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Where does it go? (mismatched power)
On Sat, 12 Jun 2010 19:52:15 GMT, Owen Duffy wrote:
To be usable, any pretence of linearity at least over a limited range of loads, power, frequency, Zeq must be sufficiently constant within that range. Hi Owen, Well I see neither data of that Z over Loads over Power over Frequency, nor do I read what you would call what is "usable." The meaning of "sufficiently" is proposed in the reference article describing the test and providing the mathematical basis for the test. "Sufficiently" is a subjective term for which I see no objective criteria. My recollection of Walt's tests were that they tested at points other than Zl=0 and Zl=infinity. Steps 1 and 2 are quite explicit. You dwell at some further length on the implicit accuracy of the stated quantity, but ignore the explicit discussion about a reasonable tolerance for the test. I see no further discussion of my observation of the possibility of 51 Ohms being, in your terms, "usable, sufficient, or reasonable," so I dwell on what is known, and not on vacant adjectives. 73's Richard Clark, KB7QHC |
Where does it go? (mismatched power)
Richard,
The article does propose a practical tolerance. I quote the relevant paragraph below. "Of course, nothing is perfect so an acceptable tolerance for depending on the assumed Zs=50+j0? for Mismatch Loss calculations might be that ‘forward power’ doesn’t vary by more than 10% of the ‘reflected power’ at any point. The worst case ‘reflected power’ for the experiment as described is 4%, so a variation of ‘forward power’ by more than 0.4% (ie 0.4W in 100W) at any point would indicate significant error in any Mismatch calculations based on an assumed Zs=50+j0?." I explained in the articles how I am able to reliably detect such small relative power variation. In one of the tests, the measured variation was 21%. My intention in publishing the two articles wasn't to prove the propostion one way or the other, but to show practical amateurs a test that they could make with relatively simple equipment, one that is relevant to the application of Zs if it was known, and an explanation of why it works so that they can understand the test and make their own interpretations about significance. Owen |
Where does it go? (mismatched power)
On 12 jun, 17:28, Owen Duffy wrote:
lu6etj wrote in news:da3e5147-cad8-47f9-9784- : ... OK. Thank you very much. This clarify so much the issue to me. Please, another question: On the same system-example, who does not agree with the notion that the reflected power is never dissipated in Thevenin Rs? (I am referring to habitual posters in these threads, of course) Thevenin's theorem says nothing of what happens inside the source (eg dissipation), or how the source may be implemented. It is the implementation of the source that provides the answer to your question, and the word "never" is too strong for the general case. In respect of typical HF ham transmitters, you may find my article entitled "Does SWR damage HF ham transmitters?" athttp://vk1od.net/blog/?p=1081of interest. Owen Hello Owen thank you for your answer: Sorry I do not quite understand your answer. I choose a Thevenin model of circuit theory because it is an idealization consisting of an idealized constant voltaje source in series with an idealized resistance without any relation with practical implementation of such imaginary electrical (and mathematical) entity. I first interested get from you such idealized model answer as a reductionistic aproximation method to try arrive later at subsequent interpretations of practical situations. I think we all used to working with idealized models and we accept its limitations, but we also know frequently they are very useful to clear the "field" (as in football "field") (I said "never" because Cecil seem say "sometimes"). For example: ideal conjugate mirror in Maxwell article in my interpretation implicates "never". Reflected power do not return to the source in that context. If you prefer I would be equally satisfied knowing who agree with "never", who with "sometimes" and who with "always". But I would not be too annoying :) 73 Miguel Ghezzi LU6ETJ |
Where does it go? (mismatched power)
On Jun 12, 4:34*pm, K1TTT wrote:
ok, so you defined a case where the superposition of the reflected and refracted waves at a discontinuity results in a zero sum. *is that supposed to prove something? *did i ever say that you could not define such a case?? I would call two waves superposing to zero indefinitely, "wave cancellation". If that is not wave cancellation, where did the reflected and refracted wavefronts go along with their energy components? The answer to that question will reveal exactly what happens to the reflected energy. Here's a brain teaser for you and others. Given a Z01 to Z02 impedance discontinuity with a power reflection coefficient of 0.25 at the '+' discontinuity: ------Z01------+------Z02-------load Pfor1 in the Z01 section is 100 watts. Pref1 in the Z01 section is zero watts. What is Pfor2, Pref2, and the SWR in the Z02 section? -- 73, Cecil, w5dxp.com |
Where does it go? (mismatched power)
lu6etj wrote in
: On 12 jun, 17:28, Owen Duffy wrote: lu6etj wrote in news:da3e5147-cad8-47f9-9784- : ... OK. Thank you very much. This clarify so much the issue to me. Please, another question: On the same system-example, who does not agree with the notion that the reflected power is never dissipated in Thevenin Rs? (I am referring to habitual posters in these threads, of course) Thevenin's theorem says nothing of what happens inside the source (eg dissipation), or how the source may be implemented. It is the implementation of the source that provides the answer to your question, and the word "never" is too strong for the general case. In respect of typical HF ham transmitters, you may find my article entitled "Does SWR damage HF ham transmitters?" athttp://vk1od.net/blog/?p=1081of interest. Owen Hello Owen thank you for your answer: Sorry I do not quite understand your answer. I choose a Thevenin model of circuit theory because it is an idealization consisting of an idealized constant voltaje source in series with an idealized resistance without any relation with practical implementation of such imaginary electrical (and mathematical) entity. I first interested get from you such idealized model answer as a reductionistic aproximation method to try arrive later at subsequent interpretations of practical situations. I think we all used to working with idealized models and we accept its limitations, but we also know frequently they are very useful to clear the "field" (as in football "field") Miguel, From Wikipedia: "Thévenin's theorem for linear electrical networks states that any combination of voltage sources, current sources and resistors with two terminals is electrically equivalent to a single voltage source V and a single series resistor R. For single frequency AC systems the theorem can also be applied to general impedances, not just resistors." The theorem does not state or imply that the Thevenin equivalent circuit dissipates the same internal power as the real source, just that any *linear* two terminal circuit containing sources and impedances can be reduced to this two component equivalent (at a single frequency), and V and I at the network terminals will be the same as the original network, irrespective of the external load attached to the network terminals. It is a simple exercise to develop two source networks with the same Thevenin equivalent circuit, but that have quite different internal efficiencies. It is easy to demonstrate that both networks deliver the same power to any given load, but that the internal dissipation of those source networks is different in both cases, and not explainable simply as absorbing 'reflected power'. This is basic linear circuit theory. If there was a valid Thevenin equivalent circuit for a transmitter (and that is questionable), then you can not use that equivalent circuit to make any inference about the internal dissipation of the source (the transmitter in this case), or its efficiency. Nevertheless, I see people trying to do this one way or another in the various threads here. (I said "never" because Cecil seem say "sometimes"). For example: ideal conjugate mirror in Maxwell article in my interpretation implicates "never". Reflected power do not return to the source in that context. If you prefer I would be equally satisfied knowing who agree with "never", who with "sometimes" and who with "always". But I would not be too annoying :) I know that in this age of instant gratification, people reading posts in these fora tend to accept simple dogmatic statements as sure sign of author credibility, and qualifications such as 'often', 'usually' etc as a sign of uncertainty, of a lack of understanding, of weakness in the author. The opposite is often, if not usually true. In English, we have a saying "never say never". What 'never'? 'Hardly ever'... to borrow some dialogue. A man who is hardly ever wrong doesn't use words like 'always' and 'never' much, or imply as much in general statements. Owen |
Where does it go? (mismatched power)
On Sat, 12 Jun 2010 14:21:29 -0700 (PDT), K1TTT
wrote: 1. *How could you tell if a lossless line lost energy by radiation? there would be missing energy? A lossless line infinite in extent is the typical definition that corresponds to its characteristic "non-dissipative" resistance. That, or it is terminated in a lossy resistor (and the loss is suddenly in everone's face, full and foursquare). How long are you going to wait to finish the energy budget to measure IF there is missing energy from an infinite line? 73's Richard Clark, KB7QHC |
Where does it go? (mismatched power)
On Sat, 12 Jun 2010 21:52:41 GMT, Owen Duffy wrote:
Richard, The article does propose a practical tolerance. I quote the relevant paragraph below. "Of course, nothing is perfect so an acceptable tolerance for depending on the assumed Zs=50+j0? for Mismatch Loss calculations might be that ‘forward power’ doesn’t vary by more than 10% of the ‘reflected power’ at any point. The worst case ‘reflected power’ for the experiment as described is 4%, so a variation of ‘forward power’ by more than 0.4% (ie 0.4W in 100W) at any point would indicate significant error in any Mismatch calculations based on an assumed Zs=50+j0?." Hi Owen, Excuse me for incorrectly referencing your material as lacking in that regard. I explained in the articles how I am able to reliably detect such small relative power variation. In one of the tests, the measured variation was 21%. What is the residual VSWR of your directional wattmeter? My intention in publishing the two articles wasn't to prove the propostion one way or the other, but to show practical amateurs a test that they could make with relatively simple equipment, one that is relevant to the application of Zs if it was known, and an explanation of why it works so that they can understand the test and make their own interpretations about significance. On Fri, 11 Jun 2010 20:31:42 GMT, Owen Duffy wrote: However, that proposition is easily proven wrong by valid experiments But what lead us here was that you had proof, at least through some third party (the experience of your having seen something that diminished the "proposition"). I asked for that specifically. I have not seen any reputable counter to Walt's data supporting the "proposition." The point remains that out of tolerance loads do not invalidate the "proposition:" On Fri, 11 Jun 2010 20:31:42 GMT, Owen Duffy wrote: there is a proposition that a transmitter "designed/adjusted for, and expecting a 50 + j 0 ohm load" can be well represented by a Thevenin equivalent circuit and naturally has Zeq=50+j0. In fact they announce themselves as violating the "proposition." I hope this does not return us to the vacant adjectives, which as an English major, I can full well argue to greater advantage. I don't think that is productive, but choices remain to pursue them, or to introduce new facts. *********** Now, let's return to your paragraph, how do you know where the 50 Ohm point was? You are relying on relative accuracy to make an absolute measurement. This only works if you have a standard to make a transfer from. Walt did this but it is arguable that his 1400 Ohm resistor was, in fact, that value - however, he had the correct tools to measure it. Your two test results could be inverted (fail/pass for pass/fail), or they could both be pass, or both fail. I have calibrated many loads from DC to 12 GHz - and most of them failed for many and sundry reasons and had to be "qualified." In the vernacular of the standards laboratories that means a table of correction values that are valid as long as certain characteristics are met. I prepared many such lengthy reports as no one was going to buy a new load each calibration cycle (typically 3 or 6 months). I own one that met 1% accuracy out to 1GHz (@150W), but that was luck of the draw and I wouldn't be so naive as to claim it retains that accuracy - however, experience has revealed that with care it should. Aging loads is like aging wine - there is no stasis. Here we get back into subjectives, but I know the limits of care, and I know how to practice it. If pressed to prove my inference of 1%, I also have the skill to do so to that accuracy according to methods practiced by Metrologists. It would be exceedingly tedious. Exceedingly tedious. Or I could pay for it to be done. 73's Richard Clark, KB7QHC |
Where does it go? (mismatched power)
On 12 jun, 22:52, Owen Duffy wrote:
lu6etj wrote : On 12 jun, 17:28, Owen Duffy wrote: lu6etj wrote in news:da3e5147-cad8-47f9-9784- : ... OK. Thank you very much. This clarify so much the issue to me. Please, another question: On the same system-example, who does not agree with the notion that the reflected power is never dissipated in Thevenin Rs? (I am referring to habitual posters in these threads, of course) Thevenin's theorem says nothing of what happens inside the source (eg dissipation), or how the source may be implemented. It is the implementation of the source that provides the answer to your question, and the word "never" is too strong for the general case. In respect of typical HF ham transmitters, you may find my article entitled "Does SWR damage HF ham transmitters?" athttp://vk1od.net/blog/?p=1081ofinterest. Owen Hello Owen thank you for your answer: Sorry I do not quite understand your answer. I choose a Thevenin model of circuit theory because it is an idealization consisting of an idealized constant voltaje source in series with an idealized resistance without any relation with practical implementation of such imaginary electrical (and mathematical) entity. I first interested get from you such idealized model answer as a reductionistic aproximation method to try arrive later at subsequent interpretations of practical situations. I think we all used to working with idealized models and we accept its limitations, but we also know frequently they are very useful to clear the "field" (as in football "field") Miguel, From Wikipedia: "Thévenin's theorem for linear electrical networks states that any combination of voltage sources, current sources and resistors * with two terminals is electrically equivalent to a single voltage source V and a single series resistor R. For single frequency AC systems the theorem can also be applied to general impedances, not just resistors." The theorem does not state or imply that the Thevenin equivalent circuit dissipates the same internal power as the real source, just that any *linear* two terminal circuit containing sources and impedances can be reduced to this two component equivalent (at a single frequency), and V and I at the network terminals will be the same as the original network, irrespective of the external load attached to the network terminals. It is a simple exercise to develop two source networks with the same Thevenin equivalent circuit, but that have quite different internal efficiencies. It is easy to demonstrate that both networks deliver the same power to any given load, but that the internal dissipation of those source networks is different in both cases, and not explainable simply as absorbing 'reflected power'. This is basic linear circuit theory. If there was a valid Thevenin equivalent circuit for a transmitter (and that is questionable), then you can not use that equivalent circuit to make any inference about the internal dissipation of the source (the transmitter in this case), or its efficiency. Nevertheless, I see people trying to do this one way or another in the various threads here. (I said "never" because Cecil seem say "sometimes"). For example: ideal conjugate mirror in Maxwell article in my interpretation implicates "never". Reflected power do not return to the source in that context. If you prefer I would be equally satisfied knowing who agree with "never", who with "sometimes" and who with "always". But I would not be too annoying :) I know that in this age of instant gratification, people reading posts in these fora tend to accept simple dogmatic statements as sure sign of author credibility, and qualifications such as 'often', 'usually' etc as a sign of uncertainty, of a lack of understanding, of weakness in the author. The opposite is often, if not usually true. In English, we have a saying "never say never". What 'never'? 'Hardly ever'... to borrow some dialogue. A man who is hardly ever wrong doesn't use words like 'always' and 'never' much, or imply as much in general statements. Owen- Ocultar texto de la cita - - Mostrar texto de la cita - Hello Owen, good day in Australia I hope! Sorry, with due respect, your answer throws back the ball out of the soccer field :) I like poetry also but would you mind search the web for another scientific uses of "never" word?, such as in http://www.upscale.utoronto.ca/PVB/H...y/Entropy.html. Of course many thanks for your time and your kind reply. Miguel LU6ETJ |
Where does it go? (mismatched power)
On 13 jun, 03:07, lu6etj wrote:
On 12 jun, 22:52, Owen Duffy wrote: lu6etj wrote : On 12 jun, 17:28, Owen Duffy wrote: lu6etj wrote in news:da3e5147-cad8-47f9-9784- : ... OK. Thank you very much. This clarify so much the issue to me. Please, another question: On the same system-example, who does not agree with the notion that the reflected power is never dissipated in Thevenin Rs? (I am referring to habitual posters in these threads, of course) Thevenin's theorem says nothing of what happens inside the source (eg dissipation), or how the source may be implemented. It is the implementation of the source that provides the answer to your question, and the word "never" is too strong for the general case. In respect of typical HF ham transmitters, you may find my article entitled "Does SWR damage HF ham transmitters?" athttp://vk1od.net/blog/?p=1081ofinterest. Owen Hello Owen thank you for your answer: Sorry I do not quite understand your answer. I choose a Thevenin model of circuit theory because it is an idealization consisting of an idealized constant voltaje source in series with an idealized resistance without any relation with practical implementation of such imaginary electrical (and mathematical) entity. I first interested get from you such idealized model answer as a reductionistic aproximation method to try arrive later at subsequent interpretations of practical situations. I think we all used to working with idealized models and we accept its limitations, but we also know frequently they are very useful to clear the "field" (as in football "field") Miguel, From Wikipedia: "Thévenin's theorem for linear electrical networks states that any combination of voltage sources, current sources and resistors * with two terminals is electrically equivalent to a single voltage source V and a single series resistor R. For single frequency AC systems the theorem can also be applied to general impedances, not just resistors." The theorem does not state or imply that the Thevenin equivalent circuit dissipates the same internal power as the real source, just that any *linear* two terminal circuit containing sources and impedances can be reduced to this two component equivalent (at a single frequency), and V and I at the network terminals will be the same as the original network, irrespective of the external load attached to the network terminals. It is a simple exercise to develop two source networks with the same Thevenin equivalent circuit, but that have quite different internal efficiencies. It is easy to demonstrate that both networks deliver the same power to any given load, but that the internal dissipation of those source networks is different in both cases, and not explainable simply as absorbing 'reflected power'. This is basic linear circuit theory. If there was a valid Thevenin equivalent circuit for a transmitter (and that is questionable), then you can not use that equivalent circuit to make any inference about the internal dissipation of the source (the transmitter in this case), or its efficiency. Nevertheless, I see people trying to do this one way or another in the various threads here. (I said "never" because Cecil seem say "sometimes"). For example: ideal conjugate mirror in Maxwell article in my interpretation implicates "never". Reflected power do not return to the source in that context. If you prefer I would be equally satisfied knowing who agree with "never", who with "sometimes" and who with "always". But I would not be too annoying :) I know that in this age of instant gratification, people reading posts in these fora tend to accept simple dogmatic statements as sure sign of author credibility, and qualifications such as 'often', 'usually' etc as a sign of uncertainty, of a lack of understanding, of weakness in the author. The opposite is often, if not usually true. In English, we have a saying "never say never". What 'never'? 'Hardly ever'... to borrow some dialogue. A man who is hardly ever wrong doesn't use words like 'always' and 'never' much, or imply as much in general statements. Owen- Ocultar texto de la cita - - Mostrar texto de la cita - Hello Owen, good day in Australia I hope! Sorry, with due respect, your answer throws back the ball out of the soccer field :) I like poetry also but would you mind search the web for another scientific uses of "never" word?, such as inhttp://www.upscale.utoronto.ca/PVB/Harrison/Entropy/Entropy.html. Of course many thanks for your time and your kind reply. Miguel LU6ETJ- Ocultar texto de la cita - - Mostrar texto de la cita - Sorry I ommited one comment: The final Thevenin circuit is an idealization built with an ideal voltage source in series with an ideal resistor. This new idealized circuit It is a new born entity whose properties are now fully described for these only two idealized circuit elements. These are the virtues and the defects of reductionist models :( |
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