Toni wrote:
Thanks four your answers.

I was forgetting you normally use coax in a unbalanced configuration
where the braid is supposed to be at 0 voltage so only currents matter.

How do you define "0 voltage"? Do a groups.google.com search of this
newsgroup and you'll find quite a bit of discussion about the futility
of trying to define a voltage between two distant points in the presence
of a field.

Would all this still hold if you used the coax as a _balanced_
transmission line? (unusual but -I think- possible). In this case
wouldn't voltages develop on the braid that could capacitively couple to
other conductors?

(assuming perfect solid shield, ...)

A coax line is balanced when the common mode current is zero. It's
unbalanced when common mode current exists. See
http://eznec.com/Amateur/Articles/Baluns.pdf for more information.

Voltages don't couple, fields do.

There was also some discussion not too long ago on this group about the
role of current in generating both electric and magnetic fields.

Roy Lewallen, W7EL

Dave wrote:
the voltage on the braid is not zero on the inside, it varies along with the
wave traveling along the inside of the coax. and the currents are exactly
balanced inside the coax also, they have to be or it wouldn't work. this
notion of balanced vs un-balanced transmission lines is totally confusing to
most people, in a proper system, say just with a dummy load on a coax the
currents on the shield exactly balance the current on center conductor. so
why do we go through all this stuff with bal-uns?? and coax chokes?? the
currents are already balanced, so WHY?? come on you gurus out there,
explain this one!

The currents on the inside are always balanced -- they're purely
differential mode. The purpose of baluns or common mode chokes is to
reduce the common mode current which, on coax, flows entirely on the
outside.

If you're driving a dummy load from your transmitter, the common mode
current will be zero in an ideal system and negligible in a real system.
A balun or common mode choke will do nothing in that situation.

See http://eznec.com/Amateur/Articles/Baluns.pdf for a more complete
explanation.

Roy Lewallen, W7EL

Gene Fuller wrote:
Cecil, You still don't get it.

I get what you said. Here it is again.

Gene Fuller wrote:
The only "phase" remaining is the cos (kz) term, which is really
an amplitude description, not a phase.

So you alluded to phase information in the standing wave
current amplitude.

When I said the phase information was gone, I meant it.

But you also said:

Gene Fuller wrote:
However, there is not one bit of additional physical information
in the traveling waves that is not in the standing wave.

We know that there is phase information in the traveling waves.
So for your statement to be true, there has to be phase information
in the standing wave.

Both of your statements cannot be true. Which one are you
willing to stick with and which one are you going to retract?

If you look at: http://www.qsl.net/w5dxp/travstnd.GIF
you will see that the standing wave amplitude is indeed
a cosine function of the phase. Taking the arc-cosine
of the normalized amplitude yields the phase angle.

I'm sorry, but you have contradicted yourself a couple of times
so I don't know which assertion you want to go with.
--
73, Cecil http://www.qsl.net/w5dxp

Gene Fuller wrote:
Cecil Moore wrote:
Gene Fuller wrote:

However, there is not one bit of additional physical information in
the traveling waves that is not in the standing wave.


I agree with you but W8JI and W7EL have rejected the concept that
there is any phase information in the standing wave current magnitude.
They have rejected any use of the arc-cosine function in calculating
that phase. The following graphs show the difference in the standing
wave current and the traveling wave current.
. . .

Egad. Of course I reject the notion that there's "phase information in
the standing wave current magnitude". Magnitude and phase are
orthogonal. There's no phase in the magnitude and no magnitude in the
phase. There's no real portion of the imaginary part and no imaginary
portion of the real part. I haven't a clue what you mean by "use of the
arc-cosine,function to calculate that phase", but I certainly reject any
method that assigns a phase value to a magnitude or vice versa. I get
the total voltage or current simply by adding the traveling waves. No
trig functions necessary, just simple vector addition.

Traveling waves have phase information. In a steady state system they
can be expressed as phasors, which consist of a magnitude, a time phase
reference value, and an implicit time varying time rotation. When you
add them to get the total (which Cecil likes to characterize as a
standing wave as though it's something different than just the total
voltage or current), you get the simple vector sum of the constituent
traveling waves. This sum is also a phasor, with magnitude, time phase
reference value, and the same implicit time varying phase rotation.

In summary, both traveling waves and the total voltage or current are
phasors, and both have phase.

What's so complicated about adding a couple of phasors? Cecil, you need
to go back and read, and understand, your freshman circuit analysis text.

What a bunch of irrational smoke and mirrors.

I don't care less what Cecil will make of this. But Gene, do you really
disagree with what I've just said?

Roy Lewallen, W7EL

Roy Lewallen wrote:
Egad. Of course I reject the notion that there's "phase information in
the standing wave current magnitude".

And, of course, you are showing your ignorance. Let's say that
at the current maximum point, the forward current is 0.5 at 0 deg
and the reflected current is 0.5 at 0 deg. The standing wave
current at the current maximum point is 1.0 at 0 deg just like
a cosine function is 1.0 at 0 deg.

Now let's go 45 degrees away from that current maximum point. The
forward current is 0.5 at -45 deg and the reflected current is
0.5 at +45 deg so the standing wave current is 0.707 at 0 deg.

The magnitude of the standing wave current is 0.707. The arc-
cosine of 0.707 is 45 degrees. Do you really and truly believe
that is just a coincidence? Exactly as Gene Fuller said previously,
there is phase information in the standing wave current magnitude.

Here's a quote from Gene:

Gene Fuller wrote:
The only "phase" remaining is the cos (kz) term, which is really
an amplitude description, not a phase.

Your statement above is in direct contradiction to Gene's statement.

What's so complicated about adding a couple of phasors?

I suspect you know how to add phasors. I suspect you don't have
a clue what that answer means in reality. Please try to convince
us that the 0.707 result above for a 45 degree shift is sheer
coincidence.
--
73, Cecil http://www.qsl.net/w5dxp

Roy Lewallen wrote:

I don't care less what Cecil will make of this. But Gene, do you really
disagree with what I've just said?

Roy Lewallen, W7EL

Roy,

I do not disagree with anything you have said. Cecil is up to his
standard trick of selective quoting along with a subtle change of topic
to make it appear that there are conflicts when there are none.

I am sure Cecil will find some other quote to remove from context in
order to prove me wrong.

73,
Gene
W4SZ

Cecil Moore wrote:
Gene Fuller wrote:

Cecil, You still don't get it.


I get what you said. Here it is again.

Gene Fuller wrote:
The only "phase" remaining is the cos (kz) term, which is really
an amplitude description, not a phase.

So you alluded to phase information in the standing wave
current amplitude.

When I said the phase information was gone, I meant it.


But you also said:

Gene Fuller wrote:

However, there is not one bit of additional physical information

in the traveling waves that is not in the standing wave.

We know that there is phase information in the traveling waves.
So for your statement to be true, there has to be phase information
in the standing wave.

Both of your statements cannot be true. Which one are you
willing to stick with and which one are you going to retract?

If you look at: http://www.qsl.net/w5dxp/travstnd.GIF
you will see that the standing wave amplitude is indeed
a cosine function of the phase. Taking the arc-cosine
of the normalized amplitude yields the phase angle.

I'm sorry, but you have contradicted yourself a couple of times
so I don't know which assertion you want to go with.


Cecil,

I have not contradicted myself, and I have nothing to retract. Only in
your imagination is there any useful phase information in the traveling
waves that make up a standing wave. There can be other waves that don't
exactly balance out into a standing wave, but that is another topic.

I am not sure to whom the "we" refers in your statement, "We know that
there is phase information in the traveling waves." Perhaps that is the
Royal We, because it certainly does not include me. The phase
information you might find is of no use, and it is simply an artifact of
the mathematical analysis.

If the standing wave adequately and completely describes the
electromagnetic situation, then there is no additional available from an
arbitrary decomposition in traveling waves. If you try to look at the
traveling waves one at a time, then you are no longer considering a
standing wave.

73,
Gene
W4SZ

"Gene Fuller" wrote in message
...
Cecil Moore wrote:
Gene Fuller wrote:

Cecil, You still don't get it.
I get what you said. Here it is again.
So you alluded
I meant it.
But you also said:
there is not one bit of additional physical information
So for your statement to be true, there has to be Both of your statements
cannot be true. Which one are you
willing to stick with and which one are you going to retract?
If you look at
I'm sorry, but you have contradicted yourself a couple of times
so I don't know which assertion you want to go with.
I have not contradicted myself, and I have nothing to retract. but that is
another topic.
I am not sure to whom the "we" refers in your statement,
Perhaps that is the Royal We, because it certainly does not include me.
there is no additional available from

COME ON! KEEP IT GOING!! this rainy wet weekend is almost over and I could
use one more good round of laughter!! Perhaps we cut straight to the
conclusion and have something that is completely a personal attack devoid of
any possible technical statements, that would do nicely! DON'T STOP NOW!

Gene Fuller wrote:
I do not disagree with anything you have said.

Please answer this question. Does the amplitude of the
standing wave current contain any phase information?

You have previously asserted that it does. Roy says
it doesn't. Time to chose between technical fact
and agreeing with your friend (who is technically
incorrect).
--
73, Cecil http://www.qsl.net/w5dxp

Gene Fuller wrote:
I have not contradicted myself, ...

Either the standing wave current magnitude contains phase
information, as you previously asserted, or it doesn't.
I'll make it easy for you. Just insert an 'X' for the one
you agree with.

_____ Standing wave current magnitude contains some phase
information.

_____ Standing wave current magnitude contains zero phase
information.
--
73, Cecil http://www.qsl.net/w5dxp