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Internal Resistance (?)
About all that anyone needs to know about an amateur radio amplifier
(transmitter) in order to use it properly is the output power level and the required load resistance. The latter is usually 50 ohms for a variety of reasons, most of which relate to convenience, availability of coax cables, test equipment impedance environment, etc. Beyond those values, there is nothing about the amplifier design which is used in designing and adjusting the remainder of the tuner, transmission line and antenna system. The power level is of importance only in telling us how much voltage and current is involved in various parts of the system. The result is the ultimate in convenience. We need have no intimate knowledge of "what is in the black box" in order to use it properly. In fact, even if we had full knowledge of all the particulars of the design, we would still use only its required load resistance and power levels associated with it modulation waveforms, etc. Our modern amateur transmitters and amplifiers even have a convenient meter on the front panel that tells us when we have met our obligation to provide a 50+j0 ohm load. It may be labeled "SWR" and calibrated in an unusual scale, but the important thing is that when it reads 0 or "1:1 SWR" that tells us that we have met the load resistance obligation - nothing more or less. I think that a great deal of confusion over this whole issue comes from two sources: 1. vague efforts to apply the infamous "Maximum Power Transfer Theorem" from the early days in undergrad EE school; and 2. confusing an r-f transmitter output stage with the classical "signal generator" with a dissipative 50-ohm internal resistance. Forget both of those irritants and concentrate on the required load for the transmitter, which the designer will provide and insist upon, and then adjust the antenna system to provide that load and all will be well. At no point will anyone, including the r-f amp designer in all likelihood, know or even care what the so-called "internal resistance" of the amplifier happens to be. He demands only one thing: the specified load resistance. Given that, his design will deliver the required power, efficiency, heat load, harmonic content, distortion levels, etc. etc. I know of no instance in the design of everything connected to the output port of the transmitter where there is need to know anything other than the required load resistance for the amplifier and the power levels (average, peak, etc.). Why do folks make this so complicated, Ian? 73/72, George Amateur Radio W5YR - the Yellow Rose of Texas Fairview, TX 30 mi NE of Dallas in Collin county EM13QE "In the 57th year and it just keeps getting better!" ----- Original Message ----- From: "Ian White, G3SEK" Newsgroups: rec.radio.amateur.antenna Sent: Thursday, August 14, 2003 1:42 AM Subject: Length of Coax Affecting Incident Power to Meter? Dr. Slick wrote: As Roy says, the equations relating any one of these parameters to any other are all well known. NONE of them ever involves source impedance. Assuming the source impedance is 50 ohms, which it usually isn't with most PAs. NO - and this is the central point. When Roy and I are saying: NONE of them ever involves source impedance. - that is exactly what we mean. We didn't mean there is a hidden assumption about what the source impedance is - we meant what we said: it isn't there at all, in any of the equations we're talking about. Look them up; and then go deeper and look at how they are derived. They involve only the load impedance and Z0. That's "only", as in "no hidden additives." -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
On Fri, 15 Aug 2003 07:45:32 GMT, "George, W5YR"
wrote: About all that anyone needs to know about an amateur radio amplifier (transmitter) in order to use it properly is the output power level and the required load resistance. Hi George, And us folk need never worry about what is beneath the hood as long as we don't need a mechanic. Sheesh, haven't you learned to turn the knob until the meter is full scale? All you have to really remember to push the button before you talk! The latter is usually 50 ohms for a variety of reasons, most of which relate to convenience, availability of coax cables, test equipment impedance environment, etc. For which us same folk STILL don't give a fig. Are you some sort of salesman? Who uses coax when telephone wire is free? You got stock in this cable stuff? I got satellite and I don't need it. Beyond those values, there is nothing about the amplifier design which is used in designing and adjusting the remainder of the tuner, transmission line and antenna system. What are you talking about designing? Is your charge card void? Do the sales clerks ignore you? Have you consider stitching your own semaphore flags for a hobby instead? At least no one would laugh as much for all the arm waving. The power level is of importance only in telling us how much voltage and current is involved in various parts of the system. None of us folk even think of voltage or current, this impotence is not needed to make a contact. What's the point? The result is the ultimate in convenience. Something that us folk take for granted and never give a thought to because it is exactly that: convenient. Are you writing a magazine article no one reads? I hope you include lots of pictures. I prefer Reader's Dogma myself. We need have no intimate knowledge of "what is in the black box" in order to use it properly. Us folk would ask "what is in the black box? What are YOU talking about?" My boxes are brown like any from the liquor store. The only black box I've seen was at the cemetery. I don't think I will worry how to use THAT properly - thank you! In fact, even if we had full knowledge of all the particulars of the design, we would still use only its required load resistance and power levels associated with it modulation waveforms, etc. WE? You don't talk like one of us folk! Our modern amateur transmitters and amplifiers even have a convenient meter on the front panel that tells us when we have met our obligation to provide a 50+j0 ohm load. It may be labeled "SWR" and calibrated in an unusual scale, but the important thing is that when it reads 0 or "1:1 SWR" that tells us that we have met the load resistance obligation - nothing more or less. Who looks at that - are you one of those goggle-eyed professors that try to 'splain the meaning of life? You missed that by a country mile and still don't seem to have learned about what knobs are for. Twist one and push buttons until someone talks back. Your black box obviously has none of the modern conveniences, is it a telegraph? I think that a great deal of confusion over this whole issue comes from two sources: 1. vague efforts to apply the infamous "Maximum Power Transfer Theorem" from the early days in undergrad EE school; and Us folk never went to this underground school, nothing to be confused about at all. Are your problems from being a squinty-eyed miner? Maybe that's why you can't read these meters. Pull the blinds and take a load off your peepers. 2. confusing an r-f transmitter output stage with the classical "signal generator" with a dissipative 50-ohm internal resistance. What language are you trying to talk? Forget both of those irritants and concentrate on the required load for the transmitter, which the designer will provide and insist upon, and then adjust the antenna system to provide that load and all will be well. Gawd this is complexity for its own sake, you white coated pencil necked geeks need to get a life. If you are looking for the good times, pop the cap off a cold long-neck. I hope you don't need a glass, you would strangle fun out of TV. At no point will anyone, including the r-f amp designer in all likelihood, know or even care what the so-called "internal resistance" of the amplifier happens to be. He demands only one thing: the specified load resistance. Given that, his design will deliver the required power, efficiency, heat load, harmonic content, distortion levels, etc. etc. Infernal resistance is right. distortion is what I don't want to hear and what you are spouting on about is rattling the cone on my speaker. I know of no instance in the design of everything connected to the output port of the transmitter where there is need to know anything other than the required load resistance for the amplifier and the power levels (average, peak, etc.). Is this bragging or complaining? Talk to your chaplain for relief. Why do folks make this so complicated, Ian? 73/72, George Oh! a philosopher hmm? About the only complication is the broken lever of my Lazy Boy. Do you have a screw driver? Drink it college boy, but don't ralph on the couch when you pass out. 73's The mythical lurker.... ;-) |
Well said, George.
Roy Lewallen, W7EL |
I agree with every word, George. Why do folks make this so complicated, Ian? Mostly by insisting on asking questions that may not even *have* an answer! The US Constitution guarantees every citizen's right to ask whatever questions they wish - but the Universe does not guarantee there'll be any answers. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
Ian White, G3SEK wrote:
I agree with every word, George. Why do folks make this so complicated, Ian? Mostly by insisting on asking questions that may not even *have* an answer! The problem is that finding the output impedance analytically is usually very difficult. Measurement methods (usually questionable) have been proposed that "estimate" the output impedance. These tests can often be manipulated to get some desired result (for example 50 ohms). The value of output impedance depends especially on signal level and also several other parameters, such as negative feedback. Is the value of output impedance important? Sometimes in critical situations it can be. For example, a lowpass filter connected to the output of the PA may not be exactly correctly terminated at the input end. The error slightly affects the filter response, especially at the filter cutoff frequency. The passband ripple can also be affected. Most lowpass filter types can be designed for unequal values of generator and load impedances. If the PA is broadband solid-state a sweep method can be used to optimize the filter design. Usually these errors are unimportant, especially in typical Ham Radio. Bill W0IYH |
"George, W5YR" wrote in message ...
.... I think that a great deal of confusion over this whole issue comes from two sources: 1. vague efforts to apply the infamous "Maximum Power Transfer Theorem" from the early days in undergrad EE school; and 2. confusing an r-f transmitter output stage with the classical "signal generator" with a dissipative 50-ohm internal resistance. Forget both of those irritants and concentrate on the required load for the transmitter, which the designer will provide and insist upon, and then adjust the antenna system to provide that load and all will be well. Those of us who _do_ have to worry, in intimate detail, about generator source impedances, are most thankful that we do NOT when we put loads on our ham rigs. Thanks for a great posting that nicely summarizes what a lot of us have been saying for a long time. Perhaps Reg is right. Perhaps we SHOULD quit calling it an SWR meter and instead call it a "Transmitter Load Indicator" (or perhaps transmitter load error indicator). When you plug an appliance into the mains, do you worry about what the mains source impedance is, so long as it's low enough to maintain the proper voltage? When you connect speakers to an amplifier, do you worry about what the source impedance is, so long as it's low enough to not materially affect damping? If not, why would you worry about transmitter source impedance? Why would you not worry instead about proving the proper load so the amplifier can do it's job right? Cheers, Tom |
proper voltage? When you connect speakers to an amplifier, do you
worry about what the source impedance is, so long as it's low enough to not materially affect damping? If not, why would you worry about I would not go there on the audio . The speakers do need to match the design of the amp just as the load on a transmitter needs to match the design impedance. Most power output devices are designed to produce maximum power and /or minimum distortion into a specific load. |
Richard,
It always astounds me how the technically challenged are wont to launch ad hominem attacks instantly when matters evidently beyond their understanding, or perhaps in disagreement with their preconceived notions and prejudices, are brought to light. I note that not a single statement that I made in my posting is either declared incorrect or is replaced by your version of "truth." All I read is a lot of disconnected, poorly conceived and worded "slams" at me for posting the piece in the first place. The note was addressed to Ian who points out that he agrees totally with everything that I said. Why not select him as a target as well ? Double your pleasure with two targets! And, of course, appear the fool twice for making such an inane posting in the first place. Further to the point, no one has offered a single word of disagreement with the factual content of the posting. Only you have felt compelled to take your valuable time to post nonsense mouthings having nothing to do with the subject matter. Richard, in the past I have had a small degree of respect for your postings and your viewpoints, but if this is the best you can do now, then clearly it is time for you to resume your meds. Historically, you seldom if ever contribute anything of substance to a discussion but rather tend to sit on the sidelines making learned comments about the abilities of the participants to present their material and the degree to which they fail to meet your high standards for discourse. Yep, time for the meds . . . Or, perhaps you could actually contribute something of value by telling us where my posting is in error in *fact*, not in error for having been posted. I presume that you feel capable of tackling that chore. But, you are right about one thing: if you are an example of "us folks" then I am definitely not one of you, and very proud of it. 73/72, George Amateur Radio W5YR - the Yellow Rose of Texas Fairview, TX 30 mi NE of Dallas in Collin county EM13QE "In the 57th year and it just keeps getting better!" "Richard Clark" wrote in message ... On Fri, 15 Aug 2003 07:45:32 GMT, "George, W5YR" wrote: About all that anyone needs to know about an amateur radio amplifier (transmitter) in order to use it properly is the output power level and the required load resistance. Hi George, And us folk need never worry about what is beneath the hood as long as we don't need a mechanic. Sheesh, haven't you learned to turn the knob until the meter is full scale? All you have to really remember to push the button before you talk! The latter is usually 50 ohms for a variety of reasons, most of which relate to convenience, availability of coax cables, test equipment impedance environment, etc. For which us same folk STILL don't give a fig. Are you some sort of salesman? Who uses coax when telephone wire is free? You got stock in this cable stuff? I got satellite and I don't need it. Beyond those values, there is nothing about the amplifier design which is used in designing and adjusting the remainder of the tuner, transmission line and antenna system. What are you talking about designing? Is your charge card void? Do the sales clerks ignore you? Have you consider stitching your own semaphore flags for a hobby instead? At least no one would laugh as much for all the arm waving. The power level is of importance only in telling us how much voltage and current is involved in various parts of the system. None of us folk even think of voltage or current, this impotence is not needed to make a contact. What's the point? The result is the ultimate in convenience. Something that us folk take for granted and never give a thought to because it is exactly that: convenient. Are you writing a magazine article no one reads? I hope you include lots of pictures. I prefer Reader's Dogma myself. We need have no intimate knowledge of "what is in the black box" in order to use it properly. Us folk would ask "what is in the black box? What are YOU talking about?" My boxes are brown like any from the liquor store. The only black box I've seen was at the cemetery. I don't think I will worry how to use THAT properly - thank you! In fact, even if we had full knowledge of all the particulars of the design, we would still use only its required load resistance and power levels associated with it modulation waveforms, etc. WE? You don't talk like one of us folk! Our modern amateur transmitters and amplifiers even have a convenient meter on the front panel that tells us when we have met our obligation to provide a 50+j0 ohm load. It may be labeled "SWR" and calibrated in an unusual scale, but the important thing is that when it reads 0 or "1:1 SWR" that tells us that we have met the load resistance obligation - nothing more or less. Who looks at that - are you one of those goggle-eyed professors that try to 'splain the meaning of life? You missed that by a country mile and still don't seem to have learned about what knobs are for. Twist one and push buttons until someone talks back. Your black box obviously has none of the modern conveniences, is it a telegraph? I think that a great deal of confusion over this whole issue comes from two sources: 1. vague efforts to apply the infamous "Maximum Power Transfer Theorem" from the early days in undergrad EE school; and Us folk never went to this underground school, nothing to be confused about at all. Are your problems from being a squinty-eyed miner? Maybe that's why you can't read these meters. Pull the blinds and take a load off your peepers. 2. confusing an r-f transmitter output stage with the classical "signal generator" with a dissipative 50-ohm internal resistance. What language are you trying to talk? Forget both of those irritants and concentrate on the required load for the transmitter, which the designer will provide and insist upon, and then adjust the antenna system to provide that load and all will be well. Gawd this is complexity for its own sake, you white coated pencil necked geeks need to get a life. If you are looking for the good times, pop the cap off a cold long-neck. I hope you don't need a glass, you would strangle fun out of TV. At no point will anyone, including the r-f amp designer in all likelihood, know or even care what the so-called "internal resistance" of the amplifier happens to be. He demands only one thing: the specified load resistance. Given that, his design will deliver the required power, efficiency, heat load, harmonic content, distortion levels, etc. etc. Infernal resistance is right. distortion is what I don't want to hear and what you are spouting on about is rattling the cone on my speaker. I know of no instance in the design of everything connected to the output port of the transmitter where there is need to know anything other than the required load resistance for the amplifier and the power levels (average, peak, etc.). Is this bragging or complaining? Talk to your chaplain for relief. Why do folks make this so complicated, Ian? 73/72, George Oh! a philosopher hmm? About the only complication is the broken lever of my Lazy Boy. Do you have a screw driver? Drink it college boy, but don't ralph on the couch when you pass out. 73's The mythical lurker.... ;-) |
On Sat, 16 Aug 2003 07:07:16 GMT, "George, W5YR"
wrote: Richard, It always astounds me how the technically challenged are wont to launch ad hominem attacks instantly Do you accept that yours similarly deflates your credentials? It would at least place us on equal footing - in the gutter I suppose, but I brought my snorkel. ;-) 73/72, George Hi George, If you suffer the heat of taking a stand, so much for a test of faith. I have not seen you respond to the chain of evidence I have supplied to these matters. I will offer that this body of work long preceded my missive. You might or might not find that work interesting/correct/or worthy of your attention, but that does not erase if from the archive nor detract its intrinsic merit in desired measure to bruised ego. Pick any ONE of your cherished notions that I so soiled and put it up for a clear and concise examination. OR Let me head that off with a very simple question that most dodge; and in fact lies at the very heart of your subject line: Given the premise that the amateur's rig output Z is NOT 50 Ohms, what value does it have (cite any assembly of conditions)? You will no doubt get many thumps on the back from well-wishers who spit in my direction. How many will offer a numeric response to that technical enquiry? I can forecast that will stand at the current exchange rate of 0. I will also forecast there will be either total silence, or scattered muttering about why they wouldn't engage such a scurvy fellow as me. And yet the absence of that number from the discussion under this subject line mocks the charter of this group more than my humor did you. Is it lower than 50? Higher than 50? How much? The stunned silence in response to such simple, forced speculation is more a result of intellectual catatonia than moral indignation. Those who have offered numbers (I count among them), who have revealed methods of their derivation (I count among them), who performed actual bench work (I count among them), who offer rationale as to the subject's correlation to other observables (I count among them) is notable in contrast to those who have nothing to show but the shallow rhetoric of impotent denial. 73's Richard Clark, KB7QHC |
On Sat, 16 Aug 2003 09:38:18 GMT, Richard Clark
wrote: On Sat, 16 Aug 2003 07:07:16 GMT, "George, W5YR" wrote: Richard, It always astounds me how the technically challenged are wont to launch ad hominem attacks instantly Do you accept that yours similarly deflates your credentials? It would at least place us on equal footing - in the gutter I suppose, but I brought my snorkel. ;-) 73/72, George Hi George, If you suffer the heat of taking a stand, so much for a test of faith. I have not seen you respond to the chain of evidence I have supplied to these matters. I will offer that this body of work long preceded my missive. You might or might not find that work interesting/correct/or worthy of your attention, but that does not erase if from the archive nor detract its intrinsic merit in desired measure to bruised ego. Pick any ONE of your cherished notions that I so soiled and put it up for a clear and concise examination. OR Let me head that off with a very simple question that most dodge; and in fact lies at the very heart of your subject line: Given the premise that the amateur's rig output Z is NOT 50 Ohms, what value does it have (cite any assembly of conditions)? You will no doubt get many thumps on the back from well-wishers who spit in my direction. How many will offer a numeric response to that technical enquiry? I can forecast that will stand at the current exchange rate of 0. I will also forecast there will be either total silence, or scattered muttering about why they wouldn't engage such a scurvy fellow as me. And yet the absence of that number from the discussion under this subject line mocks the charter of this group more than my humor did you. Is it lower than 50? Higher than 50? How much? The stunned silence in response to such simple, forced speculation is more a result of intellectual catatonia than moral indignation. Those who have offered numbers (I count among them), who have revealed methods of their derivation (I count among them), who performed actual bench work (I count among them), who offer rationale as to the subject's correlation to other observables (I count among them) is notable in contrast to those who have nothing to show but the shallow rhetoric of impotent denial. 73's Richard Clark, KB7QHC Hi All, I note by the absence of response that at least my mystical powers of clairvoyance are unparalleled. No one dare step up to the bar to answer the question: "What is the Z of a transmitter, if it is not 50 Ohms?" For those who would rather argue the mystic ability than answer the question, I will allow that this same absence may be due in part to the Blaster virus and the power black out. Now that I've braced up your crutches, let's proceed with a telling example of both the academic principle and the practical implication. I will simply choose a value for you. In other words, we will venture where these angels fear to tread. We will start with a deliberately mismatch transmitter, and a deliberately mismatched load. We will then throw in the practical necessity of line loss and ask the question that is my acid test for the wide-eyed inventors: "Does it make more than 1dB difference?" The scenario begins: "A 50-Ohm line is terminated with a load of 200+j0 ohms. The normal attenuation of the line is 2.00 decibels. What is the loss of the line?" Having stated no more, the implication is that the source is matched to the line (source Z = 50+j0 Ohms). This is a half step towards the full blown implementation such that those who are comfortable to this point (and is in fact common experience) will observe their answer and this answer a "A = 1.27 + 2.00 = 3.27dB" "This is the dissipation or heat loss...." we then proceed: "...the generator impedance is 100+0j ohms, and the line is 5.35 wavelengths long." "A = 1.27 + 2.00 + 1.62 = 4.9 decibels" Thus the answer to my question is: Yes. 1.62dB is greater than 1dB. Now, as to the application of this knowledge to the typical user. It becomes: "does my standard of 1dB meet the thresh hold of your caring?" Perhaps not and even 3 dB may be of no concern. For such folk I offer my best wishes and we each proceed happily on in life. [This, of course, presumes they do not in fact have a rig that exhibits a 600 Ohm output Z and hence the danger of nay saying the obvious without expressing a value to replace it.] Now, as to the application of this knowledge to the critical user. By this I mean those here who want to have a complete answer, and being thus informed can make their own choices. Is there anyone corresponding here that want to dispute that this is the charter of this group? I have then twice shown how a transmission line being bound by two reflecting planes introduces a Mismatch Uncertainty. This example has enlarged on that slightly through my advice that this uncertainty can be reduced to zero through the description of all paths. As I have also pointed out in the past, this is a simple truism of wave interference math - very simple. The fact of the matter is that nearly every correspondent to this forum employs a transmitter designed to and exhibiting 50 Ohms source Z. The simple fact of the matter is that none of those same correspondents will typically encounter that additional 1.67dB because of this. Those who choose to operate their transmitter outside of this specification may; but those same operators rarely, if ever, examine the evidence of Mismatch Uncertainty because they never move their load nor their SWR meter (the path never changes). They instead will observe a reading in their complacency and accept the error without being aware (unless they have read this, that is). I will add that even when operating outside of the characteristic source Z, that is not significantly off enough to match the issue portrayed above unless you cut power dramatically - and even then the issue is moot even though the loss is not. So, part and parcel to the subject header above and having shown how ignorance and rejection of the obvious has a concomitant loss; the question, as always, remains: Given the premise that the amateur's rig output Z is NOT 50 Ohms, what value does it have (cite any assembly of conditions)? What constitutes the silence from this point on? My proven clairvoyant skill being elevated by the day, the Blaster virus, the power outage, or that same intellectual catatonia? 73's Richard Clark, KB7QHC |
Richard Clark wrote:
Richard Clark wrote: Given the premise that the amateur's rig output Z is NOT 50 Ohms, what value does it have (cite any assembly of conditions)? What constitutes the silence from this point on? Nobody knows and nobody cares. All voltage to current ratios are determined by the system outside of the transmitter. The only thing a transmitter need furnish is a voltage (or current or power). No matter what the output Z of a transmitter, it can put out a voltage (or current or power). What happens inside a transmitter doesn't affect anything except transmitter efficiency. Any coherent energy re-reflected inside the transmitter simply superposes with the forward wave and becomes indistinguishable from the generated power. If modulation is added and the feedline is long enough, the re- reflection could be detected. With an unmatched TV generator and about 1000 ft of open-wire line, the TV ghosts would give an indication of how much reflected power is actually re-reflected inside the generator. For those who assert there are no reflections from a generator, this would be an easy experiment to run. -- 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 Sun, 17 Aug 2003 14:41:58 -0500, W5DXP
wrote: What constitutes the silence from this point on? Nobody knows and nobody cares. Hi Cecil, Then I count you in that group who finds the additional 1.62dB loss as inconsequential. I also note you have no answer to the question, but in that regard I wish you well, and we are both content. 73's Richard Clark, KB7QHC |
Richard Clark wrote:
W5DXP wrote: What constitutes the silence from this point on? Nobody knows and nobody cares. Then I count you in that group who finds the additional 1.62dB loss as inconsequential. I also note you have no answer to the question, but in that regard I wish you well, and we are both content. I think everyone appreciates the fact that if he/she destroys the efficiency of his/her transmitter by whatever means, then that is not inconsequential. But that's not really what the discussion is about, is it? SWR doesn't depend upon the efficiency of the transmitter, does 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! =----- |
On Sun, 17 Aug 2003 15:09:40 -0500, "H. Adam Stevens"
wrote: "Richard Clark" wrote in message .. . On Sun, 17 Aug 2003 14:41:58 -0500, W5DXP wrote: What constitutes the silence from this point on? Nobody knows and nobody cares. Hi Cecil, Then I count you in that group who finds the additional 1.62dB loss as inconsequential. I also note you have no answer to the question, but in that regard I wish you well, and we are both content. 73's Richard Clark, KB7QHC Hi Richard Since Cecil's reference to "nobody" implicitly includes me, I beg to be removed from that group. How to measure source impedance. Connect an adjustable load directly to the source, forget the transmission line. When the load gets hottest for the least power into the source, their impedances are matched. 73 H. NQ5H -------1.62 db here, 1.62 db there-------;^) Hi OM, You are stricken from that group then. Your conscription is ended and we still all remain content by universal acclamation. ;-) Myself I can tolerate up to 10dB without care so 1.62dB is hardly as monumental as the vivid reactions to this news would evoke. I only test claims to the level of 1dB to be generous. I would note that most claims fail to achieve even that value. 73's Richard Clark, KB7QHC |
"H. Adam Stevens" wrote:
How to measure source impedance. Connect an adjustable load directly to the source, forget the transmission line. When the load gets hottest for the least power into the source, their impedances are matched. Unless of course that shuts down, or even destroys, the source device in the process. -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
"Ralph Mowery" wrote in message ...
proper voltage? When you connect speakers to an amplifier, do you worry about what the source impedance is, so long as it's low enough to not materially affect damping? If not, why would you worry about I would not go there on the audio . The speakers do need to match the design of the amp just as the load on a transmitter needs to match the design impedance. Most power output devices are designed to produce maximum power and /or minimum distortion into a specific load. Just my point, Ralph... you should worry about your speakers being within the range of LOAD impedances that the amplifier is designed for, but you seldom would worry about the SOURCE impedance. You should worry about the antenna-load you present to your transmitter or amplifier being within the range of impedances for which the transmitter or amplifier is designed, but why worry about the transmitter or amplifier source impedance? (Some folk worry about audio amp damping factor, but it tends to be grossly overemphasized...see postings over the years by Dick Pierce in the audio groups for the simple explanation why it doesn't matter all that much.) Cheers, Tom |
Richard Clark wrote in message . ..
On Fri, 15 Aug 2003 07:45:32 GMT, "George, W5YR" wrote: About all that anyone needs to know about an amateur radio amplifier (transmitter) in order to use it properly is the output power level and the required load resistance. Hi George, And us folk need never worry about what is beneath the hood as long as we don't need a mechanic. Sheesh, haven't you learned to turn the knob until the meter is full scale? All you have to really remember to push the button before you talk! .... Richard, I'm seriously worried about you. Was that posting, and many of the others I've seen from you recently, a plea for help? I'm sure we can come up with appropriate help lines for you to call, if only you will tell us what's at the root of your problem. Regards, Tom |
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Floyd Davidson wrote:
"Unless of course that shuts down ,or even destroys the source devices in the process (adjustable load gets hottest for least power to the source as proposed by H. Adam Stevens)." H.`s variable load can determine a match because maximum power transfers if the load impedance is the conjugate of the source. But, least power input may not coincide with maximum power output. Low internal source impedance as compared with the load impedance usually is more efficient, but not necessarily so. With impedance produced by switched-off time as in the Class C amplifier, impedance is not only a function of internal loss. A Class A amplifier has constant power input so that the more power delivered to a load, the less power is dissipated in the amplifier. Simple determination of source impedance is to divide the open-circuit voltage by the short-circuit current out of the device. That requires a source impedance that is the same at matched loading as with a shorted load. As Floyd notes, the extremes, open and shorts, can shut-down or destroy from too much voltage or current. Near the region of a conjugate match, less severe voltage and current are likely. Maximum power transfer to the load occurs at the conjugate match point. Heat rise would be the likely cause of damage to a transmitter at maximum output. Power output measurements can be made quickly to limit transmitter and load temperature rise in and around the load impedance which gives maximum power output. A versatile load can be used to determine the conjugate match and thus the source impedance. The transmitter may not be designed to deliver maximum power output even momentarily and may have built-in protection to prevent it. Feedback may not increase maximum power output without regard to distortion. In an audio amplifier, the output impedance may be made to look like a short to the speaker and thereby put the brakes on its movement as it tends to ring on after excitation. The same feedback lowers distortion at a given power level, or said another way increases power output for a given level of distortion, but maximum power output without regard to distortion is unaffected by the feedback. R-F amplifier negative feedback likewise has no effect on the all-out maximum power. Best regards, Richard Harrison, KB5WZI |
H. Adam Stevens wrote:
I have a class A audio amp (BAT VK500) and it definitely gets cooler when The Carmina Burana gets louder. Take a lesson from the power companies. They run coolest when their output impedances are the lowest. :-) -- 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! =----- |
Until one breaker goes and the rest of the grid can't handle the load.
;^))))))))) 73, H. "W5DXP" wrote in message ... H. Adam Stevens wrote: I have a class A audio amp (BAT VK500) and it definitely gets cooler when The Carmina Burana gets louder. Take a lesson from the power companies. They run coolest when their output impedances are the lowest. :-) -- 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! =----- |
(Richard Harrison) wrote:
Floyd Davidson wrote: "Unless of course that shuts down ,or even destroys the source devices in the process (adjustable load gets hottest for least power to the source as proposed by H. Adam Stevens)." If you are going to quote me, the least you could do is quote what *I* said, without editing it to suit your needs. Regardless, whatever it is that the rest of this nonsense is supposed to mean, it certainly doesn't relate to what I posted. H.`s variable load can determine a match because maximum power transfers if the load impedance is the conjugate of the source. But, least power input may not coincide with maximum power output. Low internal source impedance as compared with the load impedance usually is more efficient, but not necessarily so. With impedance produced by switched-off time as in the Class C amplifier, impedance is not only a function of internal loss. A Class A amplifier has constant power input so that the more power delivered to a load, the less power is dissipated in the amplifier. Simple determination of source impedance is to divide the open-circuit voltage by the short-circuit current out of the device. That requires a source impedance that is the same at matched loading as with a shorted load. As Floyd notes, the extremes, open and shorts, can shut-down or destroy from too much voltage or current. Near the region of a conjugate match, less severe voltage and current are likely. Maximum power transfer to the load occurs at the conjugate match point. Heat rise would be the likely cause of damage to a transmitter at maximum output. Power output measurements can be made quickly to limit transmitter and load temperature rise in and around the load impedance which gives maximum power output. A versatile load can be used to determine the conjugate match and thus the source impedance. The transmitter may not be designed to deliver maximum power output even momentarily and may have built-in protection to prevent it. Feedback may not increase maximum power output without regard to distortion. In an audio amplifier, the output impedance may be made to look like a short to the speaker and thereby put the brakes on its movement as it tends to ring on after excitation. The same feedback lowers distortion at a given power level, or said another way increases power output for a given level of distortion, but maximum power output without regard to distortion is unaffected by the feedback. R-F amplifier negative feedback likewise has no effect on the all-out maximum power. Best regards, Richard Harrison, KB5WZI -- Floyd L. Davidson http://web.newsguy.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
Floyd Davidson wrote:
"Unless of course that shuts down, or even destroys the source device in the process." Floyd was commenting on H. Adam Stevens` suggestion of how to measure source impedance. I appended the gist of H.`s comment in parentheses to define "that" in Floyd`s statement. I am sorry I misplaced the quotation marks which should have been placed as they are above. I don`t disagree with either Floyd or H. Best regards, Richard Harrison, KB5WZI |
Richard,
If you do indeed need help, it's far more help than I can give you. My posting was not in jest, nor was it to poke fun at you or your postings. I was dead serious about it. Cheers, Tom Richard Clark wrote in message . .. On 17 Aug 2003 21:12:52 -0700, (Tom Bruhns) wrote: Richard, I'm seriously worried about you. Was that posting, and many of the others I've seen from you recently, a plea for help? I'm sure we can come up with appropriate help lines for you to call, if only you will tell us what's at the root of your problem. Regards, Tom Hi Tom, You only need drive down the road some 25 minutes if you are serious. Less time than that spent in all these postings that have you worried. I've driven to Mukilteo 5 days a week for several years and its not all that far and almost a straight shot especially with you on the speedway. When can I expect you? ;-) 73's Richard Clark, KB7QHC |
H. Adam Stevens wrote:
"W5DXP" wrote in message Take a lesson from the power companies. They run coolest when their output impedances are the lowest. :-) Until one breaker goes and the rest of the grid can't handle the load. ;^))))))))) 73, H. Incidentally, the argument that Thomas Edison used to prove that power distribution systems would never be AC is that they would burn themselves up trying to provide maximum power transfer. He never conceived that they would be more interested in efficiency than maximum power transfer. :-) So why can't we have a 95% efficient RF power amplifier? -- 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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Roy Lewallen wrote:
H. Adam Stevens wrote: If the source is matched to the line, is the reflected wave dissipated as heat in the source? Nope. I've shown this definitively a number of times on this newsgroup. Yep, by assuming something that is true only by definition. :-) If the source is hidden in a black box and includes a circulator with load, the reflected wave *IS* dissipated as heat in the source. For some phases of reflected energy, the dissipation does increase. You say it is because of the mismatch but the mismatch is because of the reflected waves. So which came first, the mismatch or the reflected waves? I suggest that the mismatch will not happen until the reflected waves arrive. Try it with a one second long transmission 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! =----- |
Aren't the switching amps used in AM broadcast highly efficient?
Do folks still use class C amps in FM service? (It's been decades) H. NQ5H "W5DXP" wrote in message ... H. Adam Stevens wrote: "W5DXP" wrote in message Take a lesson from the power companies. They run coolest when their output impedances are the lowest. :-) Until one breaker goes and the rest of the grid can't handle the load. ;^))))))))) 73, H. Incidentally, the argument that Thomas Edison used to prove that power distribution systems would never be AC is that they would burn themselves up trying to provide maximum power transfer. He never conceived that they would be more interested in efficiency than maximum power transfer. :-) So why can't we have a 95% efficient RF power amplifier? -- 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! =----- |
I've made homebrew transmitters with efficiencies exceeding 85%. See for
example Fig. 2.97 on p. 2.36 of the new _Experimental Methods in RF Design_. Sokal and Sokal got better than 90% as I recall with their Class E designs. Roy Lewallen, W7EL |
Well, I guess help is not wanted for whatever reason. I'd rather
offer sincerely and be refused than not offer and learn later that it was in order. Regards, Tom Richard Clark wrote in message . .. On 18 Aug 2003 09:37:59 -0700, (Tom Bruhns) wrote: Richard, If you do indeed need help, it's far more help than I can give you. My posting was not in jest, nor was it to poke fun at you or your postings. I was dead serious about it. Cheers, Tom Hi Tom, Yes, I have noticed the 30 cent jump in the cost of gas. ;-) How about lunch at Lake Stevens then? I drove that for a couple of years too, back when your outfit was called HP. I worked in Larry Whatley and Nick Pendergas's group during the Marysville to L.S. move (to set a time frame). 1,000,000 lines of Pascal FFT code in that project. It was fun and I still have a lot of drawings of waveforms generated. For those who are interested in the nuances of FFT's (and why their own implementation transforms lack resolution or dynamic range); my tenure provided me with a wealth of insight that is commonly unimplemented in current discussions here and generally in trade publications. 73's Richard Clark, KB7QHC |
"Tom Bruhns" wrote:
...... Perhaps Reg is right. Perhaps we SHOULD quit calling it an SWR meter and instead call it a "Transmitter Load Indicator" (or perhaps transmitter load error indicator). I propose that we call it a "Reflected Energy Guessimator", or REG for short. Jim, K7JEB k7jeb(at)arrl(dot)net Glendale, AZ |
Has it not yet occurred to you the impedance of the usual amateur's
transmitter changes when the load impedance is changed? In the present context this not only makes a mess of maximum-power theorems, conjugate matches, and referrals to renouned authors, it also reduces the years and gigabtres of 'learned' arguments on this newsgroup to nonsense. However, it's been great entertainment. Long may it contiunue. ;o) --- Reg, G4FGQ |
On Fri, 22 Aug 2003 03:59:13 +0000 (UTC), "Reg Edwards"
wrote: Has it not yet occurred to you the impedance of the usual amateur's transmitter changes when the load impedance is changed? Few seem willing to put a -um- a number to it. They could then respond coyly "change from what?" The assembled throng not only didn't give you quarter, they didn't even give you ha' pence. ;-) I share your amusement tho' and if I had a glass of wine, I would click it to the monitor in front of me. 73's Richard Clark, KB7QHC |
Few seem willing to put a -um- a number to it. ========================== Rich, As a qualified engineer, and someone who has participated in futile discussions, how would YOU obtain a number for it? Such a number must exist. |
Richard's numbers are average for what seems to be the RF component of
the waveform. It does not include any variations cause by modulation characteristics. A single number does not exist!! An average value for my voice characteristics will be different from an average value with your voice characteristics, etc. The spectral and intensity characteristics of each voice is different and will cause the instantaneous and average V/I ratio in the finals to vary. Therefore, a single number does not exist. It may be possible to develop an equation with variable functions for spectral and intensity density functions to modulate the output but each solution would be unique. A nice thevinin model would be a constant voltage, example 12 volts dc, with a dynamically varying source resistor. The source resistor has two components in the modulation scheme: 1) the RF frequency variation, constant frequency, 2) and the second term the audio spectral power density of my voice. This would be loaded by a constant 50 ohm load. Anyway, it's nice to think about. Averages are much easier to work with though! DD, W1MCE Reg Edwards wrote: Few seem willing to put a -um- a number to it. [SNIP] Such a number must exist. |
Richard Clark wrote:
"I keyed down and made sure the excitation was disconnected---." Supposing you were measuring the impedance the source shunts its output with, and supposing your amplifier is linear so it can be used for AM and SSB, and supposing that it is Class AB or Class B for more efficiency than Class A, and supposing that it has a small amount of forward bias to reduce crossover distortion, you should measure a much higher impedance while idling than when the transmitter puts full power into a load. The output impedance has a meaning at maximum power output. This can be determined by trying different loads to find the load that gets the most power from the transmitter. The source impedance is its conjugate. Best regards, Richard Harrison, KB5WZI |
On Fri, 22 Aug 2003 14:02:35 GMT, Dave Shrader
wrote: A single number does not exist!! An average value for my voice characteristics will be different from an average value with your voice characteristics, etc. Hi Dave, Are you one of those who whistles, hums, and recites the Gettysburg Address into the mike while tuning up? Many on the band would offer you as an example of Infernal Resistance. ;-) 73's Richard Clark, KB7QHC |
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"Richard Clark" said
Are you one of those who whistles, hums, and recites the Gettysburg Address into the mike while tuning up? ========================= "Patriotism is not enough". (Nurse Edith Cavel) |
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