"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

"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.

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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"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

"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.

"David Robbins" wrote in message ...

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.


Please post this derivation again.

When they say "ideal line" do they mean purely real?


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.

Not at all really. The impedance seen by the load can be from
either a source or a source hooked up with a transmission line. It
doesn't matter with this equation.


As Reg points out about the normal equation:


"Dear Dr Slick, it's very easy.

Take a real, long telephone line with Zo = 300 - j250 ohms at 1000 Hz.

Load it with a real resistor of 10 ohms in series with a real
inductance of
40 millihenrys.

The inductance has a reactance of 250 ohms at 1000 Hz.

If you agree with the following formula,

Magnitude of Reflection Coefficient of the load, ZL, relative to line
impedance

= ( ZL - Zo ) / ( ZL + Zo ) = 1.865 which exceeds unity,

and has an angle of -59.9 degrees.

The resulting standing waves may also be calculated.

Are you happy now ?"
---
Reg, G4FGQ



Well, i wasn't happy, because how can you have a R.C. greater than
one into a passive network??? Quite impossible.

But, if you use the conjugate formula, the R.C. will indeed be
less than one.

Convince yourself.


Slick

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

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.


Please post this derivation again.

sorry, i don't have time for this. its really quite simple, just apply
kirchoff's and ohm's laws at the connection point and it falls right out.


When they say "ideal line" do they mean purely real?

yes, purely real with no loss terms.



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.

Not at all really. The impedance seen by the load can be from
either a source or a source hooked up with a transmission line. It
doesn't matter with this equation.


the reference you gave is looking at a generator connected to a load. true,
it doesn't matter if there is a transmission line in between the generator
and the 'load' but the impedance being used is the one transformed back to
the generator end of the line, not the one at the far end of the line... so
basically that equation is not a transmission line equation, it is a
generator to load reflection calculation done to maximize power not to
satisfy kirchoff.

On Tue, 26 Aug 2003 22:35:29 -0000, "David Robbins"
wrote:
the reference you gave is looking at a generator connected to a load. true,
it doesn't matter if there is a transmission line in between the generator
and the 'load' but the impedance being used is the one transformed back to
the generator end of the line, not the one at the far end of the line... so
basically that equation is not a transmission line equation, it is a
generator to load reflection calculation done to maximize power not to
satisfy kirchoff.

Hi David,

If it is time invariant (linear), it doesn't matter.

73's
Richard Clark, KB7QHC