On Apr 17, 12:09 pm, Jim Kelley wrote:
Richard Harrison wrote:
At a short or an open on a line , it is the current or voltage the
discontinuity generates which turns the wave around.

That is more or less true. But the claim being disputed here is the
other way around; that voltages and currents generate discontinuities.

If a virtual condition can generate the energy surge or
escalation needed for a reversal in direction, it is as acceptable as a
real discontinuity, in my opinion.

If it can do that it is acceptable as a miracle, in my opinion. :-)

73, Jim AC6XG


Since it's easy in a lab to set up situations that clearly demonstrate
that there is no echo of a transient off a "virtual short" or "virtual
open", even if you could show me that miracle, it's not a miracle I
could rely on. I'd forever know that I can demonstrate situations
where the miracle does not occur.

Mind you, if you did show such a miracle, I'd very much want
resolution between the line equations based on however far back you
want to go toward Maxwell's equations (J. C. Maxwell in this case) and
the "newly discovered phenomenon." In my opinion, which probably
matches pretty closely with Jim's here, the fundamental line equations
I know specifically disallow such a happening; at the very least we'd
have to add a nonlinearity to the system. (Imagine a spark gap across
the line, set off by voltage over a certain level...)

The fundamental line equations have always given me acceptable results
when I deal with transmission lines. It's certainly possible that
they are flawed, just as Newtonian physics is flawed. But just as we
continue to use Newtonian physics in areas where we know we won't be
running into, or even close to its "speed of light" or "tiny quanta of
energy" limitations, I suspect we'll continue using the fundamental
line equations to solve line problems in our real world. Since we
have computers to handle the calculations for us easily, it seems to
me there's not much reason to OVER-simplify the models we abstract
from the real world problems we're trying to solve.

I see a lot of value to simplifications that let us visualize problems
more clearly. I see a lot of value to modifying, or even throwing
out, "classic" equations and models if we move to new ground and
discover those classic models fail. But I don't see any value in
throwing out details that are easy to let a computer handle for me--in
other words, in possibly simplifying a model until it is no longer
accurate.

Cheers,
Tom