Reflection coefficient for total re-reflection
 

On Jun 13, 2:55*pm, K7ITM wrote:
walt wrote:
I have a question for W5DXP, KB7QHC, W7ITM and K0TAR relating to
transmission lines.This is not a trick question. *This is a straight-
forward question for which I 'm dead serious. *The answer will involve
a resulting reflection coefficient.

Assume a 50-ohm line terminated in a purely resistive 150-ohm load,
yielding a 3:1 mismatch with a voltage reflection coefficient Vñ equal
to 0.5 at 0°. We want to place a stub on the line at the position
relating to the unit-resistance circle on the Smith Chart. For a 3:1
mismatch this position is exactly 30° rearward from the load, and has
a voltage reflection coefficient Vñ equal to 0.5 at -60°. The
normalized line resistance at this point is 1.1547 chart ohms, or
57.735 ohms on the 50-ohm line, for a line impedance of 50 - j57.735
ohms.

Placing a short-circuited stub having an inductive reactance of
+j57.735 ohms on the line cancels the line reactance, establishing a
new line impedance at this matching point of 50 + j0. However, a lot
more is involved than just canceling the reactances to establish the
impedance match. To begin, the stub generates a new, secondary,
canceling reflection that cancels the primary reflected wave generated
by the mismatched line termination.

Recall the voltage reflection coefficient Vñ of the line impedance
prior to placing the stub--Vñ = 0.5 at -60°. The corresponding current
reflection coefficient Iñ = 0.5 at +120°

We now look at the voltage reflection coefficient of the stub, which
is Vñ = 0.5 at +60°, and the corresponding current reflection
coefficient of the stub which is Iñ = 0.5 at -120°.

Observe that resultant angle of the voltage coefficients is 0° and
resultant angle of the current coefficients is 180°, all with the same
magnitude--0.5. It is well known that when these respective
coefficients exist at this point, the matching point, this condition
establishes a virtual open circuit to rearward traveling waves at this
point, prohibiting any further rearward travel of the reflected waves,
thus reversing their direction toward the load.

Consequently, the result is total re-reflection of the two sets of
reflected waves at the match point.

Now the question--what is the resultant voltage coefficient of
reflection at the match point? My position is that ñ = 1.0, which
indicates total reflection. However, I've been criticized on this
value, my critics saying that because this virtual open circuit was
established by wave interference, ñ cannot equal 1.0. They assert
that *ñ = 1.0 can be obtained only through a physical open circuit.

Reflection coefficient for total re-reflection
 

On Jun 12, 9:09*pm, walt wrote:
Sorry Cecil, I can't correlate a two-port configuration using S
parameters with the problem I have.

In a one-port analysis, virtual impedances cause reflections. In a two-
port analysis, only physical impedance discontinuities cause
reflections. As I see it, that is the entire problem in a nutshell.
You are using a one-port analysis for virtually :-) all of your
analyses, including your source analysis. Your detractors are trying
to talk you into using a two-port analysis.
--
73, Cecil, w5dxp.com

Reflection coefficient for total re-reflection
 

On Jun 13, 6:17*pm, Cecil Moore wrote:
On Jun 12, 9:09*pm, walt wrote:

Sorry Cecil, I can't correlate a two-port configuration using S
parameters with the problem I have.

In a one-port analysis, virtual impedances cause reflections. In a two-
port analysis, only physical impedance discontinuities cause
reflections. As I see it, that is the entire problem in a nutshell.
You are using a one-port analysis for virtually :-) all of your
analyses, including your source analysis. Your detractors are trying
to talk you into using a two-port analysis.
--
73, Cecil, w5dxp.com


Cecil, as I said earlier, I can't see any relation between a two-port
configuration and the tank circuit of an RF power amp. Why are you
pushing it? Can't you just tell me whether you agree that the
reflection coefficient at the output of the tank circuit is rho = 1.0
or not. If you don't believe it does, even though it re-reflects all
the reflected power incident on it, then please explain what you
believe the reflection coefficient is at this point.

Walt, W2DU

Reflection coefficient for total re-reflection
 

Cecil Moore wrote:
On Jun 13, 1:55*pm, K7ITM wrote:
*It doesn't make any sense to me to put a shorted
section of line in series with another line, so my confusion starts.

Tom, I didn't know initially that the example was in "Reflections
III". A series stub can be used instead of a loading coil on a wire
antenna. I had never seen a series stub used in such a manner on a
transmission line and that's why I was confused. I'm assuming that the
center conductor is broken and one side is connected to the inner
conductor and one side is connected to the braid on a stub, but I am
not sure that is correct. There's got to be a less complicated example
that we can use.
--
73, Cecil, w5dxp.com

Ah, OK. Now I understand what Walt meant... Though it's possible to
use a series stub on a transmission line, as you say, it's not all
that common in practice. I suppose that's why my mind wasn't going
there. Mea culpa. Perhaps now I can go back and look at Walt's
original question and make more sense out of it.

When a series stub is used in an antenna (as in a quarter-wave stub
coupling colinear half-waves), King points out that coupling from the
antenna fields to the wires in the stub, when the stub is an open-wire
line perpendicular to the axis of the half-waves, is an important
factor in how the stub operates to establish in-phase currents on the
adjacent half-waves... I see you made a comment about antenna
currents on the stub in John Smith's example, too.

Cheers,
Tom

Reflection coefficient for total re-reflection
 

On 6/13/2011 3:05 PM, Cecil Moore wrote:
On Jun 13, 3:08 pm, John wrote:
http://www.ittc.ku.edu/~jstiles/723/...b%20Tuning.pdf

Thanks John, but I would like to see the schematic for coax. Shirley,
one doesn't cut the braid and add a stub?
--
73, Cecil, w5dxp.com

LOL!

Never lose that sense of humor, love it!

--

Regards,
JS
“The Constitution is not an instrument for the government to restrain
the people, it’s an instrument for the people to restrain the
government.” -- Patrick Henry

Reflection coefficient for total re-reflection
 

walt wrote:
I have a question for W5DXP, KB7QHC, W7ITM and K0TAR relating to
transmission lines.This is not a trick question. This is a straight-
forward question for which I 'm dead serious. The answer will involve
a resulting reflection coefficient.

Assume a 50-ohm line terminated in a purely resistive 150-ohm load,
yielding a 3:1 mismatch with a voltage reflection coefficient Vñ equal
to 0.5 at 0°. We want to place a stub on the line at the position
relating to the unit-resistance circle on the Smith Chart. For a 3:1
mismatch this position is exactly 30° rearward from the load, and has
a voltage reflection coefficient Vñ equal to 0.5 at -60°. The
normalized line resistance at this point is 1.1547 chart ohms, or
57.735 ohms on the 50-ohm line, for a line impedance of 50 - j57.735
ohms.

Placing a short-circuited stub having an inductive reactance of
+j57.735 ohms on the line cancels the line reactance, establishing a
new line impedance at this matching point of 50 + j0. However, a lot
more is involved than just canceling the reactances to establish the
impedance match. To begin, the stub generates a new, secondary,
canceling reflection that cancels the primary reflected wave generated
by the mismatched line termination.

Recall the voltage reflection coefficient Vñ of the line impedance
prior to placing the stub--Vñ = 0.5 at -60°. The corresponding current
reflection coefficient Iñ = 0.5 at +120°

We now look at the voltage reflection coefficient of the stub, which
is Vñ = 0.5 at +60°, and the corresponding current reflection
coefficient of the stub which is Iñ = 0.5 at -120°.

Observe that resultant angle of the voltage coefficients is 0° and
resultant angle of the current coefficients is 180°, all with the same
magnitude--0.5. It is well known that when these respective
coefficients exist at this point, the matching point, this condition
establishes a virtual open circuit to rearward traveling waves at this
point, prohibiting any further rearward travel of the reflected waves,
thus reversing their direction toward the load.

Consequently, the result is total re-reflection of the two sets of
reflected waves at the match point.

Now the question--what is the resultant voltage coefficient of
reflection at the match point? My position is that ñ = 1.0, which
indicates total reflection. However, I've been criticized on this
value, my critics saying that because this virtual open circuit was
established by wave interference, ñ cannot equal 1.0. They assert
that ñ = 1.0 can be obtained only through a physical open circuit.

So I now ask you, am I correct in saying that the reflection
coefficient in this situation is 1.0? I'm holding my breath for your
answers.

Walt

OK, now that I understand the series stub configuration, I have to
ask: "the" reflection coefficient looking into WHAT? Looking back
toward the source in its feedline? Looking back toward the source but
including the series stub? Looking toward the load, including the
series stub?

The way I look at this problem is as a measurements person: once I
know where I'm looking, how will I measure the value of the reflection
coefficient? The way I would normally do it is with a network
analyzer. If I want to do it in the presence of significant power
coming from a source, I can set up directional couplers to allow me to
introduce a test signal (that I must be able to distinguish from the
power coming from the source) and observe the reflection.

You can also replace each piece of transmission line (including the
piece that's the stub) with an S-parameter two-port, and the source
and load as S-parameter one-ports, and apply standard S-parameter math
to see what the reflection coefficient is looking into any particular
port.

I suppose this is going to give you an answer different from the one
you're hoping for...but I believe it's consistent with the definitions
for linear system analysis that I've always used.

Consider the case of two identical sources generating the same signal
but 180 degrees out of phase. Each source is connected to a length of
transmission line, and the two lines are identical. Just for fun, the
line impedance equals the source impedance. The free ends of the
lines are connected in parallel and to a resistive load. Of course,
we find that the signals cancel and there is no power dissipated in
the load. Would we say that the reflection coefficient magnitude
looking back into either line toward the source is unity? I would
not! I would say it is zero, since any signal I send in that
direction is absorbed in the source. Note in this example that you
can disconnect the load and not change anything. Then you simply have
the signal from each source traveling to the other source and being
absorbed; if you put the sources on two different frequencies, you'll
see no standing wave for either frequency (though you'll have to
average for a while to be sure about that, if the frequencies are
close together). And note, please, that "absorbed" is not in general
the same thing as "dissipated."

Cheers,
Tom

Jackass 3D dvd Download The True Grit Film Online How To Download The Truth Download The Resident Movie Online Were Can I Watch Westbrick Murders The Movie Nude Nuns with Big Guns Film Review Tucker & Dale vs Evil Film For Sale Gulliver's Travels download movie The Spy Next Door film posters William & Kate Direct Download Kushti Downloading Hi-def Quality Your Highness Download Movie Good Intentions Hd

Reflection coefficient for total re-reflection
 

On Jun 12, 10:31*pm, walt wrote:
So I've got to
make the decision whether to delete my criticism of his equation or
leave it in and be accused of criticizing him incorrectly. What to do!

Personally, I didn't find anything wrong with parts 1 and 2. It's in
part 3 where Dr. Best gets lost. In an exchange on this newsgroup
before the article was published, he asserted that there was no
interference occurring at an impedance discontinuity on a transmission
line. When he published his component powers, he took into account
P1and P2 while completely ignoring (what I have dubbed) the component
powers, P3 and P4 in the opposite direction. He even invented
something like two phantom waves traveling forever in the direction of
total destructive interference while transporting energy but
completely canceling each other in the process, obviously a physical
impossibility.
--
73, Cecil, w5dxp.com

Reflection coefficient for total re-reflection
 

On Jun 14, 12:25*am, K7ITM wrote:
Cecil Moore wrote:
On Jun 13, 1:55*pm, K7ITM wrote:
*It doesn't make any sense to me to put a shorted
section of line in series with another line, so my confusion starts.

Tom, I didn't know initially that the example was in "Reflections
III". A series stub can be used instead of a loading coil on a wire
antenna. I had never seen a series stub used in such a manner on a
transmission line and that's why I was confused. I'm assuming that the
center conductor is broken and one side is connected to the inner
conductor and one side is connected to the braid on a stub, but I am
not sure that is correct. There's got to be a less complicated example
that we can use.
--
73, Cecil, w5dxp.com

Ah, OK. *Now I understand what Walt meant... *Though it's possible to
use a series stub on a transmission line, as you say, it's not all
that common in practice. *I suppose that's why my mind wasn't going
there. *Mea culpa. *Perhaps now I can go back and look at Walt's
original question and make more sense out of it.

When a series stub is used in an antenna (as in a quarter-wave stub
coupling colinear half-waves), King points out that coupling from the
antenna fields to the wires in the stub, when the stub is an open-wire
line perpendicular to the axis of the half-waves, is an important
factor in how the stub operates to establish in-phase currents on the
adjacent half-waves... *I see you made a comment about antenna
currents on the stub in John Smith's example, too.

Cheers,
Tom


Tom and Cecil,

My use of the series stub wasn't meant to be of practical use. I used
it only as a tool to explain a simple matching procedure. I used
series rather than parallel, because I wanted it to be simple to use
for those who are not as accustomed to admittance procedure as they
are with impedance. Sorry if I misled you.

Walt

Reflection coefficient for total re-reflection
 

On Jun 14, 12:25*am, K7ITM wrote:
Cecil Moore wrote:
On Jun 13, 1:55*pm, K7ITM wrote:
*It doesn't make any sense to me to put a shorted
section of line in series with another line, so my confusion starts.

Tom, I didn't know initially that the example was in "Reflections
III". A series stub can be used instead of a loading coil on a wire
antenna. I had never seen a series stub used in such a manner on a
transmission line and that's why I was confused. I'm assuming that the
center conductor is broken and one side is connected to the inner
conductor and one side is connected to the braid on a stub, but I am
not sure that is correct. There's got to be a less complicated example
that we can use.
--
73, Cecil, w5dxp.com

Ah, OK. *Now I understand what Walt meant... *Though it's possible to
use a series stub on a transmission line, as you say, it's not all
that common in practice. *I suppose that's why my mind wasn't going
there. *Mea culpa. *Perhaps now I can go back and look at Walt's
original question and make more sense out of it.

When a series stub is used in an antenna (as in a quarter-wave stub
coupling colinear half-waves), King points out that coupling from the
antenna fields to the wires in the stub, when the stub is an open-wire
line perpendicular to the axis of the half-waves, is an important
factor in how the stub operates to establish in-phase currents on the
adjacent half-waves... *I see you made a comment about antenna
currents on the stub in John Smith's example, too.

Cheers,
Tom


I'm sorry to have misled you in bringing up the series stub problem.
What I'm really concerned about is the reflection coefficient at the
output of the tank circuit of the RF power amp. Being non-dissipative
it cannot absorb the reflected power, so it must re-reflect it.
Therefore, my position is that its reflection coefficient rho = 1.0,
My critics say that a rho = 1.0 cannot be established when the virtual
short is caused by wave interference. However, if Best's Eq 8 is
valid, then why does it yield an incorrect answer when I plug in rho s
= 1, and rho a = 0.5, which gives 2 as the answer, instead of the
correct 1.1547 as the correct answer.

Now that I've narrowed the problem down, what do you believe is the
answer? Your answer will determine whether I need to delete the
pertinent paragraph from Chapter 25 in Reflections 3, in which I have
declared Best's Eq 8 invalid.

Walt

Walt