Standing-Wave Current vs Traveling-Wave Current
 

Yuri Blanarovich wrote:
"Dave" wrote in message
news:cwPbj.1073$ML6.117@trndny04...

you can do it when it makes physical sense. it does not make sense in
standing waves for all the obvious reasons that i have pointed out. it
does make sense in the individual traveling waves. just accept what your
little swr meter tells you, it shows the forward power and reflected
power, that is all you need and the only powers that make sense.


Little SWR meter shows forward AND reflected power in one direction, and
reflected power only in reverse direction. Why is the Bird wattmeter
calibrated in Watts, measuring power (forward and reverse) and has chart to
calculate SWR, when there are no standing waves and no power in them?
Laying waves or sitting waves???

Seems to me that the PROBLEM is that some consider standing wave to be some
imaginary, stopped, frozen wave, no good, while some of us consider standing
wave to be the result of superposition of forward and reverse waves, that
can be (their components) measured, current heats when flowing through
resistance, voltage "burns" when poor dielectric.
Like there is standing wave current, but no standing wave, huh????
Or are we forgetting that we are dealing with electromagnetic waves?
Can someone sort out the terminology and definitions?

Yuri, K3BU



Hi, Yuri,
Cecil and Dave aren't taking resistance into account when they
talk about waves. In other words, they're not writing about real
transmission lines, coils, and such. The only lines they care about are
the ones in their minds: the simple ones where the attenuation constants
are always zero, and current and voltage are always either in phase, or
90 degrees out of phase, and there is never any dielectric breakdown, no
matter the voltage. You can only feel sorry for guys like that.
73,
Tom Donaly, KA6RUH

Standing-Wave Current vs Traveling-Wave Current
 

"Tom Donaly" wrote in message
. net...
Yuri Blanarovich wrote:
"Dave" wrote in message
news:cwPbj.1073$ML6.117@trndny04...

you can do it when it makes physical sense. it does not make sense in
standing waves for all the obvious reasons that i have pointed out. it
does make sense in the individual traveling waves. just accept what
your little swr meter tells you, it shows the forward power and
reflected power, that is all you need and the only powers that make
sense.


Little SWR meter shows forward AND reflected power in one direction, and
reflected power only in reverse direction. Why is the Bird wattmeter
calibrated in Watts, measuring power (forward and reverse) and has chart
to calculate SWR, when there are no standing waves and no power in them?
Laying waves or sitting waves???

Seems to me that the PROBLEM is that some consider standing wave to be
some imaginary, stopped, frozen wave, no good, while some of us consider
standing wave to be the result of superposition of forward and reverse
waves, that can be (their components) measured, current heats when
flowing through resistance, voltage "burns" when poor dielectric.
Like there is standing wave current, but no standing wave, huh????
Or are we forgetting that we are dealing with electromagnetic waves?
Can someone sort out the terminology and definitions?

Yuri, K3BU

Hi, Yuri,
Cecil and Dave aren't taking resistance into account when they
talk about waves. In other words, they're not writing about real
transmission lines, coils, and such. The only lines they care about are
the ones in their minds: the simple ones where the attenuation constants
are always zero, and current and voltage are always either in phase, or
90 degrees out of phase, and there is never any dielectric breakdown, no
matter the voltage. You can only feel sorry for guys like that.
73,
Tom Donaly, KA6RUH

using any decent coax of a reasonable length and typical amateur power
levels the assumptions we have stated are very close to the actual results.
if you want to examine lossy lines in detail then go ahead, the formulas get
much messier and without proper formula rendering on a newsgroup they are
almost impossible to discuss... and for the concepts that have been proposed
the ideal lossless line case is perfectly acceptable.

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
On Dec 24, 11:18 am, "Dave" wrote:
"Keith Dysart" wrote in message

...

Can you kindly articulate the rules you use to know
when it is appropriate to use P = V * I?
it is extremely simple. use traveling waves then V*I works everywhere all
the time. use standing waves and it fails. period, end of story.

What happens on a line that is terminated in a real
impedance that is not equal to Z0?

There are aspects of both travelling waves and
standing waves present on the line.

Is it appropriate to use P = V * I?

...Keith

And from an earlier post, Keith wrote

"Are you really saying that if I measure the instantaneous
voltage and the instantaneous current then I can NOT multiply
them together to obtain the instantaneous power?

It certainly works some of the time.

If I can not do it all the time, when can I do it?"

You give a good example Keith. It would be correct for measurement at
the load and at every point 1/2 wavelength back to the source from the
load, because the standing wave has the same measurements at these
points. At the 1/4 wavelength point back from the load and every
successive 1/2 wave point back to the source, the equation would also be
correct as demonstrated in Roy's example earlier today.

Excepting for these points, we would also be measuring a reactive
component that could be described as the charging and discharging of the
capacity or inductive component of the transmission line. (Imagine that
we are measuring the mismatched load through a 1/8 wave length long
transmission line, using an Autek RX VECTOR ANALYST instrument) The
inclusion of this reactive component would invalidate the power reading
if we were assuming that the measured power was all going to the load.

I would visualize the situation by saying that at the points mentioned,
the peaks of the traveling waves match as they pass each other going in
opposite directions each cycle. At all other points, the matching is
peak of one plus part of the second, so that the resulting measurement
can always be described as containing a quadrature (or reactive) component.

73, Roger, W7WKB

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
I am having great difficulty matching the words you
wrote with the request for an unambiguous definition
of "standing wave power".

Are you saying the concept is meaningless?
Or do you think you provided a definition?

"Standing wave power" is an oxymoron. There is simply
zero power in standing waves. The dot product of the
net voltage and net current in an ideal standing wave
is always ZERO.

Power (watts) is the measure of energy (joules) passing
a measuring point in one second. One can measure the
forward power. One can measure the reflected power. One
cannot measure any standing wave power because it is
always equal to (Pfor - Pref) which for ideal standing
waves is *always* zero.

If the net energy flow is zero, as it is in ideal standing
waves, the power is zero, by definition, because zero net
joules are flowing. And, sure enough, the standing wave
voltages phasors are *always* 90 degrees away from the
standing wave current phasors and they are not moving left
or right. They are rotating around a fixed spacial point
on the wire.

Standing waves are a very sophisticated illusion.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
And if I had meant *NET* I would have written "net".

Since you are talking about *NET* voltage, *NET*
current, *NET* energy, and *NET* power, don't you
think it would be wise to use the word *NET* (unless
your motive is to obscure)?

Since Pfor = Pref, then Pfor - Pref = 0

Isn't that superposition of power? Something that
most agree is not a legal operation.

No, that is simply an accepted engineering convention
that has been around since long before you and I
were born.

PLoad = (+Pfor) - (+Pref)

The negative sign doesn't mean negative power. It is
simply a directional convention for the Poynting vector
that indicates the direction of energy flow.

A negative sign is often used to denote direction (or
a 180 degree shift).

Dollars going into your bank account and coming out of
your bank account are all the same scalar dollars. The
direction in which they are flowing is denoted by a
plus or minus sign.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
On Dec 24, 11:50 am, "Yuri Blanarovich" wrote:
Why is the Bird wattmeter
calibrated in Watts, measuring power (forward and reverse) and has chart to
calculate SWR, when there are no standing waves and no power in them?

Why indeed? The decision of Bird Electronic to build
an instrument that measured actual line voltage and
current and then compute forward or reverse voltage
but display the result in watts has lead to enormous
confusion about the nature of forward and reverse
waves.

If only they had decided to display forward or
reverse volts, life would be much better. People
would not have internalized "forward and reverse
power" to such a degree.

On the other hand, it would have then required
more arithmetic to compute actual power.

But they did it, and it can not be undone.

Do you have an unambiguous definition of "standing
wave power" that can be used?

...Keith

Hi Keith,
When you take the real part of P = VI*, where
I* is the complex conjugate of the current, you're computing
the power in the transmission line. However, the imaginary
part of VI* doesn't disappear, and you should be aware of
its existence if you're going to put a lot of energy into
said line (unless it's a perfect Cecil//Dave line with no
attenuation etc). Yuri is probably arguing from experience
with real lines. Cecil/Dave are arguing from an idealized,
but flawed understanding of the subject. All of them should
go back to school and study the whole elephant, so they won't
keep making the same mistakes the three blind men made.
73,
Tom Donaly, KA6RUH

Standing-Wave Current vs Traveling-Wave Current
 

Dave wrote:
... today there are better things to do, like scrape ice

Dave, you really should get a self-defrosting refrigerator
so you won't have to scrape ice ever again. :-)
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Cecil Moore wrote:
Gene Fuller wrote:
This photonic limitation is something that exists only in your head.

Good Grief, Gene, I don't have time to teach you
quantum electrodynamics. Go read a book that tells
you about the nature of photons. It is also the
cornerstone of relativity.

Cecil, you couldn't teach anyone quantum electrodynamics if
they put a gun to your head. Quit pretending.
73,
Tom Donaly, KA6RUH

Standing-Wave Current vs Traveling-Wave Current
 

Dave wrote:
"Keith Dysart" wrote:
Is it appropriate to use P = V * I?

it is always appropriate to use P=V*I on the forward and reflected traveling
waves. it is never appropriate to use it on the standing wave voltage and
current. period... plonk.

Arguments like this are usually semantic. Is it possible
that Keith is talking about phasors and you are talking
about scalars?
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Tom Donaly wrote:
Cecil and Dave aren't taking resistance into account when they
talk about waves. You can only feel sorry for guys like that.

Do you also feel sorry for Slater, Ramo, Whinnery, Johnson,
Chipman, Kraus, and Balanis who all wrote about systems
without taking resistance into account?
--
73, Cecil http://www.w5dxp.com