Keith Dysart wrote:
On Mar 22, 12:20 am, Cecil Moore wrote:
This is a lot like the 1/2WL W7EL example in his food for
thought articles. The generator is *NOT* matched to the line
as it sees an open circuit and cannot continue to stuff 50
watts into the open circuit. The generator is as mismatched
as it can possibly be. The reflected wave also sees that open
circuit and is 100% reflected. Since the generator is not
delivering any power and there is a forward power and a
reflected power, the reflected power is supplying the
forward power. Anything else violates the conservation
of energy principle.

I suggest that you have quite mixed up your impedances here
thus rendering all further analysis invalid.

No, I may have confused you but I did not mix up the
impedances. What the generator and reflected wave "sees"
above refers to the effective or virtual impedance, the
ratio of V/I designated by Z1, Z2, etc. The characteristic
impedances are designated by Z01, Z02, etc.

At any point in the system there are 4 impedances.

There is the characteristic impedance looking left and the
characteristic impedance looking right. For systems in
sinusoidal steady-state, there is also the effective impedance
looking left and the effective impedance looking right.

Yes, nothing I said disagrees with that. I will try to
draw an ASCII block diagram from now on.

The characteristic impedance is dependant only the elements of
the system. It does not depend on the length of the line or
the frequency of excitation. At changes in the characteristic
impedance, reflections occur. This impedance can be used for
transient as well as steady-state analysis of a system.

Yes, nothing I said disagrees with that.

The effective impedance is dependant on the characteristic
impedances of the components of the system, as well as line
length and excitation frequency. It can only be used for
steady-state analysis. It does not cause reflections.

Yes, nothing I said disagrees with that.

Until these impedances are kept straight in discussions, there
is no hope for correctness.

OK, I will insert the impedances for you in what you quoted
above.

This is a lot like the 1/2WL W7EL example in his food for
thought articles.

50wGen---1/2WL open-circuit stub---Z=infinity
Pfor=50w--
--Pref=50w

The generator is *NOT* matched to the load as it sees an
open circuit (effective Z=infinity) and cannot continue
to stuff 50 watts into the open circuit. The generator
is as mismatched as it can possibly be. The reflected wave
also sees that open circuit (Z=infinity) and is 100% reflected.
The reflected wave encounters the source wave which puts the
voltages in phase and the currents 180 degrees out of phase.
That's what happens at an open circuit.

Since the generator is not delivering any power and there is
a forward power and a reflected power, the reflected power is
supplying the forward power, i.e. being 100% re-reflected. The
re-reflection is associated with total destructive interference
toward the generator and total constructive interference
toward the load. Anything else violates the conservation of
energy principle.
--
73, Cecil http://www.w5dxp.com