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max power transfer theorem
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Dave wrote:
have you guys read this one yet? www.qsl.net/w9dmk/MPTT.pdf Yes, as a matter of fact, I have. It tends to support my argument with Jeff Anderson, wa6ahl, on this newsgroup from about a decade ago, but is much more thorough and eloquent than I ever could be. -- 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! =----- |
Dave wrote:
"Have you guys read this one yet?" I can`t read pdf. I learned about maximum power transfer in the 1940`s and it hasn`t changed. Terman says in his 1955 edition on page 76: "Alternatively, a load impedance may be matched to a source of power in such a way as to make the power delivered to the load a maximum. The power delivered to the load under these conditions is termed "available power" of a power source. This is accomplished by making the load impedance the conjugate of the generator impedance as defined by Thevenin`s theorem." Anything else I need to know is likely also clearly explained by Terman. Best regards, Richard Harrison, KB5WZI |
What a load of crap!
The only difficulty in the MPTT occurs when some folks create new definitions and new constraints that are not shared by others in the discussion. Allowing the problem to float at will means that the solutions will float as well. The longstanding MPTT argument in amateur radio circles is not really about power transfer and conjugate matching. The argument is typically about what happens to the source impedance under varying load conditions. Steam engines? Gear boxes? Yeah, sure, they help a lot. 73, Gene W4SZ Cecil Moore wrote: Dave wrote: have you guys read this one yet? www.qsl.net/w9dmk/MPTT.pdf Yes, as a matter of fact, I have. It tends to support my argument with Jeff Anderson, wa6ahl, on this newsgroup from about a decade ago, but is much more thorough and eloquent than I ever could be. |
"Richard Harrison" wrote in message
... I can`t read pdf.... ____ Amazing. Are you incapable of downloading and using the free PDF Reader from the Acrobat website??? |
On Mon, 1 Mar 2004 16:36:46 -0600, "Richard Fry"
wrote: "Richard Harrison" wrote in message ... I can`t read pdf.... ____ Amazing. Are you incapable of downloading and using the free PDF Reader from the Acrobat website??? Richard subscribes to WebTV. 73's Richard Clark, KB7QHC |
Richard Harrison wrote:
Dave wrote: "Have you guys read this one yet?" I can`t read pdf. For anyone who wants it, the free pdf reader SW is available at: http://www.adobe.com/products/acrobat/readstep2.html -- 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! =----- |
On Mon, 01 Mar 2004 22:23:56 GMT, Gene Fuller
wrote: What a load of crap! The only difficulty in the MPTT occurs when some folks create new definitions and new constraints that are not shared by others in the discussion. Allowing the problem to float at will means that the solutions will float as well. The longstanding MPTT argument in amateur radio circles is not really about power transfer and conjugate matching. The argument is typically about what happens to the source impedance under varying load conditions. Steam engines? Gear boxes? Yeah, sure, they help a lot. That's a fair question, Gene - what does happen to the source impedance under varying load conditions? While you're at it, could you please explain how you would separate the issues of maximum power transfer and conjugate matching from the question of what happens to the source impedance under varying load conditions? I have no problem in supplying copies of the article to anyone who requests a particular format by e-mail - available choices are pdf, html, or Word for Windows 97 or 2003. The complete file is approximately 1 MB in any of the formats. 73, Bob |
Web TV doesn't do PDF and can't run the software.
"Richard Fry" wrote in message ... "Richard Harrison" wrote in message ... I can`t read pdf.... ____ Amazing. Are you incapable of downloading and using the free PDF Reader from the Acrobat website??? |
It won't run on a VIC-20
"Richard Fry" wrote in message ... "Richard Harrison" wrote in message ... I can`t read pdf.... ____ Amazing. Are you incapable of downloading and using the free PDF Reader from the Acrobat website??? |
Bob,
Sorry for the strong words, but the intent remains the same. I don't know what happens to the source impedance when the load is changed, because the system is undefined. However, read carefully the definition at the beginning of your paper. The Maximum Power Transfer Theorem: The maximum power will be absorbed by one network from another joined to it at two terminals, when the impedance of the receiving network is varied, if the impedance looking into the two networks at the junction are conjugates of each other [1] |
Gene Fuller wrote:
"I don`t know what happens to the source impedance when the load is changed, because the system is undefined." Yes. Maximum power transfer is accomplished by making the load impedance the conjugate of the generator impedance as defined by Thevenin`s theorem. The value of the Thevinen impedance is that which might be measured by a generator`s open-circuit voltage devided by its short-circuit current. You don`t need to know the generator`s specifics other than, drop in the output voltage is proportional to the current delivered. The current which flows in a linear load impedance connected to a Thevenin generator is the open-circuit voltage divided by the sum of the generator`s internal impedance and the load impedance. These may be complex impedances. At maximum power transfer, internal and load impedances are equal in resistance and their reactances are conjugate (opposite and equal). There is no requirement that resistance in either the generator or load be dissipative, and frequently, lossless resistance is a part of the generator impedance so that we can get maximum possible power into the load without losing 50% in the generator. Best regards, Richard Harrison, KB5WZI |
On Tue, 02 Mar 2004 15:37:25 GMT, Gene Fuller
wrote: Bob, Sorry for the strong words, but the intent remains the same. I don't know what happens to the source impedance when the load is changed, because the system is undefined. However, read carefully the definition at the beginning of your paper. The Maximum Power Transfer Theorem: The maximum power will be absorbed by one network from another joined to it at two terminals, when the impedance of the receiving network is varied, if the impedance looking into the two networks at the junction are conjugates of each other [1] . . . [1] W. L. Everitt, "Communication Engineering", McGraw-Hill, 1937 The maximum power transfer theorem describes the impact from change of the load impedance. It is not the Grand Unified Theory for all the universe. If someone tries to expand this elegant concept to all sorts of pathological cases then it is likely that confusion will ensue. The MPTT analysis is straightforward if the problem is well defined. The ongoing argument in amateur radio circles is about the source characteristics of amplifiers and tank circuits. The MPTT does not address that argument, but rather it is a victim of the silliness. Including the down-home touch of steam engines adds nothing to the technical content. Dear Gene, No problem, I will try to understand where you're coming from. Obviously, there have been some experiences in your tour of duty that have caused you some heartburn - it happens with all of us. Relative to your points about amplifiers, etc., I hope to have my article on that topic available before the end of this month. Actually, it has been "almost ready" for several days now, but there are some things that need to "cook" awhile before I release it. As soon as you get into the details of a Class-B linear, you're up to your butt in alligators, not to mention all of the myths surrounding them and the matching problem. I'll do my best to keep it "on topic" - Hi! 73, Bob |
From the design side, MPTT is defined at an interface, and minimizes
"reflected power" at that interface, and that is it. The other items about matching are also quite important, such as stability, loading, impedance transfer (both directions), bandwidth, Qs, loaded Qs etc. But that is Not MPTT. There is a tradeoff between these, if one can also obtain mptt, great, but close is good too. mptt is just one of several parameters needed to optimize a match. At times there are too many unknowns and the matching is experimental (class C) .................................................. ........................... ........................ "Robert Lay W9DMK" wrote in message ... On Mon, 01 Mar 2004 22:23:56 GMT, Gene Fuller wrote: What a load of crap! The only difficulty in the MPTT occurs when some folks create new definitions and new constraints that are not shared by others in the discussion. Allowing the problem to float at will means that the solutions will float as well. The longstanding MPTT argument in amateur radio circles is not really about power transfer and conjugate matching. The argument is typically about what happens to the source impedance under varying load conditions. Steam engines? Gear boxes? Yeah, sure, they help a lot. That's a fair question, Gene - what does happen to the source impedance under varying load conditions? While you're at it, could you please explain how you would separate the issues of maximum power transfer and conjugate matching from the question of what happens to the source impedance under varying load conditions? I have no problem in supplying copies of the article to anyone who requests a particular format by e-mail - available choices are pdf, html, or Word for Windows 97 or 2003. The complete file is approximately 1 MB in any of the formats. 73, Bob |
"John Smith" said - MPTT is defined at an interface, and minimizes "reflected power" at that interface, and that is it. =============================== Indeed it is. R+jX one way and R-jX the other. Why the vast amount of palaver and bickering about such an obvious and elementary notion defeats the imagination. |
Reg Edwards wrote:
Indeed it is. R+jX one way and R-jX the other. Why the vast amount of palaver and bickering about such an obvious and elementary notion defeats the imagination. Reg, you are in a room with a transmission line passing through it. You measure all voltages, currents, and powers. How do use your "obvious and elementary notions" to tell if the transmission line is conjugately matched or not? How do you measure the impedance looking toward a typical amateur radio transmitter without changing the very thing you are trying to measure? Many have tried and many have failed. -- 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! =----- |
Check for reflected power in either direction.
If none, then it is conjugally matched exactly. If it is about -14 dB down, that is good and close enough. One can try to measure Tx output Z (looking into Tx) and then the Z looking backup the antenna line, and try matching the two as a start, but reflected power quicker, faster, more accurate. (also I agree with you in trying to measure Tx output Z (looking into the output) tried and got a mess many times,...) "Cecil Moore" wrote in message ... Reg Edwards wrote: Indeed it is. R+jX one way and R-jX the other. Why the vast amount of palaver and bickering about such an obvious and elementary notion defeats the imagination. Reg, you are in a room with a transmission line passing through it. You measure all voltages, currents, and powers. How do use your "obvious and elementary notions" to tell if the transmission line is conjugately matched or not? How do you measure the impedance looking toward a typical amateur radio transmitter without changing the very thing you are trying to measure? Many have tried and many have failed. -- 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! =----- |
Cecil,
Are you suggesting that a steam engine is needed in addition to "obvious and elementary notions"? Let's see, how about a nice triple expansion engine fed from a Scotch boiler fueled with the finest Welsh coal. Don't forget to raise steam slowly, and make sure you don't tie down the safety valve. 8-) 73, Gene W4SZ Cecil Moore wrote: Reg Edwards wrote: Indeed it is. R+jX one way and R-jX the other. Why the vast amount of palaver and bickering about such an obvious and elementary notion defeats the imagination. Reg, you are in a room with a transmission line passing through it. You measure all voltages, currents, and powers. How do use your "obvious and elementary notions" to tell if the transmission line is conjugately matched or not? How do you measure the impedance looking toward a typical amateur radio transmitter without changing the very thing you are trying to measure? Many have tried and many have failed. |
On Tue, 2 Mar 2004 14:40:02 -0600, "John Smith"
wrote: Check for reflected power in either direction. Hi John, You would be surprised how hard that is for some, especially when an argument about the direction of current flow becomes part of the turmoil. If none, then it is conjugally matched exactly. Still too simple, not enough gristle to chew on. ;-) If it is about -14 dB down, that is good and close enough. In three sentences you've said enough to resolve the matter. But not enough to end the debate.... 73's Richard Clark, KB7QHC |
Well sed!
Jack K9CUN |
"Lossless resistance?" Would that be zero resistance,
or perhaps a negative resistance, as in the active part of a tunnel diode's V-I characteristic? I am a career EE, with a couple of graduate EE degrees; and this is something entirely new to me. Could you explain this concept, and/or provide some references? Thanks, Ed |
What he is analyzing is not directly applicable to an RF amplifier. He is
looking at the whole thing, power source and generator. An RF analogy would be a poorly regulated DC supply that is feeding an RF amplifier. Reduce the load, and the DC voltage goes up. This changes the RF output. RF amps are not power limited, up to the point where the transistor melts. They are voltage limited; you can not get a peak RF drain voltage (inside the die) greater than the DC supply voltage. A secondary effect of a load change is caused by the gain of the transistor being current and voltage dependent. Tam/WB2TT "Dave" wrote in message ... have you guys read this one yet? www.qsl.net/w9dmk/MPTT.pdf |
On Wed, 03 Mar 2004 00:56:57 GMT, "Old Ed"
wrote: "Lossless resistance?" Would that be zero resistance, or perhaps a negative resistance, as in the active part of a tunnel diode's V-I characteristic? I am a career EE, with a couple of graduate EE degrees; and this is something entirely new to me. Could you explain this concept, and/or provide some references? Thanks, Ed Hi Ed, This is the most useless term employed in these threads; what I call a difference without a distinction. To put it shortly, it is the resistance observed in an infinite transmission line (better known as the Characteristic Z) or the resistance of an antenna (better known as the Radiation Resistance). You will note that a competent engineer already understands the nature of this resistance, shrubs may need more words to obtain the same knowledge. Some explanations like to force it into the same definition of Z, and then add more words to denote there is not reactance, and then more words to add there is no heat generated. In other words (too many of them) the issue is driven from the physics of heat which if anyone peeled back the onion layers, then they would find they have not actually escaped from it all, and more words are forced into the definition to argue what dissipation means. Principally, a new instrument has been added to the Ohm Meter, the thermometer, to prove you have in fact measured the value of a carbon composition resistor. No one actually does this; no one actually could offer a suitable caloric answer if their life depended on it; and certainly no one could tell you what the resistance is from a thermometer reading. But they would demand it is necessary none the less. ;-) 73's Richard Clark, KB7QHC |
John Smith wrote:
Check for reflected power in either direction. If none, then it is conjugally matched exactly. Isn't a 50 ohm transmitter conjugately matched to a 50 ohm load when fed through 1/2 wavelength of 450 ohm ladder-line? -- 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! =----- |
Gene Fuller wrote:
Are you suggesting that a steam engine is needed in addition to "obvious and elementary notions"? I didn't say anything about a steam engine, Gene. The question is: How do you prove a conjugate match exists through measurements when you are completely ignorant of the source impedance? -- 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! =----- |
Cecil,
8-) 8-) 8-) 8-) 8-) 8-) (You seemed to miss the single smiley on my previous message, so I though I would try a few more.) The "proof" of something when one does not have adequate information is often called "faith". More to the point, there are several possible answers. 1. Who cares? If you can't measure it and you can't adjust it, just forget about it. Lack of maximum power transfer is rarely fatal. 2. If you are operating an amateur radio station just twist the knobs on the tuner until the transmitter is happy. 3. If you are designing a system to be sent into space then analyze and test the heck out of it. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: Are you suggesting that a steam engine is needed in addition to "obvious and elementary notions"? I didn't say anything about a steam engine, Gene. The question is: How do you prove a conjugate match exists through measurements when you are completely ignorant of the source impedance? |
Gene Fuller wrote:
(You seemed to miss the single smiley on my previous message, so I though I would try a few more.) Why do you use 8's in your smileys? That's why I missed it. -- 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! =----- |
"John Smith" wrote in message ...
From the design side, MPTT is defined at an interface, and minimizes "reflected power" at that interface, and that is it. The other items about matching are also quite important, such as stability, loading, impedance transfer (both directions), bandwidth, Qs, loaded Qs etc. But that is Not MPTT. There is a tradeoff between these, if one can also obtain mptt, great, but close is good too. mptt is just one of several parameters needed to optimize a match. At times there are too many unknowns and the matching is experimental (class C) Experimental ! Not any more, the computor does it quite easily Regards Art |
When a candidate for an EE faculty position visits, someone, usually at
lunch, will bring the conversation around to the MPTT. If he or she does anything other than giggle they do not get my vote. Let us leave this tar-baby out in the field. 73 Mac N8TT -- J. Mc Laughlin - Michigan USA |
Why do you use 8's in your smileys? That's why I missed it. -- 73, Cecil http://www.qsl.net/w5dxp They must be inteligent smileys, with glasses 8-) or divers 0-) or rich ones $-) BUm |
Yuri Blanarovich wrote:
They must be inteligent smileys, with glasses 8-) or divers 0-) or rich ones $-) I'm not very internet savvy. What is an intelligent smiley? -- 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! =----- |
"Isn't a 50 ohm transmitter conjugately matched to a 50 ohm load
when fed through 1/2 wavelength of 450 ohm ladder-line?" ============== Heck yes, I'm assuming u mean 50 + j 0 Ohms. 73 de Jack, K9CUN |
Everybody keeps going on and on and on about 50-ohm transmitters when in
fact there's no such thing. |
Gene Fuller wrote:
"The maximum power transfer theorem describes the impact from change of the load impedance." That`s true. When impedances at a junction become matched, you can cut the matched line at any place and the impedances looking in opposite directions are conjugates of each other. It is not pathological to take full advantage of the theeorem. Conjugate matching is the same as d-c matching except that reactance must be neutralized not to get into the way of a-c maximum power transfer. W.L. Everitt is one of many authors who state the maximum power transfer theorem. I quoted Terman early in this thread. Here is a quote from King, Mimno, annd Wing on page 43 of "Transmission Lines, Antennas, and Wave Guides": If a dissipationless network is inserted between a constant-voltage generator of internal impedance ZG and a load of impedance ZR such that maximum power is delivered to the load, at every pair of terminals the impedances looking in opposite directions are conjugates of each other. There`s lots more. Read the book. Best regards, Richard Harrison, KB5WZI |
On Wed, 3 Mar 2004 15:48:38 +0000 (UTC), "Reg Edwards"
wrote: Everybody keeps going on and on and on about 50-ohm transmitters when in fact there's no such thing. Yes, you do keep going on and on about it, don't you? That and Q and SWR meter alternative names - all pretty lame stuff. |
Richard Harrison wrote:
If a dissipationless network is inserted between a constant-voltage generator of internal impedance ZG and a load of impedance ZR such that maximum power is delivered to the load, at every pair of terminals the impedances looking in opposite directions are conjugates of each other. Since dissipationless networks don't exist in reality, doesn't this imply that it is impossible to achieve a conjugate match at *all* points in a real-world system? - Not trying to be ornery, just realistic. -- 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! =----- |
Old Ed wrote:
"Couild you explain this concept, and/or provide some references?" Suppose we adjust a variable d-c supply to full-scale indication on an external meter. Next, install a chopper (lossless on-off circuit) driven at a high frequency to produce a square wave interruption of the d-c with a 50% duty cycle, and insert the chopper contacts in series with the external meter. The chopper connects the external meter 50% of the time and disconnercts it 50% of the time. The meter reads 50% of full scale. Another way to reduce the scale reading to 50% is to insert a resistor in series with the meter. If it is an 0-1 ma meter and if it has an internal resistance of 1000 ohms, insertion of a 1000-ohm resistor in series with the meter will reduce the meter scale indication to 50%. The chopper as part of the meter source eliminates current to the meter 50% of the time. The resistor which has the same effect and produces the same scale indication as the chopper on the effective output current exacts its loss of 0.0005 amp x 0.5 volt or 0.25 milliwatt during 100% of the time. The chopper eliminates the power-losing resistor by substituting off-time in the power source. The source only supplies the power used by the load. With a resistor limiting power to the load, the source supplies its loss and the load power. The power in the load, a meter in our example, is the same using either the resistor or the chopper. The resistor is analogous to a Class-A amplifier. The chopper is analogous to a Class-C amplifier. The off-time has the same effective opposition to current to a load as a dissipative resistance. As the time-limited currented opposition to load current consumes no power, it is called a dissipationless resistance. Best regards, Richard Harrison, KB5WZI |
It is in the same class of parts with inductancless inductors,
and capacitanceless capacitors are in. With lossless resistance they can form a lossless, non-energy storing, extremely low/high Q, network. No need for tuning either! (sorry-just not serious today) "Old Ed" wrote in message hlink.net... "Lossless resistance?" Would that be zero resistance, or perhaps a negative resistance, as in the active part of a tunnel diode's V-I characteristic? I am a career EE, with a couple of graduate EE degrees; and this is something entirely new to me. Could you explain this concept, and/or provide some references? Thanks, Ed |
"Richard Clark" wrote in message ... On Wed, 3 Mar 2004 15:48:38 +0000 (UTC), "Reg Edwards" wrote: Everybody keeps going on and on and on about 50-ohm transmitters when in fact there's no such thing. Yes, you do keep going on and on about it, don't you? That and Q and SWR meter alternative names - all pretty lame stuff. and on, and on, and on, and on... i knew this would be a good thread. |
John Smith wrote:
"It is in the same class of parts with inductanceless inductors, and capacitanceless capacitors are in." Lossless resistance makes volts per amp. Inductors and capacitors are lossless because they only store energy and give it all back. A lossless resistance stores no energy. Its action is immediate. An inductance or capacitance with zero reactance also stores no energy and makes no volts per amp as opposition. Best regards, Richard Harrison, KB5WZI |
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