Dave wrote:
if the frequency is fixed, is sinusoidal, and steady state,
then every box that measures -j567 ohms is perfectly equal.

If the goal is to measure the phase shift at an
impedance discontinuity in a transmission line, why
would someone deliberately put the impedance discontinuity
inside a black box? That defeats the goal of measuring
the phase shift.
--
73, Cecil http://www.w5dxp.com

wrote:

But Ian,

I don't propose to upstage or speak for Ian, but I'll add my comments in
advance to his response.

Suppose the box is labeled -j567 ohms.

Then I ask, "at what frequency is this impedance -j567?".

I find that the impedance for -j567 ohms is 4 Mhz.

And in this case we have four black boxes which all measure -j567 ohms
at that same frequency.

Now I take a length of 600 ohm VF = 1 transmission line and vary the
length until I am at resonance with whatever is in the black box at 4
MHz. Resonance would imply 90 degrees total phase shift.

My measurement shows that the length of 600 ohm line to cause this
effect is 43 degrees.

Assuming my measurement is correct, doesn't that tell us a little more
about what is inside the box? It isn't just "any" -j567 ohm impedance
that can cause resonance with a 43 degree 600 ohm line. It is probably
not a discreet capacitor, it would likely be some sort of transmission
line or something that that has 10 deg length, correct?

No, that's not correct. As I've said several times before, you can't
tell anything about the contents of the boxes by doing measurements at a
single frequency, except to determine the terminal impedance at that
frequency. No matter what kind of test you do (at that one frequency at
which the impedances are the same), you cannot distinguish among them.
You can't tell which box is which, or detect anything about them which
is different. If you have a theory which predicts otherwise, you should
investigate where the flaw in the theory is. If you're not convinced,
simply describe in detail the tests you would do and the numerical
results you expect to get for the different boxes. Anyone with a
background in transmission line theory (which include several regular
group participants) will be able to tell you what results you should
expect from your tests, which will be the same for all the boxes. And
several of us are also able to make decent measurements as well as
provide equations to show why. That's how engineering is done.

With a few more measurements, we can determine the Zo of the
transmission line that "appears' to be in the black box, correct and
essentially verify that it a transmission line.

Not if you measure only at the one frequency. Not only can you not tell
the Z0, you can't even tell if it's a transmission line at all. It might
be a capacitor, a complex LC network, or some combination of
transmission lines, capacitors, and inductors.

We should be able to
both measure and calculate Zo.

If we choose our independent measurements carefully enough, we should
be able to define exactly what is in the black box with only 2
terminals.

It's a bit frustrating to continue posting the same thing over and over
and see continued claims that the boxes can be distinguished. We'd both
save a lot of bandwidth if you would, instead of just claiming that you
can do it, show that you can. Even theoretically -- describe the tests
you would make and the results you would expect which would be different
for each box. Then we'd have something which could be discussed objectively.

I agree you need more than a smith chart (which was where I made my
mistake before).

Yes, I'm afraid you'll need a lot more.

Let me reiterate that the contents of the boxes can certainly be
distinguished with tests made at multiple frequencies. But the objective
of my comments has been to counter the claim that there's some terminal
property such as "electrical degrees" which the various lines (box
contents) have which is different at the single frequency at which their
reactances are the same. I hear this claim still being made, but so far
not any evidence to support it. When such evidence (not including
typical Cecil-style hand-waving, but real numbers) is presented, I'll be
glad to point out where it's in error.

Roy Lewallen, W7EL

Roy Lewallen wrote:
Let me reiterate that the contents of the boxes can certainly be
distinguished with tests made at multiple frequencies. But the objective
of my comments has been to counter the claim that there's some terminal
property such as "electrical degrees" which the various lines (box
contents) have which is different at the single frequency at which their
reactances are the same. I hear this claim still being made, but so far
not any evidence to support it.

I provided the evidence in the thread titled,
"Please verify (or disprove)". You have yet
to respond to it. Here's your chance to nail
me to the wall for good, Roy. Why are you so
silent on that thread?
--
73, Cecil http://www.w5dxp.com

On Thu, 20 Dec 2007 18:21:28 -0600, Cecil Moore
wrote:

Why

Everyone knows "why" but you, apparently. This has been explained
many times, and quite clearly with a very simple explanation. No
theory is involved, no proofs required, no data needs to be offered, a
simple statement has resolved "why" a loooooooong time ago.

Ask "why" again. Confirm the stereotype and pick up the doorprize.
;-)

Roy Lewallen wrote:
When such evidence (not including
typical Cecil-style hand-waving, but real numbers) is presented, I'll be
glad to point out where it's in error.

OK Roy, here's your chance. From the previous example:

--43.4 deg 600 ohm line--+--10 deg 100 ohm line--open
Vfor1--|--Vfor2 Vf--|
Vref1--|--Vref2 Vr--|

Given Vf = 100 volts at 0 deg.

Vfor2 = 100 volts at -10 deg

Vref2 = 100 volts at +10 deg

Vfor2 = tau1*Vfor1 + rho2*Vref2 = 100 volts at -19 deg

Solving for Vfor1 = 143.33 volts at -46.6 degrees

Vref1 = rho1*Vfor1 + tau2*Vref2 = 143.33 volts at +46.6 deg

Note that the two above equations are equivalent to
the s-parameter equations:

b1 = s11*a1 + s12*a2 and b2 = s21*a1 + s22*a2
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Vfor2 = tau1*Vfor1 + rho2*Vref2 = 100 volts at -19 deg

Obvious Typo: should be 100 volts at -10 deg
--
73, Cecil http://www.w5dxp.com

AI4QJ wrote:
"Cecil Moore" wrote in message
...
wrote:
It isn't just "any" -j567 ohm impedance
that can cause resonance with a 43 degree 600 ohm line.
Dan, I believe you will find that any -j567 impedance
in the black box will put the forward and reflected
waves back in phase, i.e. resonant.

OK but if you can measure Zo of whatever is in the box, then you know the
length by virtue of it being -j567. It should only take 2 terminals to
measure Zo.
Knowing Zo, then I can normalize the smith chart and directly read the
electrical length in degrees. True, it would help to know that the box
contains a transmission line.

The "other side" will not allow you to assume a transmission
line. The "other side" will not even allow you four terminals
on your black box. The entire purpose of the black box, in this
present context, is to confuse and confound the unwashed masses
so the "other side" can maintain their guru status.
--
73, Cecil http://www.w5dxp.com

On Dec 20, 11:35*am, Cecil Moore wrote:
Keith Dysart wrote:
On Dec 20, 11:02 am, Cecil Moore wrote:
Michael Coslo wrote:
Just a phase they are going through.............
Exactly what is the reference for that phase? :-)

Fire hydrant.

Hey Keith, have you been able to disprove my figures
in my other thread "Please verify (or disprove)"?
If not, why not? Seems it would be an ideal time
to nail me to the wall with some math that disagrees
with mine.

Your math is typically fine (although you messed
up big time with your use of "reference"), when you
allow yourself to use it. It is the interpretations,
conclusions, and allocations of importance that
are flawed.

But now that you have declared black boxes a
conspiracy to hide "the facts", I'm thinking maybe
you should go join the MI5 guy.

Anyway, along the way you learned (or maybe
already knew and just articulated) that the effect
on the 600 ohm line is the same regardless of
the content of the black box producing -j567,
and for the black boxes, the phase shift at the
terminals is undecidable. And since the problem
can be solved without this information, it is also
irrelevant.

A bit of progress.

...Keith

8 to go.

Keith Dysart wrote:
Your math is typically fine ...

Aha, so you agree that there is a 36.6 degree phase
shift between Vfor1 and Vfor2? That is certainly
progress. Now if you can only convince the gurus.

But now that you have declared black boxes a
conspiracy to hide "the facts", I'm thinking maybe
you should go join the MI5 guy.

I didn't say all black boxes are a conspiracy to
hide the facts. But consider that when the goal
is to measure the phase shift at an impedance
discontinuity and someone insists on putting the
impedance discontinuity inside a black box where
the phase shift cannot possibly be measured, then
that person desperately wants to keep the results
from that measurement from being known.

Anyway, along the way you learned (or maybe
already knew and just articulated) that the effect
on the 600 ohm line is the same regardless of
the content of the black box producing -j567,

There was never any argument there so that statement
is just a straw man - go ahead and knock it down and
get it over with. Nobody disagrees with you.

and for the black boxes, the phase shift at the
terminals is undecidable. And since the problem
can be solved without this information, it is also
irrelevant.

The phase shift at the impedance discontinuity *CANNOT*
be solved without information about the impedance discontinuity.
Exactly what is it that you are so afraid that someone is
going to discover? The technical facts? You already admitted
that my calculations were accurate and valid. What more could
you possibly want to hide?
--
73, Cecil http://www.w5dxp.com

On Thu, 20 Dec 2007 21:09:53 -0500, "AI4QJ" wrote:

But I am only trying to find out what is in the box
so it is a mental
exercize.

Hi Dan,

Then you have missed the entire point.

I know it is a transmission line, open, and the impedance at 4MHz
is -j567.

You know? Then why try to find out? This is a contradiction on the
face of it. And what if it is not what you know it to be, and it
still presents -j567 at 4MHz?

If Zo for example were 100 Ohms, then -j567 would correspond
to -j5.67 on a smith chart normalized to 100 ohms and it is 10 degrees long.

If indeed!

What electrical length corresponds to -j567 if Zo measures 200 ohms? 300
ohms? They will all be different right?

Of course, any one of an infinite number of different possible
contents could reside within the box; but you don't know which one is
inside the box unless you look.

This reminds me of an argument I had with a Chief Boatswain's Mate
when I challenged him that "you can't make a horse drink water." His
(like Cecil's) solution was:
"You hold his head under water and suck on his ass!"

I hear this particular solution has been used to solve an unrelated
problem: a way of curing chapped lips (it keeps you from licking
them).

The better part of the members here use chapstick.

73's
Richard Clark, KB7QHC