Dave Shrader wrote:
So, are you pursuing Physics or Applications type knowledge?

And apparently, never the twain shall meet. :-)



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What happens if the twisted short is grounded as in lightning protection?
Is there any succinct difference?

--
73
Hank WD5JFR

"Cecil Moore" wrote in message
...
Reg Edwards wrote:

By how much does the length of the short-circuiting bar at the end of
the
1/4-wave stub affect its resonant length?

I just twist the ends together. I don't use a bar.

What open-circuit resonant frequency does the stub change to when the
short
circuiting bar is removed?

Same resonant frequency - virtual impedance at the input is reversed.
--
73, Cecil http://www.qsl.net/w5dxp



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Dave wrote:
you can look at it various ways.

As I mentioned above; engineers, technicians, wave mechanics,
physicists, experimenters, etc., ALL live on this list grin. Mea
Culpa, I'm a retired engineer.

Just remember, stubs WORK very well. Thank the owner of your local
repeater for tuning the stubs [AKA CAVITIES] to reduce the desense below
receiver response levels, typically -120 dB or more attenuation.


1. the wave traveling wave analysis... the harmonic goes down the stub,
reflects back, and when it gets back to the transmission line it is 180
degress out of phase with the next cycle so it cancels it at the junction...
therefore there is no harmonic to propagate down the line past the junction.
this of course will raise the hackles of the anti-reflectionists who will
then say there is also no harmonic left to propagate down the stub which
means there is a virtual short at the junction, but no way to generate it
since nothing can be there to go down the stub.

2. the power analysis. power goes in, power comes out, it all reflects back
and forth until the energy becomes infinite and the amp blows up... but of
course energy is conserved and momentum must go somewhere so the stub
probably walks across the table with each wave reflection.

3. the sinusoidal steady state analysis. this takes the stub and transforms
the shorted impedance at the far end back to the junction and then does all
calculations as if the real short existed at the junction.... this will of
course annoy the reflectionists who will point out in never ending detail
how you can't explain tv ghosts, radar, or other transient phenomena this
way... of course by assuming the sinusoidal steady state at the start you
exclude those systems from this type of analysis, but that won't stop the
protests.

4. the s analysis... who know what this will say except cecil who will find
some way to steer the discussion over to it.

5. the optical layer analysis... see above.

"Henry Kolesnik" wrote in message
...

I know they work! One of my reasons for asking the question is I've not
found any mention in the literature of where the
"attenuation/rejection/reflection/filter residue" goes.

--
73
Hank WD5JFR
"Dave" wrote in message
...

the harmonic is 'attenuated' in that the magnitude of it is reduced when

the

stub is in line. i look at it like you could replace the stub with a

lumped

filter at the same point so the term attenuation makes more sense than
reflections or rejections... i don't really care where the harmonic

goes,

i

want to know how much it is attenuated by so i can compare with other

types

of filters.

"Henry Kolesnik" wrote in message
.com...

Dave

Nice site, I like the "white paper" approach as I prefer the info

without

the glitter. I've only read a few items and I
quote: "This is a plot of the attenuation provided by the stub. You

can

see

that it provides about 32db of attenuation at 28.25Mhz. " I've

noticed

that

the literature I've purused indicates that stubs either attenuate or

reject.

None say reflect! I don't want to get into a discussion of word

definitions

becasue reflect and feject are close but attenuate is not in the same

class.

Comments...

--
73
Hank WD5JFR

"Dave" wrote in message
news
"Henry Kolesnik" wrote in message
y.com...

I know that a shorted 1/4 wave stub exhibits a very high

impedance.

But

for the 2nd harmonic it's a 1/2 wave stub and exhibits a very low

impedance

or a short. There are claims that this can be used to filter the

even

harmonics. Shorts can't diisipate power and must reflect, so how

does

a

stub work?

stubs work very nicely. you can get practical stub information at

my

web

site, including how to build a 40m to 15m 3rd harmonic stub filter:
http://www.k1ttt.net/technote/techref.html#filters

as you may have noticed by now you have kicked the proverbial

hornets

nest.

reflections are a touchy word in this group, usually attracting the

endless

argument that travels from thread to thread. in time this will

deteriorate

into name calling and endless argument over reflections,

interference,

virtual impedances, and a few other topics.

On Fri, 11 Jun 2004 18:32:14 GMT, "Henry Kolesnik"
wrote:
What if the source doesn't or can't dissipate?

Hi Hank,

Simple enough to find out. Disconnect the output of your transmitter.
Set the drive level of your transmitter for full power. Defeat the
ALC. Key down. By the clock or watch, take notes at 1 minute
intervals for, say, 10 minutes. Prepare notes into report. Submit
report here. Total time to perform: 30 seconds - 30 minutes depending
mostly on access to the ALC defeat.

This answers all equivocations about does/doesn't; will/won't;
might/mightn't; could/couldn't; or can/can't. Think about it, you
have probably spent more time than that writing to and reading from
this thread to no certain conclusion.

73's
Richard Clark, KB7QHC

Cecil Moore wrote:

SNIP

Heh, heh, you're on your own for that discussion. I personally
believe it is possible for reflected energy to wind up decreasing
the power consumption from the DC source that is supplying the finals,
which winds up decreasing the load on the 60 Hz power grid, which
decreases the oil required from the Middle East, which tends to
decrease the possibility of world war, which bodes well for the human
race, but that is another thread for another time.
--
73, Cecil http://www.qsl.net/w5dxp


Good engineering CAN solve the world's problems!!!

Just use enough 1/4 wavelength stubs and we can totally eliminate the #1
or #2 cause of international tension!!

Now, the Oil exporting states will face economic ruin! We will have to
give them foreign aid!! Damn ... taxes will have to go up!! That means
we have to elect a Demo Krapp as president.

Cecil, I didn't know you were campaigning for what's his name!!

I better be careful or my tongue may slip out of my cheek.

Sometimes, it's useful to think about problems such as this in terms of
analogous systems that behave in similar ways.

For example, imagine a gasoline-powered engine driving a water pump though a
friction belt and pulley. The pump is attempting to pump water into a short
plugged pipe (shorted transmission line). After the first couple of seconds
the reflected water from the plugged end creates a back pressure on the
pump, a situation in which the pump is then not capable of delivering
additional water to that which is stored in the pipe. Now, a number of
things can occur, short of mechanical failure of some part of the system:

1) the belt between the motor and pump can start to slip, dissipating the
energy generated by the motor as heat lost to friction in the belt and
pulley

2) the motor can slow or cease to function, incapable of working against the
increased torque (impedance) created by the belt that has been constrained
by the pump that can't pump water into the plugged pipe.

In case 1), the power is being generated by the motor, but it is not being
delivered to the load. It is being dissipated (converted to heat) `in
between.
In case 2), the power simply cannot be created. The motor can't work against
such a load. The power is not being dissipated anywhere -- it's simply not
being generated. As Cecil has suggested, in this case, the engine stops,
which stops using gasoline, which reduces the demand on the Middle East oil
supply, which lowers prices, which .....

Case 2) is not one in which reflections "cancel" the energy being generated,
although it can be thought of that way. Energy can't be "canceled" ( a
fundamental law). If a generator isn't delivering energy to a load, it's
because the energy either doesn't exist (isn't being generated), or it's
being rerouted, stored, or being converted to another form.

Although this analogy could be complicated by making it a pumping system
that generates sinusoidal water pressure waves with wavelength-related pipe
lengths, it doesn't need to be for it to work.

Al WA4GKQ


"Cecil Moore" wrote in message
...
Henry Kolesnik wrote:
What if the source doesn't or can't dissipate?

Heh, heh, you're on your own for that discussion. I personally
believe it is possible for reflected energy to wind up decreasing
the power consumption from the DC source that is supplying the finals,
which winds up decreasing the load on the 60 Hz power grid, which
decreases the oil required from the Middle East, which tends to
decrease the possibility of world war, which bodes well for the human
race, but that is another thread for another time.
--
73, Cecil http://www.qsl.net/w5dxp



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Better specify the kind of pump because a centrifugal will have a different
outcome versus a positive displacment!

--
73
Hank WD5JFR
"Al" wrote in message
...
Sometimes, it's useful to think about problems such as this in terms of
analogous systems that behave in similar ways.

For example, imagine a gasoline-powered engine driving a water pump though
a
friction belt and pulley. The pump is attempting to pump water into a
short
plugged pipe (shorted transmission line). After the first couple of
seconds
the reflected water from the plugged end creates a back pressure on the
pump, a situation in which the pump is then not capable of delivering
additional water to that which is stored in the pipe. Now, a number of
things can occur, short of mechanical failure of some part of the system:

1) the belt between the motor and pump can start to slip, dissipating the
energy generated by the motor as heat lost to friction in the belt and
pulley

2) the motor can slow or cease to function, incapable of working against
the
increased torque (impedance) created by the belt that has been constrained
by the pump that can't pump water into the plugged pipe.

In case 1), the power is being generated by the motor, but it is not being
delivered to the load. It is being dissipated (converted to heat) `in
between.
In case 2), the power simply cannot be created. The motor can't work
against
such a load. The power is not being dissipated anywhere -- it's simply not
being generated. As Cecil has suggested, in this case, the engine stops,
which stops using gasoline, which reduces the demand on the Middle East
oil
supply, which lowers prices, which .....

Case 2) is not one in which reflections "cancel" the energy being
generated,
although it can be thought of that way. Energy can't be "canceled" ( a
fundamental law). If a generator isn't delivering energy to a load, it's
because the energy either doesn't exist (isn't being generated), or it's
being rerouted, stored, or being converted to another form.

Although this analogy could be complicated by making it a pumping system
that generates sinusoidal water pressure waves with wavelength-related
pipe
lengths, it doesn't need to be for it to work.

Al WA4GKQ


"Cecil Moore" wrote in message
...
Henry Kolesnik wrote:
What if the source doesn't or can't dissipate?

Heh, heh, you're on your own for that discussion. I personally
believe it is possible for reflected energy to wind up decreasing
the power consumption from the DC source that is supplying the finals,
which winds up decreasing the load on the 60 Hz power grid, which
decreases the oil required from the Middle East, which tends to
decrease the possibility of world war, which bodes well for the human
race, but that is another thread for another time.
--
73, Cecil http://www.qsl.net/w5dxp



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-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

This place is where one can just about learn anything or nothing or learn
incorreclty. AKA the politics of reflections.

--
73
Hank WD5JFR
"Richard Clark" wrote in message
...
On Fri, 11 Jun 2004 18:32:14 GMT, "Henry Kolesnik"
wrote:
What if the source doesn't or can't dissipate?

Hi Hank,

Simple enough to find out. Disconnect the output of your transmitter.
Set the drive level of your transmitter for full power. Defeat the
ALC. Key down. By the clock or watch, take notes at 1 minute
intervals for, say, 10 minutes. Prepare notes into report. Submit
report here. Total time to perform: 30 seconds - 30 minutes depending
mostly on access to the ALC defeat.

This answers all equivocations about does/doesn't; will/won't;
might/mightn't; could/couldn't; or can/can't. Think about it, you
have probably spent more time than that writing to and reading from
this thread to no certain conclusion.

73's
Richard Clark, KB7QHC

Is there any objective reality when it comes to reflections? How do we
really know?

Henry Kolesnik wrote:

This place is where one can just about learn anything or nothing or learn
incorreclty. AKA the politics of reflections.

Well perhaps I should reword my comment. It seems like many responders are
getting into the politics of reflections, some into the theory but I believe
it's a science and should be explainable. Theories are used to explain what
goes on inside a black box that we can't open, just an input and output.
But a shorted 1/4 wave stub is about as far as you can get from a black
box.. I'm curious!
There are no stupid questions, just stupid people asking and that's me.

--
73
Hank WD5JFR
"Dave Shrader" wrote in message
news:Mp1zc.42427$HG.38082@attbi_s53...
Is there any objective reality when it comes to reflections? How do we
really know?

Henry Kolesnik wrote:

This place is where one can just about learn anything or nothing or
learn
incorreclty. AKA the politics of reflections.