Standing-Wave Current vs Traveling-Wave Current
 

On Dec 27, 10:42*am, Cecil Moore wrote:
Keith Dysart wrote:
Cecil Moore wrote:
A schematic shows exactly what is happening. There is no
path from SGCL1 to R1. There is no path from SGCL2 to R2.

SGCL1---1---2------2---1---SGCL2
* * * * *\ / * * * *\ /
* * * * * 3 * * * * *3
* * * * * | * * * * *|
* * * * * R1 * * * * R2

There is nothing in the circuit to cause any reflections.
So the power dissipated in R2 comes from SGCL1 and the
power in R1 comes from SGCL2.

Can not happen after cutting the branches.

The inclusion of circulators in the example
ensures that it is a distributed network example.
Cutting the branches is not a valid action in
distributed network examples because technically
it is a zero current "point" and not a zero current
"branch", i.e. the current is not zero throughout
the entire branch. See below.

The beauty of the distributed model is that it has
a lot of very, very (say infinitely) small branches.
(Review your calculus, it is much the same). One
can indeed therefore, cut the branch at a point.

If you wish, feel free to view the branch as having,
the width of a point.

Sorry, the lumped circuit model is known to fail for
distributed network problems. That's probably why
the distributed network model still survives today
but has been discarded and forgotten by many in the
rather strange rush to use a shortcut method at all costs.

Or are you disuputing the validity of cutting branches
with zero current?

Of course, it is obviously invalid in distributed
network problems. We can add 1/2WL of lossless
transmission line to the example to see why it is
invalid.
* * * * * * * * * *1/2WL 50 ohm
SGCL1---1---2--+--lossless line--+--2---1---SGCL2
* * * * * \ / * * * * * * * * * * * * \ /
* * * * * *3 * * * * * * * * * * * * * 3
* * * * * *| * * * * * * * * * * * * * |
* * * * * *R1 * * * * * * * * * * * * *R2

Your zero current "branch" is now 1/2WL long and in
the center of that zero current "branch", the current
is at a maximum value of 0.4 amps for 50 ohm signal
generator voltages of 10 volts as in your original example.

Using the distributed network approach, you have added
an infinite number of branches, and now there are two
branches which are appropriate places to make the cut.

Of course the branch in the middle of your line is not
one of them.

How can the current in the middle of the line be 0.4 amps
when the current at both points '+' is zero? Does that
0.4 amps survive a cut at point '+'?

Absolutely, if the line is lossless. Cut both "+" and the
current in middle of the line still remains.

...Keith

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
[...]

I believe RF knows length, it has to be aware of movement--time? Time,
I think it has little use of that ...

Regards,
JS

Standing-Wave Current vs Traveling-Wave Current
 

Roger wrote:
Cecil Moore wrote:
Where did that current come
from if current cannot flow into the stub?

Stored in the 1/4 WL between the short and mouth. No more current
needed once stability is reached.

EM RF current is stored in the stub? In what form?
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:

Cecil Moore wrote:
1/2WL 50 ohm
SGCL1---1---2--+--lossless line--+--2---1---SGCL2
\ / \ /
3 3
| |
R1 R2

Your zero current "branch" is now 1/2WL long and in
the center of that zero current "branch", the current
is at a maximum value of 0.4 amps for 50 ohm signal
generator voltages of 10 volts as in your original example.

Using the distributed network approach, you have added
an infinite number of branches, and now there are two
branches which are appropriate places to make the cut.

The point is that in the above example, there are absolutely
no reflections. When you cut the line you cause reflections
where none existed before. It is obviously invalid to completely
change the operation of the circuit in that manner. We could
be sending data from SG1 to R2 and from SG2 to R1. Those data
streams stop when you cut the line.

How can the current in the middle of the line be 0.4 amps
when the current at both points '+' is zero? Does that
0.4 amps survive a cut at point '+'?

Absolutely, if the line is lossless. Cut both "+" and the
current in middle of the line still remains.

We both know that is a physical impossibility. Sometimes you
are just forced to accept reality and get on with it.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
Perhaps try googling "in the limit as t approaches 0..."

So how many joules can pass a point in zero seconds?

But at least you now see the utility.

Nope, I don't. I don't think the concept of instantaneous
power is mentioned at all in "Optics", by Hecht.
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Keith Dysart wrote:
1/2WL 50 ohm
SGCL1---1---2--+--lossless line--+--2---1---SGCL2
\ / \ /
3 3
| |
R1 R2

Using the distributed network approach, you have added
an infinite number of branches, and now there are two
branches which are appropriate places to make the cut.

Assume your life depends upon the information transmitted
from SGCL1 to R2. Would you make the cut?
--
73, Cecil http://www.w5dxp.com

Standing-Wave Current vs Traveling-Wave Current
 

Cecil Moore wrote:
Dave Heil wrote:
Please note that I now say and have previously written that I do not
believe that the Sun rises, sets or travels across the sky.

Very good, that is all I was trying to get you to admit -
that the "rising of the sun" is an illusion which was
my original point.

You've danced and dodged, Cecil.

What do you call the first and last appearances of the Sun's rays each
day?

Incidentally, Webster's says the sun does actually rise. :-)

My local TV meteorologist talks of Sunrise and Sunset. My logging
program uses the terms. NASA uses the terms as well.


Dave K8MN

Standing-Wave Current vs Traveling-Wave Current
 

On Dec 28, 1:02*am, Cecil Moore wrote:
Keith Dysart wrote:

* Cecil Moore wrote:

* * * * * * * * * *1/2WL 50 ohm
SGCL1---1---2--+--lossless line--+--2---1---SGCL2
* * * * *\ / * * * * * * * * * * * * \ /
* * * * * 3 * * * * * * * * * * * * * 3
* * * * * | * * * * * * * * * * * * * |
* * * * * R1 * * * * * * * * * * * * *R2

Your zero current "branch" is now 1/2WL long and in
the center of that zero current "branch", the current
is at a maximum value of 0.4 amps for 50 ohm signal
generator voltages of 10 volts as in your original example.

Using the distributed network approach, you have added
an infinite number of branches, and now there are two
branches which are appropriate places to make the cut.

The point is that in the above example, there are absolutely
no reflections. When you cut the line you cause reflections
where none existed before.

This is what makes the example so fascinating.

Before the cut, there is a distribution of voltage, current
and power on the line. The functions representing these can
be written as

V(x,t)
I(x,t)
P(x,t)

After the cut(s), the voltage, current and power distributions
are exactly the same: V(x,t), I(x,t), P(x,t).

The cuts changed nothing about the conditions in the circuit.

And yet the claim is made that before the cuts there are no
reflections and after the cut there are a bunch. And yet the
conditions in the circuit are EXACTLY the same.
But befonone, after:bunch. But conditions are exactly
the same.

It is obviously invalid to completely
change the operation of the circuit in that manner.

Just cutting a branch. Completely legal.

Is the operation of the circuit completely different?
Perhaps it is reasonable to view a virtual open as
producing a reflection. You have to work this out for
yourself. But as you do so, keep front and center the
fact that the voltage, current and power distributions
are identical before and after the cut(s). The before
and after circuits are behaving identically.

If you were merely provided with V(x,t), I(x,t) and
P(x,t) you could not determine whether there were cuts
or not.

We could
be sending data from SG1 to R2 and from SG2 to R1. Those data
streams stop when you cut the line.

The specification of the conditions in the experiment mean
that there can be no data stream. If there were data, the
current would not be always 0.

How can the current in the middle of the line be 0.4 amps
when the current at both points '+' is zero? Does that
0.4 amps survive a cut at point '+'?

Absolutely, if the line is lossless. Cut both "+" and the
current in middle of the line still remains.

We both know that is a physical impossibility. Sometimes you
are just forced to accept reality and get on with it.

It is completely possible for a lossline line.
It is no different than a connected capacitor and inductor
which will ring for ever given the appropriate initial
conditions.

...Keith

Standing-Wave Current vs Traveling-Wave Current
 

On Dec 28, 1:38*am, Cecil Moore wrote:
Keith Dysart wrote:
Perhaps try googling "in the limit as t approaches 0..."

So how many joules can pass a point in zero seconds?

You have descended into silliness. You are out on your
Harley doing 60 miles/hour. How far do you travel in 0
seconds?

So your point was?

But at least you now see the utility.

Nope, I don't. I don't think the concept of instantaneous
power is mentioned at all in "Optics", by Hecht.

Ahhh. The difficulty is because you don't "think" that
the concept is mentioned in Hecht. Could that be because
at 5E14 Hz, it is difficult to measure? Try a circuit
analysis or transmission line book. You will have more
luck. There is a good chance that your Ramo and Whinery
mention it. Look near where they derive
Pavg = Vrms * Irms * cos(theta)

...Keith

Standing-Wave Current vs Traveling-Wave Current
 

On Dec 28, 1:44*am, Cecil Moore wrote:
Keith Dysart wrote:
* * * * * * * * * *1/2WL 50 ohm
SGCL1---1---2--+--lossless line--+--2---1---SGCL2
* * * * *\ / * * * * * * * * * * * * \ /
* * * * * 3 * * * * * * * * * * * * * 3
* * * * * | * * * * * * * * * * * * * |
* * * * * R1 * * * * * * * * * * * * *R2

Using the distributed network approach, you have added
an infinite number of branches, and now there are two
branches which are appropriate places to make the cut.

Assume your life depends upon the information transmitted
from SGCL1 to R2. Would you make the cut?

With the current always 0, data is not being successfully
transmitted. So with the experiment at hand, life is over.

...Keith