On Dec 14, 10:00 pm, "AI4QJ" wrote:
"Keith Dysart" wrote in message

...

On Dec 14, 9:10 pm, "AI4QJ" wrote:
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?

The original problem statement discused -j567 as
an impedance. This is implicitly frequency dependant.

Not if I change the capacitance.

Each of the different ways mentioned for obtaining -j567
will produce a different impedance if the frequency is
changed. They were all frequency dependant.

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?

Everything is done in terms of degrees along a wave.
This implicitly normalizes for frequency.

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.

In the example, -j567 was merely due to a phase change due to the abrupt
impedance discontinuity. You are the one who suggested putting things in
black boxes. I suppose you could devise ways to phase shifts due to -j567 in
black boxes but I will have to leave that to you since you are the one who
brought up the idea.

Several ways were mentioned for obtaining the -j567:
a capacitor, some length of 100 ohm line, a different
length of 600 ohm line. Regardless of how the -j567
impedance is obtained, the same input impedance
to the 600 ohm line results. And yet each appears
to have a different phase shift occurring at the terminals.

Putting things in black boxes is a thought experiment
which helps isolate which aspects are important.
Any box containing a circuit which produces -j567
at the terminals will result in exactly the same
impedance at the input to the 600 ohm line, so
clearly -j567 is important.

Is the "phase shift" at the discontinuity important
when the results can be determined without knowing
the value. In fact, the "phase shift", in all the
examples, was computed last, after all the results
were known. How important can it be?

Do you suggest that there is no phase shift?

I suggest that there is no value in thinking about
the "phase shift" at the discontinuity (which depending
on the black box chosen might not be present), and
merely think about the results of connecting the
-j567 impedance to the 600 ohm line.

Then how do you explain the smith chart results?

Starting with the 100 ohm line, the normalized
input impedance was computed using the Smith
chart. This impedance was denormalized and then
renormalized to the 600 ohm. The new value was
plotted on a new Smith chart (the chart normalized
to 600 ohms) and the length of the 600 ohm line
was determined. The two lines have lengths, call
them Z1len and Z2len. 90 - (Z1len + Z2len) will
give a number which Cecil/you have called the
"phase shift" at the discontinuity. Alternatively,
it is just what happens when -j567 is attached
to the appropriate length of 600 ohm line.

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?

I suggest that there is no need to refuse
since the only information that is required
is -j567. Whether the box achieves this with
600 ohm line ("no phase shift"), 100 ohm
line ("some phase shift"), a capacitor or
some other technique is irrelevant.

....Keith

Keith Dysart wrote:
Each of the different ways mentioned for obtaining -j567
will produce a different impedance if the frequency is
changed. They were all frequency dependant.

Moral: Change the frequency and then observe what one
is dealing with?

I suggest that there is no value in thinking about
the "phase shift" at the discontinuity (which depending
on the black box chosen might not be present), and
merely think about the results of connecting the
-j567 impedance to the 600 ohm line.

The refusal to think about the phase shift at the
discontinuity is what got this whole thread started.

All you have to do to observe the calculated phase
shift is to use the s-parameter equations. When you
have done that, please get back to us.

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?

Let's see you prove that it is really -j567 ohms
without applying any signal at all. How's that
for a requirement?
--
73, Cecil http://www.w5dxp.com

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

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

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

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

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

It just occurred to me that you and I may be talking
about two different phases.

---Z01---+---Z02---

Vfor1--|--Vfor2

Vref1--|--Vref2

I am talking about the phase shift in the forward waves
across the impedance discontinuity, i.e. the phase shift
between Vfor1 and Vfor2. The list of phase shifts is
the phase shift in the forward voltages at the impedance
discontinuity. It is different for all the black boxes.

If you are talking about the phase between Vfor1 and Vref1,
then, yes, that phase is the same for all the black boxes.
It is impossible for it to be otherwise.
--
73, Cecil http://www.w5dxp.com