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Old August 25th 03, 04:00 AM
W5DXP
 
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Dr. Slick wrote:
Cecil, email me privately and i will send you the paper. He calls
the voltage reflection coefficient the "power wave reflection
coefficient". And then squares this to get the "power reflection
coefficient".

It's really a bad nomenclature, and no wonder there is confusion.


I agree, it is bad nomenclature. He should have called it the amplitude
or voltage reflection coefficient, the square of which is the power
reflection coefficient.
--
73, Cecil http://www.qsl.net/w5dxp



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Old August 25th 03, 12:36 PM
David Robbins
 
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"Dr. Slick" wrote in message
om...
"David Robbins" wrote in message

...
"Dr. Slick" wrote in message
om...

[s]**2 = [(ZL - Zo*) / (ZL + Zo)]**2 the "power reflection
coefficent".

Note the squares.

yes, please do note the squares.... and remember, just because

[s]**2 = [(ZL - Zo*) / (ZL + Zo)]**2
does NOT mean that
s = (ZL - Zo*) / (ZL + Zo)

this is the one big trap that all you guys that like to use power in

your
calculations fall into. just because you know the power doesn't mean

that
you know squat about the voltage and current on the line. you can not

work
backwards. that is why it is always better to work with voltage or

current
waves and then in the end after you have solved all those waves you can
always calculate power if you really need to know it.



yes, but he does say that s = (ZL - Zo*) / (ZL + Zo) , first.

But he foolishly calls it a "power wave R. C."

Then he squares the magnitudes [s]**2 = [(ZL - Zo*) / (ZL +
Zo)]**2

And calls this the "power R. C."


The bottom label is fine, we've all see this before, as the ratio
of the RMS incident and reflected voltages, when squared, should give
you the ratio of the average incident and reflected powers, or the
power R. C.


But to call the voltage reflection coefficient a "power wave R.
C."
is really foolish, IMO.


Slick


i don't know what he is refering to as the 'power wave rc' but its not the
voltage or current reflection coefficient, they do not have a conjugate in
the numerator.



  #83   Report Post  
Old August 25th 03, 03:43 PM
Tarmo Tammaru
 
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Richard,

Thanks. *Really* sharp guy. Must be 90 years old by now.

Tam/WB2TT
"Richard Clark" wrote in message
...
On Sun, 24 Aug 2003 12:57:36 -0400, "Tarmo Tammaru"
wrote:


"Richard Clark" wrote in message
.. .
Chipman also discusses the relevancy of the characteristic Z of a
source to SWR, which is tucked away in the unread part. ;-)

73's
Richard Clark, KB7QHC


Richard,

There used to be a Dr. Chipman who taught a fields/waves course at the
University of Toledo (OH) in the 60s. Do you know if it is the same guy?

Tam/WB2TT


Hi Tam,

According to the front cover, one in the same.

73's
Richard Clark, KB7QHC



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Old August 25th 03, 03:52 PM
W5DXP
 
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David Robbins wrote:
i don't know what he is refering to as the 'power wave rc' but its not the
voltage or current reflection coefficient, they do not have a conjugate in
the numerator.


And since the power reflection coefficient (Reflectance) is simply the
square of the voltage (amplitude) reflection coefficient, presumably
neither would it. There is no conjugate in these equations in the field
of optics.
--
73, Cecil http://www.qsl.net/w5dxp



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  #86   Report Post  
Old August 25th 03, 08:17 PM
Dr. Slick
 
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"David Robbins" wrote in message ...

i don't know what he is refering to as the 'power wave rc' but its not the
voltage or current reflection coefficient, they do not have a conjugate in
the numerator.



Incorrect. You need the conjugate in the numerator if the Zo is
complex. If it is purely real, WHICH MOST TEXTS ASSUME, then you can
use the normal equation.

Look he

http://www.zzmatch.com/lcn.html

And look up Les Besser's notes on the Fundamentals of RF.


Slick
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Old August 25th 03, 08:18 PM
Dr. Slick
 
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W5DXP wrote in message ...
Dr. Slick wrote:
Cecil, email me privately and i will send you the paper. He calls
the voltage reflection coefficient the "power wave reflection
coefficient". And then squares this to get the "power reflection
coefficient".

It's really a bad nomenclature, and no wonder there is confusion.


I agree, it is bad nomenclature. He should have called it the amplitude
or voltage reflection coefficient, the square of which is the power
reflection coefficient.


Agreed. I will send you the paper.


Slick
  #89   Report Post  
Old August 25th 03, 08:35 PM
David Robbins
 
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"Dr. Slick" wrote in message
om...
"David Robbins" wrote in message

...

i don't know what he is refering to as the 'power wave rc' but its not

the
voltage or current reflection coefficient, they do not have a conjugate

in
the numerator.



Incorrect. You need the conjugate in the numerator if the Zo is
complex. If it is purely real, WHICH MOST TEXTS ASSUME, then you can
use the normal equation.


sorry, the derivation for the table in the book i sent before is for the
general case of a complex Zo. they then go on to simplify for an ideal line
and for a nearly ideal line... nowhere does a conjugate show up.

and that reference you give is not for a load on a transmission line, it is
talking about a generator supplying power to a load... a completely
different animal.



  #90   Report Post  
Old August 26th 03, 12:24 AM
Roy Lewallen
 
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Dan wrote:
Now that the various typo mistakes have been corrected, and putting
aside for the moment the name calling and ad hominem arguments, could
it be that _both_ sides in this discussion are correct? Camp 'A' says
that the reflection coefficient is computed the classical way, without
using Zo conjugate, and offers various mathematical proofs and
discussions of infinitely long lines. Camp 'B' says the reflection
coefficient is computed with Zo* (Zo conjugate) in the numerator, and
offers explanations dealing with the conservation of energy and
maximum transfer of power.


No one from "Camp B" has given any justification for the assumption that
the condition for minimum reflection is the condition for maximum power
transfer. We're lacking either a proof, a derivation from known
principles, or even a numerical example. I maintain that this assumption
is false.

Likewise, there's no evidence that the conventional and universally
accepted (within the professional community) formula for reflection
coefficient violates the conservation of energy. If it did, it would
have been shown to be in error long ago.

Both sides may be correct since they are talking about _two different_
meanings for the term "reflection coefficient." One has to do with
voltage (or current) traveling waves and the other has to do with
power. . .


Perhaps. Yet both groups have used it as though it's a voltage
reflection coefficient, and as justification for statements made about
the reflection of voltage waves.

If people want to argue about the reflection of power waves, I'll gladly
bow out and let Cecil and his colleagues resume their interminable
arguments without me. If anyone wants to discuss voltage or current
waves, I'll try to continue to contribute, as long I don't have to deal
with Slick and the insults he uses in place of supporting evidence.

. . .


So, it seems to me, everybody can agree as long as it is understood
that there are different meanings for the term "reflection
coefficient." One meaning, and its mathematical definition, applies
to voltage or current waves. The other, with a slightly different
mathematical definition, applies to the power transfer from a line to
a load. They are one and the same only when the reactive portion of
Zo (Xo) is ignored. It may or may not be acceptable to do so,
depending on the attenuation of the line and the frequency. Lossy
lines and lower frequencies yield more negative values for the Xo
component of Zo.


I suggest that those who are using "reflection coefficient" as meaning
the ratio of reflected to forward power so state, and restrict their
conclusions dervived from it to power waves.

. . .


Roy Lewallen, W7EL



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