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Old August 24th 03, 05:33 PM
Richard Clark
 
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On Sun, 24 Aug 2003 12:22:34 +0100, "Ian White, G3SEK"
wrote:

[*] Well-known to some college students in the USA, perhaps? I'd never
heard of him, but Dan's summary suggests this book might be worth
looking for.


Hi Ian,

Any university student in course work relating to Transmission lines
would have a copy. It comes from a successful line of tutorials known
as "Schaum's Outlines."

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

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Old August 24th 03, 05:45 PM
Richard Clark
 
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On Sun, 24 Aug 2003 11:26:00 -0500, "William E. Sabin"
[email protected] wrote:

Richard Clark wrote:


To date their best argument is you cannot possibly know
that value (for any of a variety of reasons, unrelated to simply
sitting down at the bench and measuring an actual value). In short,
institutionalized ignorance, embraced with a mystic missionary zeal,
is their crowing logic.


The problem lies in the difficulty of measuring or
calculating Zs, especially for signals that have
large variations in amplitude, such as SSB.

There is no institutionalized ignorance, just a
lot of skepticism regarding the reliability of the
analysis methods and the measurement methods.

Bill W0IYH


Hi Bill,

If the best that skeptics can offer to methods described and data
obtained are "it's not important" or "the time is not justified going
there;" then that is not a particularly high bar of excellence in
reasoning and remains thinly veiled institutionalized ignorance.

Or call it intellectual glaciation, the insurmountable obstacles plea
as argument defending naysaying is frayed and time worn. This is all
"special engineering olympics" caliber justification. Perhaps the
correspondents who enter into these debates should have their
handicaps posted somewhere so the odds makers could weigh the risks of
following such gold medal champions.

73's
Richard Clark, KB7QHC
  #63   Report Post  
Old August 24th 03, 05:57 PM
Tarmo Tammaru
 
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"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


  #65   Report Post  
Old August 24th 03, 07:25 PM
Dr. Slick
 
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(Dan) wrote in message . com...

From Kurokawa, "Power Waves and the Scattering Matrix," IEEE
Transactions on Microwave Theory and Techniques, March 1965:

Section 2, explanation of and mathematical definition of the concept
of "power waves," explicitly noted by the author to be distinct from
the more commonly discussed voltage and current traveling waves.

Section 3, definition of the reflection coefficient [for power waves]:
s = (ZL - Zo*) / (ZL + Zo)
with a footnote "[Only w]hen Zo is real and positive this is the
voltage wave reflection coefficient." Kurokawa takes pains to make it
clear that his "s" power wave reflection coefficient is not the same
as the (usually rho or Gamma) voltage wave reflection coefficient.


I've got the same paper. It's a bit confusing, because then he
calls

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

Where if you take the square root to the power reflection
coefficient, you should get the voltage r. c.

So perhaps s = (ZL - Zo*) / (ZL + Zo) really IS the voltage R.
C., even in this paper!





Section 9, comparison with [voltage and current] traveling waves:
"... since the [voltage or current] traveling wave reflection
coefficient is given by (ZL - Zo) / (ZL + Zo) [note no conjugate] and
the maximum power transfer takes place when ZL=Zo*, ... it is only
when there is a certain reflection in terms of [voltage or current]
traveling waves that the maximum power is transferred from the line to
the load."



Perhaps he is confused on this point, because he previously
stated:

"When the matching condition (4) is satisfied , the power
reflection
coefficient becomes zero, as expected."

Condition (4) is the Zl=Zo*, which is also called the conjugate
matched condition for maximum power delivered to the load.

It's only when you have a simultaneous conjugate match with a
transistor, that you get the max gain.



So Kurokawa agrees with Chipman concerning the condition for maximum
power transfer. Kurokawa also defines two different reflection
coefficients, both in the same paper.


Again, you failed to mention that he defined:

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

Note the squares.


Copy of the Kurokawa paper, in pdf format, available on request
via
private email.


Slick


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Old August 24th 03, 09:07 PM
David Robbins
 
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"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.




  #69   Report Post  
Old August 24th 03, 09:36 PM
W5DXP
 
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Peter O. Brackett wrote:
s11 is a reflection coefficient that has the special condition that
a2 must be equal zero. When a2 is not equal zero, the s11 reflection
coefficient and the apparent reflection coefficient (rho) are not the same.


No! The scattering paramters, e.g for a two-port the s11, s12, s21 and s22
are all parameters fixed by the network and are not dependent upon either
the independent or dependent variables! i.e. b1 = s11*a1 + s12*a2, and b2
= s21*a1 + s22* a2.


I'm sorry, Peter, but you probably misunderstood me. s11 cannot possibly
be the same as 'rho' when a2=100 watts.

s11 = b1/a1 when a2=0.

b1 is equal to something else if a2 is not zero.

rho = Sqrt(Pref/Pfwd)

These do NOT have to be the same values. That's all I was saying.
--
73, Cecil http://www.qsl.net/w5dxp



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Old August 24th 03, 09:39 PM
W5DXP
 
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Peter O. Brackett wrote:
Only the "electricals" the v and I are "real"! The "waves" the a and b are
just different manifestations of v and i as viewed through and instrument
[reflectometer] using a, perhaps arbitrary, reference impedance, or matrix
transformation.

Sorry Cecil. :-)


Sorry Peter, quantum physics disagrees with you. It's the electrons,
photons, and virtual photons that are real. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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