Loading Coils; was : Vincent antenna
 

"AI4QJ" wrote in
:

...
reflected currents in time. For a transmission line that is
electricall 2pi radians, I will always measure 0 volts at the
feedpoint and the endpoint of the line.

You must be assuming s/c at the endpoint?

For an open circuited transmission line, the phase shift between the
forward and reflected waves will have to be pi radians. The maximum
amplitude will be 2X.

The term "waves" isn't very clear. To resolve the issue that current into
the load is zero, a reflected wave of -I and consequently +V is required.
Now which "wave" is "phase shifted pi radians".

We are talking the same language now. We can agree that the only phase

Hmmm!

Owen

Loading Coils; was : Vincent antenna
 

Tom Donaly wrote:

He's trying the old if-I'm-unreasonable-enough-I-can-get-him-to-quit-
posting routine. In other words, he's hoping you'll give up in anger.
I think it's about time to boycott Cecil - and his Sancho Panzas -
again. He makes no more sense than he ever did, and arguing with him
is a waste of energy anyway.
73,
Tom Donaly, KA6RUH

It's useful to remember that in certain regions of and sub-cultures in
this country, the "winner" of a brawl or an argument is defined as the
last man standing. So all tactics are based on this goal. There's no
doubt this is the result being sought here.

Roy Lewallen, W7EL

Loading Coils; was : Vincent antenna
 

Richard Clark wrote:

...
It would appear that our author has some doubt about the statement
above to have prefaced it with "if." A grammarian would point out
that there is no corresponding "then." As this doubt is obviously a
contorted product of tension, I won't look for spelling errors that
Cecil would expect me to find.
...
73's
Richard Clark, KB7QHC

Richard:

The majority of your text has turned to attacking personalities instead
of attacking ignorance, "wifes' tales", inaccuracies, mis-calculations, etc.

Not only is this boring, it is plain disgusting. My gawd man, step back
for a moment or two and get a hold of yourself.

When you play the Shakespearian-antagonist in this comedic melodrama, I
find it amusing and entertaining (if sometimes trying.)

Come back to reality man ... you ain't done nothing yet which we have
not all been guilty of at one time or another. I enjoy the debate and
the flurry of "boning up on smith charts", don't ruin it for the rest of
us ... since I have adopted Arts' "Gaussian Theory", I have to keep iron
objects away from my antenna, thats' bad enough! Let us who would like
to have some fun--have it! grin

A lot of this is above my head, I have to strive to get the tools to
understand it--isn't that how it was meant to be when we entered the
ranks of amateur radio. I don't want a "Radio Oracle(s)" in r.r.a.a who
tells me of visions or "all is already known", it just ruins the
mistique, adventure and technical challenge which drew me here ... of
course, you are chatting with a fellow which used to listed to "theater
radio" on SW--"Only the Shadow knows!"

Besides, it's Christmas!

Regards,
JS

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:

...
It's useful to remember that in certain regions of and sub-cultures in
this country, the "winner" of a brawl or an argument is defined as the
last man standing. So all tactics are based on this goal. There's no
doubt this is the result being sought here.

Roy Lewallen, W7EL

Hmmm, I can't seem the .ez file attachment to support your text--did you
forget to attach it?

Regards,
JS

Loading Coils; was : Vincent antenna
 

On Sun, 09 Dec 2007 16:40:55 -0600, Cecil Moore
wrote:

Richard Clark wrote:
It's not like you have actually pointed to any specific datum that was
in error.

If you believe that, you have your blinders on, which
any rational person already knew. A 3 ns delay through
a 2" dia, 100T, 10" coil at 4 MHz is impossible!!! Is
that specific enough for you?

Your data was more eloquent. Gad! you must hate it as much as you
avoid its mention.

Unfortunately, in the last 127 postings ...

You are responsible for half of those. I predicted
that you were going to complain about my number of
postings engineered by you and I was right.

After the bruising testimony of your own measurement, you certainly
needed some victory. :-)

Um, does your personal tragedy lead anywhere? I'm not interested in
reading the repetition of "impossible" being cried into your pillow.
Certainly you still have time to rummage up something lost in the
folds and recesses of that MENSA approved mind. Tom and your results
could have happened with Arthur's principle of antigravity, couldn't
it? That doesn't need anymore proof than your plaintive wails into
the cold void of an uncaring universe.

Roy and the others call this "last man standing." Myself, I would say
it is what the law calls an attractive nuisance - and barring
correspondence with any technical content, it is far more fun. Your
legacy is that for many, this is your ONLY exposure.

You want to be last? Hug Tom and pull the pin!

Loading Coils; was : Vincent antenna
 

Tom Donaly wrote:
I think it's about time to boycott Cecil

Which means that you have run my suggested experiments
and realize that I am right so you are going to ploink
me like others have done in the past. Somehow, I
expected more out of you, Tom, than simply the guru
party line.

If I am wrong, it should be easy to prove. If I am
right, I deserve to be boycotted???? Shades of Galileo.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Roger wrote:
Hi Roy,

Could I add this observation? Both traveling waves and standing waves
can be measured. A single volt meter or ammeter will measure the
standing wave which is the sum of the traveling waves..

This isn't quite correct. A standing wave is the result of isn't the sum
of traveling waves. It's a description of the envelope of the current
distribution that sum produces. The sum of the traveling wave voltages
is the total voltage. The sum of the traveling wave currents is the
total current. It's relatively to measure the total voltage or current
at any point and, if you measure them at enough points you can use the
measurements to draw a graph of the standing wave.

A DIRECTIONAL
volt meter or ammeter will measure only the traveling wave within the
design direction, but can not distinguish between components from
multiple reflections that might combine.

Yes.

A directional voltmeter or ammeter will measure the same voltage or
current no matter where it is placed in the transmission line under
steady state conditions, assuming no resistive losses in the
transmission line.

That's only partially true. Both the traveling waves and the total
voltage and current have not only magnitude but also phase. A
directional coupler can measure both the magnitude and phase of the
traveling waves (but some directional detectors like a Bird wattmeter
indirectly measure only the amplitude). Traveling wave measurements at
different points along a lossless line will have the same magnitude, but
different phases. So the voltages or currents at those points aren't the
same.

Roy Lewallen, W7EL

Loading Coils; was : Vincent antenna
 

Owen Duffy wrote:
"AI4QJ" wrote in
We are talking the same language now. We can agree that the only phase

Hmmm!

Be careful, Dan, the gurus are positioning you within
their politically incorrect sights. Next will come an
inquisition level attack with zero technical content
that will leave you wondering what happened.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:
It's useful to remember that in certain regions of and sub-cultures in
this country, the "winner" of a brawl or an argument is defined as the
last man standing. So all tactics are based on this goal. There's no
doubt this is the result being sought here.

So let us in on your strategy, Roy. You freely admit
that the phase of standing-wave current is unchanging
yet you use exactly that current to "measure" the phase
shift through a loading coil. You admit that your methods
are meaningless but you continue to stand by them. Please
explain your agenda. Are you trying to establish a new
religion or what?
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

AI4QJ wrote:
That is the ONLY phase information I can glean. It is fairly useless
knowledge. It says NOTHING about the delay of the current through the coil
including a loading coil that is functioning partially as an antenna.

Now if you can only convince W7EL and W8JI, you will
have accomplished more than I have in the past 3 years.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Richard Clark wrote:
You want to be last? Hug Tom and pull the pin!

"He who laughs last, laughs best." Stand by.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

On Sun, 09 Dec 2007 15:11:49 -0800, John Smith
wrote:

The majority of your text has turned to attacking personalities

Personal advice from the anonymous. More irony than value there; and
you could as easily be Ossama Bin Forgotten wishing us Deadly
Christmas and a Satan hugging New Year muttered under your beard.

Others might teach me about manners, but they haven't weighed in, have
they? They would put the substance of their names behind their
lesson, and they would have a reputation of civil discourse in
contrast to mine. It's happened before, but you and Cecil aren't
standing in that long line.

Not only is this boring, it is plain disgusting. My gawd man, step back
for a moment or two and get a hold of yourself.

As for being bored? This has been a grind, certainly; 600+ postings
informs us all of that! [Talk about the bleeding obvious. Reggie
would have his thumb in your eye.] You getting bored, however, speaks
only to your own veiled hedonism. Your moral balance is seized with
the rust of anonymity.

Want to move away from personalities? Try participating with
technical comments or providing data. Cecil abandoned it with his
claim of being hounded with 20 questions. How many more than 20
questions litter this thread from him? How much data arrived from
those 20 questions? Did you find yourself informed during that
interchange? Did none of them raise your interest to engage your own
participation? Was there anything in their relation to the
measurement that revealed success or failure? Did you find anything
"personal" in their revelation? Did you laud or challenge that
enquiry or its analysis? Did it elicit any questions? Frankly, you
show very little interest in these topics except when the
entertainment becomes a bit too purple. It has, no doubt about it;
but you don't even have the critic's qualifications to do anything
more than phone in a vote to American Idol and hope Simon doesn't pick
up the line.

You chose to respond to the comedy, and stood silent in the exchange
of idea and information. No, I don't see any lesson offered here by
you that you don't need learning first.

73's
Richard Clark, KB7QHC

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
Tom Donaly wrote:
I think it's about time to boycott Cecil

Which means that you have run my suggested experiments
and realize that I am right so you are going to ploink
me like others have done in the past. Somehow, I
expected more out of you, Tom, than simply the guru
party line.

If I am wrong, it should be easy to prove. If I am
right, I deserve to be boycotted???? Shades of Galileo.

I don't have time to run your suggested experiments, Cecil.
I'm sure that even you will be able to do them, yourself, given the will.
73,
Tom Donaly, KA6RUH

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:
A standing wave is the result of isn't the sum
of traveling waves. It's a description of the envelope of the current
distribution that sum produces.

At least three years ago, I told W7EL that the equation
for standing wave current is K*cos(kx)*cos(wt) so he
is well aware that his above assertion is false. I
have no idea why he chooses to promote some personal
agenda instead of technical facts.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Tom Donaly wrote:
I don't have time to run your suggested experiments, Cecil.

I suspect that you have run those experiments and know
that I am right so you can't afford to post the results.
Many gurus have sacrificed their integrity in like manner.

If I am so wrong, someone should have been able to prove
it by now based on bench experiments. The lack of proof
that I am wrong speaks volumes.

What I don't understand is the agenda to promote false
technical concepts. Could you explain that to us?
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Richard Clark wrote:
...
Personal advice from the anonymous. More irony than value there; and
you could as easily be Ossama Bin Forgotten wishing us Deadly
Christmas and a Satan hugging New Year muttered under your beard.


As Cecil, so eloquently, pointed out--others will know you by your
posts, they'll figure me out too ...

Others might teach me about manners, but they haven't weighed in, have
they? They would put the substance of their names behind their
lesson, and they would have a reputation of civil discourse in
contrast to mine. It's happened before, but you and Cecil aren't
standing in that long line.


Yes, shallow "Hero Worship" is at the core of your being ... we already
knew that, you kiss the gods butt, they kiss yours--sometimes ...


As for being bored? This has been a grind, certainly; 600+ postings
informs us all of that! [Talk about the bleeding obvious. Reggie
would have his thumb in your eye.] You getting bored, however, speaks
only to your own veiled hedonism. Your moral balance is seized with
the rust of anonymity.


I pity newbie hams, they have to figure out that your kind can be easily
avoided and the hobby can still be enjoyable, too bad we lose a few that
can't stomach the BS ...

Want to move away from personalities? Try participating with
technical comments or providing data. Cecil abandoned it with his
claim of being hounded with 20 questions. How many more than 20
questions litter this thread from him? How much data arrived from
those 20 questions? Did you find yourself informed during that
interchange? Did none of them raise your interest to engage your own
participation? Was there anything in their relation to the
measurement that revealed success or failure? Did you find anything
"personal" in their revelation? Did you laud or challenge that
enquiry or its analysis? Did it elicit any questions? Frankly, you
show very little interest in these topics except when the
entertainment becomes a bit too purple. It has, no doubt about it;
but you don't even have the critic's qualifications to do anything
more than phone in a vote to American Idol and hope Simon doesn't pick
up the line.


Frankly, and certainly, at this point, I do not feel accustomed enough
to a smith chart, the "nuiances" of reflected waves nor the esoteric
concepts which are being argued--I am attempting to come up to speed.
Nothing wrong with being a student and that is what I am in this
debate/exchange/discourse/argument/etc.

You chose to respond to the comedy, and stood silent in the exchange
of idea and information. No, I don't see any lesson offered here by
you that you don't need learning first.


Richard, if you could not have made it as a test tech, you could have
always joined the circus as a clown, I am sure you would have been quite
successful! I only wonder how clowns of the Shakespearian era dressed? ;-)

73's
Richard Clark, KB7QHC

3's right back at 'ya--good buddy,
and regards,
JS

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:
Roger wrote:
Hi Roy,

Could I add this observation? Both traveling waves and standing
waves can be measured. A single volt meter or ammeter will measure
the standing wave which is the sum of the traveling waves..

This isn't quite correct. A standing wave is the result of isn't the
sum of traveling waves. It's a description of the envelope of the
current distribution that sum produces. The sum of the traveling wave
voltages is the total voltage. The sum of the traveling wave currents
is the total current. It's relatively to measure the total voltage or
current at any point and, if you measure them at enough points you can
use the measurements to draw a graph of the standing wave.
Yes, you have said it better than I.

A DIRECTIONAL volt meter or ammeter will measure only the traveling
wave within the design direction, but can not distinguish between
components from multiple reflections that might combine.

Yes.

A directional voltmeter or ammeter will measure the same voltage or
current no matter where it is placed in the transmission line under
steady state conditions, assuming no resistive losses in the
transmission line.

That's only partially true. Both the traveling waves and the total
voltage and current have not only magnitude but also phase. A
directional coupler can measure both the magnitude and phase of the
traveling waves (but some directional detectors like a Bird wattmeter
indirectly measure only the amplitude). Traveling wave measurements at
different points along a lossless line will have the same magnitude,
but different phases. So the voltages or currents at those points
aren't the same.

Roy Lewallen, W7EL
This last paragraph gets to the heart of the issue. One concept of a
transmission line is that the traveling wave is always in phase in the
sense that the power contained in the wave is the envelope that is
properly considered. In this concept, the voltage and current are
always in phase, MUST be in phase. This power wave may be split as at a
reflection point, but the components will never be out of phase because
the power calculation would be incorrect.if it was out of phase.

The second concept of a transmission line allows the traveling wave to
have voltage out of phase with the current. Here the power can be all
stored in either the current (magnetic) field or the voltage field,
depending upon the phase of the traveling wave. The character of the
wave changes (so to speak) depending upon location and phase.

If the transmission line is terminated with a resistance, the
constantly-in-phase traveling wave concept provides the theoretical
basis for calculation of the reflection coefficient.

I think that consideration of the conditions at the end of a
transmission line are a good place to examine as we try to get some
experimental guidance.

If the transmission line is shorted (or open), it is hard to visualize
how the voltage (or current) could flow to the short (or open) and then
just disappear. Does the wave cancel (or disappear) at the
intersection (open end)? Do the waves pass through each other, so we
see only the vector sum? Do the waves "pile up" at the open end, but
not at the short?

The constantly-in-phase traveling wave concept requires the
difficult-to-believe observation that a directional ammeter placed very
near the end of an open transmission line will read the same current as
if it were placed at the source end. Perhaps someone can perform that
experiment some day, but I can not imagine how it can be done without
placing a load on the line, thus invalidating the initial assumptions.

73, Roger, W7WKB

Loading Coils; was : Vincent antenna
 

Roger wrote:
Roy Lewallen wrote:

That's only partially true. Both the traveling waves and the total
voltage and current have not only magnitude but also phase. A
directional coupler can measure both the magnitude and phase of the
traveling waves (but some directional detectors like a Bird wattmeter
indirectly measure only the amplitude). Traveling wave measurements at
different points along a lossless line will have the same magnitude,
but different phases. So the voltages or currents at those points
aren't the same.

Roy Lewallen, W7EL
This last paragraph gets to the heart of the issue. One concept of a
transmission line is that the traveling wave is always in phase in the
sense that the power contained in the wave is the envelope that is
properly considered. In this concept, the voltage and current are
always in phase, MUST be in phase. This power wave may be split as at a
reflection point, but the components will never be out of phase because
the power calculation would be incorrect.if it was out of phase.

Sorry, I can't make much sense out of that. Voltage and current don't
have to be in phase in order for power (energy flow) to be present. But
I'd rather not introduce power into the discussion. It's not necessary
in explaining what I've presented, and brings the opportunity for a
whole new level of misunderstanding and folklore.

The second concept of a transmission line allows the traveling wave to
have voltage out of phase with the current. Here the power can be all
stored in either the current (magnetic) field or the voltage field,
depending upon the phase of the traveling wave. The character of the
wave changes (so to speak) depending upon location and phase.

The ratio of V to I of the traveling wave is the Z0 of the line. In a
lossless line, this is a pure resistance, so the V and I of traveling
waves are in phase.

If the transmission line is terminated with a resistance, the
constantly-in-phase traveling wave concept provides the theoretical
basis for calculation of the reflection coefficient.

The reflection coefficient can easily be calculated regardless of
whether or not the load impedance is resistive or reactive. The load
impedance doesn't have any effect on the relationship between V and I
traveling waves going the same direction; it affects only the amplitude
and phase relationship between waves going in opposite directions.

I think that consideration of the conditions at the end of a
transmission line are a good place to examine as we try to get some
experimental guidance.
If the transmission line is shorted (or open), it is hard to visualize
how the voltage (or current) could flow to the short (or open) and then
just disappear. Does the wave cancel (or disappear) at the
intersection (open end)? Do the waves pass through each other, so we
see only the vector sum? Do the waves "pile up" at the open end, but
not at the short?

The voltage and current at any point along a line, including the ends,
equals the sum of the forward and reflected voltage or current waves at
that point. At a short circuit, the voltage is zero. This means that the
sum of the forward and reverse waves at that point is zero, which in
turn means that the two are equal in magnitude and out of phase.
(Another way of saying this is that the voltage reflection coefficient
is -1 at that point.) At an open circuit, the current is zero. I'll
leave it as an exercise to the reader to figure out what this means
about the relationship between the forward and reverse traveling current
waves.

The constantly-in-phase traveling wave concept requires the
difficult-to-believe observation that a directional ammeter placed very
near the end of an open transmission line will read the same current as
if it were placed at the source end. Perhaps someone can perform that
experiment some day, but I can not imagine how it can be done without
placing a load on the line, thus invalidating the initial assumptions.

73, Roger, W7WKB

Sounds like a good experiment for you to do. Please post your results
here so others can learn from them.

Roy Lewallen, W7EL

Loading Coils; was : Vincent antenna
 

Correction:

Roy Lewallen wrote:

This isn't quite correct. A standing wave is the result of isn't the sum
of traveling waves. It's a description of the envelope of the current
distribution that sum produces. . .

It should read:

This isn't quite correct. A standing wave isn't the sum of traveling
waves. It's a description of the envelope of the current distribution
that sum produces. . .

Roy Lewallen, W7EL

Loading Coils; was : Vincent antenna
 

On Dec 9, 9:36 pm, Roger wrote:
The constantly-in-phase traveling wave concept requires the
difficult-to-believe observation that a directional ammeter placed very
near the end of an open transmission line will read the same current as
if it were placed at the source end. Perhaps someone can perform that
experiment some day, but I can not imagine how it can be done without
placing a load on the line, thus invalidating the initial assumptions.

The experiment will show the expected result but will
not help understand why. For that, examination of
the measurements and arithmetic performed by
a directional ammeter is useful.

Below, all voltages and currents are instantaneous.

Total voltage, Vt = Vf + Vr
Total current, It = If - Ir

Vf = If * Z0
Vr = Ir * Z0

Substituting....

Vt = (If + Ir) * Z0
Ir = Vt/Z0 - If

If = It + Ir
If = It + (Vt/Z0 - If)
If = (It + Vt/Z0)/2

Similarly, Ir = (It - Vt/Z0)/2

The directional ammeter measures instantaneous
Vt and It, does the above arithmetic and presents
If. A directional ammeter that presents a single
number rather than the time varying If has probably
converted the instantaneous values to RMS.

Examing It and Vt at various points on the line
and doing the above arithmetic will reveal why
the same value for If is obtained everywhere.

Directional wattmeters are more common
than directional ammeters. A directional
wattmeter does the above arithmetic then
squares If, multiplies by Z0 and presents
the results in watts.

All this from just measuring Vt and It.

....Keith

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:
This isn't quite correct. A standing wave isn't the sum of traveling
waves. It's a description of the envelope of the current distribution
that sum produces. . .

Look at this standing wave:

http://www.chemmybear.com/standing.html

The equation for that standing wave is:

Ex = E*e^j(wt-Bz) + E'*e^j(wt+Bz) [see quote below]

At one time in the cycle, the standing wave equals zero
all up and down the line.

A STANDING WAVE *IS* THE SUM OF TRAVELING WAVES.

On page 285 of "Fields and Waves in Modern Radio",
2nd edition, by Ramo and Whinnery, it gives the
equations for the forward wave, the reflected wave,
and the standing wave. Begin quote:
--------------------------------------------------
Incident Wave --- E*e^j(wt-Bz)

Reflected Wave --- -E*e^j(wt+Bz)

If Ex = 0 at z = 0 for all values of time, E' = -E.

[Standing Wave equation]
Ex = E*e^j(wt-Bz) + E'*e^j(wt+Bz) = -2jE*sin(Bz e^jwt)

[Standing wave envelope equation on page 42]
V = -2jV1*sin(Bz)

End quote:
--------------------------------------------------
The standing wave equation is simply the sum of the
traveling wave equations.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

"Keith Dysart" wrote in message
...

text cut.....
The directional ammeter measures instantaneous
Vt and It, does the above arithmetic and presents
If. A directional ammeter that presents a single
number rather than the time varying If has probably
converted the instantaneous values to RMS.
text cut......

...Keith

I don't think that the directional ammeter reads instantaneous Vt and It.
The circuits I am thinking of sample a length of line (NOT A POINT) so the
sample records average voltage (or current) from a period of time.

If I understand the methodology of the directional ammeter correctly, it
extracts energy from the wave from both magnetic (current) and voltage
components. If the components are in phase, they add, and that only occurs
with the wave going in the design direction. Yes, this is a reading of
power, not voltage or current individually. Current and voltage are
related by the Zo of the transmission line, so if we know current, we also
know voltage, and visa versa.

Agreed?

73, Roger, W7WKB

Loading Coils; was : Vincent antenna
 

On Dec 10, 10:08 am, "Roger Sparks" wrote:
"Keith Dysart" wrote in message

...

text cut.....

The directional ammeter measures instantaneous
Vt and It, does the above arithmetic and presents
If. A directional ammeter that presents a single
number rather than the time varying If has probably
converted the instantaneous values to RMS.
text cut......

...Keith

I don't think that the directional ammeter reads instantaneous Vt and It.
The circuits I am thinking of sample a length of line (NOT A POINT) so the
sample records average voltage (or current) from a period of time.

If I understand the methodology of the directional ammeter correctly, it
extracts energy from the wave from both magnetic (current) and voltage
components. If the components are in phase, they add, and that only occurs
with the wave going in the design direction. Yes, this is a reading of
power, not voltage or current individually. Current and voltage are
related by the Zo of the transmission line, so if we know current, we also
know voltage, and visa versa.

Agreed?

Only partly. If you look at the element on an instrument
like a Bird 43, you will find that it is both capacitively
and inductively coupled to the line. The capactive
coupling is sensitive to the total voltage on the line
at the point of the element, while the inductive coupling
is sensitive to the total current in the line.

The subtraction (or addition) is done in the element
where the voltage sample and the current sample
(scaled by Z0) are subtracted before being applied
to the diode. The output of the diode is the
rectified instantaneous difference of the voltage and
scaled current from the equations originally provided.
This is fed to an average responding meter which has
a scale marked to show (Vf**2)/Z0 (i.e. power).

You are correct that the element does not sample
at a point, but rather over the width of the coupling
element. This is done because of design
limitations and is one of the sources for error in the
instrument, though small if the wavelength is long
compared to the element.

There are many ways to obtain the instaneous
voltage and current for the subtraction (or addition).
Some designs measure the voltage by using
an electrical connection to the line, so these are
essentially measuring at a point. Other designs
measure the current by detecting the voltage
drop across a resistor in series with the line.

Diagrams of the internals of the Bird 43 element
are available in the Operations Manual he
http://www.bird-electronic.com/produ...uct.aspx?id=81

....Keith

Loading Coils; was : Vincent antenna
 

Keith Dysart wrote:
There are many ways to obtain the instaneous
voltage and current for the subtraction (or addition).

Here are the associated equations:

Vz = V*e^-jBz + V'*e^+jBz

Iz*Z0 = V*e^-jBz - V'*e^+jBz

Current is sampled in such a way as to perform
the multiplication by Z0. That's where the calibration
to Z0 comes in.

If one adds the two equations (samples) the reflected
terms drop out and the result is a voltage proportional
to the forward wave.

If one subtracts the two equations (samples) the
forward terms drop out and the result is a voltage
proportional to the reflected wave.
--
73, Cecil http://www.w5dxp.com

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Cecil Moore wrote:
If one adds the two equations (samples) the reflected
terms drop out and the result is a voltage proportional
to the forward wave.

If one subtracts the two equations (samples) the
forward terms drop out and the result is a voltage
proportional to the reflected wave.

Continuing: The phase of the standing-wave current
in a 1/4WL stub is constant from feedpoint to tip.
However, two directional couplers, one placed at the
1/3 point and the other placed at the 2/3 point
would allow one to see the 30 degree phase shift in
the traveling-waves at the points before diode
rectification takes place.
--
73, Cecil http://www.w5dxp.com

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Keith Dysart wrote:

Only partly. If you look at the element on an instrument
like a Bird 43, you will find that it is both capacitively
and inductively coupled to the line. The capactive
coupling is sensitive to the total voltage on the line
at the point of the element, while the inductive coupling
is sensitive to the total current in the line.

The subtraction (or addition) is done in the element
where the voltage sample and the current sample
(scaled by Z0) are subtracted before being applied
to the diode. The output of the diode is the
rectified instantaneous difference of the voltage and
scaled current from the equations originally provided.
This is fed to an average responding meter which has
a scale marked to show (Vf**2)/Z0 (i.e. power).
. . .

Another common directional wattmeter circuit is the Bruene type circuit.
This uses an ordinary current transformer to get the current sample and
a direct connection for the voltage sample. The voltage sample is
reduced to the correct proportional value via a transformer or
capacitive voltage divider. It shouldn't be hard to find a diagram of
one on the web.

Roy Lewallen, W7EL

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Roy Lewallen wrote in news:13lr7u2mueltrb3
@corp.supernews.com:

....
Another common directional wattmeter circuit is the Bruene type circuit.
This uses an ordinary current transformer to get the current sample and
a direct connection for the voltage sample. The voltage sample is
reduced to the correct proportional value via a transformer or
capacitive voltage divider. It shouldn't be hard to find a diagram of
one on the web.

The article at http://www.vk1od.net/VSWR/VSWRMeter.htm includes a simple
circuit analysis of the Breune design and some comment on the application
of the instrument.

Owen

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"Roger Sparks" wrote in
:


"Keith Dysart" wrote in message
.
..

text cut.....
The directional ammeter measures instantaneous
Vt and It, does the above arithmetic and presents
If. A directional ammeter that presents a single
number rather than the time varying If has probably
converted the instantaneous values to RMS.
text cut......

...Keith

I don't think that the directional ammeter reads instantaneous Vt and
It. The circuits I am thinking of sample a length of line (NOT A
POINT) so the sample records average voltage (or current) from a
period of time.


Many simple reflectometer designs do indeed sample the line over a short
length of line, and that short length may be 100mm or more.

Ideally, they would take the sample at a point. (Since a point has zero
length, I can't quickly think of a sampling technique that truly takes a
point sample.)

Although sampling over a non-zero length limits their accuracy somewhat,
if that length is kept sufficiently short, they are still able to provide
sufficiently accurate measurements.

Owen

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Owen Duffy wrote:
"Roger Sparks" wrote in
:


"Keith Dysart" wrote in message
.
..

text cut.....

The directional ammeter measures instantaneous
Vt and It, does the above arithmetic and presents
If. A directional ammeter that presents a single
number rather than the time varying If has probably
converted the instantaneous values to RMS.

text cut......

...Keith

I don't think that the directional ammeter reads instantaneous Vt and
It. The circuits I am thinking of sample a length of line (NOT A
POINT) so the sample records average voltage (or current) from a
period of time.



Many simple reflectometer designs do indeed sample the line over a short
length of line, and that short length may be 100mm or more.

Ideally, they would take the sample at a point. (Since a point has zero
length, I can't quickly think of a sampling technique that truly takes a
point sample.)

The voltage sample is easy... measure the voltage using an infinitely
thin probe.

The current sample is measured in a similar way by measuring the
magnetic field over a infinitely small segment of the conductor. There
are sensitivity issues or bandwidth issues, but there are lots of very,
very small magnetic field probe schemes around.


If one says, "point sample" == "less than 1/1000 wavelength), I think
it's actually pretty straight forward, certainly for 100 MHz or less.
(3mm is 1/1000 lambda).






Although sampling over a non-zero length limits their accuracy somewhat,
if that length is kept sufficiently short, they are still able to provide
sufficiently accurate measurements.

Owen

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Cecil Moore wrote:
Gene Fuller wrote:

So how many nanoseconds does that 36.6 degree phase shift represent?


As far as impedance discontinuity *points* go, a nonsense
question.

The question was excellent. 'Impedance discontinuity points' is nonsense.

How many nanoseconds does it take for a signal to travel
through a dimensionless point???? Well, let's see. What
is the speed of light multiplied by zero? Hmmmm, that's
a really tough one.

The hard part would be inverting zero sec^-1 in order to get units of
time. :-)

73, ac6xg

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Keith Dysart wrote:


It takes many more reflections of reflections before the
impedance at the input starts to look like a short.

An excellent point, Keith. And applications for it abound.

Problem is that it conflicts with the predictions made by the power
propagation model. (The politically correct name is the Joules/sec
propagation model.) That model shows that only a single reflection of
power is needed to explain the whole thing. Of course in some cases
the wave of power has to figure out how to turn around and go back the
other direction after it's been cancelled in order to conserve energy.
(A problem it wouldn't have to solve had it not violated it in the
first place.) Admittedly, some of the details have yet to be worked
out. :-)

73, ac6xg

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Jim Kelley wrote:
The question was excellent. 'Impedance discontinuity points' is nonsense.

It is common practice during an analysis to consider
the impedance discontinuity where Z0 changes to be point
connections at a plane. All of my technical books draw
the connections that way. None of them attempt to
treat the connection as anything other than points.
If you choose to analyze what happens at a 1 mm drop
of solder, be my guest.
--
73, Cecil http://www.w5dxp.com

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On Mon, 10 Dec 2007 21:04:06 GMT, Owen Duffy wrote:

I can't quickly think of a sampling technique that truly takes a
point sample.

Slotted line.

73's
Richard Clark, KB7QHC

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Richard Clark wrote:
On Mon, 10 Dec 2007 21:04:06 GMT, Owen Duffy wrote:


I can't quickly think of a sampling technique that truly takes a
point sample.


Slotted line.

Doesn't take current sample

Probe is of finite size (albeit small fraction of lambda in most cases)

The difficulty of making accurate RF current measurements at a point is
why things like slotted lines were invented. You can measure voltage at
a series of points and calculate what the current *must* be.

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Richard Clark wrote in
:

On Mon, 10 Dec 2007 21:04:06 GMT, Owen Duffy wrote:

I can't quickly think of a sampling technique that truly takes a
point sample.

Slotted line.

73's
Richard Clark, KB7QHC


Thanks Richard and Jim,

I mean't literally a point sample, and I doubt that we can manufacture a
probe for either voltage or current that has zero dimensions (ie is
influenced ONLY by conditions at a point of no physical size.).

I go on to say (if you read on) in different words that notwithstanding
that, practical probes can be made that give acceptable accuracy.

They unsaid key thing is that these probes do not depend on averaging
over a length of line (as Roger suggested), that is actually a defect
that limits their usable upper frequency.

Owen

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Jim Kelley wrote:
Problem is that it conflicts with the predictions made by the power
propagation model. (The politically correct name is the Joules/sec
propagation model.) That model shows that only a single reflection of
power is needed to explain the whole thing. Of course in some cases the
wave of power has to figure out how to turn around and go back the other
direction after it's been cancelled in order to conserve energy. (A
problem it wouldn't have to solve had it not violated it in the first
place.) Admittedly, some of the details have yet to be worked out. :-)

Wow Jim, you need to repeat Fields and Waves 310. :-)
You have misunderstood virtually every principle
of the wave reflection model.
--
73, Cecil http://www.w5dxp.com

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Cecil Moore wrote:
Jim Kelley wrote:

Problem is that it conflicts with the predictions made by the power
propagation model. (The politically correct name is the Joules/sec
propagation model.) That model shows that only a single reflection of
power is needed to explain the whole thing. Of course in some cases
the wave of power has to figure out how to turn around and go back the
other direction after it's been cancelled in order to conserve energy.
(A problem it wouldn't have to solve had it not violated it in the
first place.) Admittedly, some of the details have yet to be worked
out. :-)


Wow Jim, you need to repeat Fields and Waves 310. :-)
You have misunderstood virtually every principle
of the wave reflection model.

I wouldn't presume to take credit for any of the above. I learned it
on r.r.a.a. from someone who I think needs to take Fields and Waves 1.
:-)

73, ac6xg

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On Mon, 10 Dec 2007 16:16:15 -0800, Jim Lux
wrote:

Richard Clark wrote:
On Mon, 10 Dec 2007 21:04:06 GMT, Owen Duffy wrote:


I can't quickly think of a sampling technique that truly takes a
point sample.


Slotted line.

Doesn't take current sample

Hi Jim,

Never needed to with a slotted line.

Probe is of finite size (albeit small fraction of lambda in most cases)

And the time to measure anything is finite too.

The difficulty of making accurate RF current measurements at a point is
why things like slotted lines were invented. You can measure voltage at
a series of points and calculate what the current *must* be.

At worst, only three points, and generally for SWRs folks here would
agree were astronomical (and incalculable, but I could measure them
anyway).

With four fixed points (nominally eighth wave, but a range of
frequencies can be accommodated), I could determine the complex
impedance of any load. [re. "Microwave Measurements," Ginzton, Sec.
5.12] There are a myriad of other slotted line techniques, but I will
leave them for a suitable occasion.

I have never had to consider what the current *must* be - an
unnecessary elaboration.

73's
Richard Clark, KB7QHC

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Jim Kelley wrote:

Cecil Moore wrote:
Jim Kelley wrote:
Problem is that it conflicts with the predictions made by the power
propagation model. (The politically correct name is the Joules/sec
propagation model.) That model shows that only a single reflection
of power is needed to explain the whole thing. Of course in some
cases the wave of power has to figure out how to turn around and go
back the other direction after it's been cancelled in order to
conserve energy. (A problem it wouldn't have to solve had it not
violated it in the first place.) Admittedly, some of the details
have yet to be worked out. :-)

Wow Jim, you need to repeat Fields and Waves 310. :-)
You have misunderstood virtually every principle
of the wave reflection model.

I wouldn't presume to take credit for any of the above. I learned it on
r.r.a.a. from someone who I think needs to take Fields and Waves 1. :-)

If you are talking about me, you have either misunderstood
what I said or you enjoy bearing false witness. Here's a quote
from my 2005 magazine article at:

http://www.w5dxp.com/energy.htm

"The author has endeavored to satisfy the purists in this
series of articles. The term "power flow" has been avoided
in favor of "energy flow". Power is a measure of that energy
flow per unit time through a plane. Likewise, the EM fields
in the waves do the interfering. Powers, treated as scalars,
are incapable of interference. Any sign associated with a power
in this paper is the sign of the cosine of the phase angle
between two voltage phasors."

Also, here is an EXCEL spreadsheet version of what happens
during the transient buildup to steady-state.

http://www.w5dxp.com/1secsgat.gif

Do you really consider 30 iterations to be only a single
reflection?
--
73, Cecil http://www.w5dxp.com

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On Tue, 11 Dec 2007 00:36:02 GMT, Owen Duffy wrote:

I mean't literally a point sample, and I doubt that we can manufacture a
probe for either voltage or current that has zero dimensions (ie is
influenced ONLY by conditions at a point of no physical size.).

Hi Owen,

I would say that is arguable given my exposure to research in
Nanotechnology. I've seen one molecule probes (illustrated actually,
by microscopes that do enjoy vastly higher resolutions than were state
of the art 10 years ago; and they can image complex atoms and small
molecules).

These scales are commonly referred to as 1D, or quantum dots. Now,
given a measurement must be made, it demands a probe. Further, given
a quantum dot sized probe, it necessarily describes the smallest size
for which any smaller size yields no more information.

The practicality of it is that this quantum dot would have to reside
at the end of a very thin lead. A carbon nanotube so qualifies, and
they can be grown to considerable length (for this field), and they
themselves occupy no more than 1nM diameter (for a single walled
construction which is not terribly difficult to obtain).

In the practical field of RF, I seriously doubt such a probe/lead
combination would perturb a slotted line. In fact, their influence
would be lost in the decimals far to the right of the accuracy of the
line's construction. Or, I could easily imagine that most computers
would suffer rounding errors long before the probe/lead's influence
could be calculated if the line were perfect.

Yes, for the absolutist (no speaking of you Owen), a probe could never
be small enough, but if it were smaller it would be impossible to
obtain a reading. Sort of self-extermination of the absolutist
argument.

73's
Richard Clark, KB7QHC