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#1
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On Fri, 3 Oct 2003 07:39:15 +0100, "Ian White, G3SEK"
wrote: Sorry! Just to continue and further confuse the haggling, the forward voltages are unknown because one does not know, in the case of amateur systems, what is the internal voltage and internal impedance of the transmitter. It is this unknown voltage and internal impedance which the so-called SWR (Rho) meter merely ASSUMES. Reg, that can't possibly be you. Someone has hijacked your e-mail. Where is either of those assumptions required? Those are transmitter properties, and they only affect the overall level of power/voltage/current on the line. Reflection coefficient (rho) and SWR are properties exclusively of the line and its load, not the transmitter. Hi Ian, There are one of two possible explanations for your posting: 1. You have not obtained that copy of Chipman that you ordered. 2. You have not read it. Of course, you can add a third, fourth or fifth... in complete absence of Chipman's discussion if his material does not agree with your interpretations. This is not an unexplored topic, and in fact dates back to earlier discussions whose citations to Chipman were offered by me to no refute - merely denial and the general wholesale abandonment of learned posters who preferred to chase after specious claims (simpler game). 73's Richard Clark, KB7QHC |
#2
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Richard Clark wrote:
There are one of two possible explanations for your posting: 1. You have not obtained that copy of Chipman that you ordered. 2. You have not read it. Of course, you can add a third, fourth or fifth... in complete absence of Chipman's discussion if his material does not agree with your interpretations. Richard, you might be interested to know that HP's s-parameter ap note, AN 95-1, page 22 under Transducer Power Gain, lists the power available from the source as the (square of the magnitude of the source voltage) divided by [one minus the (square of the magnitude of the source's complex reflection coefficient)], i.e. |Vs|^2/(1-|rho|^2)=power available from the source where presumably source-rho = (Zs-Z0)/(Zs+Z0) -- 73, Cecil, W5DXP |
#3
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On Fri, 03 Oct 2003 12:01:08 -0500, Cecil Moore
wrote: Richard Clark wrote: There are one of two possible explanations for your posting: 1. You have not obtained that copy of Chipman that you ordered. 2. You have not read it. Of course, you can add a third, fourth or fifth... in complete absence of Chipman's discussion if his material does not agree with your interpretations. Richard, you might be interested to know that HP's s-parameter ap note, AN 95-1, page 22 under Transducer Power Gain, lists the power available from the source as the (square of the magnitude of the source voltage) divided by [one minus the (square of the magnitude of the source's complex reflection coefficient)], i.e. |Vs|^2/(1-|rho|^2)=power available from the source where presumably source-rho = (Zs-Z0)/(Zs+Z0) Hi Cecil, -sigh- even when you offer confirmatory recitations you still miss the details. There are only 11 pages in Application Note 95-1 and the material you describe appears on page 4 not 22. The voltage from the generator is also portrayed in Fig. 3 entitled "Flow graph of network of Fig. 2." Figure 2, of course, shows the generator complete with Zs which most here deny exists, or dismiss as immaterial to any discussion. This is due entirely to their speed reading past their own sources' discussion that ALL DISCUSSION OF SWR assumes the source matches the line it feeds. Such an explicit or implicit relationship is fundamentally required, or the entire text that they cite is rendered useless gibberish. The most garbled of those proclamations is that the source Z has no bearing on line SWR. This same flowgraph is present in many similar works (AN 95-1 is hardly unique) and being presented early in the work (like Chipman's similar observation of requiring source-line matching) is skipped so that the reader (sic) can scrounge their favorite snippet of math and remove it from its required context. Chipman also presents much the same treatment in non S-Parameter discussion, but that is quite obviously from the part unread by the great mass of so called adherents to his discussion. However, to give some flexibility to the discussion; such shortfalls of understanding how SWR works is simply through lack of experience in the matter. It is understandable when the usual approach to this topic is taken by employing a transmitter that both specifies its output at a Z of 50 Ohms and exhibits a Z of 50 Ohms. Given such a source, the casual debater is lulled into the comfortable illusion of having been born on third base thinking they hit a triple in the debate against source Z (no, the count is three strikes). Simply because they encounter no ill consequence of source mismatch is NOT evidence of the source Z being immaterial to the process of measuring SWR. Luck counts for nothing in debate - unless it is admitted to. None here count themselves lucky - it would diminish their sense of erudition. I don't expect there will be any substantive discussion following this that will change physics to conform to those illusions (my comments here will not "change their minds"). 73's Richard Clark, KB7QHC |
#4
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Richard Clark wrote:
wrote: -sigh- even when you offer confirmatory recitations you still miss the details. There are only 11 pages in Application Note 95-1 and the material you describe appears on page 4 not 22. -sigh- The PDF version of HP ap note AN 95-1 contains 79 pages. Simply because they encounter no ill consequence of source mismatch is NOT evidence of the source Z being immaterial to the process of measuring SWR. A source mismatch affects the power available from the source. The SWR does not depend upon the power available from the source. The SWR is the same whether the source is 1% efficient or 99% efficient. Efficiency depends upon Zs. SWR does not. -- 73, Cecil, W5DXP |
#5
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On Fri, 03 Oct 2003 13:49:15 -0500, Cecil Moore
wrote: A source mismatch affects the power available from the source. The SWR does not depend upon the power available from the source. The SWR is the same whether the source is 1% efficient or 99% efficient. Efficiency depends upon Zs. SWR does not. Hi Cecil, So, a source exhibiting 200 Ohms Resistive feeding a 50 Ohm line that is then terminated in a load of 200 Ohms Resistive exhibits what SWR? The absence of a numeric answer is par for the course here. The answer, of course, can be found in Chipman's text but that requires the act of reading, not snipping (which would still be available to the literate). Many here stumble when it comes to measuring SWR employing (in this case) 2 resistors and a hank of line - how they could imagine they respond faithfully to more elaborate enquiries is quite amusing, especially when they argue the Source Z has nothing to do with it. My mental image of that assemblage of pundits is that of them crowded on a small desert isle, each proclaiming it to be a vast, lush continent. Another SWR Don added to that bunch will teeter someone into the brine. ;-) Do any of you know how to tread water? Seems to be the perfect Darwinian thinning mechanism; but in fact most already tread water at high tide. 73's Richard Clark, KB7QHC |
#6
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Richard Clark wrote:
So, a source exhibiting 200 Ohms Resistive feeding a 50 Ohm line that is then terminated in a load of 200 Ohms Resistive exhibits what SWR? Assuming a lossless 50 ohm line, the steady-state SWR is 4:1 no matter what the source impedance (assuming there exists a source voltage not equal to zero volts). Steady-state SWR in a lossless feedline is a constant fixed voltage ratio from end to end. -- 73, Cecil, W5DXP |
#7
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On Fri, 03 Oct 2003 14:58:15 -0500, Cecil Moore
wrote: Richard Clark wrote: So, a source exhibiting 200 Ohms Resistive feeding a 50 Ohm line that is then terminated in a load of 200 Ohms Resistive exhibits what SWR? Assuming a lossless 50 ohm line, the steady-state SWR is 4:1 no matter what the source impedance (assuming there exists a source voltage not equal to zero volts). Steady-state SWR in a lossless feedline is a constant fixed voltage ratio from end to end. Hi Cecil, WRONG! The method of computation you employ violates Chipman and any other of a host of authoritative sources on the topic. If you actually attempted to verify this at the bench you would "perhaps" find it at only one point, or at harmonic distances (wavelength specific) along the line. That means you would stand only a couple of percent chance of that with a random choice. Guesses are not responsive to the intent and no points are awarded. I will leave you to discover Chipman's means to find SWR any where along any line for yourself. You might enjoy the celebrity of being the second to do so. ;-) 73's Richard Clark, KB7QHC |
#8
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On Fri, 03 Oct 2003 18:11:14 GMT, Richard Clark wrote:
On Fri, 03 Oct 2003 12:01:08 -0500, Cecil Moore wrote: Richard Clark wrote: There are one of two possible explanations for your posting: 1. You have not obtained that copy of Chipman that you ordered. 2. You have not read it. Of course, you can add a third, fourth or fifth... in complete absence of Chipman's discussion if his material does not agree with your interpretations. Richard, you might be interested to know that HP's s-parameter ap note, AN 95-1, page 22 under Transducer Power Gain, lists the power available from the source as the (square of the magnitude of the source voltage) divided by [one minus the (square of the magnitude of the source's complex reflection coefficient)], i.e. |Vs|^2/(1-|rho|^2)=power available from the source where presumably source-rho = (Zs-Z0)/(Zs+Z0) Hi Cecil, -sigh- even when you offer confirmatory recitations you still miss the details. There are only 11 pages in Application Note 95-1 and the material you describe appears on page 4 not 22. The voltage from the generator is also portrayed in Fig. 3 entitled "Flow graph of network of Fig. 2." Figure 2, of course, shows the generator complete with Zs which most here deny exists, or dismiss as immaterial to any discussion. This is due entirely to their speed reading past their own sources' discussion that ALL DISCUSSION OF SWR assumes the source matches the line it feeds. Such an explicit or implicit relationship is fundamentally required, or the entire text that they cite is rendered useless gibberish. The most garbled of those proclamations is that the source Z has no bearing on line SWR. This same flowgraph is present in many similar works (AN 95-1 is hardly unique) and being presented early in the work (like Chipman's similar observation of requiring source-line matching) is skipped so that the reader (sic) can scrounge their favorite snippet of math and remove it from its required context. Chipman also presents much the same treatment in non S-Parameter discussion, but that is quite obviously from the part unread by the great mass of so called adherents to his discussion. However, to give some flexibility to the discussion; such shortfalls of understanding how SWR works is simply through lack of experience in the matter. It is understandable when the usual approach to this topic is taken by employing a transmitter that both specifies its output at a Z of 50 Ohms and exhibits a Z of 50 Ohms. Given such a source, the casual debater is lulled into the comfortable illusion of having been born on third base thinking they hit a triple in the debate against source Z (no, the count is three strikes). Simply because they encounter no ill consequence of source mismatch is NOT evidence of the source Z being immaterial to the process of measuring SWR. Luck counts for nothing in debate - unless it is admitted to. None here count themselves lucky - it would diminish their sense of erudition. I don't expect there will be any substantive discussion following this that will change physics to conform to those illusions (my comments here will not "change their minds"). 73's Richard Clark, KB7QHC Richard, I'm dismayed with your statements above. Are you really serious? Or are you just giving Cecil a bad time? I've been grappling with your last email to me concerning the nature of the source resistance of RF amps, and as with your statements above, I'm at a loss as to how to respond, because we are 180 degrees apart on the source resistance issue. I'm still going to respond to it, but right now I want to address the SWR issue. Richard, how can you possibly believe that the output impedance of the source has any effect on the SWR on a transmission line? The only conditions responsible for SWR are the Zo of the line and the ZL of the load--nothing else. I've been bench measuring SWR for more than 50 years, beginning with using the slotted line before more sophisticated machinery was available. It didn't matter what the source impedance was, the SWR remained the same, whatever the source. Ian told it like it is, and so does Walter C. Johnson in his "Transmission Lines and Networks, Page 100, where he says: "The steady state ratio Eplus/Eminus was determined in Eq 11 as the reflection coefficient k...This ratio is determined only by the load and the line, not by the generator. It is completely unaffected by the quantity kg = (Zg - Zo)/(Zg + Zo), which is the reflection coefficient seen by an individual backward-traveling wave as it reaches the generator terminals. ...the latter affects the steady state solution only on its influence on the sending-end voltage, i.e., through its influence on the magnitude of the entire solution." Your reply comments, please. Walt, W2DU |
#9
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On Fri, 03 Oct 2003 21:41:15 GMT, Walter Maxwell wrote:
Richard, I'm dismayed with your statements above. Are you really serious? Or are you just giving Cecil a bad time? That wouldn't take much to push Cecil off dead center. I've been grappling with your last email to me concerning the nature of the source resistance of RF amps, and as with your statements above, I'm at a loss as to how to respond, because we are 180 degrees apart on the source resistance issue. I'm still going to respond to it, but right now I want to address the SWR issue. Richard, how can you possibly believe that the output impedance of the source has any effect on the SWR on a transmission line? Stephen Adam of HP using Beatty describes it quite well. The data you have by email and has been posted here demonstrates it equally well. It takes no more than two resistors and a length of line to confirm or deny. My data confirms it, absolutely no one has offered negative evidence, simply denials. The only conditions responsible for SWR are the Zo of the line and the ZL of the load--nothing else. I've been bench measuring SWR for more than 50 years, beginning with using the slotted line before more sophisticated machinery was available. It didn't matter what the source impedance was, the SWR remained the same, whatever the source. Ian told it like it is, and so does Walter C. Johnson in his "Transmission Lines and Networks, Page 100, where he says: If Walter Johnson was not explicit about it, he was certainly implicit about the requirement that the source match the line it is driving for any discussion of SWR. This is so commonplace that no one ever examines the situation where the source is a mismatch. Too many here simply flip to the section in their favorite book about SWR and wholly neglect the fundamentals that present this simple requirement. I have presented quotes, chapter and verse from Chipman where he explicitly says as much, and those who hold Chipman have abandoned discussion rather than refute those quotes or accept their error. As one scribbler put it I was not going to "change his mind." I have no doubt of that, such a statement paints one into an extremely embarrassing corner once having uttered it. One thing I learned as a Metrologist is that I am always wrong, the significance is in the degree of error, not the philosophy of sin and the rejection in ignorance. Any number of correspondents here "might" have the capacity to simply repeat my methods and report their data; but absolutely none demonstrate it. I might be so far in error the meter is pegged, but the quality of "sneer review" absolves me of sin. ;-) Hi Walt, I await your response by email for our last round of discussion. What is presented above is old material already discussed. There is nothing new presented by me in it that has not found its way to your mailbox. 73's Richard Clark, KB7QHC |
#10
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Richard Clark wrote:
I have presented quotes, chapter and verse from Chipman where he explicitly says as much, ... And I have presented quotes, chapter and verse from Chipman, that disprove your interpretations of what he said. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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