Owen Duffy wrote:
You assertion that you have travelling forward and reflected power waves
on the transmission line runs into a problem when you try to analyse the
combination of both at a point (eg the input to the line) as power
doesn't combine vectorially.

But it does combine according to the following formula
which is the irradiance equation from the field of
optics.

Ptot = P1 + P2 + 2*SQRT(P1*P2)cos(A)

where 'A' is the angle between V1 and V2 and V1 is
the voltage associated with P1 and V2 is the voltage
associated with P2.

The first time I saw this equation was in Dr. Best's
Nov/Dec 2001 QEX article on Transmissions Lines. It
really does work for "adding" the two powers in two
coherent waves.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote in
:

Owen Duffy wrote:
You assertion that you have travelling forward and reflected power
waves on the transmission line runs into a problem when you try to
analyse the combination of both at a point (eg the input to the line)
as power doesn't combine vectorially.

But it does combine according to the following formula
which is the irradiance equation from the field of
optics.

Ptot = P1 + P2 + 2*SQRT(P1*P2)cos(A)

where 'A' is the angle between V1 and V2 and V1 is
the voltage associated with P1 and V2 is the voltage
associated with P2.

Cecil,

A is not a property of P1 or P2, and cannot be derived from them. I
maintain that you cannot vectorially combine P1 and P2.

Owen

Owen Duffy wrote:
A is not a property of P1 or P2, and cannot be derived from them. I
maintain that you cannot vectorially combine P1 and P2.

P1 is a property of V1^2/Z0, A is a property of V1.
P2 is a property of V2^2/Z0, A is a property of V2.
There is an unbroken chain of cause and effect.
It is true that one cannot directly vectorially
combine P1 and P2 because P1 and P2 are not vectors.

However, the ability to combine the P1 and P2 of
coherent EM waves dates back to before you were born.
Optical engineers didn't have the luxury of being
able to measure the phase angles. All they could
measure was the total amplitude. Please don't try
to tell us that their total amplitude measurements
were wrong throughout the 20th century and are
still wrong in the 21st century.

The rules for combining P1 and P2 when they are
coherent are known as the irradiance equations in
optics. Dr. Best applied them to RF quantities.
Please reference "Optics", by Hecht, 4th edition,
page 388 and Dr. Best's, "Wave Mechanics of Transmission
Lines, Part 3: ..." in the Nov/Dec 2001 issue of "QEX".
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote in news:wnIEh.2899$8x.278
@newssvr14.news.prodigy.net:

Owen Duffy wrote:
A is not a property of P1 or P2, and cannot be derived from them. I
maintain that you cannot vectorially combine P1 and P2.

....
It is true that one cannot directly vectorially
combine P1 and P2 because P1 and P2 are not vectors.

Thanks

....

Owen Duffy wrote:
Cecil Moore wrote in news:wnIEh.2899$8x.278
It is true that one cannot directly vectorially
combine P1 and P2 because P1 and P2 are not vectors.

Thanks

That doesn't mean that there are not valid rules for
combining P1 and P2. Optical engineers have been doing
it for decades. RF engineers seem to lag behind.

You seemed to be questioning the validity of the power
combination equation. Have you changed your mind?
--
73, Cecil http://www.w5dxp.com