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W2DU's Reflections III is now available from CQ Communications, Inc.
To order a copy of the 3rd edition of Reflections, authored by Walter
Maxwell, W2DU, go to the W2DU website at www.w2du.com, then go to page 2 and click on the following: Order Reflections III from CQ Online BookStore Walt, W2DU |
W2DU's Reflections III is now available from CQ Communications,Inc.
walt wrote:
To order a copy of the 3rd edition of Reflections, authored by Walter Maxwell, W2DU, go to the W2DU website at www.w2du.com, then go to page 2 and click on the following: Order Reflections III from CQ Online BookStore Excellent! Congratulations and thank you, Walt! 73, Tad Danley, K3TD EM10dq |
W2DU's Reflections III is now available from CQ Communications,Inc.
On 4/16/2010 8:10 PM, walt wrote:
To order a copy of the 3rd edition of Reflections, authored by Walter Maxwell, W2DU, go to the W2DU website at www.w2du.com, then go to page 2 and click on the following: Order Reflections III from CQ Online BookStore Walt, W2DU Ordered mine. Didn't see any discounts, unless the discount was just included transparently. tom K0TAR |
W2DU's Reflections III is now available from CQ Communications, Inc.
"walt" wrote in message ... To order a copy of the 3rd edition of Reflections, authored by Walter Maxwell, W2DU, go to the W2DU website at www.w2du.com, then go to page 2 and click on the following: Order Reflections III from CQ Online BookStore Walt, W2DU Done. Thanks for the heads up, and congrats to you Walt. --Wayne W5GIE |
W2DU's Reflections III is now available from CQ Communications,Inc.
On 4/18/2010 5:48 PM, Edwin Johnson wrote:
On 2010-04-18, wrote: Ordered mine. Didn't see any discounts, unless the discount was just included transparently. Free shipping if ordered before May 10 or some date like that. Ordered mine also. Kudos to Walt for getting this out. 73 ...Edwin, KD5ZLB That must be it, I checked my order confirmation and have free shipping. tom K0TAR |
W2DU's Reflections III is now available from CQ Communications, Inc.
Free shipping if ordered before May 10 or some date like that. Ordered
mine also. Kudos to Walt for getting this out. 73 ...Edwin, KD5ZLB That must be it, I checked my order confirmation and have free shipping. tom K0TAR I even got free shipping to Canada. Frank (VE6CB) |
W2DU's Reflections III is now available from CQ Communications,Inc.
Order Reflections III from CQ Online BookStore
Excellent! Congratulations and thank you, Walt! Good deal, Walt, thanks for the notice.... and, yeah, congrats on the publication Jim, K7JEB |
W2DU's Reflections III is now available from CQ Communications, Inc.
"walt" skrev i en meddelelse
... To order a copy of the 3rd edition of Reflections, authored by Walter Maxwell, W2DU, go to the W2DU website at www.w2du.com, then go to page 2 and click on the following: Order Reflections III from CQ Online BookStore Walt, W2DU Dear Walt, Ever since reading your 1973 QST articles, being a second-year student at the Polytechnics/Technical University of Copenhagen, I have referred to your ground-breaking work for removing the myths and misunderstandings of the (un)importance of the swr over and over again. Somewhere I still have the ageing photocopies of all the articles. But having the opportunity to get it all and more in one piece in Reflections III is really greast. I have ordered my copy right away. Later on, both in my professional life after receiving my MSc(EE) as a radio engineer and during my 19 years as Technical Editor of 'OZ' (the Danisk QST) I have had to weed out misconceptions about swr and transmission lines. My early understanding from your work was a great help. Thanks! All the best, vy 73 OZ7S Sven |
W2DU's Reflections III is now available from CQ Communications,Inc.
On Apr 16, 8:10*pm, walt wrote:
To order a copy of the 3rd edition of Reflections, authored by Walter Maxwell, W2DU, go to the W2DU website atwww.w2du.com, then go to page 2 and click on the following: * * * * * * * * * * * *Order Reflections III from CQ Online BookStore Walt, W2DU I've seen people talking about it in the other forums, and I looked at the three sample excerpts at w2du.com. That's all I know about it. It sounds interesting, but I need to at least see a table of contents (index would be nice, too) before I think about ordering it. Is that possible? TIA. 73 Mike |
W2DU's Reflections III is now available from CQ Communications, Inc.
Walt: For somebody who missed out on Reflections II, it looks like a lot of
fine reading - many thanks! Sven: Got delivery here in Holland today. 73, Kjell PB3SM - SM6CPI "Sven Lundbech" wrote in message k... "walt" skrev i en meddelelse ... To order a copy of the 3rd edition of Reflections, authored by Walter Maxwell, W2DU, go to the W2DU website at www.w2du.com, then go to page 2 and click on the following: Order Reflections III from CQ Online BookStore Walt, W2DU Dear Walt, Ever since reading your 1973 QST articles, being a second-year student at the Polytechnics/Technical University of Copenhagen, I have referred to your ground-breaking work for removing the myths and misunderstandings of the (un)importance of the swr over and over again. Somewhere I still have the ageing photocopies of all the articles. But having the opportunity to get it all and more in one piece in Reflections III is really greast. I have ordered my copy right away. Later on, both in my professional life after receiving my MSc(EE) as a radio engineer and during my 19 years as Technical Editor of 'OZ' (the Danisk QST) I have had to weed out misconceptions about swr and transmission lines. My early understanding from your work was a great help. Thanks! All the best, vy 73 OZ7S Sven |
W2DU's Reflections III is now available from CQ Communications, Inc.
"Kjell W. Strom" skrev i en meddelelse ... Walt: For somebody who missed out on Reflections II, it looks like a lot of fine reading - many thanks! Sven: Got delivery here in Holland today. 73, Kjell PB3SM - SM6CPI "Sven Lundbech" wrote in message k... "walt" skrev i en meddelelse ... To order a copy of the 3rd edition of Reflections, authored by Walter Maxwell, W2DU, go to the W2DU website at www.w2du.com, then go to page 2 and click on the following: Order Reflections III from CQ Online BookStore Walt, W2DU Dear Walt, Ever since reading your 1973 QST articles, being a second-year student at the Polytechnics/Technical University of Copenhagen, I have referred to your ground-breaking work for removing the myths and misunderstandings of the (un)importance of the swr over and over again. Somewhere I still have the ageing photocopies of all the articles. But having the opportunity to get it all and more in one piece in Reflections III is really greast. I have ordered my copy right away. Later on, both in my professional life after receiving my MSc(EE) as a radio engineer and during my 19 years as Technical Editor of 'OZ' (the Danisk QST) I have had to weed out misconceptions about swr and transmission lines. My early understanding from your work was a great help. Thanks! All the best, vy 73 OZ7S Sven Got delivery to-day. As mentioned earlier, most of the stuff is old hat to me - but I really look forward to dig into the chapters concerning tx output impedance. A highly controversial subject for decades. vy 73 OZ7S Sven |
W2DU's Reflections III is now available from CQ Communications, Inc.
"Sven Lundbech" wrote in
k: .... As mentioned earlier, most of the stuff is old hat to me - but I really look forward to dig into the chapters concerning tx output impedance. A highly controversial subject for decades. Here is a simple little test for the hypothesis that Zs=50+j0 that uses equipment found in many if not most HF ham shacks. Owen |
W2DU's Reflections III is now available from CQ Communications, Inc.
Owen Duffy wrote in news:Xns9D81BC11E3183nonenowhere@
61.9.191.5: "Sven Lundbech" wrote in k: ... As mentioned earlier, most of the stuff is old hat to me - but I really look forward to dig into the chapters concerning tx output impedance. A highly controversial subject for decades. Here is a simple little test for the hypothesis that Zs=50+j0 that uses equipment found in many if not most HF ham shacks. Oh, the URL: http://vk1od.net/blog/?p=1028 . Owen |
W2DU's Reflections III is now available from CQ Communications,Inc.
On Apr 25, 3:40*am, W0BTU wrote:
On Apr 16, 8:10*pm, walt wrote: To order a copy of the 3rd edition of Reflections, authored by Walter Maxwell, W2DU, go to the W2DU website atwww.w2du.com, then go to page 2 and click on the following: * * * * * * * * * * * *Order Reflections III from CQ Online BookStore Walt, W2DU I've seen people talking about it in the other forums, and I looked at the three sample excerpts at w2du.com. That's all I know about it. It sounds interesting, but I need to at least see a table of contents (index would be nice, too) before I think about ordering it. Is that possible? TIA. 73 Mike Hi Mike, Since attachments aren't allowed on these NGs I can't send what you want. If you'll send me your email address I'll send you some material from the book. My email address is . Walt, W2DU |
W2DU's Reflections III is now available from CQ Communications,Inc.
Dear Walt, Ever since reading your 1973 QST articles, being a second-year student at the Polytechnics/Technical University of Copenhagen, I have referred to your ground-breaking work for removing the myths and misunderstandings of the (un)importance of the swr over and over again. Somewhere I still have the ageing photocopies of all the articles. But having the opportunity to get it all and more in one piece in Reflections III is really greast. I have ordered my copy right away. Later on, both in my professional life after receiving my MSc(EE) as a radio engineer and during my 19 years as Technical Editor of 'OZ' (the Danisk QST) I have had to weed out misconceptions about swr and transmission lines. My early understanding from your work was a great help. Thanks! All the best, vy 73 OZ7S Sven Got delivery to-day. As mentioned earlier, most of the stuff is old hat to me - but I really look forward to dig into the chapters concerning tx output impedance. A highly controversial subject for decades. vy 73 OZ7S Sven Hello Sven, Glad you received your copy today. To pique your interest in tx output impedance, Chapter 19 will do that for you, especially Sec 19.14 on Page 19.22. This section describes in detail, in fourteen steps, how the output Z is measured. I've seen a lot of discussion on this subject, and most of it shows that many who discuss it don't have a clue to the correct answer. Which is why I have made many measurements of the output Z to determine the truth. The output Z is determined principally by the proper adjustment of the tank circuit with respect to the load. I'm talking now only about tube amps with pi-network tank circuit coupling the amp tube to the load. I cannot comment on solid-state rigs, or those that have no tuning adjustments. There are those who believe that the output Z = 50 + j0, and there are those who believe the Z is much higher. Here's what really happens. With any practical grid drive, load and tune the amp into a 50 + j0 dummy load to deliver all the available power. In this case the output Z of the amp will be 50 + j0 ohms. Now add 50 ohms of inductive reactance to the same dummy load. The result is now a load impedance of 50 + j50 ohms. Now reload and retune the pi-network to again deliver all the available power into the new complex-impedance load. The new output Z? 50 - j50 ohms, the conjugate of the complex load impedance. In other words, to determine the output Z of the amp, simply load it into an impedance of known value such that all the available power is delivered at a reasonable drive level. The output Z is then the conjugate of the load impedance. You say you want proof of this simplistic procedure? Fine. It's all right there in the fourteen steps in Sec 19.14 that describe the entire measurement procedure. I'm sure you'll find the procedure enlightening. Walt, W2DU |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 23, 10:01*pm, walt wrote:
On Apr 25, 3:40*am, W0BTU wrote: On Apr 16, 8:10*pm, walt wrote: To order a copy of the 3rd edition of Reflections, authored by Walter Maxwell, W2DU, go to the W2DU website atwww.w2du.com, then go to page 2 and click on the following: * * * * * * * * * * * *Order Reflections III from CQ Online BookStore Walt, W2DU I've seen people talking about it in the other forums, and I looked at the three sample excerpts at w2du.com. That's all I know about it. It sounds interesting, but I need to at least see a table of contents (index would be nice, too) before I think about ordering it. Is that possible? TIA. 73 Mike Hi Mike, Since attachments aren't allowed on these NGs I can't send what you want. If you'll send me your email address I'll send you some material from the book. My email address is . Walt, W2DU Mike, apparently one can't divulge one's email address on this NG. However, we'll fool 'em--the word preceding @ is walt. So there, too. Walt |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 23, 4:31*am, Owen Duffy wrote:
Owen Duffy wrote in news:Xns9D81BC11E3183nonenowhere@ 61.9.191.5: "Sven Lundbech" wrote in . dk: ... As mentioned earlier, most of the stuff is old hat to me - but I really look forward to dig into the chapters concerning tx output impedance. A highly controversial subject for decades. Here is a simple little test for the hypothesis that Zs=50+j0 that uses equipment found in many if not most HF ham shacks. Oh, the URL:http://vk1od.net/blog/?p=1028. Owen While the analysis of transmitter output impedance in Reflections is flawed, experiments (claimed to be repeatable) described in Reflections appear to support the conclusions of the flawed analysis. It would be highly valuable if the results of these experiments could be explained in a manner that aligns with established understandings. Such an explanation might start by describing the circuit conditions that result from following the manufacturer’s tuning procedures. After all, these usually depend on measuring currents and voltages so are only indirectly related to power. Perhaps the resulting conditions are not as they are usually assumed to be. Try as I might, I have not been able to derive a mechanism to explain the observations in Reflections. But the explanations offered in Reflections require large chunks of linear circuit theory to be discarded, so this does not seem to be an appropriate path. ....Keith |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 24, 6:30*am, Keith Dysart wrote:
Such an explanation might start by describing the circuit conditions that result from following the manufacturer’s tuning procedures. On an old tube transmitter, e.g. a Globe Scout, when the manufacturer specifed a particular grid current and a particular plate current, does that imply a particular single resistive load line for the final tube? Why were those particular grid and load currents chosen? Maximum efficiency? Tube life? Minimum distortion? -- TNX & 73, Cecil, w5dxp.com |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 24, 9:23*am, Cecil Moore wrote:
On May 24, 6:30*am, Keith Dysart wrote: Such an explanation might start by describing the circuit conditions that result from following the manufacturer’s tuning procedures. On an old tube transmitter, e.g. a Globe Scout, when the manufacturer specifed a particular grid current and a particular plate current, does that imply a particular single resistive load line for the final tube? Why were those particular grid and load currents chosen? Maximum efficiency? Tube life? Minimum distortion? Excellent questions. I have often wondered if the manufacturer's tuning procedures had anything to do with maximizing output power transfer, or were they, in fact, optimizing some other aspect. ....Keith |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 24, 7:30*am, Keith Dysart wrote:
On May 23, 4:31*am, Owen Duffy wrote: Owen Duffy wrote in news:Xns9D81BC11E3183nonenowhere@ 61.9.191.5: "Sven Lundbech" wrote in . dk: ... As mentioned earlier, most of the stuff is old hat to me - but I really look forward to dig into the chapters concerning tx output impedance. A highly controversial subject for decades. Here is a simple little test for the hypothesis that Zs=50+j0 that uses equipment found in many if not most HF ham shacks. Oh, the URL:http://vk1od.net/blog/?p=1028. Owen While the analysis of transmitter output impedance in Reflections is flawed, experiments (claimed to be repeatable) described in Reflections appear to support the conclusions of the flawed analysis. It would be highly valuable if the results of these experiments could be explained in a manner that aligns with established understandings. Such an explanation might start by describing the circuit conditions that result from following the manufacturer’s tuning procedures. After all, these usually depend on measuring currents and voltages so are only indirectly related to power. Perhaps the resulting conditions are not as they are usually assumed to be. Try as I might, I have not been able to derive a mechanism to explain the observations in Reflections. But the explanations offered in Reflections require large chunks of linear circuit theory to be discarded, so this does not seem to be an appropriate path. ...Keith Keith, would you please elaborate on why you believe my analysis of transmitter output impedance is flawed? And what is the basis for your belief that my explanations in Reflections require large chunks of linear circuit theory to be discarded. Could it be because you consider the source resistance in the transmitter to be dissipative, as in the classical generator? If so, you must be made to realize that the source resistance of the transmitter is non-dissipative, which is the reason that its efficiency can exceed 50%. Or are you considering the output characteristic of the transmitter to be non-linear? This is not the case, because the effect of energy storage in the tank circuit isolates the non-linear input from the output circuit, which is linear as evidenced by the almost perfect sine wave appearing at the output of the tank. One last question: Are you basing your dissatisfaction of Reflections from reviewing the 2nd or 3rd edition? Chapter 19 has been expanded in the 3rd edition, in which I presented additional proof of my position on the subject that you should be aware of. If you haven't yet seen the addition that appears in the 3rd ed, please let me know so that I can send you a copy of the addition. Also include your email address so I can send it. Keith, you are the only person I know of who appears to have found flaws in my presentation on this subject. Which is why I'm anxious to know exactly why you believe my presentation is flawed. Walt Maxwell, W2DU |
W2DU's Reflections III is now available from CQ Communications, Inc.
On Mon, 24 May 2010 07:06:44 -0700 (PDT), Keith Dysart
wrote: I have often wondered if the manufacturer's tuning procedures had anything to do with maximizing output power transfer, or were they, in fact, optimizing some other aspect. This resolves quickly in measurement - no need to wonder unless it offers some secondary benefit of not measuring things. An alternative is to simply examine conventional design considerations. One can add to Plate current by throwing a lot of power into the grid. More plate current yields more output power results, but grid lifetime plumments. One can do innumerable things to force an artificial outcome that strains to prove a distorted logic. Examining a suite of sources, in initial conditions that are average for their application quickly reveals a common design paradigm. ****** The fundamental answer to your question is the manufacturer ultimately designs for market domination, or maximum investment return (the two don't necessarily converge). Thus the marketplace gives us a spectrum of choice and the norm of the distribution reveals cautious design that has its eye on a value exchange expressed in money. THAT is the only optimization you can expect = in an honest barter, you get what you pay for. 73's Richard Clark, KB7QHC |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 24, 10:55*am, walt wrote:
Keith, would you please elaborate on why you believe my analysis of transmitter output impedance is flawed? And what is the basis for your belief that my explanations in Reflections require large chunks of linear circuit theory to be discarded. Could it be because you consider the source resistance in the transmitter to be dissipative, as in the classical generator? If so, you must be made to realize that the source resistance of the transmitter is non-dissipative, which is the reason that its efficiency can exceed 50%. No problems there. There has been much confusion in this area and anything that reduces this confusion is beneficial. Or are you considering the output characteristic of the transmitter to be non-linear? This is not the case, because the effect of energy storage in the tank circuit isolates the non-linear input from the output circuit, which is linear as evidenced by the almost perfect sine wave appearing at the output of the tank. This may be the root of my disagreement. Certainly the output can be an arbitrarily perfect sine wave, but this simply depends on the characteristics of the filter and not on whether the system is linear. But the way the filter transforms the impedances is the crux of the issue. It is my understanding that the input impedance to a filter can be computed by starting with the load impedance applied to the filter and then, using the rules for series and parallel connected components, compute the way through the filter until reaching the input and the result is the input impedance to the filter. Similarly, the output impedance of the filter can be computed by starting with source impedance driving the filter, series and paralleling the components until reaching the output and the result is the output impedance of the filter. The desired impedance for the input to the filter is that impedance which produces the desired load on the tube. And the component values are computed to produce this load on the tube when the correct load is attached to the output. For the output impedance of the filter, the question then becomes: What is the source impedance driving the filter? If the source is constructed as a Class A amplifier, then it depends on the controlling device, and for the simplest of circuits would be Rp of the tube. (Just for clarity, in this discussion Rp is the slope of the plate E/I curve with constant grid voltage. In an ideal tube, these lines are equidistant apart and the slopes are the same. Real tubes, of course, are not so well behaved, but this should not affect the basic discussion.) Since the component values for the filter were chosen to provide the optimum load to the tube, and the optimum load value has no relation to Rp, there is no reason to expect the filter will transform Rp to be the conjugate of the load impedance. For amplifiers where conduction is not for 360 degrees (Class AB, B, C), the controlling device is no longer time-invariant so the rules for linear circuit analysis no longer apply. None-the-less, for example, consider a Class AB amplifier where the tube is only cut off for 1 degree. This short cut-off would not have much affect so the analysis for Class A would apply. As the cut-off period increases the behaviour will diverge more and more from that of the Class A amplifier. Simulations produce some interesting results: Another way of measuring the source impedance is to observe the effect on a reflected wave entering the amplifier from the load. With a Class C amplifier, simulation reveals that the effect on the reflected wave depends on the phase of that wave with respect to the drive signal applied to the tube. As the phase of the reflected wave is changed, the reflection co-efficient experienced by the wave changes. Truly a non-linear behaviour. Intriguingly, when the conduction angle is exactly 180 degrees, this effect largely disappears, and the result is much as if the source impedance of the tube was 2 times Rp, which seems to make some sense since the tube is only conducting one-half of the time. One last question: Are you basing your dissatisfaction of Reflections from reviewing the 2nd or 3rd edition? Chapter 19 has been expanded in the 3rd edition, in which I presented additional proof of my position on the subject that you should be aware of. If you haven't yet seen the addition that appears in the 3rd ed, please let me know so that I can send you a copy of the addition. I have been reading the .pdfs at w2du.com along with correspondence and other writings in QST, QEX and newsgroups. The expanded Chapter 19 at w2du.com offers more experimental evidence that seems to support the hypothesis that the transmitter is conjugate matched to the load after tuning, But given, from circuit analysis, that the output impedance can not be well defined for any but a Class A amplifier, the fascinating question is why is there experimental evidence that agrees with the premise that the output impedance of a tuned transmitter is the conjugate match of the load? One simple example to consider which has similar behaviour is a bench power supply that also has a constant current limiter. Set such a power supply to produce a voltage of 100V (more precisely a maximum voltage) and a current limit of 2A. Apply a variable load. Maximum power will be drawn when the load resistance is 50 ohms. Varying the resistance on either side of 50 ohms will reduce the power which might be misconstrued to suggest that the power supply has an output impedance of 50 ohms, when, in fact, it has a infinite output impedance when the load is below 50 ohms and a zero output impedance when the load is above. I have looked for such a simple explanation in the circuits of the transmitters used in the experiments but was not able to find one. So I am still puzzled by the observations. Also include your email address so I can send it. Keith.dot.dysart.at.gmail.com .dot. = . .at. = @ …Keith |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 24, 6:58*pm, Richard Clark wrote:
On Mon, 24 May 2010 07:06:44 -0700 (PDT), Keith Dysart wrote: I have often wondered if the manufacturer's tuning procedures had anything to do with maximizing output power transfer, or were they, in fact, optimizing some other aspect. This resolves quickly in measurement - no need to wonder unless it offers some secondary benefit of not measuring things. * An alternative is to simply examine conventional design considerations. *One can add to Plate current by throwing a lot of power into the grid. *More plate current yields more output power results, but grid lifetime plumments. One can do innumerable things to force an artificial outcome that strains to prove a distorted logic. *Examining a suite of sources, in initial conditions that are average for their application quickly reveals a common design paradigm. ****** The fundamental answer to your question is the manufacturer ultimately designs for market domination, or maximum investment return (the two don't necessarily converge). *Thus the marketplace gives us a spectrum of choice and the norm of the distribution reveals cautious design that has its eye on a value exchange expressed in money. *THAT is the only optimization you can expect = in an honest barter, you get what you pay for. 73's Richard Clark, KB7QHC You have gone to a bit higher level than I intended with my question and I agree with you conclusions at that level. But my question was more basic. When designing the filter for a PA, among other things, one uses the desired load to be applied to the tube and the disired load impedance to be supported and selects filter components to perform the desired transformation. When operating the radio, the operator has meters that measure some values, some knobs that control some component values and a procedure for adjusting these knobs. It is not at all obvious what exactly the result of performing the procedure is. Does it result in the same load being applied to the tube that was computed by the designer? There are some hints that the procedure will result in the load applied to the tube being real, but beyond that, what exactly are the circuit conditions that result? ....Keith |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 24, 6:15*pm, Keith Dysart wrote:
This may be the root of my disagreement. Certainly the output can be an arbitrarily perfect sine wave, but this simply depends on the characteristics of the filter and not on whether the system is linear. Since anything except a class-A amplifier is non-linear and since we are talking about linear analysis, it seems we need to locate a point in the system where V is a sine wave, I is a sine wave, and V/I is the constant impedance at that point. IMO, that is the first point at which we can use a linear math analysis and maybe that point is what Walt is talking about. It's certainly not going to be the plate of a class-C amplifier and it may not even be the load-line of the class-C amplifier. There is probably some point in an otherwise non-linear system where a linear analysis becomes possible. I think that point is what Walt considers to be the linear source point, wherever that point might be located. In fact, here is my personal take on the subject. Given an antenna system that presents 50+j0 ohms looking into 50 ohm coax, the internal impedance of the source doesn't matter. For any voltage source, irrespective of the source impedance, if reflected energy doesn't reach the source, the source impedance doesn't matter (except for efficiency). Seems to me, the highest efficiency would be achieved by a source with zero ohms of source impedance. -- 73, Cecil, w5dxp.com |
W2DU's Reflections III is now available from CQ Communications, Inc.
On Mon, 24 May 2010 16:23:26 -0700 (PDT), Keith Dysart
wrote: It is not at all obvious what exactly the result of performing the procedure is. Does it result in the same load being applied to the tube that was computed by the designer? Hi Keith, By and large, Yes. There are some hints that the procedure will result in the load applied to the tube being real, but beyond that, what exactly are the circuit conditions that result? I am a little lost on that. The load applied is the load applied (sorry for the Zen). If you mean that the load is transformed by tuning to a real R for the Plate to see, then, yes, that is operative. However, that is not the end of it. That R is seen as the loss of a now-poorer Q for the Plate tank. This is the distinction between loaded and unloaded Q. The Plate tank Q expressed in terms of loaded Q, to be effective, is quite low in comparison to its unloaded value. This value of loaded Q is roughly between 10 and 20 where the components in isolation (unloaded) could easily achieve 10 to 30 times that. The term "loaded" includes BOTH the plate and the applied load (whatever is presented to the antenna connection). The only time the unloaded Q of the Plate tank is at peak value is when it is sitting in isolation from the chassis, circuitry, and even mounts - which means it is not very useful in that configuration, except as a trophy. Many silver plate their tanks as trophies (because this rarely results in better operation). Now, let's return to my statement about what Q is "effective" AND that it measures out at roughly 10 to 20. This is straight out of Terman if you need a citation. As for explanation (also found in Terman), you have to consider that the Plate tank is the gate-keeper (as well as transformer of Z) of power. If you have too high a Q, the power is not getting THROUGH the tank as it must, and necessarily it remains in the tank (as energy, albeit). Consider further that ALL resonant circuits can be cast from series circuits to parallel circuits or parallel to series (a fact lost on some inventors of antennas). To describe the Plate tank in series terms as I do, then the plate resistance and load resistance combine in series through a simple circular path through ground. There are parallel tank designs where the resistances combine in parallel. The net result is the same insofar as Q is concerned. Consult Terman if that is confusing. No doubt others will either more clearly cite him, or add to the confusion. 73's Richard Clark, KB7QHC |
W2DU's Reflections III is now available from CQ Communications, Inc.
On Mon, 24 May 2010 16:15:52 -0700 (PDT), Keith Dysart
wrote: I have looked for such a simple explanation in the circuits of the transmitters used in the experiments but was not able to find one. So I am still puzzled by the observations. Hi Keith, Consult Terman. That should be sufficient for both the instructor and the student to use as a benchmark design for tubes, at least. The design of the transistorized finals' deck of Ham grade HF rigs has been stable for nearly 4 decades. Any departure from HF Ham grade equipment capable of 100W is going to lead to equivocal statements. 73's Richard Clark, KB7QHC |
W2DU's Reflections III is now available from CQ Communications,...
Cecil Moore, W5DXP wrote:
"Seems to me, the highest efficiency would be achieved by a source with zero source impedance." Me too, but zero source impedance does not match the load as required for maximum power transfer. The best combination is then a source impedance matching the load and which is also pracrically lossless. The Class C amplifier does this by acting as a switch which is infinite in impedance when open during a large part of the RF cycle and a near short circuit to a low impedance (near zero Z) D.C. power source for the short part of the RF cycle it is switched on. It is the time averaged impedance which counts. Is this linear? No way, but the tank circuit is able to remove the harmonics and turn current pulses into a low distortion sine wave. Efficiency? Terman says on page 450 of his 1955 opus that Class C eddiciency is typically 60% to 80%. Compare that with 50% efficiency in a Class A amplifier. Best regards, Richard Harrison, KB5WZI |
W2DU's Reflections III is now available from CQ Communications,Inc.
On 25/05/2010 01:55, walt wrote:
.... Or are you considering the output characteristic of the transmitter to be non-linear? This is not the case, because the effect of energy storage in the tank circuit isolates the non-linear input from the output circuit, which is linear as evidenced by the almost perfect sine wave appearing at the output of the tank. Well, for the purposes of application of linear circuit theory, linearity means that V is linearly related to I, or at least dV/dI over the operating range is substantially constant. If the circuit is not linear in those terms, then you cannot form a valid Thevenin equivalent circuit, and discussion of the Thevenin equivalent series source impedance is a nonsense... it cannot be used. Owen |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 24, 7:49*pm, Cecil Moore wrote:
On May 24, 6:15*pm, Keith Dysart wrote: This may be the root of my disagreement. Certainly the output can be an arbitrarily perfect sine wave, but this simply depends on the characteristics of the filter and not on whether the system is linear. Since anything except a class-A amplifier is non-linear and since we are talking about linear analysis, it seems we need to locate a point in the system where V is a sine wave, I is a sine wave, and V/I is the constant impedance at that point. IMO, that is the first point at which we can use a linear math analysis and maybe that point is what Walt is talking about. It's certainly not going to be the plate of a class-C amplifier and it may not even be the load-line of the class-C amplifier. There is probably some point in an otherwise non-linear system where a linear analysis becomes possible. I think that point is what Walt considers to be the linear source point, wherever that point might be located. Recalling that if a conjugate match is achieved at one ponit in a system it is achieved at all points.... It does not seem possible for a system to be non-linear at one end and turn in to a linear system at some other point. In fact, here is my personal take on the subject. Given an antenna system that presents 50+j0 ohms looking into 50 ohm coax, the internal impedance of the source doesn't matter. For any voltage source, irrespective of the source impedance, if reflected energy doesn't reach the source, the source impedance doesn't matter (except for efficiency). Seems to me, the highest efficiency would be achieved by a source with zero ohms of source impedance. True, if the source impedance originates in dissipative components and it is a voltage source. For a current source, infinite impedance offers the best efficiency. ....Keith |
W2DU's Reflections III is now available from CQCommunications,...
On May 25, 12:32*am, (Richard Harrison)
wrote: Cecil Moore, W5DXP wrote: "Seems to me, the highest efficiency would be achieved by a source with zero source impedance." Me too, but zero source impedance does not match the load as required for maximum power transfer. It seems to me that much too much is made of 'maximum power transfer' in the RF world. In the world of 50 and 60 Hz, where significantly more energy is moved, 'maximum power transfer' is never mentioned. Efficiency is much more of interest. For the most part, 'maximum power transfer' is just an interesting ideosyncracy of linear circuit theory. ....Keith |
W2DU's Reflections III is now available from CQCommunications,...
On May 24, 11:32*pm, (Richard Harrison)
wrote: Cecil Moore, W5DXP wrote: "Seems to me, the highest efficiency would be achieved by a source with zero source impedance." Me too, but zero source impedance does not match the load as required for maximum power transfer. A 60 Hz Power Generation Plant operates at high efficiency, not at the maximum power transfer point. If they were 50% efficient, they would go out of business. (That's what Edison expected.) Why is maximum power transfer desirable in ham transmitters? Is such a design the highest power/cost ratio? Is it possible to build an output amp with a 10 ohm source impedance designed to be 80% efficient? 1 ohm source impedance designed to be 98% efficient? Is co$t the driving parameter? -- 73, Cecil, w5dxp.com |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 25, 3:30*am, Owen wrote:
If the circuit is not linear in those terms, then you cannot form a valid Thevenin equivalent circuit, and discussion of the Thevenin equivalent series source impedance is a nonsense... it cannot be used. Quoting "Fields and Waves ...", by Ramo and Whinnery, "... the (Thevenin) equivalent circuit was derived to tell what happens *IN THE LOAD* under different load conditions, and significance cannot be automatically attached to a calculation of power loss in the internal impedance of the equivalent circuit." -- 73, Cecil, w5dxp.com |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 25, 5:29*am, Keith Dysart wrote:
It does not seem possible for a system to be non-linear at one end and turn in to a linear system at some other point. Well, consider the following two systems. Z01 is 50 ohms and Z02 is 300 ohms. The two systems are identical except for the circuits hidden inside the two identical source black boxes. Both sources are supplying a 100v sine wave to the system. Source1----Z01----+----1/4WL Z02----1800 ohm Source2----Z01----+----1/4WL Z02----1800 ohm Every passive voltage, current, power, and impedance measurement is identical in both systems. As far as we can passively measure, both systems are identical and linear. The only thing we don't know is what is inside the two source boxes.. Inside the Source1 box is a linear ideal 50 ohm Thevenin equivalent source delivering an ideal 100v sine wave. Inside the Source2 box is a non-linear class-C amplifier filtered to provide an ideal 100v sine wave. Without changing the system conditions, can one make a passive measurement to determine which system is conjugately matched and which one is not conjugately matched? If one cannot tell the difference, are they both conjugately matched, or both not conjugately matched, or what? Here's my take. A 50 ohm Z0-match exists in both systems and all conditions are identical on the load side of that Z0-match. In particular, at any point in the system on the load side of the Z0- match, the impedance looking in one direction is the conjugate of the impedance looking in the other direction. That is a characteristic of a conjugate match. So are both systems conjugately matched between the Z0-match and the load? If it walks and quacks like a duck ... -- 73, Cecil, w5dxp.com |
W2DU's Reflections III is now available from CQ Communications, Inc.
On Tue, 25 May 2010 08:30:30 GMT, Owen wrote:
If the circuit is not linear in those terms, then you cannot form a valid Thevenin equivalent circuit, and discussion of the Thevenin equivalent series source impedance is a nonsense... it cannot be used. The counter argument, as I understand it, is that the tank circuit isolates the linear from the non-linear, and that the tank also performs the action of transformation. Thus the proposal is an analysis of their combination (I had to struggle to avoid superposition). Thus, the non-linear Tube (because, I presume, the circuit is in Class C operation) exhibits a higher efficiency than would be found in a resistance matched system. What I call the resistance matched system is the unfortunate appeal to a source "resistance" equaling the load "resistance." Thevenin/Norton do not mandate resistors, rather impedances. What I understand, comes from lengthy emails with multiple contributors in years past: Walt and Richard being two of them. My saved mail only goes back nine years, so the other two contributors' names are lost to me right now. Of course what I "understand" may be wholly misrepresented by my exposition here. So be it. The source authorities can correct my deviations. 73's Richard Clark, KB7QHC |
W2DU's Reflections III is now available from CQ Communications,Inc.
On 25/05/2010 23:19, Cecil Moore wrote:
Quoting "Fields and Waves ...", by Ramo and Whinnery, "... the (Thevenin) equivalent circuit was derived to tell what happens *IN THE LOAD* under different load conditions, and significance cannot be automatically attached to a calculation of power loss in the internal impedance of the equivalent circuit." Yes, that is quite correct Cecil, and nothing that I have written says or implies or is intended to mean otherwise. However, your own words in another post (news://news.bigpond.com:119/c8b7540a...oglegroups.com) "A 60 Hz Power Generation Plant operates at high efficiency, not at the maximum power transfer point. If they were 50% efficient, they would go out of business." demonstrates that whilst you apparently can quote from text books, you do not necessarily understand what you are quoting. You do talk nonsense sometimes! Owen |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 25, 2:33*pm, Owen wrote:
Yes, that is quite correct Cecil, and nothing that I have written says or implies or is intended to mean otherwise... You do talk nonsense sometimes! Owen, my reference supported what you said! Why are you trying to pick an argument? As my mother would have said, "You would argue with a fence post". -- 73, Cecil, w5dxp.com |
W2DU's Reflections III is now available from CQ Communications,Inc.
Hello Keith,
Thank you for your response. I’m starting my answer to your statements by first quoting from one of your posts: “Try as I might, I have not been able to derive a mechanism to explain the observations in Reflections. But the explanations offered in Reflections require large chunks of linear circuit theory to be discarded, so this does not seem to be an appropriate path.” That you have been unable to derive a mechanism that explains the action in an RF power amplifier is evidence that you do not understand it. So let’s examine the action that follows an appropriate path that does not require any linear circuitry to be discarded. Further evidence that you do not understand it is that you used a bench power supply to describe the action, which you state has an infinite source resistance when the load exceeds 50 ohm, and zero source resistance when the load is less than 50 ohms. Unfortunately, this power supply in no way resembles an RF power amplifier, either in components or action. We’ll begin by stipulating that the ‘filter’ is a pi-network tank circuit, having a tuning capacitor at the input and a loading- adjustment capacitor at the output. We’ll also stipulate that the plate voltage and the grid bias are set to provide the desired conditions at the input of the tank circuit, which means that the desired grid voltage is that which results in the desired conduction time for the applied plate voltage. The result provides a dynamic resistance RL, which is determined by the average plate voltage VPavg and the average plate current IPavg appearing at the terminals leading to the input of the tank circuit. In other words, RL = VPavg/IPavg. To permit delivery of all available power to be delivered by the dynamic resistance RL, we want the input impedance appearing at the input of the tank circuit to be equal to RL. We’ll now go to the output of the tank circuit. We’ll assume the load to be the input of a transmission line on which there are reflections. The result is that the input to the line contains a real component R and a reactance jX. The output terminals of the tank circuit are the two terminals of the output-loading capacitor. When the line is connected to the output terminals of the tank circuit the reactance appearing at the line input is reflected into the tank circuit. This reactance is then cancelled by the tuning capacitor at the input of the tank circuit, resulting in a resonant tank circuit. We now need to adjust the output-loading capacitor to apply the correct voltage across the input of the transmission line so that the real component R appearing at the line input is reflected into the tank circuit such that the resistance RL appears at the input of the tank circuit, thus allowing all the available power to enter the tank circuit. In other words, adjusting the loading capacitor to deliver all the available power into the line also makes the output resistance of the tank circuit equal to the real component R appearing at the line input. With any other value of output resistance of the source, all the available power would not be delivered to the line. A corollary to that condition follows from the Maximum Power Transfer Theorem that for a given output resistance of the source (the tank circuit), if the load resistance is either increased for decreased from the value of the source resistance, the delivery of power will decrease. This condition also accurately describes the condition for the conjugate match. Keep in mind that the input impedance of the line is complex, or reactive, but the reactance of the correctly-adjusted tuning capacitor has introduced the correct amount of the opposite reactance to cancel the reactance appearing at the line input. Thus the line input impedance is R + jX and the output impedance of the source is R – jX, providing the conjugate match. You stated in one of your posts that the phase of the reflected wave in relation to that of the source wave results in a non-linear condition. This is totally untrue. The tuning action of the input capacitor in the tank circuit that cancels the line reactance caused by the reflection on the line in no way introduces any non-linearity in the circuit, and the condition in the vicinity of the output of the tank circuit is totally linear. Thus, circuit theorems that require linearity to be valid are completely valid when used with the RF power amplifier as described above. This applies to all RF power amplifiers, Class A, AB, B and C. I hope my comments above assist in understanding the action that occurs in RF power amplifiers. Walt Maxwell, W@DU |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 25, 8:45*am, Cecil Moore wrote:
On May 25, 5:29*am, Keith Dysart wrote: It does not seem possible for a system to be non-linear at one end and turn in to a linear system at some other point. Well, consider the following two systems. Z01 is 50 ohms and Z02 is 300 ohms. The two systems are identical except for the circuits hidden inside the two identical source black boxes. Both sources are supplying a 100v sine wave to the system. Source1----Z01----+----1/4WL Z02----1800 ohm Source2----Z01----+----1/4WL Z02----1800 ohm Every passive voltage, current, power, and impedance measurement is identical in both systems. As far as we can passively measure, both systems are identical and linear. The only thing we don't know is what is inside the two source boxes.. Inside the Source1 box is a linear ideal 50 ohm Thevenin equivalent source delivering an ideal 100v sine wave. Inside the Source2 box is a non-linear class-C amplifier filtered to provide an ideal 100v sine wave. Without changing the system conditions, can one make a passive measurement to determine which system is conjugately matched and which one is not conjugately matched? If one cannot tell the difference, are they both conjugately matched, or both not conjugately matched, or what? Here's my take. A 50 ohm Z0-match exists in both systems and all conditions are identical on the load side of that Z0-match. In particular, at any point in the system on the load side of the Z0- match, the impedance looking in one direction is the conjugate of the impedance looking in the other direction. That is a characteristic of a conjugate match. So are both systems conjugately matched between the Z0-match and the load? If it walks and quacks like a duck ... Methinks you have so constrained the experiment as to make it unsolvable. But let us test that. Consider a Source3, much like Source1: linear, ideal, but 100 ohms output impedance. It is connected to the same load you specify for Source1 and Source2 and adjusted to drive 100 volts in to the 50 ohm Z01 line. You are presented with the circuits using Source1 and Source3. We know that Source1 and Source3 can not both be conjugately matched. "Without changing the system conditions, can one make a passive measurement to determine which system is conjugately matched and which one is not conjugately matched? If one cannot tell the difference, are they both conjugately matched, or both not conjugately matched, or what?" ....Keith |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 25, 4:20 pm, walt wrote:
Hello Keith, Thank you for your response. I’m starting my answer to your statements by first quoting from one of your posts: “Try as I might, I have not been able to derive a mechanism to explain the observations in Reflections. But the explanations offered in Reflections require large chunks of linear circuit theory to be discarded, so this does not seem to be an appropriate path.” That you have been unable to derive a mechanism that explains the action in an RF power amplifier is evidence that you do not understand it. So let’s examine the action that follows an appropriate path that does not require any linear circuitry to be discarded. Further evidence that you do not understand it is that you used a bench power supply to describe the action, which you state has an infinite source resistance when the load exceeds 50 ohm, and zero source resistance when the load is less than 50 ohms. Unfortunately, this power supply in no way resembles an RF power amplifier, either in components or action. “No way” is a bit strong. The RF PA is constructed from a constant voltage source (the power supply) and a constant current controller (the tube), both aspects present in the bench supply example previously offered. A tube is often modelled as an ideal variable constant current source but unlike an ideal source, which can produce whatever voltage is needed to drive the current, the current produced by the tube is limited by the power supply voltage. Thus, assertions of linear behaviour need to be tempered by ensuring that such voltage limits are not exceeded. We’ll begin by stipulating that the ‘filter’ is a pi-network tank circuit, having a tuning capacitor at the input and a loading- adjustment capacitor at the output. We’ll also stipulate that the plate voltage and the grid bias are set to provide the desired conditions at the input of the tank circuit, which means that the desired grid voltage is that which results in the desired conduction time for the applied plate voltage. The result provides a dynamic resistance RL, which is determined by the average plate voltage VPavg and the average plate current IPavg appearing at the terminals leading to the input of the tank circuit. In other words, RL = VPavg/IPavg. To permit delivery of all available power to be delivered by the dynamic resistance RL, we want the input impedance appearing at the input of the tank circuit to be equal to RL. Most references use Vpeak and Ipeak, though they are usually related to average values with constants of proportionality so the computed RL will be the same. None-the-less, I prefer peak values since it ties better to the choices made in the design. The power that can be controlled by a control device (be it a switch, tube or transistor) is related to device limitations. So, for example, the maximum power that can be controlled by a 250V 1A switch is 250W. This occurs with a supply voltage of 250V and a load of 250 ohms. Increasing the supply voltage exceeds the switch capability as does reducing the load resistance. If the supply voltage is less than 250V then the maximum power occurs with a load that causes 1A to flow and is now a limit based on circuit choices and device capabilities. Note that these power limits have nothing to do with maximum power transfer in a linear circuit. Similarly in a tube circuit, the maximum power is limited by the supply voltage and the tube drive level (which sets the current that will flow in the tube). Maximum controlled power is then V*I and occurs with a load resistance of V/I. Increasing the load resistance reduces the power because there is insufficient voltage from the supply to drive more current through the load and reducing the load resistance reduces the power because less voltage is impressed across the load. Note that neither of these effects is related to the maximum power transfer in a linear circuit. We’ll now go to the output of the tank circuit. We’ll assume the load to be the input of a transmission line on which there are reflections. The result is that the input to the line contains a real component R and a reactance jX. The output terminals of the tank circuit are the two terminals of the output-loading capacitor. When the line is connected to the output terminals of the tank circuit the reactance appearing at the line input is reflected into the tank circuit. This reactance is then cancelled by the tuning capacitor at the input of the tank circuit, resulting in a resonant tank circuit. We now need to adjust the output-loading capacitor to apply the correct voltage across the input of the transmission line so that the real component R appearing at the line input is reflected into the tank circuit such that the resistance RL appears at the input of the tank circuit, thus allowing all the available power to enter the tank circuit. In other words, adjusting the loading capacitor to deliver all the available power into the line also makes the output resistance of the tank circuit equal to the real component R appearing at the line input. With any other value of output resistance of the source, all the available power would not be delivered to the line. A corollary to that condition follows from the Maximum Power Transfer Theorem that for a given output resistance of the source (the tank circuit), if the load resistance is either increased for decreased from the value of the source resistance, the delivery of power will decrease. This condition also accurately describes the condition for the conjugate match. While a conjugate match does result in a situation where altering the load will reduce the power transfer, it is not true that any situation where altering the load reduces the power transfer is also a conjugate match. The two examples above (bench power supply, tube in a circuit) amply demonstrate this. Keep in mind that the input impedance of the line is complex, or reactive, but the reactance of the correctly-adjusted tuning capacitor has introduced the correct amount of the opposite reactance to cancel the reactance appearing at the line input. Thus the line input impedance is R + jX and the output impedance of the source is R – jX, providing the conjugate match. This is quite in error, unless, by happenstance, RL is equal to Rp (plus the other contributors to source impedance). You stated in one of your posts that the phase of the reflected wave in relation to that of the source wave results in a non-linear condition. This is totally untrue. The tuning action of the input capacitor in the tank circuit that cancels the line reactance caused by the reflection on the line in no way introduces any non-linearity in the circuit, and the condition in the vicinity of the output of the tank circuit is totally linear. Thus, circuit theorems that require linearity to be valid are completely valid when used with the RF power amplifier as described above. This applies to all RF power amplifiers, Class A, AB, B and C. For any circuit with a conduction angle of less than 360 degrees, my simulations indicate otherwise. The reflection coefficient experienced by the reflected wave when it arrives at the amplifier output varies with the phase of the reflected wave. Since the reflection coefficient is a function of source impedance and line impedance, and the line impedance is not changing, this means that the source impedance is changing with the phase of the reflected wave. This is not a behaviour that is consistent with a linear circuit. Given the non-linearities in a circuit with a conduction angle of less than 360 degrees, this should not be a surprise. More, it would be a surprise if such a circuit did behave as a linear circuit. I hope my comments above assist in understanding the action that occurs in RF power amplifiers. Thank you. They have indeed helped clarify my thinking. We are still left with the puzzle of why the observations documented in Reflections report a reduction in power transfer when the load is changed in either direction. It seems unlikely that RL is, by happenstance, equal to Rp, which would be one explanation. It seems plausible that it is related to the behaviours associated with the examples I provided above, but I can not articulate a mechanism that satisfies. …Keith |
W2DU's Reflections III is now available from CQ Communications,Inc.
On May 25, 8:45*pm, Keith Dysart wrote:
We know that Source1 and Source3 can not both be conjugately matched. But what difference does it make if all external conditions are identical? If reflected energy is not allowed to reach the source, why does the source impedance matter at all? -- 73, Cecil, w5dxp.com |
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