On 19 mayo, 14:03, Cecil Moore wrote:
On May 18, 6:13*pm, John KD5YI wrote:

So, you're saying that the Smith chart is wrong?

The Smith Chart is a tool *- a blank graph. How could it be wrong?
Like any tool, it has limitations and can be abused.

On May 19, 4:05 am, Wimpie wrote:

Would you please remind me to the example where I was completely wrong
with S11?

----50 ohm--+--1/4WL Z0=100--200 ohm load

s11 is 0.3333 at point '+'. Put it in a box and s11 magically becomes
0.0?

The first s11 is a physical reflection coefficient, the second s11 is
a virtual reflection coefficient. The virtual 50 ohm impedance is
lossless. All the power is dissipated in the 200 ohm resistor at a
reflection coefficient of 0.3333.

Cecil,

It is very simple, the 1/4 lamba line (100 Ohms) looks into a 200 Ohms
load, so seen from that line, VSWR = 2, hence resulting in RC=0.3333.

The 50 Ohms source looks into a 50 Ohms load (you can use the quarter
wave formula). This equals VSWR=1, so RC=0. I think I wasn't wrong!
As mentioned before, a source (whether PA or small signal) doesn't see
the difference between a lumped 50 Ohms load or your quarter wave line
with 200 Ohms load. Whether or not it is "physical" or "virtual" is
also not relevant, just the complex V/I ratio (we call that impedance)
counts.

The RC inside the line is of no relevance for the PA.


Did you ever DESIGNED some serious electronic hardware?

No, but being a good designer has nothing to do with the present
academic exercise.

It may be of importance w.r.t. selecting the right model to solve
technical problems. A good example what can happen when selecting
over-the-top approaches is this thread.

W8JI is a good designer yet concepts like yours led
him to "measure" a 3 ns delay through a 100 uH air-core 80m loading
coil when the actual delay time is closer to 21.5 ns. That's what
happens when one relies on the lumped-circuit model and ignores
reflected energy. The relative phase of a standing wave doesn't change
with length which gives the illusion that the signal is traveling
faster than the speed of light, i.e. zero phase delay.

I will turn the coil example into a brainteaser and post it to my web
page.
--
73, Cecil, w5dxp.com

Wim
PA3DJS
www.tetech.nl