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! =-----

Cecil Moore wrote:

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.

Of course if you let go of Pfwd and Pref and just used Vfwd and Vref
you would quickly learn that you had no interest in Pfwd and Pref
and thus your inability to determine them would not cause you
much distress.

Which is good since it will turn out that there is no value in
forward and reverse power on a line with non-real Z0.

....Keith

wrote:
Of course if you let go of Pfwd and Pref and just used Vfwd and Vref
you would quickly learn that you had no interest in Pfwd and Pref
and thus your inability to determine them would not cause you
much distress.

Uh Keith, radiated *POWER* is what we are trying to get from our
antennas.
--
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! =-----

Cecil Moore wrote:

wrote:
Of course if you let go of Pfwd and Pref and just used Vfwd and Vref
you would quickly learn that you had no interest in Pfwd and Pref
and thus your inability to determine them would not cause you
much distress.

Uh Keith, radiated *POWER* is what we are trying to get from our
antennas.

Yes indeed. Net power. The only power that counts.
Pnet = average( v(t) * i(t) )

Forget that forward and reverse stuff. That's not what is radiated.

....Keith

wrote:
Forget that forward and reverse stuff. That's not what is radiated.

Uh Keith, power delivered to the antenna equals forward power minus
reflected power. I notice you have not provided a way for standing
waves to develop without the existence of reflected waves. Do you
also believe that standing waves don't exist?
--
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:
"---it will turn out that there is no value in forward and reverse power
on a line with non-real Zo."

The Bird wattmeter works well enough on coax lines used between the
usual transmitter and antenna. Loss produces reactance in coax. We don`t
seek lossy coax. If it becomes lossy, the line is likely to be replaced.

If a transmitter isn`t matched when the load is matched to the coax, an
improved match between the transmitter and the coax may come from
mismatching the load.

A true conjugate match exists everywhere in the system between the
transmitter and the antenna. That is, one could check the impedances in
both directions at any place in the system and find that the two
inpedances are conjugates of each other.

There is reactance in every non-resonant length of coax which is not
terminated in its characteristic impedance value.

The vector sum of the incident and reflected wave voltages is less than
the arithmetic sum at a point 1/8 wavelength back from the reflection
point. At 1/8 wavelength back from a reflection, the incident and
reflected wave voltage vectors are 90-degrees apart. At 1/8 wavelength
in coax, the reactance is numerically equal to the Zo of the line, as a
piece of trivia.

At 1/4 wavelebgth back from the reflection, the incident and reflected
wave voltage vectors are 180-degrees apart. The line voltage total is
thus the arithmetic difference of the incident and reflected wave
voltages.

At 1/2 wavelength back from the reflection, the incident and reflected
wave phases have continued their phase changes in opposite directions
with distance back from the reflection until the voltages have reached
the in-phase condition. In a lossless line, the conditions at the
reflection point would be repeated at a point 1/2-wavelength back.

When a resistance load matches the Zo of its feedline, the reflection
coefficient is zero, so there is no reflection from the load. The load
absorbs all the incident wave. The effect of a reactive load is merely
to displace the positions of the minima and maxima along the line but
not with respect to each other.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

Keith wrote:
"---it will turn out that there is no value in forward and reverse power
on a line with non-real Zo."

The Bird wattmeter works well enough on coax lines used between the
usual transmitter and antenna. Loss produces reactance in coax. We don`t
seek lossy coax. If it becomes lossy, the line is likely to be replaced.

You, of course, are correct. I overstate the case slightly in
an attempt to get readers to let go of their model. Once they
are free of forward and reverse power as being an accurate
model of reality, they are then free to understand what a
Bird really indicates.

And it is useful for lines with near real impedances (as many
RF lines are) as a TLI. And in cases where reflected power is
near zero, it will even give a hint as to how much power is
being delivered to the load (within 5% of full scale).

The question is, does the reader understand how it works,
why it is useful and its limitation; or does the reader
believe the markings on the scale and think that it is
actually MEASURING the power in a forward and reverse
wave.

....Keith

Keith wrote:
"---does the reader believe the markings on the scale and think that it
is actually MEASURING the power in a forward and reverse wave?"

The wattmeter markings have been calibrated to indicate watts. One only
must measure a quantity proportional to watts then interpret that
accurately.

A speedometer indicates miles per hour but gets that from electricity
which is proportional to speed. Neither miles nor hours are measured.

Best regards, Richard Harrison, KB5WZI