Keith Dysart wrote:
On Dec 31, 11:11 am, Roger wrote:
Cecil Moore wrote:
Richard Clark wrote:
To cut to the chase, Norton and Thevenin sources are appropriate to
network analysis irrespective of your perception.
All my references indicate that those sources are only
appropriate for *steady-state* use. Roger is searching
for a transient state source.
Right!

73, Roger, W7WKB

Odd. Cecil has not named his "references" which is
quite unusual for he truly likes to name-drop: Ramo,
Whinnery, Hecht, IEEE, ...

You would be well served to google "reflection diagram"
or "bounce diagram" where you will find fine examples
of computing re-reflection using the source impedance
of generators modelled using the Thevenin equivalent
circuit. It is not particularly complicated, though
it can be tedious.

...Keith

One of Cecil's common techniques is to declare any combination of
perfect voltage source and resistance to be a "Thevenin equivalent",
which he then claims relieves him of any obligation to consider the
power supplied by the source or dissipated in the resistor.

Of course, that combination of components has no special properties or
restrictions, and must conform to the same rules as any linear
components. It is, in fact, an excellent choice for many examples and
illustrations because of its bare simplicity. Only when a substitution
is made for some other combination of linear components does the perfect
voltage source and resistor become an "equivalent", and in that case you
can correctly state that the power supplied by the perfect source and
dissipated by the resistor aren't necessarily the same as for the
circuit being replaced. But any analysis which isn't valid when driven
by a perfect voltage source in series with a resistance (or current
source in parallel with a resistance) is fundamentally flawed. Waving
your hands and declaring it a "Thevenin equivalent" and therefore not
subject to the rules all linear circuits must abide by is simply a way
of saying your theory can't handle simple cases.

Moving on, my electrical circuits texts abound with examples in which
some initial condition is assumed, then a source is "turned on" or
connected with an imaginary switch at t = 0, and the transition from the
initial state to steady or final state is studied -- exactly as I did in
my analysis. The source is most often a perfect voltage or current
source and, in the sections dealing with sine wave AC circuits, produces
a sine wave. The assumption of an initial condition (usually, but not
always, that all voltages and currents in the circuit are zero) is
absolutely required when solving the fundamental integro-differential
equations which result from circuits containing inductances and
capacitances.

I'll be glad to give page references from Pearson & Maler and Van
Valkenburg, but it's really not necessary since anyone having any
electric circuits text can find abundant examples. It appears that some
of the posters either never took a basic course in electrical circuits,
or forgot some very fundamental principles which were taught. But used
circuits texts can be purchased for a very modest price, so there's
little excuse for remaining ignorant if a person is truly interested in
learning about the topic. (There's also the Internet, but you have to be
more careful in sorting out the good information from the bad, and this
can be difficult if you're not already pretty well acquainted with the
topic.) I'd really like it, too, since I'd be able to present an
analysis now and then without having the most basic principles of linear
circuit analysis questioned and debated.

I'm afraid that the fuss about the source is primarily a way to avoid
confronting the facts, which are apparently disturbing to some of the
imaginative alternative theories being promoted.

The SPICE simulation of the circuit I analyzed was, of course, a
transient analysis. The source was a perfect voltage source which
produced a sine wave beginning at t = 0 and continuously after that,
just as in my analysis. For anyone having SPICE, here's the netlist:

* 360 degree transmission line with open end and voltage source,
* transient response showing runup

..TRAN .05 30

v0 1 0 sin(0 1 1hz)
tl1 1 0 2 0 td=1 z0=50
tl4 2 0 3 0 td=4 z0=50
rl 3 0 1meg

..PROBE
..END

TL_1_sec.gif is a plot of v(2), which is the junction of tl1 and tl4.
TL_5_sec.gif is a plot of v(3), which is the open far end of the line. A
plot of v(1) would of course show the source voltage, a constant 1 volt
peak sine wave beginning at t = 0. As I mentioned, the 1 megohm
terminating resistor rl is necessary to keep the version of SPICE I have
from blowing up; it can be any value that's large enough to not have an
appreciable effect on the result.

Roy Lewallen, W7EL