Standing-Wave Current vs Traveling-Wave Current
 

Roger wrote:
Hmmm, Like Roy, I thought there was still a traveling wave in this
situation. The voltage at the far end of the line must reverse polarity
as time passes, so the waves must continue to travel, or so I would think.

It is common practice to divide the waves into standing waves
and traveling waves so they can be discussed separately. For
instance, if the forward voltage is 200 volts and the reflected
voltage is 100 volts, we have a mixture of standing waves and
traveling waves.

It is common practice to allocate 100 volts of the forward wave
to the standing wave in order to exactly match the reflected
voltage with the resultant *pure standing wave*.

The other 100 volts is allocated to the *pure traveling wave* that
is making its way from the source to the load. That's how my profs
at Texas A&M chose to teach the subject. It's a sort of reverse
superposition technique that makes everything crystal clear in
a system of mixed standing waves and traveling waves.

Is this a "tongue-in-cheek" comment?

You think? :-)

Note that in a pure standing wave, the magnitudes of the forward
wave and reflected wave are identical.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Roger wrote:

Hmmm, Like Roy, I thought there was still a traveling wave in this
situation. The voltage at the far end of the line must reverse polarity
as time passes, so the waves must continue to travel, or so I would think.

In the case of an open circuited line, the voltage traveling wave
maintains the same polarity upon reflection from the end of the line.
Mathematically, the voltage reflection coefficient is +1. The voltage
and current traveling waves continue to travel after reflection, which
results in the interference pattern known as a standing wave.

Maybe it could be said better, but I thought Roy was trying to say that
although power could not be detected at the center or ends, it was
flowing as a result of the initial impetus charged into the system.

It's easy to confuse power and energy, and I've been careful to use
those terms correctly. Power is the rate of energy flow, and I said
nothing about power flowing. (That's Cecil's concept, and careless
application of it leads to irreconcilable problems.)

I
would understand that this power would be the power needed to charge the
impedance and capacity of the line as it continually reversed polarity.

Capacitance is charged by charge, which is the integral of current, so
you can if you want track the charging and discharging of the line's
capacitance by integrating the current. Impedance is the ratio of V to I
and isn't something that's charged.

This would be real power from energy stored (but constantly moving) on
the 1/2 wavelength line so long as the system is active. We know we
have power present because we find energy distributed as V and I on the
time plot (viewed as a "standing wave" on the time plot).

The existence of both voltage and current at any point along the line
tells us that there is instantaneous power at that point, which means
that energy is flowing past that point. At any point along the open
circuited line except the ends and middle (where the power is always
zero), we can see that the power is in the form of a sine wave having
twice the period of v(t) or i(t) and no offset. This means that at any
point, energy flows first one direction, then back, equal amounts and
for equal amounts of time, twice during each v(t) or i(t) cycle. The
result is no net energy flow in either direction.

Roy Lewallen, W7EL

Standing-Wave Current vs Traveling-Wave Current
 

It's sad to see that the response to my analysis and equations is insult
and derision rather than any coherent counter argument, but I'm
unfortunately not surprised. I don't see in it any evidence that my
posted calculation was in error -- the only objections I see are that it
doesn't support a flawed theory, so it therefore must be wrong. The
calculations I made are based on solid theory which has been
successfully used for more than a century, and you won't be able to make
any measurement which will refute them. They're also entirely self
consistent with all other transmission line phenomena which can be
calculated or measured.

So I wouldn't bother to respond at all except that it does provide the
opportunity to elaborate a bit on what I posted. If further responses
are as devoid of substance as this one, I'll probably end up plonking
Dave as I did Cecil some time ago, for the same reason.

Dave wrote:
so roy has correctly calculated the standing wave 'power' to be zero at two
points on the line. i am sure that yuri will take great exception to this
result showing there is no power in the standing wave.

I did what I claimed to be able to do -- correctly calculate the power
from v(t) * i(t). Yuri takes exception to many things I say, but frankly
that bothers me not in the least.

but he missed the definition of pr and pf...

Indeed I did. Can you define them for me please?

p(t) = v(t) * i(t)
v(t) = vf(t) + vr(t)
i(t) = if(t) + ir(t)

Therefore,

p(t) = [vf(t) + vr(t)] * [if(t) + ir(t)]
= vf(t) * if(t) + vr(t) * ir(t) + vf(t) * ir(t) + vr(t) * if(t)

Of these four terms, which, if any, are pf(t) and pr(t)? What are the
two remaining terms called?

dave in problem statement:
now, calculate vf(t), if(t),pf(t), vr(t), ir(t), pr(t) at that point,
where
the 'f' terms are the forward wave, the 'r' terms are the reflected wave.

so he conveniently skipped that step and instead writes this cop out:

No, I did calculate all except pf(t) and pr(t), which you didn't define.
As soon as you do (see the question above), I'll be glad to calculate
them also. Or you could do it for us -- it won't involve more than
simple arithmetic.

roy:
I haven't seen a definition of pr and pf, but they're not relevant to
the discussion. If you get a different result for power than zero by
using whatever you take them to mean, then the concept is invalid.

pr and pf are, as i stated, the power in the forward and reflected waves.

What would that be, then, vr(t) * ir(t) and vf(t) * if(t)? Where does
the power in those remaining two terms come from or go?

There is of course power in these two waves and it is indeed 'sloshing' back
and forth in the line.

Please note that I didn't say that power was "sloshing" back and forth.
I said that energy was. Power is not the same as energy -- they bear the
same relationship as speed and distance.

These are the waves that can be measured by any of
the simple devices such as neon bulbs or bird watt meters that clearly show
equal and opposite powers in the waves. so you can indeed have power in the
traveling waves, but no power in the standing waves... which will always be
the case.

Unfortunately, people assume that the units indicated on a meter are the
quantity actually being measured, which often they're not. But this has
been explained many times before here.

i will give him this point as being correct for a lossless open (or shorted)
line:

There
is no average power leaving the source and no average power being
dissipated in the load(*). So there had better be no average power
anywhere in the line.

but then he loses it again:

There will be non-zero instantaneous power
everywhere along the line except at the input, far end, and midway, but
its average value will be zero,

the traveling waves will have power EVERYWHERE on the line, the special
cases are are just the ones where the standing wave is most easily shown as
having no power. obviously if there is power in a wave at one point on a
line it is not going to stop and bypass the quarter wave points, the forward
and reflected waves continue end to end and their power goes with them... it
is at those 'special' points where the voltage or currents in the forward
and reflected waves always cancel each other so if you measure with a simple
tool you will see the voltage or current nulls at those points. that does
not mean there is no power passing those points, only that the voltage or
current in the traveling waves has conveniently canceled each other out at
those points.

Here's just one of the problems with assigning powers to the traveling
waves, attempting to keep track of them separately, and applying
superposition to nonlinear quantities. The conclusion that there is
power at the ends of the line, for example, is demonstrably not true.
There is no current at the far end of the line at any time, and
therefore no power, as I showed. My comment at the end further shows why
the power at the end of the line must be zero.

and then he has to end up with an obvious contradiction:

indicating the movement of energy back
and forth but no net energy flow.

how does energy not flow if it is moving back and forth???

Hopefully most of the readers were more astute than this and noticed the
word "net". If equal amounts of energy flow in each direction during a
cycle (as indicated by a power waveform with no offset), there is no net
energy flow. It means that energy is being stored at some location in
one direction, then returned during the other half of the power cycle.
This is true in any purely reactive circuit, for example a tank circuit,
where exactly the same calculation I made can be done with the same result.

Consider our open ended line for a moment, and imagine it laid out from
left to right with the open end to the right, so I can name directions.
There's no place to the right of the line to store energy, so no energy
can be moved past that point to the right. If we consider the positive
direction of energy flow as being to the right, this means that the
power at the end of the line can never go positive, even for an instant
-- if it did, it would mean energy is moving past the end of the line
during that time. But since there's no storage mechanism beyond the end,
this can't happen. And since we can't have net energy moving past the
end, either, the power therefore can't go negative at any time either.
So the power at the end of the line must be zero at all times. This is
of course the result I got from v(t) * i(t).

Roy Lewallen, W7EL

Standing-Wave Current vs Traveling-Wave Current
 

Cecil Moore wrote:


The net voltage and net current are real but their independent
existence apart from the underlying traveling waves is just
an illusion.

Cecil,

This sums it up pretty nicely. Reality is an illusion. No wonder many
people have a hard time accepting your nonsense. You have built your own
little world where reality and illusion are randomly intertwined as
suits the needs of the moment.

73,
Gene
W4SZ

Standing-Wave Current vs Traveling-Wave Current
 

Dave wrote:
so roy has correctly calculated the standing wave 'power' to be zero at two
points on the line. i am sure that yuri will take great exception to this
result showing there is no power in the standing wave.

but he missed the definition of pr and pf...

dave in problem statement:
now, calculate vf(t), if(t),pf(t), vr(t), ir(t), pr(t) at that point,
where
the 'f' terms are the forward wave, the 'r' terms are the reflected wave.

so he conveniently skipped that step and instead writes this cop out:

roy:
I haven't seen a definition of pr and pf, but they're not relevant to
the discussion. If you get a different result for power than zero by
using whatever you take them to mean, then the concept is invalid.

pr and pf are, as i stated, the power in the forward and reflected waves.
There is of course power in these two waves and it is indeed 'sloshing' back
and forth in the line. These are the waves that can be measured by any of
the simple devices such as neon bulbs or bird watt meters that clearly show
equal and opposite powers in the waves. so you can indeed have power in the
traveling waves, but no power in the standing waves... which will always be
the case.

i will give him this point as being correct for a lossless open (or shorted)
line:

There
is no average power leaving the source and no average power being
dissipated in the load(*). So there had better be no average power
anywhere in the line.

but then he loses it again:

There will be non-zero instantaneous power
everywhere along the line except at the input, far end, and midway, but
its average value will be zero,

the traveling waves will have power EVERYWHERE on the line, the special
cases are are just the ones where the standing wave is most easily shown as
having no power. obviously if there is power in a wave at one point on a
line it is not going to stop and bypass the quarter wave points, the forward
and reflected waves continue end to end and their power goes with them... it
is at those 'special' points where the voltage or currents in the forward
and reflected waves always cancel each other so if you measure with a simple
tool you will see the voltage or current nulls at those points. that does
not mean there is no power passing those points, only that the voltage or
current in the traveling waves has conveniently canceled each other out at
those points.

and then he has to end up with an obvious contradiction:

indicating the movement of energy back
and forth but no net energy flow.

how does energy not flow if it is moving back and forth???




I see we are back to the old business about colliding waves that
apparently carry vector power. At least it seems that way since the
counter-traveling power can cancel at some points and add up at other
points. I thought we trashed this idea a couple of years ago.

Remember, calculate fields first and then worry about power or energy.
Any change in that calculation order will surely lead to "traveling
waves of average power" and other such gems.

I hope no Joules are hurt in the collision.

73,
Gene
W4SZ

Standing-Wave Current vs Traveling-Wave Current
 

Gene Fuller wrote:

...
Remember, calculate fields first and then worry about power or energy.
Any change in that calculation order will surely lead to "traveling
waves of average power" and other such gems.

I hope no Joules are hurt in the collision.

73,
Gene
W4SZ

If two boards of a length are secured upon the surface of a body of
water, their parallel distances to each other computed to "contain"
"standing waves" of a certain frequency, and a device to "impart energy"
placed against one, to "strike" the surface of the water--much can be
seen without the necessity of "complicating maths."

Or, a substantial mud puddle, two boards and a timing circuit ...

Regards,
JS

Standing-Wave Current vs Traveling-Wave Current
 

Roy Lewallen wrote:
It's easy to confuse power and energy, and I've been careful to use
those terms correctly. Power is the rate of energy flow, and I said
nothing about power flowing. (That's Cecil's concept, and careless
application of it leads to irreconcilable problems.)

Roy, God Himself appeared to me in a vision and said that
if you don't stop bearing false witness against me, you are
going to end up in a very bad place.

For the record, here's what I said in a WorldRadio article
more than three years ago: "The author has endeavored to satisfy
the purists in this series of articles. The term "power flow" has
been avoided in favor of "energy flow". Power is a measure of that
energy flow per unit time through a plane. Likewise, the EM fields
in the waves do the interfering. Powers, treated as scalars, are
incapable of interference. Any sign associated with a power in
this paper is the sign of the cosine of the phase angle between
two voltage phasors."

The existence of both voltage and current at any point along the line
tells us that there is instantaneous power at that point, ...

Not if the voltage and current are always 90 degrees out of
phase which is a fact of physics for pure standing waves. There
is no power, instantaneous or otherwise, in pure standing waves.
The cosine of 90 degrees is *always* zero.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Roy Lewallen wrote:
... I'll probably end up plonking
Dave as I did Cecil some time ago, for the same reason.

Roy, you ploinked me because I proved you wrong about the
delay through a 75m loading coil and you didn't want to
lose face on this newsgroup. You have refused to look at
any of the EZNEC files that prove you wrong. You have
threatened to recall my copy of EZNEC because you cannot
fact the technical facts reported by your own creation.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

On 25 Dec, 11:11, Gene Fuller wrote:
Dave wrote:
so roy has correctly calculated the standing wave 'power' to be zero at two
points on the line. *i am sure that yuri will take great exception to this
result showing there is no power in the standing wave.

but he missed the definition of pr and pf...

dave in problem statement:
now, calculate vf(t), if(t),pf(t), vr(t), ir(t), pr(t) at that point,
where
the 'f' terms are the forward wave, the 'r' terms are the reflected wave.

so he conveniently skipped that step and instead writes this cop out:

roy:
I haven't seen a definition of pr and pf, but they're not relevant to
the discussion. If you get a different result for power than zero by
using whatever you take them to mean, then the concept is invalid.

pr and pf are, as i stated, the power in the forward and reflected waves..
There is of course power in these two waves and it is indeed 'sloshing' back
and forth in the line. *These are the waves that can be measured by any of
the simple devices such as neon bulbs or bird watt meters that clearly show
equal and opposite powers in the waves. *so you can indeed have power in the
traveling waves, but no power in the standing waves... which will always be
the case.

i will give him this point as being correct for a lossless open (or shorted)
line:

There
is no average power leaving the source and no average power being
dissipated in the load(*). So there had better be no average power
anywhere in the line.

but then he loses it again:

There will be non-zero instantaneous power
everywhere along the line except at the input, far end, and midway, but
its average value will be zero,

the traveling waves will have power EVERYWHERE on the line, the special
cases are are just the ones where the standing wave is most easily shown as
having no power. *obviously if there is power in a wave at one point on a
line it is not going to stop and bypass the quarter wave points, the forward
and reflected waves continue end to end and their power goes with them.... it
is at those 'special' points where the voltage or currents in the forward
and reflected waves always cancel each other so if you measure with a simple
tool you will see the voltage or current nulls at those points. *that does
not mean there is no power passing those points, only that the voltage or
current in the traveling waves has conveniently canceled each other out at
those points.

and then he has to end up with an obvious contradiction:

indicating the movement of energy back
and forth but no net energy flow.

how does energy not flow if it is moving back and forth???

I see we are back to the old business about colliding waves that
apparently carry vector power. At least it seems that way since the
counter-traveling power can cancel at some points and add up at other
points. I thought we trashed this idea a couple of years ago.



Remember, calculate fields first and then worry about power or energy.
snip-

You can't do that unless you break up the rise in voltage from
beginning to end
in segments. Each segment is different to the other when you are
considering
a tank circuit. This is why these arguments take so long, since one is
talking
about the fields at one segment and all the other corresponders are
refering
to other segments. It is quite possible that many correspondents are
correct
but only with respect to the segment they are referring to.You should
all
get on the same stage when entertaing such that the audio does not
get
to the deafining level while at the same time entertaining the same
audience
Art

Standing-Wave Current vs Traveling-Wave Current
 

Gene Fuller wrote:
Cecil Moore wrote:
The net voltage and net current are real but their independent
existence apart from the underlying traveling waves is just
an illusion.

This sums it up pretty nicely. Reality is an illusion. No wonder many
people have a hard time accepting your nonsense. You have built your own
little world where reality and illusion are randomly intertwined as
suits the needs of the moment.

Reality can certainly contain illusions. Sunrise and sunset
are a couple of examples. Magician tricks are another.

If you want to prove that standing waves are not an illusion,
take away the component forward and reverse traveling waves
and show us what you have left. As I said above, to which
you objected, standing waves cannot exist independently
of their forward and reverse components. I stand by that
statement. Prove it wrong if you can.
--
73, Cecil http://www.w5dxp.com