On Apr 1, 9:34 am, Cecil Moore wrote:
Keith Dysart wrote:
The impedance
encountered by the reflected wave at the generator is the
same as the generator's source impedance.

No, the generator's source impedance is *NOT* the
impedance encountered by the reflected wave. Please
reference w2du's article again.

http://www.w2du.com/r3ch19a.pdf

Forget about the conjugate match and concentrate on the
non-dissipative source resistance being different from
what you are calling the generator's source impedance.
An *active* source creates a source impedance looking back
into the source that is *different* from what you are
calling the generator impedance.

It would appear that you are confusing the possible complexities
of a class C power amplifier with the simplicity of the generator
in the experiment I proposed. A 2 Amp current source
in parallel with a 450 Ohm resistor does not, as far as I can
tell, have a 'non-dissipative source resistance'. It has a
dissipating source resistor. This is not a particularly efficient
implementation, but is certainly a possible one. Now that I
have clarified that there is a dissipating source resistor will
this allow you to use superposition to solve the problem?

Just for your convenience, a reminder of the problem:
- generator with 450 Ohm source resistance drives
- a line with 450 Ohm characteristic impedance
- terminated by a 75 Ohm load
- the generator is set such that it would output
450 Volts into a 450 Ohm load

Question:
- Will there be ghosts?
If the answer is yes...
- What is the magnitude of the first re-reflection?
Ancillary question:
- What 'forward power' will a directional wattmeter in the
450 Ohm line indicate?
- What 'reverse power' will a directional wattmeter in the
450 Ohm line indicate?

If necessary for answering the question:
- The line can be assumed to be 31 wavelengths long.
- The generator can be assumed to be a 2 Amp current source
in parallel with a 450 Ohm resistor.

....Keith

Keith Dysart wrote:
It would appear that you are confusing the possible complexities
of a class C power amplifier with the simplicity of the generator
in the experiment I proposed.

I am differentiating between what is possible in the
real world and what is possible in your mind. Presumably,
technical miracles are possible in your mind. The miracle
of rendering every circulator in the world obsolete by
adding a ten cent resistor is a miracle that you should
definitely pursue.

- Will there be ghosts?
If the answer is yes...
- What is the magnitude of the first re-reflection?

The answer is yes, but you have not given enough
information to solve the problem. Again, please
furnish a math model of a real world source.
--
73, Cecil http://www.w5dxp.com

On Apr 2, 5:14 pm, Cecil Moore wrote:
Keith Dysart wrote:
It would appear that you are confusing the possible complexities
of a class C power amplifier with the simplicity of the generator
in the experiment I proposed.

The miracle
of rendering every circulator in the world obsolete by
adding a ten cent resistor is a miracle that you should
definitely pursue.

You raise an interesting question. What are the design tradeoffs
that drive choosing between a ten cent resistor and a circulator?
I suspect it relates mostly to the powers involved. The ten cent
resistor seems to see application in signal generators where the
extra power it dissipates is not of concern and it really is a
ten cent resistor. In high power applications, it definitely
would not be a ten cent resistor and having an amplifier which
can provide twice the normally required output voltage would be
far from efficient. It is perhaps here that a circulator finds
application driven by simple engineering cost-benefit tradeoffs.

- Will there be ghosts?
If the answer is yes...
- What is the magnitude of the first re-reflection?

The answer is yes, but you have not given enough
information to solve the problem. Again, please
furnish a math model of a real world source.

So why don't you prove my contention that the impedance
encountered by the reflected wave is 450 Ohms incorrect.

Here is how. Using my 450 Ohm value for the impedance
compute the reflection coefficient at the generator
using RC = (Z2-Z1)/(Z2_Z1). Using the various equations
for Vthrough, Vreflected, Ithrough and Ireflected, along
with superposition compute the various currents and
voltages within the system.

Then using Kirchoff's voltage and current laws, validate
all the nodal voltages and loop currents. If 450 Ohms is
not the appropriate impedance, then the validity check
will fail.

The beauty of this approach is that you do not need to
know what the actual value is, you merely need to prove
that it is not 450 Ohms.

I await the analysis.

....Keith

Cecil Moore wrote:


You seem to have forgotten the definition and rules of
superposition. Superposition applies to fields and waves.
Superposition doesn't apply to scalars. Power is a scalar.


Cecil,

Superposition has nothing whatsoever to do with scalars vs. vectors.
Superposition has everything to do with linearity.

73,
Gene
W4SZ