"Cecil Moore" wrote in message
...
Jim Kelley wrote:
Since rho represents the fraction of forward voltage that is reflected,
what does a negative value for rho indicate?

rho = +1 means there is a zero degree phase shift in the reflected
voltage.

rho = -1 means there is a 180 degree phase shift in the reflected voltage.

So in other word the sign sometimes indicates phase, and other times
indicates a direction in propagation depending on which hand is waving..
Thanks.

73, Jim AC6XG

Jim Kelley wrote:

"Cecil Moore" wrote:
rho = +1 means there is a zero degree phase shift in the reflected voltage.

rho = -1 means there is a 180 degree phase shift in the reflected voltage.

So in other word the sign sometimes indicates phase, and other times
indicates a direction in propagation depending on which hand is waving..
Thanks.

Consider the equation, rho = (ZL-Z0)/(ZL+Z0). If ZLZ0, then the
voltage reflection coefficient is positive and there is no reflected
voltage phase shift. If ZLZ0, then the voltage reflection coefficient
is negative and there is a 180 degree phase shift in the reflected
voltage. The same holds true for the E-field of reflected light.

The RF reflected current convention differs from the reflected light
H-field convention. Kirchhoff's current convention enters into the sign
of the reflected RF current where no such convention exists for light.
--
73, Cecil, W5DXP

Cecil Moore wrote:
Consider the equation, rho = (ZL-Z0)/(ZL+Z0). If ZLZ0, then the
voltage reflection coefficient is positive and there is no reflected
voltage phase shift. If ZLZ0, then the voltage reflection coefficient
is negative and there is a 180 degree phase shift in the reflected
voltage. The same holds true for the E-field of reflected light.

The above assumes ZL and Z0 to be real numbers. The light index
of refraction is usually a real number.
--
73, Cecil, W5DXP

Yes, Cecil. I have considered it, and I agree. It just bothers me when
people forget what the minus sign means, and try using it to make
unrealistic claims.

73, Jim AC6XG

Cecil Moore wrote:

Cecil Moore wrote:
Consider the equation, rho = (ZL-Z0)/(ZL+Z0). If ZLZ0, then the
voltage reflection coefficient is positive and there is no reflected
voltage phase shift. If ZLZ0, then the voltage reflection coefficient
is negative and there is a 180 degree phase shift in the reflected
voltage. The same holds true for the E-field of reflected light.

The above assumes ZL and Z0 to be real numbers. The light index
of refraction is usually a real number.
--
73, Cecil, W5DXP

Jim Kelley wrote:
Yes, Cecil. I have considered it, and I agree. It just bothers me when
people forget what the minus sign means, and try using it to make
unrealistic claims.

At least for real Z0's, it should be consistent. Wouldn't
a rho of 0.5 at 20 degrees would be the same as a rho of
-0.5 at 200 degrees?
--
73, Cecil, W5DXP

On Fri, 26 Sep 2003 12:53:50 -0500, Cecil Moore
wrote:
At least for real Z0's, it should be consistent. Wouldn't
a rho of 0.5 at 20 degrees would be the same as a rho of
-0.5 at 200 degrees?

Hi Cecil,

The Reflection Coefficient is a characteristic of the Load or Source,
not a value projected all along the line. This is the teaching of
Chipman that you undoubtedly speed-read past on your way to the
cut-and-paste opportunities you sought.

When are you going to ride your bike back to the library to fill all
these shortfalls of his teachings you so liberally sprinkle your
missives with?

73's
Richard Clark, KB7QHC

Richard Clark wrote:
The Reflection Coefficient is a characteristic of the Load or Source,
not a value projected all along the line. This is the teaching of
Chipman that you undoubtedly speed-read past on your way to the
cut-and-paste opportunities you sought.

For lossless transmission lines, |rho| = Sqrt(Pref/Pfwd). You don't
even need to know the load and/or source impedances.

When are you going to ride your bike back to the library to fill all
these shortfalls of his teachings you so liberally sprinkle your
missives with?

Just as soon as I am over my sinusitis and have a day off.
--
73, Cecil, W5DXP

Cecil Moore wrote in message ...
....
Wouldn't
a rho of 0.5 at 20 degrees would be the same as a rho of
-0.5 at 200 degrees?

Yes, and any other complex quantity would likewise be the same
expressed either way. But it would certainly be confusing to the
readers. It would be much better to stick with rectangular or with
polar and not mix them in the same quantity. Of course, sometimes one
is easier to work with, or offers more insight, than the other and
you're welcome to convert between them at any time.

Let's see if we can keep it more along the lines of 0.5 at 20 degrees
being (very nearly) the same as .4698+j.1710

Cheers,
Tom

No. The voltage reflection coefficient is the ratio of two voltages, and
has nothing to do with their directions. The reverse voltage wave is
always traveling toward the source. The forward voltage wave is always
traveling toward the load. The angle of the reflection coefficient is
the relative phases of these two at the point the reflection coefficient
is being evaluated. It makes sense to speak of the reflection
coefficient as having a "sign" only in the two special cases of zero and
180 degree angles. Otherwise, it has an angle, not a positive or
negative "sign".

The current reflection coefficient is a little more ambiguous because of
the freedom of defining which direction represents positive flow of Ir.
If Ir is defined to be positive toward the load (the more common
definition), then the current reflection coefficient, Ir/If = -Vr/Vf. If
it's defined to be positive toward the source, then Ir/If = Vr/Vf.

Roy Lewallen, W7EL

Jim Kelley wrote:
"Cecil Moore" wrote in message
...

Jim Kelley wrote:

Since rho represents the fraction of forward voltage that is reflected,
what does a negative value for rho indicate?

rho = +1 means there is a zero degree phase shift in the reflected

voltage.

rho = -1 means there is a 180 degree phase shift in the reflected voltage.


So in other word the sign sometimes indicates phase, and other times
indicates a direction in propagation depending on which hand is waving..
Thanks.

73, Jim AC6XG