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MAXIMUM power transfer is using voltage bridging. But only if you are able to choose a LOW output impedance. You will have to use some kind of fuse for NOT transferring maximum power and overload the source. If you have to use a significant output impedance, then impedance bridging is the solution. You will loose half the power or even more (not precise impedance matching).
-- AK45500 ( talk) 14:41, 12 July 2018 (UTC)
@ Ffffrr: The short description is meaningless nonsense. Spinning Spark 17:06, 13 May 2022 (UTC)
If you have been following the recent discussions, there is some confusion over exactly what reflection and reflection coefficient is being discussed. I hope we can agree on some terminology. Let's suppose a sequence of transmission lines labeled 1, 2, 3, etc. with the load attached to #1. Power is transmitted from the highest numbered toward the load. Let's consider the junction of #2 and #3. There are two reflection coefficients of interest. One, that I propose to call the local reflection coefficient, depends on the characteristic impedances of #2 and #3. The other, which I propose to call the composite reflection coefficient, depends on the characteristic impedance of #3 and everything downstream toward the load from the junction of #2 and #3.
In the case of a transmitter connected to an antenna by a coaxial cable, there is a local reflection coefficient at each end of the cable and a composite reflection coefficient at the transmitter end looking through the cable to the antenna. The matching problem is to put some network between the transmitter and the cable to minimize the composite reflection coefficient, even if that means there is a substantial local reflection coefficient at each end of the cable.
Likewise, at each junction there is a local and composite reflection.
We might find some standard terminology in the literature of multi-layer optical coatings.
I hope some of my helpful fellow editors can suggest better terminology or confirm my proposal to use local and composite. Overall might stand in for composite. Thanks. — Preceding unsigned comment added by Constant314 ( talk • contribs)
Please correct:
instead of: ... "The reflection creates a standing wave if there is reflection at both ends of the transmission line, ... "
please write: ... "The reflection creates a standing wave if there is reflection at the end of the transmission line, ... "
Why? Please see the Figure "Coaxial transmission line with one source and one load"
and apply it's indexing to the equation given, inserting for and for .
unless .
And once , you get standing waves, independant of at the other end.
DJ7BA ( talk) 16:21, 13 June 2022 (UTC)
@Constant314:
Issue 1:<
Completely misunderstood. Read again. If that doesn't help:
I don't argue impedance bridging at all, but the existing context - not me - of the bad sentence did call impedance bridging "unsuitable".
The bad sentence (second sentence in subsection Transmission lines) said:
The reflection creates a standing wave if there is reflection at both ends of the transmission line
This bad sentence states in other words, that for standing waves to exist, there must always be two mismatched ends.
No!
Your assumption is, I didn't think of impedance bridging, thus making a false statement.
No!
But the sentence is not generally true, however. One example is:
A mismatched antenna is connected by a transmission line to the well matching pi filter of a tube amp transmitter. In this case there is just one single mismatched end of transmission line, but that single end's mismatch certainly creates reflections on the line, causing SWR.
Be that often or not, suitable or not is not the question for the absolute statement the bad sentence claims. You don't need any match or mismatch situation at the source end for that antenna end mismatch caused SWR to happen. It is a totally source mismatch independant, load mismatch caused, SWR.
And even: You didn't revert the thing you are complaining about: Often impedance bridging must be considered, but the existing context - not me - called it unsuitable. You kept the part you complained about, but reverted my reasonable contribution.
Issue 2:
You didn't even care to explain why you reverted my second contribution with one blow.
I am not amused.
In electronics, impedance matching is the practice of designing or adjusting the input impedance or output impedance of an electrical device for a desired value. Often, the desired value is selected to maximize power transfer or minimize signal reflection.
Excellent. Couldn't be better.
In the next sentence "same impedance" is not 100% correct:
"For example, a radio transmitter can most efficiently transfer power to an antenna if the antenna and interconnecting transmission line have the same impedance as the transmitter."
Based on Stutzman-Thiele, for a radio transmitter to most efficiently transfer power to the antenna, two matching networks are needed:
The network to the right matches the antenna impedance to the transmission line's characteristic impedance. It adjusts for identical impedance match.
The one to the left matches the transmitter impedance to the impedance, the transmitter sees at the left end of the transmission line. It adjusts for conjugate impedance match.
In many cases, for the sake of simplicity, there is only the (easy to reach and tune) transmittter end matching network, as shown by Stutzman-Thiele fig. 30a.
In this common case, conjugate match only is used, not identical impedance match. In many cases this will yield good overall power transfer, but not full achievable optimum.
Let's change the sentence to:
"For example, a radio transmitter can most efficiently transfer power to an antenna if the antenna and interconnecting transmission line are matched for same impedances, and the transmitter and the transmission line are matched to have conjugate impedances." [1]
If that is a bit too complicated in a lead, let's better say alternatively:
"For example, a radio transmitter can most efficiently transfer power to an antenna if the antenna is matched to the interconnecting transmission line and the transmitter is
matched to the line, too." [1]
This will postpone the different types of match to a more detailed, later section.
[1] Warren L. Stutzman, Gary A. Thiele, Antenna Theory and Design, – 3rd ed. ISBN 978-0-470-57664-9 (hardback) Antennas (Electronics) I. Thiele, Gary A. ch. 6.4.1 transmission lines. p. 176, eq. 6-30b [1]
DJ7BA ( talk) 09:33, 14 June 2022 (UTC)
Instead of:
Complex conjugate matching is used when maximum power transfer is required, namely
where a superscript * indicates the
complex conjugate. A conjugate match is different from a reflection-less match when either the source or load has a reactive component.
It should read:
Complex conjugate matching is used when maximum power transfer is required, namely
where a superscript * indicates the complex conjugate of the source impedance
Reflectionless matching is used when reflection suppression on a transmission line is required, namely
where is the characteristic impedance of the transmission line.
This will make the disputed equations visible. No convincing reason for earlier deletion was given.
The bad sentence to be removed sais:
This is bad because:
1. Comparing apples with pears is misleading: A conjugate match is always different from a reflection-less match by matching goal, physics, equation, quantities given, and character of real part of impedance type: The real part of source impedance is dissipative, while the real part of the characteristic line impedance is not (or just partially in case of a lossy line) dissipative.
2. If anything is just looking alike (though being different anyway), it is the equation in the case of a real only source impedance, when
3. means that is real only, independant of the load impedance, that does not matter for the look-alike.
4. If “either the source or the load impedance” can include the case that only the load impedance is reactive, and the source impedance is not, both equations do look alike. For some English (slang?) language backgrounds, however, the word “either” may be ambiguous and could mean “both”, but not for all backgrounds. This is why it is a bad choice of words even in that look alike case.
5. If, however, only the source impedance (or the characteristic line impedance, respectively) is reactive, but he load impedance is not, The equations d o n o t look alike. In that case the logic of the bad sentence fails.
5. A reason, why this apple-pear comparison often goes undisputed is: It is quite common practice to use a common misnomer and call reflection, what rigorously speaking is just conjugate impedance mismatch. Reflection of waves has the necessary prerequisite of a medium for the waves to travel and to be reflected, i.e. a transmission line. But many are inclined to think that both types are indeed reflections in some undefined, never proven way of meaning. The page should not endorse this misleading ambigouity, that probably had influenced the bad sentence.
6. The second bulleted quote in impedance matching devices is not saying the same thing as the bad sentence. As far as I can see, it is 100% correct. If it was the same, but it isn't, the bad sentence would mean doubling, which would not be excellent wiki style.
A final excuse:
Because of multiple editors editing at the same time, my edit summary explanation got lost and the deletion looked like an edit war attempt. Sorry for that. I certainly didn't mean edit warring.
DJ7BA (
talk)
10:20, 17 June 2022 (UTC)
Yes, I agree with both replies.
The problem was that by over-reverting to some too early date, and large scale deletions much reflectionless matching subject was co-deleted. Orphaned remainder now doesn't make sense without the lost context. Good contributions simply disappeared, too, in one blow, without explaination or discussion in talk by RF experts. So the article currently is partially truncated.
Yes, rework is needed. This means much more work collecting and arranging good puzzle pieces than quick one-blow deletions. But there is also a good chance for improvement.
Yes, we should again have sections for reflectionless matching and for maximum power transfer matching. After these sections we can use an adjusted, distinguishing, comparative statement.
Yes, the bad sentence probably was based on three impedances: source, transmission line and a load - as is common practice. An earlier figure had these, but also was victim of co-deleting.
Thanks for understanding. Good cooperation.
DJ7BA (
talk)
08:29, 18 June 2022 (UTC)
Suggestion for a new section:
Placeholder for S. Roberts Fig. 1 - Equivalent circuit of generator and load
(Naming and index Question:
Is it ok by wiki rules, to use our existing, electrically identical circuit - almost a copy of the very similar Roberts circuit - and adjust the equation quantities and indices in the derivation to conform with our existing circuit? Or must we be so narrow-minded and are indeed forced to show two almost identical circuits? Copying the original might perhaps infringe copyrights. Help me, please. As newcomer and I don't know it. And I don't want to get avoidable reverts either.)
A
Thévenin's equivalent circuit of a
generator with
voltage source and fixed, complex
source impedance is terminated by an adjustable complex
load impedance .
Maximum real power transfer to the resistive part of the load occurs, if impedances and are
conjugate complex to each other. S. Roberts in 1946 published a
derivation of how
real power in the load resistance will be affected if the
impedances differ from the optimum conjugate values.
[1]
In the following the asterisk * denotes conjugate complex:
where and are the real parts of and .
This can also be written
where
and
By analogy with transmission lines, is called the "reflection coefficient" of the load as viewed from the generator. It differs from the corresponding reflection coefficient on the ordinary image basis in that the numerator contains the complex conjugate of .
(Emphasis because of reflection coefficient ambiguaty.)
... so far for now, to be continued.
DJ7BA (
talk)
14:42, 21 June 2022 (UTC)
References
![]() | This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 | Archive 2 | Archive 3 |
MAXIMUM power transfer is using voltage bridging. But only if you are able to choose a LOW output impedance. You will have to use some kind of fuse for NOT transferring maximum power and overload the source. If you have to use a significant output impedance, then impedance bridging is the solution. You will loose half the power or even more (not precise impedance matching).
-- AK45500 ( talk) 14:41, 12 July 2018 (UTC)
@ Ffffrr: The short description is meaningless nonsense. Spinning Spark 17:06, 13 May 2022 (UTC)
If you have been following the recent discussions, there is some confusion over exactly what reflection and reflection coefficient is being discussed. I hope we can agree on some terminology. Let's suppose a sequence of transmission lines labeled 1, 2, 3, etc. with the load attached to #1. Power is transmitted from the highest numbered toward the load. Let's consider the junction of #2 and #3. There are two reflection coefficients of interest. One, that I propose to call the local reflection coefficient, depends on the characteristic impedances of #2 and #3. The other, which I propose to call the composite reflection coefficient, depends on the characteristic impedance of #3 and everything downstream toward the load from the junction of #2 and #3.
In the case of a transmitter connected to an antenna by a coaxial cable, there is a local reflection coefficient at each end of the cable and a composite reflection coefficient at the transmitter end looking through the cable to the antenna. The matching problem is to put some network between the transmitter and the cable to minimize the composite reflection coefficient, even if that means there is a substantial local reflection coefficient at each end of the cable.
Likewise, at each junction there is a local and composite reflection.
We might find some standard terminology in the literature of multi-layer optical coatings.
I hope some of my helpful fellow editors can suggest better terminology or confirm my proposal to use local and composite. Overall might stand in for composite. Thanks. — Preceding unsigned comment added by Constant314 ( talk • contribs)
Please correct:
instead of: ... "The reflection creates a standing wave if there is reflection at both ends of the transmission line, ... "
please write: ... "The reflection creates a standing wave if there is reflection at the end of the transmission line, ... "
Why? Please see the Figure "Coaxial transmission line with one source and one load"
and apply it's indexing to the equation given, inserting for and for .
unless .
And once , you get standing waves, independant of at the other end.
DJ7BA ( talk) 16:21, 13 June 2022 (UTC)
@Constant314:
Issue 1:<
Completely misunderstood. Read again. If that doesn't help:
I don't argue impedance bridging at all, but the existing context - not me - of the bad sentence did call impedance bridging "unsuitable".
The bad sentence (second sentence in subsection Transmission lines) said:
The reflection creates a standing wave if there is reflection at both ends of the transmission line
This bad sentence states in other words, that for standing waves to exist, there must always be two mismatched ends.
No!
Your assumption is, I didn't think of impedance bridging, thus making a false statement.
No!
But the sentence is not generally true, however. One example is:
A mismatched antenna is connected by a transmission line to the well matching pi filter of a tube amp transmitter. In this case there is just one single mismatched end of transmission line, but that single end's mismatch certainly creates reflections on the line, causing SWR.
Be that often or not, suitable or not is not the question for the absolute statement the bad sentence claims. You don't need any match or mismatch situation at the source end for that antenna end mismatch caused SWR to happen. It is a totally source mismatch independant, load mismatch caused, SWR.
And even: You didn't revert the thing you are complaining about: Often impedance bridging must be considered, but the existing context - not me - called it unsuitable. You kept the part you complained about, but reverted my reasonable contribution.
Issue 2:
You didn't even care to explain why you reverted my second contribution with one blow.
I am not amused.
In electronics, impedance matching is the practice of designing or adjusting the input impedance or output impedance of an electrical device for a desired value. Often, the desired value is selected to maximize power transfer or minimize signal reflection.
Excellent. Couldn't be better.
In the next sentence "same impedance" is not 100% correct:
"For example, a radio transmitter can most efficiently transfer power to an antenna if the antenna and interconnecting transmission line have the same impedance as the transmitter."
Based on Stutzman-Thiele, for a radio transmitter to most efficiently transfer power to the antenna, two matching networks are needed:
The network to the right matches the antenna impedance to the transmission line's characteristic impedance. It adjusts for identical impedance match.
The one to the left matches the transmitter impedance to the impedance, the transmitter sees at the left end of the transmission line. It adjusts for conjugate impedance match.
In many cases, for the sake of simplicity, there is only the (easy to reach and tune) transmittter end matching network, as shown by Stutzman-Thiele fig. 30a.
In this common case, conjugate match only is used, not identical impedance match. In many cases this will yield good overall power transfer, but not full achievable optimum.
Let's change the sentence to:
"For example, a radio transmitter can most efficiently transfer power to an antenna if the antenna and interconnecting transmission line are matched for same impedances, and the transmitter and the transmission line are matched to have conjugate impedances." [1]
If that is a bit too complicated in a lead, let's better say alternatively:
"For example, a radio transmitter can most efficiently transfer power to an antenna if the antenna is matched to the interconnecting transmission line and the transmitter is
matched to the line, too." [1]
This will postpone the different types of match to a more detailed, later section.
[1] Warren L. Stutzman, Gary A. Thiele, Antenna Theory and Design, – 3rd ed. ISBN 978-0-470-57664-9 (hardback) Antennas (Electronics) I. Thiele, Gary A. ch. 6.4.1 transmission lines. p. 176, eq. 6-30b [1]
DJ7BA ( talk) 09:33, 14 June 2022 (UTC)
Instead of:
Complex conjugate matching is used when maximum power transfer is required, namely
where a superscript * indicates the
complex conjugate. A conjugate match is different from a reflection-less match when either the source or load has a reactive component.
It should read:
Complex conjugate matching is used when maximum power transfer is required, namely
where a superscript * indicates the complex conjugate of the source impedance
Reflectionless matching is used when reflection suppression on a transmission line is required, namely
where is the characteristic impedance of the transmission line.
This will make the disputed equations visible. No convincing reason for earlier deletion was given.
The bad sentence to be removed sais:
This is bad because:
1. Comparing apples with pears is misleading: A conjugate match is always different from a reflection-less match by matching goal, physics, equation, quantities given, and character of real part of impedance type: The real part of source impedance is dissipative, while the real part of the characteristic line impedance is not (or just partially in case of a lossy line) dissipative.
2. If anything is just looking alike (though being different anyway), it is the equation in the case of a real only source impedance, when
3. means that is real only, independant of the load impedance, that does not matter for the look-alike.
4. If “either the source or the load impedance” can include the case that only the load impedance is reactive, and the source impedance is not, both equations do look alike. For some English (slang?) language backgrounds, however, the word “either” may be ambiguous and could mean “both”, but not for all backgrounds. This is why it is a bad choice of words even in that look alike case.
5. If, however, only the source impedance (or the characteristic line impedance, respectively) is reactive, but he load impedance is not, The equations d o n o t look alike. In that case the logic of the bad sentence fails.
5. A reason, why this apple-pear comparison often goes undisputed is: It is quite common practice to use a common misnomer and call reflection, what rigorously speaking is just conjugate impedance mismatch. Reflection of waves has the necessary prerequisite of a medium for the waves to travel and to be reflected, i.e. a transmission line. But many are inclined to think that both types are indeed reflections in some undefined, never proven way of meaning. The page should not endorse this misleading ambigouity, that probably had influenced the bad sentence.
6. The second bulleted quote in impedance matching devices is not saying the same thing as the bad sentence. As far as I can see, it is 100% correct. If it was the same, but it isn't, the bad sentence would mean doubling, which would not be excellent wiki style.
A final excuse:
Because of multiple editors editing at the same time, my edit summary explanation got lost and the deletion looked like an edit war attempt. Sorry for that. I certainly didn't mean edit warring.
DJ7BA (
talk)
10:20, 17 June 2022 (UTC)
Yes, I agree with both replies.
The problem was that by over-reverting to some too early date, and large scale deletions much reflectionless matching subject was co-deleted. Orphaned remainder now doesn't make sense without the lost context. Good contributions simply disappeared, too, in one blow, without explaination or discussion in talk by RF experts. So the article currently is partially truncated.
Yes, rework is needed. This means much more work collecting and arranging good puzzle pieces than quick one-blow deletions. But there is also a good chance for improvement.
Yes, we should again have sections for reflectionless matching and for maximum power transfer matching. After these sections we can use an adjusted, distinguishing, comparative statement.
Yes, the bad sentence probably was based on three impedances: source, transmission line and a load - as is common practice. An earlier figure had these, but also was victim of co-deleting.
Thanks for understanding. Good cooperation.
DJ7BA (
talk)
08:29, 18 June 2022 (UTC)
Suggestion for a new section:
Placeholder for S. Roberts Fig. 1 - Equivalent circuit of generator and load
(Naming and index Question:
Is it ok by wiki rules, to use our existing, electrically identical circuit - almost a copy of the very similar Roberts circuit - and adjust the equation quantities and indices in the derivation to conform with our existing circuit? Or must we be so narrow-minded and are indeed forced to show two almost identical circuits? Copying the original might perhaps infringe copyrights. Help me, please. As newcomer and I don't know it. And I don't want to get avoidable reverts either.)
A
Thévenin's equivalent circuit of a
generator with
voltage source and fixed, complex
source impedance is terminated by an adjustable complex
load impedance .
Maximum real power transfer to the resistive part of the load occurs, if impedances and are
conjugate complex to each other. S. Roberts in 1946 published a
derivation of how
real power in the load resistance will be affected if the
impedances differ from the optimum conjugate values.
[1]
In the following the asterisk * denotes conjugate complex:
where and are the real parts of and .
This can also be written
where
and
By analogy with transmission lines, is called the "reflection coefficient" of the load as viewed from the generator. It differs from the corresponding reflection coefficient on the ordinary image basis in that the numerator contains the complex conjugate of .
(Emphasis because of reflection coefficient ambiguaty.)
... so far for now, to be continued.
DJ7BA (
talk)
14:42, 21 June 2022 (UTC)
References