straight to
a buildable prototype. The necessary corrections can then be applied by
mechanical adjustment, without needing to model the distributed
properties of the loading coil in detail. Such models are to be found in
G4FGQ's MIDLOAD program, ON4UN's 'Antennas for Low Band DXing' and other
handbooks.

There was also an excellent theoretical treatment by Boyer in 'Ham
Radio', which shows in detail how the model of an antenna as an
unterminated transmission line is COMPLETELY capable of incorporating
lumped inductance."



--

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

Loading Coils; was : Vincent antenna
 

AI4QJ wrote:
"Keith Dysart" wrote:
The Smith chart is normalized for impedance
and frequency.

The smith chart is normalized *only* by Zo.

Tell me, how is Zo related to frequency :-) Or better, tell me how the smith
chart is normalized by frequency?

The Smith Chart is NOT normalized to a frequency.
EZNEC outputs frequency sweep data that can be
imported into MicroSmith.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:
Sure, you can do anything you like. But can you tell the boxes apart by
measuring at just one frequency (the one at which their impedances are
the same)? Do they have the same or different numbers of "electrical
degrees" at that frequency?

I'll do you one better with one more unreasonable condition.
Let's see you do it without applying any source power.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Richard Clark wrote:
How about that in the first place, particles
don't inhabit the explanation at all?

How about quantum physics telling us that nothing
except particles exist? You really want to take
on the body of quantum physics and physicists?
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Keith Dysart wrote:
On Dec 14, 1:52 pm, Cecil Moore wrote:
Do you think electrons support mechanical waves?

Simplicity itself. Electrons are charged. Like charges
repel. Move an electron and the next electron will tend
to move away.

So by your own admission, those are not mechanical waves.
Like charge repulsion is *NOT a mechanical phenomenon*.
Those electrons never touch each other. They are repelled
by the photons they are emitting.

I've been told that near the antenna, there are just
varying electric and magnetic fields and that some
distance from the antenna the electro-magnetic
wave forms. How does the varying field turn into a
photon?

The varying field ***IS*** made up of *PHOTONS*.
All electromagnetic fields consist of photons!
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:
Did you also conclude, then, that all
the boxes contain the same number of "electrical degrees"?

Yes, all the boxes contain the same number of electrical
degrees. That's why we can calculate the number of
electrical degrees at the impedance discontinuity.

Hint: That number of electrical degrees for a capacitor
is the same as the gamma angle for the reflection
coefficient.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Keith Dysart wrote:
I am not convinced. The value is still being determined
by accounting for all the other phase shifts and then
subtracting from 90. I would be more convinced of the
utility if the value could be computed from first principles
and then used, for example, to compute the length of
the whip.

That can easily be done. The s-parameter equations do
exactly that when applied at an impedance discontinuity.
a1, a2, b1, and b2 are all phasors each with an amplitude
and a phase.


b1 = s11*a1 + s12*a2

b2 = s21*a1 + s22*a2

The angle between b1 and b2 is the phase shift at
the impedance discontinuity.

Now are you convinced?

What happened to the missing 37 degrees?

Perhaps, like the missing dollar, it is simply a number
with no meaning.

Perhaps, if you would do the s-parameter analysis, you
would see the phase shift for yourself so it would
have meaning to you.

As an aside, allowing the possibility of this "phase shift" at
the joint, how would you compute the phase shift when a
parallel stub is used, or when multiple parallel stubs are
used to obtain the desired result? And which stub will be
used to define the 90 degrees from which the others are
subtracted?

Please don't complicate things before you have understood
the simple things.
--
73, Cecil http://www.w5dxp.com