On 8 jun, 09:54, Cecil Moore wrote:
On Jun 8, 6:04*am, Keith Dysart wrote:

It is too bad, because the time domain is quite enlightening.

Nothing wrong with a time domain analysis but analyzing problems whose
basic premises violate the laws of physics is a waste of my time and
yours.
--
73, Cecil, w5dxp.com

Good day. Sorry for the large extension of this post, my friends...

My interests lie in understanding the behaviour of transmission lines
to a level necessary to predict their basic behaviour. I did not find
that I needed power flux to achieve this so I have not explored it. I
suspect that you are right and it is an interesting topic.

OK. I understand. I suposse you are more interested in "know how".
When I complained about "the bench" at Richard, I was thinking on so
many "know how" working years in my life. Today, I have more time to
the "know WHYs" and I am trying to take my chance... :)
A knowledge on Smith Chart (or software equivalent tools) using, solve
most (if not all) of our ham practical and professional situations and
provide enough basic theory for design purposes, I think in such sense
I agree with you about it; however seems to me this topic thread have
dealt a little more in the why's than the how's :)

Look, several years ago many hams in my country -Argentine- came from
technical schools, I become a ham in my seventeens (1969) when I was a
very young electronic technician student. Here we have three
fundamental educative levels: Primary, secondary (college?) and
terciary (university). In secondary and terciary levels one of the
first matters we study is physics. If we study electronics -on RF
speciality-, only when we reach later study years of each level we
learn transmission lines in the frequency domain with infinite
lattices of RLCG, Telegrafer's equations solution, Smith charts,
impedances, reactances, etc.
If you do not go to study any RF especialities, the only knowledge you
will have about transmission lines will be the physics ones. Physics
models teach us the associated phenomena reffering basically to
electromagnetic fields = we learn about, E field, H field, power and
energy in more basics terms that frequency domain later more advanced
studies. We do not learn typical AC models in basic physics (as you
can see in Resnick-Hallyday books, for example, I can not give you
college's references books because I study from local authors).
In addition at very early physical mechanics courses we learn
stationary and traveling waves, superposition principle and late,
interference, in optics.
Probably this is not the way to approaching to this topic that medium
Ham employ because our natural ansiety to put the rig to work :D but
seems to be a consensus about what is more basic and what more complex
in formal pedagogic/understanding approaches to this matters.

May be for that some of us tend to emphasize in directional power flux
and other similar "ugly stuff" to analize transmission line questions,
Perhaps for this reason it is easy and illustrative to me the Cecil's
bridge car analogy about net energy flux, in addition, energy fluxes
crossing areas results very intuitive to me because I can easily
visualize (imagine) thousands of them hit and cross my body all the
time. Sun light and infrared energy flux, light in houses, streets
lights, sky diffused light, RF waves from broadcast and Hams, cellular
phones, etc. Instead it is not so ease visualize in such intuitive
context a single point with a permanent zero voltage (or E field,
better) all the time.

Measurement of interference phenomenom requires much more sofisticated
and special reductive technics to simplify the problem. One of this
technics it is, for example, voltage measurement on a transmission
line point with a zero volt pure AC voltage node; but as Cecil et al
said, a zero voltage point does not implicate not power flux crossing
that point, that is a very known wave interference phenomenom, it is a
little easy to visualize it if we remember that fields are "force
fields" -fields are forces acting on testing devices- (charges,
compass needles, etc), as we learnt in Coulomb laws. Fields being
forces let us intuite that having two horses pulling a rock in right
angles results in rock moving on a direction resulting of composition
of that forces. Seem to be only one force acting in movement direction
but are two!. also you can have both horses pulling in opposite
directions, then we do not measure any movement and we could think
there is not any force acting on the rock!, but our zero force
measurement do not implicate there are not two horse pulling the
rock! , zero net force it is different of zero force, I think we agree
in that.

I believe I undestand your reasoning: P=V*I, = not V, not P!, it is
OK. But power not represent the internal system energy, power
implicate "energy developed = work/time", you need energy (applied
during certain time, then "power") to accelerate a charge, but the
charge can have cinetic energy of its own; then, zero volt line point
simply are a point where not any energy it is ADDED to the charges.
not a point where there is not have (or not can have) preexistent
electric energy (current) flowing; why zero volt net force field point
would be stop travelling wave energy flow?; think of zero volt line
point as a zero potential energy point, not acceleration in it, as the
lowest part of a roller coaster...
Incidentally, Poynting vector is defined as "speed of energy flux by
unity of area", it is a different thing that power developed on
interchange of energy phenomena such electric energy converted to heat
or chemical reaction or movement, if we remember what we learn about
P=V*I in Joule law (electric to heat transformation) it is a little
more evident its transforming (not transport) energy context. Thus,
transmited power its different than "developed power" in the other
sense (perhaps here my translation not be clear enough). What is your
opinion?

Miguel Ghezzi LU6ETJ

PS: I have some more things in my inkwell about models used on our
issue but I have to leave it for future postings :)