"Cecil Moore" wrote in message
...
The forward current and reflected current cancel at the mouth of
the shorted 1/4WL stub. However, they add in-phase 1/4WL away at
the short, maybe to many amps of RF current at the shorted end.
Since there is no physical impedance at the mouth of a stub, nothing
except superposition of forward and reflected waves happens there
and nothing except a virtual impedance exists there. All of the action
is at the shorted end of the stub where there exists 100% reflection.
--
73, Cecil http://www.qsl.net/w5dxp

I just did the simulation again, and you are right. For a 1V signal feeding
a 50 Ohm line through a 450 Ohm series resistor, there is 20 ma of
current flowing through the short. Don't understand why I didn't see it the
other time. There is 0 current through the 450 Ohm
resistor.

Tam/WB2TT

If rattle-snake meat is fit for human consumption I assume you don't pepper
it with rat shot. Probably best washed down with a delicate dry white.
----
Reg.

"Tam/WB2TT" wrote in message
...
There is no current in the steady state. The steady state voltage is
independent of source impedance, which affect only how long it takes to
reach that. I ran a simulation on this, and you can see that as the
voltage
builds up, the current decreases

Tam


Whoops, ERROR. There is no current flowing from the source, but there is
current flowing through the short in steady state.

Tam

For Gawd sake, don't tell Cecil he's right. There'll be no stopping him!

"Reg Edwards" wrote in message
...
If rattle-snake meat is fit for human consumption I assume you don't
pepper
it with rat shot. Probably best washed down with a delicate dry white.
----
Reg.


Tastes just like chicken.
It was a head shot. No spoiled meat. I have JPEGs.
I gave the tail to one of my grad students.
Riesling or Pinot Noir?
H.

Tam/WB2TT wrote:
"Cecil Moore" wrote:

The forward current and reflected current cancel at the mouth of
the shorted 1/4WL stub. However, they add in-phase 1/4WL away at
the short, maybe to many amps of RF current at the shorted end.
Since there is no physical impedance at the mouth of a stub, nothing
except superposition of forward and reflected waves happens there
and nothing except a virtual impedance exists there. All of the action
is at the shorted end of the stub where there exists 100% reflection.

I just did the simulation again, and you are right. For a 1V signal feeding
a 50 Ohm line through a 450 Ohm series resistor, there is 20 ma of
current flowing through the short. Don't understand why I didn't see it the
other time. There is 0 current through the 450 Ohm resistor.

Install a Bird wattmeter at the 450 ohm resistor and you will read
forward power and reflected power. The *net* current through the 450
ohm resistor is zero. The forward current is not zero. The reflected
current is not zero. Their magnitudes (10 ma?) are equal and their phases
are 180 degrees from each other so they cancel to net zero current.

If we take the forward current at the 450 ohm resistor as a reference of
10 ma at zero degrees, the reflected current will be 10 ma at 180 degrees.
Those two current signals add up (superpose) to zero at the resistor.
--
73, Cecil http://www.qsl.net/w5dxp



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Tam/WB2TT wrote:
Whoops, ERROR. There is no current flowing from the source, but there is
current flowing through the short in steady state.

There is no net current flowing from the source, but there is net
current flowing through the short during steady-state. Where does that
current come from? It comes from the in-phase addition of forward
and reflected current. The voltage goes to zero and the current doubles
at a short. The zero net current from the source comes from the out-of-
phase addition (subtraction) of forward and reflected current.

This is where that darned definition comes into play. By definition,
the reflected current is being 100% re-reflected and the source is
delivering zero current or, in a system with losses, is delivering
only the amount of current needed to offset the losses.

We can argue whether the reflected current makes it back into the
source or not. But there is no argument that reflected current is
originating at the short in the 1/4WL stub because it can be
easily measured. Forward current and reflected current are very
close to equal magnitudes all up and down an efficient stub.
--
73, Cecil http://www.qsl.net/w5dxp




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Cecil, W5DXP wrote:
"The forward ciurrent and reflected current cancel at the mouth of the
shorted 1/4 WL stub. However, they add in-phase 1/4-WL away at the
short, maybe to many amps of RF current at the shorted end. Since----."

Very clear and concise. I am persuaded that once circulating current is
established, only the current required to supply losses is drawn at the
mouth of the shorted 1/4-WL stub.

Best regards, Richard Harrison, KB5WZI

Reg Edwards wrote:
For Gawd sake, don't tell Cecil he's right.

You wouldn't expect a Texan to be left, would you, Reg?



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Steve Nosko wrote:

"Richard Clark" wrote:

wrote:
Well Richard, here's your chance. Please enlighten us on J.C.
Slater's words in _Microwave_Transmission_.

What was the original question? [accredited stock response]

It's clear that R.C. loves tweeking Cecil.

Trouble is, I usually have no idea what his random ramblings
are all about.
--
73, Cecil http://www.qsl.net/w5dxp



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