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#1
August 15th 03, 08:45 AM
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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 |
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#2
August 15th 03, 11:01 AM
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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.... ;-) |
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#3
August 16th 03, 08:07 AM
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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 news  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.... ;-) |
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#4
August 16th 03, 10:38 AM
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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 |
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#5
August 17th 03, 07:51 PM
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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 |
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#6
August 17th 03, 08:41 PM
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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! =----- |
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#7
August 18th 03, 05:12 AM
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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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#8
August 18th 03, 07:08 AM
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#9
August 18th 03, 05:37 PM
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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 |
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