Richard Harrison wrote:

Keith wrote:
"Can anyone provide a clear definition of forward and reflected powers?"

Power in the load = forward power - reflected power.

Finally. You have seen the light.

Once you know the value of Pload, you can pick any pair of numbers
for Pfwd and Pref satisfying the above relation and you now KNOW
Pfwd and Pref. This is about as useful as the concept gets.

Toss it away.

Stick with Vfwd and Vref; they always work. There is no need for
caveats like 'sort of works when Z0 is mostly real'. And you
won't be misled into questions like 'where does the reflected
power go?' and 'how does reflected power fry the final?'

....Keith

Keith wrote:
"Toss it away."

Terman and Bird Electronic Corporation say, Power in the load = forward
power - reflected power.

Having long successful experience with the Bird wattmeter, I`ll stick
with Terman and Bird.

Best regards, Richard Harrison, KB5WZI

wrote:
Stick with Vfwd and Vref; they always work.

On the contrary, from the results of Roy's calculations, it appears
that Vfwd and Vref cannot be used to predict total forward power and
total reflected power in a lossy line system.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Keith wrote:
"Stick to the incident and reflected voltage (or current) waves for
analysis. They work."

Bird Technical Series #1 may be enlightning:
"By proper combination of the two samples (derived from volts and amps)
we obtain an RF voltage proportional to the square root of main line
power---."

"---the scale which has been marked in watts corresponding to the power
being sampled from the main line."

With a little review of wave behavior on transmission lines (I like
Terman) in almost any good text, it is seen that voltage and current
continuously vary along a line containing a reflection. This results
from interference between the forward and reflected waves.

However, The power, forward or reflected, is free of the oscillations
produced in the volts and amps by interference between forward and
reflected waves. This steady power flow makes power the electrical
property to measure and this was the impetus for the Bird wattmeter.
It`s been around for about 50 years, and I`d wager it will be around for
another 50 years.

Best regards, Richard Harrison, KB5WZI

Whichever nitwit of a Ph.D invented imaginary 'power waves' should be made
to provide a complete mathematical treatise, an indisputable proof of their
existence, before going to bed on his wedding night.

Roy Lewallen wrote:
So, I'll let you play with whatever mysterious equations you use to
predict those two quantitites, whatever they are and whatever they mean
to you, and I'll settle for just knowing all the voltages, currents,
impedances, and powers.

Point was that your fP didn't represent the total forward power
and resulted in the false conclusion that reflected power was greater
than forward power. If the total average Poynting vector points toward
the load, it is impossible for the total reflected power to be greater
than the total forward power.
--
73, Cecil, W5DXP

Yep, I restricted my definition of "forward power" fP to the same one
you've always used -- the average power calculated from the forward V
and I. And the "reverse power" rP to the same one you've always used
-- the average power calculated from the reverse V and I. (It's what
you've been calling the "power in the forward wave" and "power in the
reverse wave" respectively.) And then, using those definitions of yours,
I showed in the analysis that the "forward power" can be less than the
"reverse power", while still delivering net power to the load. Cool, huh?

Fact is, I'm not having any trouble at all resolving this. But then I
don't have any investment in the notion of waves of average power
bouncing around on a line.

Roy Lewallen, W7EL

Cecil Moore wrote:
Roy Lewallen wrote:

So, I'll let you play with whatever mysterious equations you use to
predict those two quantitites, whatever they are and whatever they
mean to you, and I'll settle for just knowing all the voltages,
currents, impedances, and powers.


Point was that your fP didn't represent the total forward power
and resulted in the false conclusion that reflected power was greater
than forward power. If the total average Poynting vector points toward
the load, it is impossible for the total reflected power to be greater
than the total forward power.
--
73, Cecil, W5DXP

Amen.

Roy Lewallen, W7EL

wrote:
Richard Harrison wrote:

Keith wrote:
"Can anyone provide a clear definition of forward and reflected powers?"

Power in the load = forward power - reflected power.


Finally. You have seen the light.

Once you know the value of Pload, you can pick any pair of numbers
for Pfwd and Pref satisfying the above relation and you now KNOW
Pfwd and Pref. This is about as useful as the concept gets.

Toss it away.

Stick with Vfwd and Vref; they always work. There is no need for
caveats like 'sort of works when Z0 is mostly real'. And you
won't be misled into questions like 'where does the reflected
power go?' and 'how does reflected power fry the final?'

...Keith

Roy Lewallen wrote:
I showed in the analysis that the "forward power" can be less than the
"reverse power", while still delivering net power to the load. Cool, huh?

Actually pretty uncool. That's what happens when you don't deal with total
average powers. You can come up with apparent violations of the conservation
of energy principle that don't actually exist in reality. Your "forward
power" is simply not all of the forward power. Just as explained in Dr. Best's
QEX article, the constructive/destructive interference terms must also be
taken into account.
--
73, Cecil, W5DXP

Roy Lewallen wrote:
The "apparent" violation is entirely in your own mind.

You claim that the reflected power is greater than the forward
power while at the same time the Poynting vector points toward
the load. That's an obvious contradiction which can be remedied
simply by collecting like terms.
--
73, Cecil, W5DXP