Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
The angle between b1 and b2 is the phase shift at
the impedance discontinuity.

Sorry, I had a migraine and a brain fart there.
The angle between b1 and a2 is the phase shift
at the impedance discontinuity. It's absolute
value should be the same as the angle between
a1 and b2 at the impedance discontinuity.

I apologize for my brain fart.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

On Sat, 15 Dec 2007 12:04:34 -0800, Roger wrote:

Am I to understand that the only use of the term "DC" that you will
accept is "A steady state without beginning or end, having always
existed, and will exist forever more". Of course such a thing would not
have a "wave front"

Hi Roger,

Exactly. This has always been the definition for DC. For anything
else, there are already terms that have been provided for decades,
unto more than a century.

73's
Richard Clark, KB7QHC

Loading Coils; was : Vincent antenna
 

AI4QJ wrote:
I vote for 3.2 and so did the Indiana legislature by 67 - 0!

I'm sorry, Dan, my 3.0 Bible reference is a lot older than
that. Now if I could only find it.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Richard Clark wrote:
On Sat, 15 Dec 2007 12:04:34 -0800, Roger wrote:

Am I to understand that the only use of the term "DC" that you will
accept is "A steady state without beginning or end, having always
existed, and will exist forever more". Of course such a thing would not
have a "wave front"

Hi Roger,

Exactly. This has always been the definition for DC. For anything
else, there are already terms that have been provided for decades,
unto more than a century.

73's
Richard Clark, KB7QHC

Hi Richard,

OK. I will remember this for making future discussions more exact.

73, Roger, W7WKB

Loading Coils; was : Vincent antenna
 

On Dec 15, 3:23 pm, Cecil Moore wrote:
Keith Dysart wrote:
Cecil did not answer the question, so I will
pose it again. If knowing the phase shift at
the terminals of the black box is important,
and you can not know it without knowing the
internals of the box, given a black box of
unknown internals but told that its terminals
present -j567 at the frequency of interest,
would you refuse to calculate the length
of 600 ohm line needed to produce 0 ohms?

Or asking the question another way: Is there
really a Santa Claus and a God?

Perhaps. Though I notice that you still have not
answered the question.

....Keith

Loading Coils; was : Vincent antenna
 

Keith Dysart wrote:

Keith Dysart wrote:
given a black box of
unknown internals but told that its terminals
present -j567 at the frequency of interest,
would you refuse to calculate the length
of 600 ohm line needed to produce 0 ohms?

Though I notice that you still have not
answered the question.

Why would anyone refuse to calculate the length of
600 ohm line needed to produce 0 ohms? I think I
was the first to calculate it at 43.4 degrees.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
Ian White GM3SEK wrote:
"Lumped inductance is often a good approximation to reality, so [most
models other than Cecil's] very sensibly use that as their
starting-point.

For the umpteenth time, Ian, I don't have a model developed
by me. The model I use is the distributed network model
invented before I was born. Dr. Corum merely expanded upon
that model
and I consider his concepts to be valid.

That last line makes it "your model" by adoption - and certainly "your
model" by advocacy.

Your lumped circuit model seems more like a religion
than a valid tool of science. Zero phase shift through
a real-world loading coil?

That wasn't what I said. What I did say - and you cut - was:

"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."




--

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

Loading Coils; was : Vincent antenna
 

On Dec 16, 1:18 am, Cecil Moore wrote:
Keith Dysart wrote:
Keith Dysart wrote:
given a black box of
unknown internals but told that its terminals
present -j567 at the frequency of interest,
would you refuse to calculate the length
of 600 ohm line needed to produce 0 ohms?

Though I notice that you still have not
answered the question.

Why would anyone refuse to calculate the length of
600 ohm line needed to produce 0 ohms? I think I
was the first to calculate it at 43.4 degrees.

Exactly. Why would anyone refuse?

So the next question is: What is the phase change
at the terminals of the black box?

1) -93 degrees? (previous answer when it was a capacitor)
2) 36.6 degrees? (previous answer when it was 10 degrees of 100 ohm
line)
3) 0 degrees? (previous answer when it was 46.6 degrees of 600 ohm
line)
4) undecidable?
5) undefined?
6) irrelevant?
7) ???

....Keith

Loading Coils; was : Vincent antenna
 

Ian White GM3SEK wrote:
In practical terms, a lumped-inductance model will take you straight to
a buildable prototype."

If you are a technician or a hobbyist, by all means
use the shortcuts. If you are an engineer or physicist,
to do so will lead your concepts astray.

Take the use of standing-wave current to try to measure
the delay through a 75m mobile loading coil. The results
of using the lumped-inductance model are off by a magnitude.
A 75m mobile loading coil is a distributed network that
is an appreciable percentage of a wavelength. As such, the
lumped inductance model is inadequate for analysis.

Here is a quote from my web page:

Many experiments and measurements have been made on loading
coils using net standing wave current. A lack of understanding
of the nature of standing wave current has resulted in some
strange and magical assertions about current through a loading
coil. The equation for standing wave current is of the form:

I(x,t) = Imax sin(kx) cos(wt)

For any point location 'x', it can be seen that the standing
wave current is not "flowing" in the ordinary sense of the word
but rather, is just oscillating in place at that fixed point.
EZNEC confirms that the phase of standing wave current is essentially
constant all up and down a typical HF mobile antenna and therefore
cannot be used to make a valid measurement of the phase shift (delay)
through a loading coil (or even through a wire.) The validity of that
statement is obvious if one understands the implications of the
standing wave current equation above. In fact, we can just as easily
write the standing wave current equation as:

I(x,t) = Imax sin(kx) cos(-wt)

We can reverse the direction of rotation of the standing wave
current phasor and still have the same value of current. Standing
wave current really doesn't have a direction of flow.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Keith Dysart wrote:
Why would anyone refuse to calculate the length of
600 ohm line needed to produce 0 ohms? I think I
was the first to calculate it at 43.4 degrees.

Exactly. Why would anyone refuse?

Nobody has refused so it is a rhetorical question
the meaning of which is obscure.

So the next question is: What is the phase change
at the terminals of the black box?

You list the phase changes at the terminals of the
black boxes. An s-parameter analysis will prove those
are valid values. Have you done that s-parameter
analysis yet?

b1 = s11*a1 + s12*a2

b2 = s21*a1 + s22*a2

The phase shift is the relative phase between b1 and a2.
And also the relative phase between b2 and a1.

1) -93 degrees? (previous answer when it was a capacitor)

I might be wrong about that one. It might instead be
180 - 93, but that would just be a stupid math mistake.
The main thing is that it is different from the other two.

2) 36.6 degrees? (previous answer when it was 10 degrees of 100 ohm
line)
3) 0 degrees? (previous answer when it was 46.6 degrees of 600 ohm
line)

There's nothing wrong with those answers except maybe
a stupid math error. Each condition indeed does have a
different phase shift that can be measured one inch on
the other side of the terminals if one is simply allowed
to make those measurements. If s11 is measured and stamped
on the black boxes, the phase changes can be easily
calculated.

This is an example of how models can get you into trouble.
Not allowing us to look inside the black box doesn't change
the laws of physics and make all the phase shifts the same.
It just means that the phase shifts are unknown and need
to be measured.

Using that same logic, if you were shackled at the bottom
of Carlsbad Caverns, night and day would stop happening
just because you couldn't see it happening.

Do you really expect us to believe that the phase shift
is the same for all the black boxes but changes abruptly
when the reflection coefficients are measured?
--
73, Cecil http://www.w5dxp.com