"Gene Fuller" wrote in message
...

That attempted under-the-hood analysis with tools suitable only for
external description drives my suggestion of the parallel to the Thevenin
model.

the Thevenin (or Norton) equivalent circuits i believe are rarely used in
analysing transmission lines and antennas, they are more commonly used for
breaking down lumped circuits and networks. In fact Jackson doesn't even
have them in the index of Classical Electrodynamics 2nd ed... It is
mentioned in Ramo,Whinnery, and VanDuzer Fields and Waves in Communications
Electronics in the index, but in scanning the 2 chapters it is listed for i
don't see an actual reference to Thevenin... one of those chapters deals
with microwave networks and components and does break them down into lumped
equivalents so that is probably where the reference belongs, the other
chapter wouldn't seem to be related so may be a typo.

The problem with the use of the Thevenin or Norton equivalents is that you
have to exactly respect the limitations in order to use them properly...
that is the part of the circuit being replaced with the 'black box'
equivelent must be linear and time invariant, and the analysis is only valid
for sinusoidal steady state. This last one is what gets everyone, it
eliminates all the transients and makes it impossible to use to figure out
what happens when that first reflection physically happens... you have to
ignore all that stuff and only consider the steady state solution.

We have seen that some posters on here don't want to accept those
limitations as they try to figure out 'what is in' the black box
equivalent... this is of course a non-sequitar as the whole purpose of
replacing a part of a circuit with the Thevenin equivalent is to simplify
the problem so you don't have to know what is inside and can focus on the
rest of the problem. So any attempts to measure the length of the line in
the black box, or figure out if it is a lumped circuit break the rules for
using it in the first place.