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Transmitter Output Impedance
On May 16, 6:03*am, Wimpie wrote:
I am not ignoring a problem (as you suggested), I am just using the right tool to solve a problem. I'm sorry, Wim, that is just not true. When you convert a V/I ratio to a lumped circuit impedance, you are switching models in mid-example and it changes everything in one direction (while keeping conditions the same in the other direction). Switching to a model that doesn't recognize reflections at all when a question about reflections arises is an obvious logical diversion. The lumped-circuit model does not recognize reflected energy and therefore does not allow the tracking of reflected energy. The distributed network/wave reflection model does allow for the tracking of reflected energy and was developed because of the limitations of the lumped circuit model. I will buy your assertion that one can use voltage and current to achieve the same thing if one is careful not to violate the known laws of EM wave physics. In my example, the reflected power on the 100 ohm line is 12.5 watts. The reflected voltage is 35.35 volts. The reflected current is 0.3535. The reflected voltage and reflected current are 180 degrees out of phase so the power is real, i.e. cos(180)=1.0, and the reflected wave has a Poynting vector magnitude of 12.5 watts (per coax cross-sectional area). In my very simple example, there is no reflected power on the 50 ohm feedline yet there is (35.35)(0.3535)=12.5 watts of reflected power from the load incident upon the 100/50 ohm impedance discontinuity. I ask you again: Exactly what phenomenon of EM wave physics causes the reflected wave to *reverse* its momentum and direction of energy flow when the magnitude of the reflection coefficient is 0.3333? As long as you refuse to answer this simple question about such a simple example, this discussion will go nowhere. Cecil, I think you have sufficient knowledge to form an opinion without hiding behind others. You also have the equipment to figure out some things yourself, and I gave some hints to help you. *The only question is, are you willing to do this? If you cannot answer the simple question about what happens to the reflected energy at a simple passive impedance discontinuity, I am not about to trust your assertions about what happens inside an active source. Trying to introduce a more complicated example while refusing to deal with the very simple example that I provided is an obvious and typical logical diversion. Again, I am not going to cooperate in your attempts at diversions. If you don't know why reflected energy reverses momentum and direction at a passive Z0-match, just say so. Here's an easier example: Two EM waves superpose in a Z0=100 ohm environment. Each wave is 100 volts at 1 amp = 100 watts. The phase angle on wave1 is +60 degrees and the phase angle on wave2 is -60 degrees. The superposition results in a new wave of 100 volts at 1 amp = 100 watts with a phase angle of zero degrees. We superposed two 100 watt waves and the result was one 100 watt wave. What happened to the other 100 watts? -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK |
Transmitter Output Impedance
On 16 mayo, 16:15, Cecil Moore wrote:
On May 16, 6:03*am, Wimpie wrote: I am not ignoring a problem (as you suggested), I am just using the right tool to solve a problem. I'm sorry, Wim, that is just not true. When you convert a V/I ratio to a lumped circuit impedance, you are switching models in mid-example and it changes everything in one direction (while keeping conditions the same in the other direction). Switching to a model that doesn't recognize reflections at all when a question about reflections arises is an obvious logical diversion. The lumped-circuit model does not recognize reflected energy and therefore does not allow the tracking of reflected energy. The distributed network/wave reflection model does allow for the tracking of reflected energy and was developed because of the limitations of the lumped circuit model. I will buy your assertion that one can use voltage and current to achieve the same thing if one is careful not to violate the known laws of EM wave physics. In my example, the reflected power on the 100 ohm line is 12.5 watts. The reflected voltage is 35.35 volts. The reflected current is 0.3535. The reflected voltage and reflected current are 180 degrees out of phase so the power is real, i.e. cos(180)=1.0, and the reflected wave has a Poynting vector magnitude of 12.5 watts (per coax cross-sectional area). In my very simple example, there is no reflected power on the 50 ohm feedline yet there is (35.35)(0.3535)=12.5 watts of reflected power from the load incident upon the 100/50 ohm impedance discontinuity. I ask you again: Exactly what phenomenon of EM wave physics causes the reflected wave to *reverse* its momentum and direction of energy flow when the magnitude of the reflection coefficient is 0.3333? As long as you refuse to answer this simple question about such a simple example, this discussion will go nowhere. Cecil, I think you have sufficient knowledge to form an opinion without hiding behind others. You also have the equipment to figure out some things yourself, and I gave some hints to help you. *The only question is, are you willing to do this? If you cannot answer the simple question about what happens to the reflected energy at a simple passive impedance discontinuity, I am not about to trust your assertions about what happens inside an active source. Trying to introduce a more complicated example while refusing to deal with the very simple example that I provided is an obvious and typical logical diversion. Again, I am not going to cooperate in your attempts at diversions. If you don't know why reflected energy reverses momentum and direction at a passive Z0-match, just say so. Hello Cecil, I answered a simple question requested several times by Walt (I had to reply to it!). It wasn't my statement but I did it. The solution I gave involved both lumped circuit theory (to calculate the net power) and transmission line theory (to calculate forward and reflected power in a 50 Ohms environment). Even other people had to help Walt to understand a voltage divider (the 212.1*50 issue). Maybe you can comment whether my simple solution (not involving momentum, Poynting vector or optics) is correct or not. I am familiar with the use (and mis-use by others) of the Poynting vector, but I don't discharge 10 kJ through a mosquito when using a newspaper does the job also. Regarding reflections: Does a PA see difference between: 1. 100 Ohms lumped circuit load 2. RC = +0.33333 (for 50 Ohms reference) 3. VSWR = 3 (voltage minimum, for a 300 Ohms reference) The answer is no, all can be converted to 100 Ohms lumped circuit. What is in between the PA and the actual load is not relevant, what matters (for the PA) is what it sees at its SO239 socket. Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
Hello Cecil,
Here's an easier example: Two EM waves superpose in a Z0=100 ohm environment. Each wave is 100 volts at 1 amp = 100 watts. The phase angle on wave1 is +60 degrees and the phase angle on wave2 is -60 degrees. The superposition results in a new wave of 100 volts at 1 amp = 100 watts with a phase angle of zero degrees. We superposed two 100 watt waves and the result was one 100 watt wave. What happened to the other 100 watts? If you want this question answered, please open a new thread as it is not relevant to the original question. Maybe people will ask you a circuit diagram showing the sources and the combiner circuitry to enable calculation of the net power delivered by each source. Otherwise people may consider your problem as a single incident wave problem (as for these type of steady state signals you first add complex amplitudes, then calculate powers). I did respond to Walt's request because it is on topic and I stated that such thing can happen (without given a numerical example). Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
On May 16, 11:19*am, Wimpie wrote:
The solution I gave involved both lumped circuit theory (to calculate the net power) and transmission line theory (to calculate forward and reflected power in a 50 Ohms environment). Lumped circuit theory presupposes that waves do not exist and that RF energy travels instantaneously, faster than the speed of light. You seem to be ignoring the numerous laws of physics violated by the lumped circuit theory. You also seem to be ignoring the fact that when lumped circuit theory yields different results than the distributed network theory, distributed network theory always wins because it is closer to Maxwell's equations. I gave an earlier CLC Pi-Network Tuner example that proved the lumped circuit model fails when reflections are present. EZNEC results are nothing alike when using the lumped inductance option vs the helical wire option for an inductance in a standing wave antenna. If you want this question answered, please open a new thread as it is not relevant to the original question. Asserting that it is not relevant for the purpose of diversion will not make it go away. If one cannot understand, explain, and solve the simplest passive interference problem, how is one ever going to understand, explain, and solve the multiple levels of interference possible within an active source being invaded by reflected energy? If one cannot add one plus one, one is not likely to be able to add two plus two and something akin to that is what I am seeing here. Until one understands exactly how a Z0-match reverses the direction and momentum of a reflected wave, one will not understand what is happening inside a source with incident reflected energy. What is actually happening in reality is revealed when one sticks with the distributed network/wave reflection theory throughout the analysis. People who whine that such is too difficult have to be satisfied with a certain level of ignorance and inaccuracy. -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK |
Transmitter Output Impedance
Cecil,
It seems that you on purpose remove/ignore things that you don't like, but (you know) are true. A CLC pi filter doesn't know the difference between: 1. 100 Ohms lumped circuit load 2. RC = +0.33333 (for 50 Ohms reference) 3. VSWR = 3 (voltage minimum, for a 300 Ohms reference) It seems you don't want to notice that. That it is convenient to use transmission line theory to calculate the load as seen by a PA when transmission line sections are involved, is OK, I didn't deny that. That lumped circuit theory has limitations is fully understood. Frequently transmission line effects are modelled using parasitic L and C additions yielding accurate models valid up to GHz frequencies (depending on the size of the component). We are below 30 MHz (for this topic). Here the experience of the Engineer comes into play: when you can use a lumped circuit model and when you need to use transmission line models (the particle/wave issue is similar)? A helical inductor of an antenna no longer small w.r.t. wavelength may be better modelled with transmission line theory, but that is OT. Even the L of the CLC filter, you can model with a lumped circuit equivalent with more than sufficient accuracy. This is daily business for manufacturers of inductive components. Generally, converting results from transmission line models to impedance in combination with lumped circuit theory to calculate the load as seen by the active device, is daily practice. Especially here, as we are dealing with narrow band signals and don't have to model the behavior for harmonics. But for some reason you don't want to see that, and you elevate transmission line theory to a goal. So again, once you did the conversion to Z, you no longer have to worry about transmission line issues in the load or cabling (including reflection coefficient) when treating your PA's CLC pi filter. Now speed of light becomes important in a CLC pi filter for a HF PA, when becomes "Gaussian" of importance (and may lose all the readers of this topic)? With kind regards, Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
On May 16, 2:58*pm, Wimpie wrote:
A CLC pi filter doesn't know the difference between: 1. 100 Ohms lumped circuit load 2. RC = +0.33333 (for 50 Ohms reference) 3. VSWR = 3 (voltage minimum, for a 300 Ohms reference) It seems you don't want to notice that. It is not worth wasting my time to notice since *everyone* already knows that a CLC pi filter is not alive and doesn't have a brain so it must necessarily be dumb as a dead stump. You, OTOH, hopefully being smarter than the average CLC pi filter, should know that the conditions existing within a resistor are different from the conditions existing within an antenna with the same feedpoint impedance. Hint: If you don't know what is in the box, alleviate your ignorance by looking inside the box. If you put on the blinders and refuse to look, then you will make errors like you did earlier while measuring an s11 of zero when it was actually 0.3333. Even the L of the CLC filter, you can model with a lumped circuit equivalent with more than sufficient accuracy. When the task is to determine the exact delay through the inductor, how the heck can the lumped circuit model tell you that? -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK |
Transmitter Output Impedance
On May 16, 3:29*pm, Cecil Moore wrote:
When the task is to determine the exact delay through the inductor, how the heck can the lumped circuit model tell you that? Wim, I forgot to note that using your stated methods, W8JI "measured" a 3ns delay through a 10" long, 2" diameter, 100 turn, 100uh, 80m mobile loading coil. Doesn't a 4 MHz RF wave traveling the length of a large 100uH air-core 80m loading coil in 3 ns give you some pause for reconsidering your methods? Every wonder why computer manufacturers don't install 100uh coils in series with their computer bus lines to speed up their computers? :-) -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK |
Transmitter Output Impedance
On 16 mayo, 22:29, Cecil Moore wrote:
On May 16, 2:58*pm, Wimpie wrote: A CLC pi filter doesn't know the difference between: 1. 100 Ohms lumped circuit load 2. RC = +0.33333 (for 50 Ohms reference) 3. VSWR = 3 (voltage minimum, for a 300 Ohms reference) It seems you don't want to notice that. It is not worth wasting my time to notice since *everyone* already knows that a CLC pi filter is not alive and doesn't have a brain so it must necessarily be dumb as a dead stump. You, OTOH, hopefully being smarter than the average CLC pi filter, should know that the conditions existing within a resistor are different from the conditions existing within an antenna with the same feedpoint impedance. Hint: If you don't know what is in the box, alleviate your ignorance by looking inside the box. If you put on the blinders and refuse to look, then you will make errors like you did earlier while measuring an s11 of zero when it was actually 0.3333. Even the L of the CLC filter, you can model with a lumped circuit equivalent with more than sufficient accuracy. When the task is to determine the exact delay through the inductor, how the heck can the lumped circuit model tell you that? Just via the capacitance to ground (for example a CLC model of an inductor well below the first self resonance frequency). But when looking to a PA, there is often an additional capacitance left and right of the inductor that causes the most of the phase shift. I did some tesla coiling, so I am aware of the various models for single layer inductors. You are further drifting away from the main subject (PA output impedance and what mismatch will do). -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
On 16 mayo, 22:55, Cecil Moore wrote:
On May 16, 3:29*pm, Cecil Moore wrote: When the task is to determine the exact delay through the inductor, how the heck can the lumped circuit model tell you that? Wim, I forgot to note that using your stated methods, W8JI "measured" a 3ns delay through a 10" long, 2" diameter, 100 turn, 100uh, 80m mobile loading coil. Doesn't a 4 MHz RF wave traveling the length of a large 100uH air-core 80m loading coil in 3 ns give you some pause for reconsidering your methods? Every wonder why computer manufacturers don't install 100uh coils in series with their computer bus lines to speed up their computers? :-) -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK I am sorry Cecil, but for the current topic, the answer is no. Please stay to the topic, or start a new one. Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
On May 16, 4:55*pm, Wimpie wrote:
You are further drifting away from the main subject Actually, you are further drifting away from basic fundamental EM physics and I am not in the mood to follow you. Since you do not understand the basic fundamentals of EM wave interference, you cannot possibly understand what is going on inside an active source with invading reflected energy. You might as well be arguing that God causes everything because your lack of the understanding of the basic physics of interference causes your concepts to resemble religion more than anything scientific. That's not an ad hominen attack, just an observation based on the technical ignorance of EM wave interference that you have presented here on this newsgroup. Sorry for being so blunt but anyone who chooses to be ignorant, when there is knowledge available, doesn't deserve much respect, IMO. Since you have failed to answer the simplest of questions about passive circuits, exactly what makes you an expert on active circuits? -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK |
Transmitter Output Impedance
On 17 mayo, 00:37, Cecil Moore wrote:
On May 16, 4:55*pm, Wimpie wrote: You are further drifting away from the main subject Actually, you are further drifting away from basic fundamental EM physics and I am not in the mood to follow you. Since you do not understand the basic fundamentals of EM wave interference, you cannot possibly understand what is going on inside an active source with invading reflected energy. You might as well be arguing that God causes everything because your lack of the understanding of the basic physics of interference causes your concepts to resemble religion more than anything scientific. That's not an ad hominen attack, just an observation based on the technical ignorance of EM wave interference that you have presented here on this newsgroup. Sorry for being so blunt but anyone who chooses to be ignorant, when there is knowledge available, doesn't deserve much respect, IMO. Since you have failed to answer the simplest of questions about passive circuits, exactly what makes you an expert on active circuits? -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK Cecil, For Walt I made an exception, but I normally don't do someone's homework. I also don't spend my time solving non-relevant problems; I have more interesting quests waiting. If you show up with a relevant quest, maybe I am willing to dive into it. I am not calling myself an expert, I just designed some PA's, ranging from kHz to GHz and from mW to kW, some of them with efficiencies to over 95%. Together with antenna design and consultancy it assures me that at the end of each month I have some money left. With kind regards, Wim PA3DJS |
Transmitter Output Impedance
On May 17, 4:49*am, Wimpie wrote:
If you show up with a relevant quest, maybe I am willing to dive into it. Wim, here is why my questions for you are more than just relevant. It is imperative that someone lecturing us on happenings inside that PA RF volcano be able to understand what is occurring during a passive event involving forward and reflected EM fields and waves occurring at an impedance discontinuity outside of a PA. Two of the physical quantities that must be conserved are energy and momentum. EM RF fields and waves contain both energy and momentum which must be conserved. I have asked you to tell us exactly what laws of physics govern the reversal of the momentum and direction of energy flow at a Z0-match at a passive impedance discontinuity in a transmission line. You have refused to do so and asserted that such is irrelevant. I contend that I could not have asked a more relevant question - thus the reluctance to provide an answer. The answer to the question is contained in my energy analysis article at: http://www.w5dxp.com/energy.htm A passive Z0-match relies on superposition of waves accompanied by interference effects to explain the reversal of reflected wave energy direction and momentum. Walter Maxwell has called the process a "virtual open-circuit" or a "virtual short". In my article, I explain how it is a two-step process involving normal reflections and interference patterns at the impedance discontinuity. It works exactly like non-reflective glass covering a picture with its 1/4WL thin-film coating where two sets of reflected light waves undergo destructive interference toward the viewer and, honoring the conservation of energy and momentum, reverse their direction and momentum and flow in the opposite direction toward the picture. This is a well-understood phenomenon from sophomore physics 201. Why most RF engineers don't understand this simple physical process involving EM wave interference is beyond belief. Here's the Florida State University web page again: micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/ waveinteractions/index.html Set the java application for opposite phase and when the result is zero, scroll down to the bottom of the page to find out what happens to the energy components in the two waves that cancel to zero. Those energy components "are redistributed to regions that permit constructive interference" just as they are at a Z0-match in an RF transmission line where there are only two possible directions for RF energy flow. For every destructive interference event in one direction, there will be an equal magnitude constructive interference event in the opposite direction. At Walt's "virtual short", total destructive interference energy toward the source is redistributed as constructive interference energy back toward the load. I studied this subject in my EE courses at Texas A&M during the 1950's. The textbook was: "Fields and Waves in Modern Radio", by Ramo and Whinnery, (c) 1944, 1953. The subject is covered under "Quarter- Wave Coating for Eliminating Reflections" in the chapter titled: "Propagation and Reflection of Electromagnetic Waves". -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK |
Transmitter Output Impedance
On 17 mayo, 14:29, Cecil Moore wrote:
On May 17, 4:49*am, Wimpie wrote: If you show up with a relevant quest, maybe I am willing to dive into it. Wim, here is why my questions for you are more than just relevant. It is imperative that someone lecturing us on happenings inside that PA RF volcano be able to understand what is occurring during a passive event involving forward and reflected EM fields and waves occurring at an impedance discontinuity outside of a PA. Two of the physical quantities that must be conserved are energy and momentum. EM RF fields and waves contain both energy and momentum which must be conserved. I have asked you to tell us exactly what laws of physics govern the reversal of the momentum and direction of energy flow at a Z0-match at a passive impedance discontinuity in a transmission line. You have refused to do so and asserted that such is irrelevant. I contend that I could not have asked a more relevant question - thus the reluctance to provide an answer. The answer to the question is contained in my energy analysis article at:http://www.w5dxp.com/energy.htm A passive Z0-match relies on superposition of waves accompanied by interference effects to explain the reversal of reflected wave energy direction and momentum. Walter Maxwell has called the process a "virtual open-circuit" or a "virtual short". In my article, I explain how it is a two-step process involving normal reflections and interference patterns at the impedance discontinuity. It works exactly like non-reflective glass covering a picture with its 1/4WL thin-film coating where two sets of reflected light waves undergo destructive interference toward the viewer and, honoring the conservation of energy and momentum, reverse their direction and momentum and flow in the opposite direction toward the picture. This is a well-understood phenomenon from sophomore physics 201. Why most RF engineers don't understand this simple physical process involving EM wave interference is beyond belief. Here's the Florida State University web page again: micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/ waveinteractions/index.html Set the java application for opposite phase and when the result is zero, scroll down to the bottom of the page to find out what happens to the energy components in the two waves that cancel to zero. Those energy components "are redistributed to regions that permit constructive interference" just as they are at a Z0-match in an RF transmission line where there are only two possible directions for RF energy flow. For every destructive interference event in one direction, there will be an equal magnitude constructive interference event in the opposite direction. At Walt's "virtual short", total destructive interference energy toward the source is redistributed as constructive interference energy back toward the load. I studied this subject in my EE courses at Texas A&M during the 1950's. The textbook was: "Fields and Waves in Modern Radio", by Ramo and Whinnery, (c) 1944, 1953. The subject is covered under "Quarter- Wave Coating for Eliminating Reflections" in the chapter titled: "Propagation and Reflection of Electromagnetic Waves". -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK Hello Cecil, I am familiar with quarter wave (and multi layer) coatings to reduce reflection. I am not waiting for a lecture on (un)bounded wave propagation. If I don't have something present in my mind, I know where to find it. As mentioned earlier, you can convert all the wave phenomena in the coaxial feed line to impedance as seen by the PA. You are unnecessary complicating things, hence loosing more public that may have interest in this topic. Maybe you (and other people) should carry out the experiments I suggested in this thread (looking to forward power, net power and DC input power versus small load mismatch [normally referenced to 50 Ohms] ). With kind regards, Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
On May 17, 9:10*am, Wimpie wrote:
On 17 mayo, 14:29, Cecil Moore wrote: On May 17, 4:49*am, Wimpie wrote: If you show up with a relevant quest, maybe I am willing to dive into it. Wim, here is why my questions for you are more than just relevant. It is imperative that someone lecturing us on happenings inside that PA RF volcano be able to understand what is occurring during a passive event involving forward and reflected EM fields and waves occurring at an impedance discontinuity outside of a PA. Two of the physical quantities that must be conserved are energy and momentum. EM RF fields and waves contain both energy and momentum which must be conserved. I have asked you to tell us exactly what laws of physics govern the reversal of the momentum and direction of energy flow at a Z0-match at a passive impedance discontinuity in a transmission line. You have refused to do so and asserted that such is irrelevant. I contend that I could not have asked a more relevant question - thus the reluctance to provide an answer. The answer to the question is contained in my energy analysis article at:http://www.w5dxp.com/energy.htm A passive Z0-match relies on superposition of waves accompanied by interference effects to explain the reversal of reflected wave energy direction and momentum. Walter Maxwell has called the process a "virtual open-circuit" or a "virtual short". In my article, I explain how it is a two-step process involving normal reflections and interference patterns at the impedance discontinuity. It works exactly like non-reflective glass covering a picture with its 1/4WL thin-film coating where two sets of reflected light waves undergo destructive interference toward the viewer and, honoring the conservation of energy and momentum, reverse their direction and momentum and flow in the opposite direction toward the picture. This is a well-understood phenomenon from sophomore physics 201. Why most RF engineers don't understand this simple physical process involving EM wave interference is beyond belief. Here's the Florida State University web page again: micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/ waveinteractions/index.html Set the java application for opposite phase and when the result is zero, scroll down to the bottom of the page to find out what happens to the energy components in the two waves that cancel to zero. Those energy components "are redistributed to regions that permit constructive interference" just as they are at a Z0-match in an RF transmission line where there are only two possible directions for RF energy flow. For every destructive interference event in one direction, there will be an equal magnitude constructive interference event in the opposite direction. At Walt's "virtual short", total destructive interference energy toward the source is redistributed as constructive interference energy back toward the load. I studied this subject in my EE courses at Texas A&M during the 1950's. The textbook was: "Fields and Waves in Modern Radio", by Ramo and Whinnery, (c) 1944, 1953. The subject is covered under "Quarter- Wave Coating for Eliminating Reflections" in the chapter titled: "Propagation and Reflection of Electromagnetic Waves". -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK Hello Cecil, I am familiar with quarter wave (and multi layer) coatings to reduce reflection. I am not waiting for a lecture on (un)bounded wave propagation. *If I don't have something present in my mind, I know where to find it. As mentioned earlier, you can convert all the wave phenomena in the coaxial feed line to impedance as seen by the PA. You are unnecessary complicating things, hence loosing more public that may have interest in this topic. Maybe you (and other people) should carry out the experiments I suggested in this thread (looking to forward power, net power and DC input power versus small load mismatch [normally referenced to 50 Ohms] ). With kind regards, Wim PA3DJSwww.tetech.nl Wim, I'm amazed that you don't find the more-detailed explanation of how impedance matching occurs via wave interference of any value. Many RF engineers have traditionally believed that a PHYSICAL open or short circuit is required to produce a reflection. As a professional antenna engineer with RCA in 1973 I discovered and published the wave mechanics that produces the VIRTUAL open and short circuits that are required for achieving an impedance match. I took bashings from those traditional engineers, who said reflections cannot be engendered by wave interference, until they studied my data more carefully and finally agreed I'm right. Remember, James Clerk Maxwell also had his detractors until they finally saw the light. Walt |
Transmitter Output Impedance
On May 17, 8:10*am, Wimpie wrote:
I am familiar with quarter wave (and multi layer) coatings to reduce reflection. I am not waiting for a lecture on (un)bounded wave propagation. Hopefully you realize that if anything of that nature is happening inside a PA, then your source impedance calculations can be off by magnitudes. -- 73, Cecil, w5dxp.com |
Transmitter Output Impedance
On 17 mayo, 17:22, walt wrote:
On May 17, 9:10*am, Wimpie wrote: On 17 mayo, 14:29, Cecil Moore wrote: On May 17, 4:49*am, Wimpie wrote: If you show up with a relevant quest, maybe I am willing to dive into it. Wim, here is why my questions for you are more than just relevant. It is imperative that someone lecturing us on happenings inside that PA RF volcano be able to understand what is occurring during a passive event involving forward and reflected EM fields and waves occurring at an impedance discontinuity outside of a PA. Two of the physical quantities that must be conserved are energy and momentum. EM RF fields and waves contain both energy and momentum which must be conserved. I have asked you to tell us exactly what laws of physics govern the reversal of the momentum and direction of energy flow at a Z0-match at a passive impedance discontinuity in a transmission line. You have refused to do so and asserted that such is irrelevant. I contend that I could not have asked a more relevant question - thus the reluctance to provide an answer. The answer to the question is contained in my energy analysis article at:http://www.w5dxp.com/energy.htm A passive Z0-match relies on superposition of waves accompanied by interference effects to explain the reversal of reflected wave energy direction and momentum. Walter Maxwell has called the process a "virtual open-circuit" or a "virtual short". In my article, I explain how it is a two-step process involving normal reflections and interference patterns at the impedance discontinuity. It works exactly like non-reflective glass covering a picture with its 1/4WL thin-film coating where two sets of reflected light waves undergo destructive interference toward the viewer and, honoring the conservation of energy and momentum, reverse their direction and momentum and flow in the opposite direction toward the picture. This is a well-understood phenomenon from sophomore physics 201. Why most RF engineers don't understand this simple physical process involving EM wave interference is beyond belief. Here's the Florida State University web page again: micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/ waveinteractions/index.html Set the java application for opposite phase and when the result is zero, scroll down to the bottom of the page to find out what happens to the energy components in the two waves that cancel to zero. Those energy components "are redistributed to regions that permit constructive interference" just as they are at a Z0-match in an RF transmission line where there are only two possible directions for RF energy flow. For every destructive interference event in one direction, there will be an equal magnitude constructive interference event in the opposite direction. At Walt's "virtual short", total destructive interference energy toward the source is redistributed as constructive interference energy back toward the load. I studied this subject in my EE courses at Texas A&M during the 1950's. The textbook was: "Fields and Waves in Modern Radio", by Ramo and Whinnery, (c) 1944, 1953. The subject is covered under "Quarter- Wave Coating for Eliminating Reflections" in the chapter titled: "Propagation and Reflection of Electromagnetic Waves". -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK Hello Cecil, I am familiar with quarter wave (and multi layer) coatings to reduce reflection. I am not waiting for a lecture on (un)bounded wave propagation. *If I don't have something present in my mind, I know where to find it. As mentioned earlier, you can convert all the wave phenomena in the coaxial feed line to impedance as seen by the PA. You are unnecessary complicating things, hence loosing more public that may have interest in this topic. Maybe you (and other people) should carry out the experiments I suggested in this thread (looking to forward power, net power and DC input power versus small load mismatch [normally referenced to 50 Ohms] ). With kind regards, Wim PA3DJSwww.tetech.nl Wim, *I'm amazed that you don't find the more-detailed explanation of how impedance matching occurs via wave interference of any value. Many RF engineers have traditionally believed that a PHYSICAL open or short circuit is required to produce a reflection. As a professional antenna engineer with RCA in 1973 I discovered and published the wave mechanics that produces the VIRTUAL open and short circuits that are required for achieving an impedance match. I took bashings from those traditional engineers, who said reflections cannot be engendered by wave interference, until they studied my data more carefully and finally agreed I'm right. Remember, James Clerk Maxwell also had his detractors until they finally saw the light. Walt Hello Walt, It is not that I don't see the importance of reflections / wave interference, as I use transmission line theory on an almost weekly basis. However one don't need to complicate the matter by using transmission line theory for a HF PA. When you open your rig, you will very likely not find a 10" long 100uh inductor in the output section of your PA. Also your capacitors have very small size w.r.t. wavelength. A lumped circuit model and a load specified as an impedance is therefore more than good enough to discuss PA complex output impedance and what CAN happen when you apply mismatch. You can't tell what happens exactly, because then you need to dive into the circuit diagram of the PA to evaluate current and voltage waveforms at the active device. With kind regards, Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
On May 17, 2:36*pm, Wimpie wrote:
However one don't need to complicate the matter by using transmission line theory for a HF PA. I can only quote Einstein (once again) for you: "Everything should be made as simple as possible, but not simpler." You have ignored Einstein's advice and "uncomplicated the matter" to the point of violating the laws of physics. When you use the distributed network model for part of the circuit and then switch, mid- stream, to the lumped circuit model, you are indeed violating the laws of physics (as I have pointed out to you before). But you are certainly free to delude yourself into ignoring reality and choosing to commit technical suicide in the process. When you switch to the lumped circuit model, you are presuming faster than light speeds and completely ignoring the existence of EM waves. The fact that an EM/RF signal cannot travel even one inch in zero time simply cannot be ignored. If you take that one inch speed of light delay into account, hopefully you will realize just how technically confused you really are about the magical reversal of cause and effect concepts that you are promoting. -- 73, Cecil, w5dxp.com |
Transmitter Output Impedance
On May 17, 12:36*pm, Wimpie wrote:
On 17 mayo, 17:22, walt wrote: On May 17, 9:10*am, Wimpie wrote: On 17 mayo, 14:29, Cecil Moore wrote: On May 17, 4:49*am, Wimpie wrote: If you show up with a relevant quest, maybe I am willing to dive into it. Wim, here is why my questions for you are more than just relevant. It is imperative that someone lecturing us on happenings inside that PA RF volcano be able to understand what is occurring during a passive event involving forward and reflected EM fields and waves occurring at an impedance discontinuity outside of a PA. Two of the physical quantities that must be conserved are energy and momentum. EM RF fields and waves contain both energy and momentum which must be conserved. I have asked you to tell us exactly what laws of physics govern the reversal of the momentum and direction of energy flow at a Z0-match at a passive impedance discontinuity in a transmission line. You have refused to do so and asserted that such is irrelevant. I contend that I could not have asked a more relevant question - thus the reluctance to provide an answer. The answer to the question is contained in my energy analysis article at:http://www.w5dxp.com/energy.htm A passive Z0-match relies on superposition of waves accompanied by interference effects to explain the reversal of reflected wave energy direction and momentum. Walter Maxwell has called the process a "virtual open-circuit" or a "virtual short". In my article, I explain how it is a two-step process involving normal reflections and interference patterns at the impedance discontinuity. It works exactly like non-reflective glass covering a picture with its 1/4WL thin-film coating where two sets of reflected light waves undergo destructive interference toward the viewer and, honoring the conservation of energy and momentum, reverse their direction and momentum and flow in the opposite direction toward the picture. This is a well-understood phenomenon from sophomore physics 201. Why most RF engineers don't understand this simple physical process involving EM wave interference is beyond belief. Here's the Florida State University web page again: micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/ waveinteractions/index.html Set the java application for opposite phase and when the result is zero, scroll down to the bottom of the page to find out what happens to the energy components in the two waves that cancel to zero. Those energy components "are redistributed to regions that permit constructive interference" just as they are at a Z0-match in an RF transmission line where there are only two possible directions for RF energy flow. For every destructive interference event in one direction, there will be an equal magnitude constructive interference event in the opposite direction. At Walt's "virtual short", total destructive interference energy toward the source is redistributed as constructive interference energy back toward the load. I studied this subject in my EE courses at Texas A&M during the 1950's. The textbook was: "Fields and Waves in Modern Radio", by Ramo and Whinnery, (c) 1944, 1953. The subject is covered under "Quarter- Wave Coating for Eliminating Reflections" in the chapter titled: "Propagation and Reflection of Electromagnetic Waves". -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK Hello Cecil, I am familiar with quarter wave (and multi layer) coatings to reduce reflection. I am not waiting for a lecture on (un)bounded wave propagation. *If I don't have something present in my mind, I know where to find it. As mentioned earlier, you can convert all the wave phenomena in the coaxial feed line to impedance as seen by the PA. You are unnecessary complicating things, hence loosing more public that may have interest in this topic. Maybe you (and other people) should carry out the experiments I suggested in this thread (looking to forward power, net power and DC input power versus small load mismatch [normally referenced to 50 Ohms] ). With kind regards, Wim PA3DJSwww.tetech.nl Wim, *I'm amazed that you don't find the more-detailed explanation of how impedance matching occurs via wave interference of any value. Many RF engineers have traditionally believed that a PHYSICAL open or short circuit is required to produce a reflection. As a professional antenna engineer with RCA in 1973 I discovered and published the wave mechanics that produces the VIRTUAL open and short circuits that are required for achieving an impedance match. I took bashings from those traditional engineers, who said reflections cannot be engendered by wave interference, until they studied my data more carefully and finally agreed I'm right. Remember, James Clerk Maxwell also had his detractors until they finally saw the light. Walt Hello Walt, It is not that I don't see the importance of reflections / wave interference, as I use transmission line theory on an almost weekly basis. *However one don't need to complicate the matter by using transmission line theory for a HF PA. When you open your rig, you will very likely not find a 10" long 100uh inductor in the output section of your PA. Also your capacitors have very small size w.r.t. wavelength. *A lumped circuit model and a load specified as an impedance is therefore more than good enough to discuss PA complex output impedance and what CAN happen when you apply mismatch. You can't tell what happens exactly, because then you need to dive into the circuit diagram of the PA to evaluate current and voltage waveforms at the active device. With kind regards, Wim PA3DJSwww.tetech.nl For what it's worth, in my work I design a lot of filters and matching networks. I regularly model the designs before I build them, using the level of detail I feel is appropriate. When I build the physical filter or network I've modeled, I compare the measured response with the response predicted by my model. I do that in some detail. I almost always modify the model as necessary, adding detail so it matches the measured performance. When I say I add detail, I don't mean that I do it haphazardly, but rather that I look closely at the physical realization and add pieces to the model that match pieces of the physical realization. Because I've gone through this design cycle many times, with many different topologies and for a variety of frequency ranges from below 1MHz to above 1GHz, I have a pretty good idea before I start a new design just what level of detail I'll need. What I find from this is that, just as Wim says about PA matching networks, I seldom need anything beyond representations of the lumped components when I'm dealing with low frequency filters that don't have high loaded-Q resonators. Up to 30MHz, I don't recall ever having to use transmission lines in my models to get excellent agreement between the model and the physical implementation (except in the rare cases where I've included transmission lines in the physical implementation of a low frequency network, of course). I do often have to add parasitic elements--sometimes even for relatively low frequency filters. (I remember having a technician build a 1MHz filter for me; he couldn't understand why his didn't work anywhere near as well as the first one I had built, until I showed him where he'd allowed other parasitics to creep in--short lengths of wire with currents shared between two high-Q resonators...) I'm _FAR_ more likely to need to include mutual inductance between two coils in a model, than I am to need to include a transmission line. On the other hand, when I'm dealing with filters above 100MHz, it's not unusual to include transmission line sections and stubs in my models. Above 200MHz or so, the models generally do benefit from including transmission lines. Mind you, there aren't any hard and fast rules; there is no magic transition frequency. But when you've built models that match reality as closely as I commonly do, you learn to just smile blandly at those who tell you that you "must" consider a coil to be a transmission line or you'll be "wrong." Finally, even when I do include transmission lines in my models, I don't worry in detail about reflections, or about a time-domain analysis of the situation. Just as there's an equivalence between time-domain waveforms and spectral analysis, a frequency sweep of a system (including phase as well as amplitude response) tells me everything I need to know, in the domain I'm already interested in. I hope Wim (and others?) will excuse the off-topic drift here. And I'm _still_ trying to figure out _why_ anyone would care about the output impedance of a PA of the sort used at HF to drive antennas. Nobody has ever convinced me that it matters at all, except perhaps as academic interest. Cheers, Tom |
Transmitter Output Impedance
On May 18, 12:33 am, K7ITM wrote:
I'm _still_ trying to figure out _why_ anyone would care about the output impedance of a PA of the sort used at HF to drive antennas. Nobody has ever convinced me that it matters at all, except perhaps as academic interest. Nobody is questioning the efficacy of design methods. Whatever works, works. What we are discussing is indeed only of academic interest. Knowing whether my IC-706 is conjugately matched or not does not affect its operation at all. From the time (t0) that a PA first outputs a Zg signal to the time (t1) that the PA senses its load impedance is NOT zero time. How does the PA know what its load impedance really is when it is not Zg? Einstein's spooky action at a distance? No, feedback from the load. Obviously, the PA receives some sort of feedback in real time. What is the nature of that feedback? What can it be besides feedback energy reflected from the load? (not in zero time, but at the speed of light). In the real world, it takes measurable time for the forward energy to reach the load and measurable time for the reflected feedback (if any) to arrive back at the PA. The load seen at the PA source is always an E/I ratio, i.e. a lossless image impedance that always experiences a delay if it is not equal to Zg, i.e. it usually contains reflected energy. -- 73, Cecil, w5dxp.com |
Transmitter Output Impedance
On 18 mayo, 07:33, K7ITM wrote:
On May 17, 12:36*pm, Wimpie wrote: On 17 mayo, 17:22, walt wrote: On May 17, 9:10*am, Wimpie wrote: On 17 mayo, 14:29, Cecil Moore wrote: On May 17, 4:49*am, Wimpie wrote: If you show up with a relevant quest, maybe I am willing to dive into it. Wim, here is why my questions for you are more than just relevant.. It is imperative that someone lecturing us on happenings inside that PA RF volcano be able to understand what is occurring during a passive event involving forward and reflected EM fields and waves occurring at an impedance discontinuity outside of a PA. Two of the physical quantities that must be conserved are energy and momentum. EM RF fields and waves contain both energy and momentum which must be conserved. I have asked you to tell us exactly what laws of physics govern the reversal of the momentum and direction of energy flow at a Z0-match at a passive impedance discontinuity in a transmission line. You have refused to do so and asserted that such is irrelevant. I contend that I could not have asked a more relevant question - thus the reluctance to provide an answer. The answer to the question is contained in my energy analysis article at:http://www.w5dxp.com/energy.htm A passive Z0-match relies on superposition of waves accompanied by interference effects to explain the reversal of reflected wave energy direction and momentum. Walter Maxwell has called the process a "virtual open-circuit" or a "virtual short". In my article, I explain how it is a two-step process involving normal reflections and interference patterns at the impedance discontinuity. It works exactly like non-reflective glass covering a picture with its 1/4WL thin-film coating where two sets of reflected light waves undergo destructive interference toward the viewer and, honoring the conservation of energy and momentum, reverse their direction and momentum and flow in the opposite direction toward the picture. This is a well-understood phenomenon from sophomore physics 201. Why most RF engineers don't understand this simple physical process involving EM wave interference is beyond belief. Here's the Florida State University web page again: micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/ waveinteractions/index.html Set the java application for opposite phase and when the result is zero, scroll down to the bottom of the page to find out what happens to the energy components in the two waves that cancel to zero. Those energy components "are redistributed to regions that permit constructive interference" just as they are at a Z0-match in an RF transmission line where there are only two possible directions for RF energy flow. For every destructive interference event in one direction, there will be an equal magnitude constructive interference event in the opposite direction. At Walt's "virtual short", total destructive interference energy toward the source is redistributed as constructive interference energy back toward the load. I studied this subject in my EE courses at Texas A&M during the 1950's. The textbook was: "Fields and Waves in Modern Radio", by Ramo and Whinnery, (c) 1944, 1953. The subject is covered under "Quarter- Wave Coating for Eliminating Reflections" in the chapter titled: "Propagation and Reflection of Electromagnetic Waves". -- 73, Cecil, w5dxp.com "Halitosis is better than no breath at all.", Don, KE6AJH/SK Hello Cecil, I am familiar with quarter wave (and multi layer) coatings to reduce reflection. I am not waiting for a lecture on (un)bounded wave propagation. *If I don't have something present in my mind, I know where to find it. As mentioned earlier, you can convert all the wave phenomena in the coaxial feed line to impedance as seen by the PA. You are unnecessary complicating things, hence loosing more public that may have interest in this topic. Maybe you (and other people) should carry out the experiments I suggested in this thread (looking to forward power, net power and DC input power versus small load mismatch [normally referenced to 50 Ohms] ). With kind regards, Wim PA3DJSwww.tetech.nl Wim, *I'm amazed that you don't find the more-detailed explanation of how impedance matching occurs via wave interference of any value. Many RF engineers have traditionally believed that a PHYSICAL open or short circuit is required to produce a reflection. As a professional antenna engineer with RCA in 1973 I discovered and published the wave mechanics that produces the VIRTUAL open and short circuits that are required for achieving an impedance match. I took bashings from those traditional engineers, who said reflections cannot be engendered by wave interference, until they studied my data more carefully and finally agreed I'm right. Remember, James Clerk Maxwell also had his detractors until they finally saw the light. Walt Hello Walt, It is not that I don't see the importance of reflections / wave interference, as I use transmission line theory on an almost weekly basis. *However one don't need to complicate the matter by using transmission line theory for a HF PA. When you open your rig, you will very likely not find a 10" long 100uh inductor in the output section of your PA. Also your capacitors have very small size w.r.t. wavelength. *A lumped circuit model and a load specified as an impedance is therefore more than good enough to discuss PA complex output impedance and what CAN happen when you apply mismatch. You can't tell what happens exactly, because then you need to dive into the circuit diagram of the PA to evaluate current and voltage waveforms at the active device. With kind regards, Wim PA3DJSwww.tetech.nl For what it's worth, in my work I design a lot of filters and matching networks. *I regularly model the designs before I build them, using the level of detail I feel is appropriate. *When I build the physical filter or network I've modeled, I compare the measured response with the response predicted by my model. *I do that in some detail. *I almost always modify the model as necessary, adding detail so it matches the measured performance. *When I say I add detail, I don't mean that I do it haphazardly, but rather that I look closely at the physical realization and add pieces to the model that match pieces of the physical realization. *Because I've gone through this design cycle many times, with many different topologies and for a variety of frequency ranges from below 1MHz to above 1GHz, I have a pretty good idea before I start a new design just what level of detail I'll need. What I find from this is that, just as Wim says about PA matching networks, I seldom need anything beyond representations of the lumped components when I'm dealing with low frequency filters that don't have high loaded-Q resonators. *Up to 30MHz, I don't recall ever having to use transmission lines in my models to get excellent agreement between the model and the physical implementation (except in the rare cases where I've included transmission lines in the physical implementation of a low frequency network, of course). *I do often have to add parasitic elements--sometimes even for relatively low frequency filters. *(I remember having a technician build a 1MHz filter for me; he couldn't understand why his didn't work anywhere near as well as the first one I had built, until I showed him where he'd allowed other parasitics to creep in--short lengths of wire with currents shared between two high-Q resonators...) *I'm _FAR_ more likely to need to include mutual inductance between two coils in a model, than I am to need to include a transmission line. On the other hand, when I'm dealing with filters above 100MHz, it's not unusual to include transmission line sections and stubs in my models. *Above 200MHz or so, the models generally do benefit from including transmission lines. *Mind you, there aren't any hard and fast rules; there is no magic transition frequency. *But when you've built models that match reality as closely as I commonly do, you learn to just smile blandly at those who tell you that you "must" consider a coil to be a transmission line or you'll be "wrong." Finally, even when I do include transmission lines in my models, I don't worry in detail about reflections, or about a time-domain analysis of the situation. *Just as there's an equivalence between time-domain waveforms and spectral analysis, a frequency sweep of a system (including phase as well as amplitude response) tells me everything I need to know, in the domain I'm already interested in. Hello Tom, Applying Cecil's rules, you and I are bad engineers/designers, as we frequently didn't apply momentum, EcrossH, reflections, full Maxwell Equations, etc. I know of some of your designs and that from others (they are successful). So something in that statement regarding bad engineers/ designers is wrong. When dealing with fresh from school engineers I frequently encountered bad results or good results, but delivered too late (so aren't good in fact). The last category is mostly caused by using approximations that are way over the top, complicating calculations, slowing down/crashing simulations, etc. Knowing to apply a suitable approximation/model separates the seasoned from the fresh engineers. Now the original topic (that was output impedance of HF PAs and using non-50 Ohms coaxial cable) is under a pile of reflections, interferences, momentum, photons, etc, it becomes clear to me whether to apply the words "fresh" or "seasoned" to some of the contributors. I hope Wim (and others?) will excuse the off-topic drift here. *And I'm _still_ trying to figure out _why_ anyone would care about the output impedance of a PA of the sort used at HF to drive antennas. Nobody has ever convinced me that it matters at all, except perhaps as academic interest. Tom, excuses are not required, I consider your reply as an attempt to get the discussion on-topic again. Cheers, Tom With kind regards, Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
On May 18, 9:41*am, Wimpie wrote:
Applying Cecil's rules, you and I are bad engineers/designers, ... Are false assertions really necessary or helpful? -- 73, Cecil, w5dxp.com |
Transmitter Output Impedance
On 18 mayo, 17:26, Cecil Moore wrote:
On May 18, 9:41*am, Wimpie wrote: Applying Cecil's rules, you and I are bad engineers/designers, ... Are false assertions really necessary or helpful? -- 73, Cecil, w5dxp.com Hello Cecil, You keep on luring us (and others) into non-relevant discussions. Snippet from your posting to Tom: From the time (t0) that a PA first outputs a Zg signal to the time (t1) that the PA senses its load impedance is NOT zero time. How does the PA know what its load impedance really is when it is not Zg? Einstein's spooky action at a distance? No, feedback from the load. Obviously, the PA receives some sort of feedback in real time. What is the nature of that feedback? What can it be besides feedback energy reflected from the load? (not in zero time, but at the speed of light). In the real world, it takes measurable time for the forward energy to reach the load and measurable time for the reflected feedback (if any) to arrive back at the PA. The load seen at the PA source is always an E/I ratio, i.e. a lossless image impedance that always experiences a delay if it is not equal to Zg, i.e. it usually contains reflected energy. There must be some (for us hidden) reason to do this. We are discussing near steady state sinusoidal signals, so amplitude and phase can only vary slowly (if not, other amateurs would not be happy with you). Especially in case of manual load pulling, it doesn't matter when there is a back and forth delay of 100 us (that is 10 km of coaxial cable!!). All such delay actions are fully covered by the concept of impedance (and steady state transmission line theory). We are not discussing wide band systems where a reflected signal may be uncorrelated with the actual output signal. Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
On May 18, 6:11*am, Cecil Moore wrote:
On May 18, 12:33 am, K7ITM wrote: I'm _still_ trying to figure out _why_ anyone would care about the output impedance of a PA of the sort used at HF to drive antennas. Nobody has ever convinced me that it matters at all, except perhaps as academic interest. Nobody is questioning the efficacy of design methods. Whatever works, works. What we are discussing is indeed only of academic interest. Knowing whether my IC-706 is conjugately matched or not does not affect its operation at all. From the time (t0) that a PA first outputs a Zg signal to the time (t1) that the PA senses its load impedance is NOT zero time. How does the PA know what its load impedance really is when it is not Zg? Einstein's spooky action at a distance? No, feedback from the load. Obviously, the PA receives some sort of feedback in real time. What is the nature of that feedback? What can it be besides feedback energy reflected from the load? (not in zero time, but at the speed of light). In the real world, it takes measurable time for the forward energy to reach the load and measurable time for the reflected feedback (if any) to arrive back at the PA. The load seen at the PA source is always an E/I ratio, i.e. a lossless image impedance that always experiences a delay if it is not equal to Zg, i.e. it usually contains reflected energy. -- 73, Cecil, w5dxp.com Cecil, just HOW do you propose to MEASURE the effect you describe, as seen at the transmitter's output port, using only our HF ham transmitter/PA that transmits a signal with a maximum bandwidth of perhaps 10kHz? If it is going to have the dire consequences you suggested a few postings ago, then it must be trivial to measure...unfortunately, I don't see how, and that bugs me, as one who strives to provide accurate, sophisticated measurement technology to engineers. Perhaps you missed it, but nobody is disagreeing that the mechanism for establishing a load impedance is reflections in the system of lines and lumped loads attached to the PA output. We are simply saying that, for the bandwidth signals involved, you'll be extremely hard-pressed to distinguish between a load consisting of any number of transmission line segments, along with one or many lumped loads wherever you want along those line segments, and a simple equivalent series RLC. I suppose it will be lost on most of the lurkers, but it's a bit of a bad joke to deny that one can make valid PA output impedance measurements with a signal very slightly off-frequency (less than 1kHz), and then claim that reflections in a system of maybe a couple hundred feet of coax makes a major difference in how the load behaves as compared with a lumped RLC. Cheers, Tom |
Transmitter Output Impedance
On May 18, 11:56*am, K7ITM wrote:
Cecil, just HOW do you propose to MEASURE the effect you describe, as seen at the transmitter's output port, using only our HF ham transmitter/PA that transmits a signal with a maximum bandwidth of perhaps 10kHz? I don't have a proposal and am just pointing out some of the technical problems associated with some of the methods being proposed. FYI, when one uses a model that presupposes faster than light propagation speeds to try to explain something happening in the real world, one should expect some skepticism - unless one can prove that he is using entangled photons. :-) -- 73, Cecil, w5dxp.com |
Transmitter Output Impedance
On 18 mayo, 19:46, Cecil Moore wrote:
On May 18, 11:56*am, K7ITM wrote: Cecil, just HOW do you propose to MEASURE the effect you describe, as seen at the transmitter's output port, using only our HF ham transmitter/PA that transmits a signal with a maximum bandwidth of perhaps 10kHz? I don't have a proposal and am just pointing out some of the technical problems associated with some of the methods being proposed. FYI, when one uses a model that presupposes faster than light propagation speeds to try to explain something happening in the real world, one should expect some skepticism *- unless one can prove that he is using entangled photons. :-) -- 73, Cecil, w5dxp.com Hello Cecil, Could you please explain why the lumped circuit approach used by many people across the world presupposes faster than light propagation (as I can't)? In my opinion it only presupposes that speed of light is not of importance and if it does, you can model that very easy by adding some additional lumped components in many cases. Just take a circuit diagram of your rig, lumped components all over the place and if there are coaxial cables, they are just for transporting a signal from one place to another place. Did you ever used a circuit simulator, if so, did you model every capacitor, resistor, etc with a transmission line model? You may evaluate for yourself a CLC section and see what the output versus input does. Of course you could also put it in some circuit simulator. And again you are trying to introduce non-relevancy into the topic. Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
On May 18, 2:33*pm, Wimpie wrote:
Could you please explain why the lumped circuit approach used by many people across the world presupposes faster than light propagation (as I can't)? http://hamwaves.com/antennas/inductance/corum.pdf "The failure of any lumped element circuit model to describe the real world lies at its core inherent *presupposition*: the speed of light is assumed infinite in the wave equation." "Lumped element circuit theory assumes that there are no wave interference phenomena present, that is - the currents entering and leaving the circuit element's terminals are identical." http://www.classictesla.com/download...ed_failure.pdf "In fact, lumped-element circuit theory inherently employs the cosmological presupposition that the speed of light is infinite, as every EE sophomore should know." "Lumped circuit theory fails because it's a theory whose presuppositions are inadequate. Every EE in the world was warned of this in their first sophomore circuits course." Give me some time and I will compose an example based on EZNEC results for a lumped inductor vs a helical inductor of equal inductance. The results are nowhere near the same. -- 73, Cecil, w5dxp.com |
Transmitter Output Impedance
On May 18, 4:05*pm, Cecil Moore wrote:
Give me some time and I will compose an example based on EZNEC results for a lumped inductor vs a helical inductor of equal inductance. The results are nowhere near the same. The example is a 4 MHz series circuit with a 100v source, a 72uH inductance, and a 2570 ohm resistor. Using a 72uH lumped inductance, the current is the same all around the circuit and is 0.032 amps at -24 degrees, i.e. the source current is 24 degrees out of phase with the source voltage. Using a 72uH helical inductance, the source current is 0.039 amps at -0.02 degrees, i.e. in phase with the source voltage. The load current is 0.039 amps at -42.4 degrees. The phase shift through the helical inductor is more than 40 degrees. As you probably know, the phase angles of superposed waves have a drastic effect on the resulting impedance. -- 73, Cecil, w5dxp.com |
Transmitter Output Impedance
On 18 mayo, 23:39, Cecil Moore wrote:
On May 18, 4:05*pm, Cecil Moore wrote: Give me some time and I will compose an example based on EZNEC results for a lumped inductor vs a helical inductor of equal inductance. The results are nowhere near the same. The example is a 4 MHz series circuit with a 100v source, a 72uH inductance, and a 2570 ohm resistor. Using a 72uH lumped inductance, the current is the same all around the circuit and is 0.032 amps at -24 degrees, i.e. the source current is 24 degrees out of phase with the source voltage. Using a 72uH helical inductance, the source current is 0.039 amps at -0.02 degrees, i.e. in phase with the source voltage. The load current is 0.039 amps at -42.4 degrees. The phase shift through the helical inductor is more than 40 degrees. As you probably know, the phase angles of superposed waves have a drastic effect on the resulting impedance. -- 73, Cecil, w5dxp.com Hello Cecil, Can you describe the complete setup, or post a simple drawing (including ground path, source and load and position of current and voltmeters). I think that I can model it by using a lumped inductor with 2 capacitors (in fact a section of an LC delay line). What is the total wire length (just curious to know)? 72 uH, seems large for a matching inductor in a PA (at say 4 MHz, just 22 pF to resonate). Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
On 5/18/2011 4:05 PM, Cecil Moore wrote:
On May 18, 2:33 pm, wrote: Could you please explain why the lumped circuit approach used by many people across the world presupposes faster than light propagation (as I can't)? http://hamwaves.com/antennas/inductance/corum.pdf "The failure of any lumped element circuit model to describe the real world lies at its core inherent *presupposition*: the speed of light is assumed infinite in the wave equation." "Lumped element circuit theory assumes that there are no wave interference phenomena present, that is - the currents entering and leaving the circuit element's terminals are identical." http://www.classictesla.com/download...ed_failure.pdf "In fact, lumped-element circuit theory inherently employs the cosmological presupposition that the speed of light is infinite, as every EE sophomore should know." "Lumped circuit theory fails because it's a theory whose presuppositions are inadequate. Every EE in the world was warned of this in their first sophomore circuits course." Give me some time and I will compose an example based on EZNEC results for a lumped inductor vs a helical inductor of equal inductance. The results are nowhere near the same. -- 73, Cecil, w5dxp.com I'm not speaking for Wim, but I think we are both saying the following: * You have a known load * You have a transmission line with known characteristics * Is is possible to use a Smith chart to get the impedance at the input to the transmission line. * We now know the load applied to the transmitter. All we need to know we get from the chart. We admit that reflections are responsible for the impedance transformation from load to line input. But, we don't need to know anything about the reflection details, energy content of the line, nor how light would like it. So, we are saying that the load at the line input can be viewed as a lumped circuit. So now we have a transmitter loaded with a lumped circuit for further analysis. That's all. It's simple. John |
Transmitter Output Impedance
On May 18, 5:21*pm, Wimpie wrote:
Can you describe the complete setup, or post a simple drawing (including ground path, source and load and position of current and voltmeters). I think that I can model it by using a lumped inductor with 2 capacitors (in fact a section of an LC delay line). What is the total wire length (just curious to know)? Do you have EZNEC? If so, I can just upload the .EZ files to my web page. 72 uH, seems large for a matching inductor in a PA (at say 4 MHz, just 22 pF to resonate). :-) It's just what I had available - an EZNEC version of a Texas Bugcatcher 80m loading coil. -- 73, Cecil, w5dxp.com |
Transmitter Output Impedance
On May 18, 5:42*pm, John KD5YI wrote:
So, we are saying that the load at the line input can be viewed as a lumped circuit. So now we have a transmitter loaded with a lumped circuit for further analysis. It doesn't quite work that well. I gave an earlier example where Wim got the the s11 parameter wrong by an infinite percentage. The s- parameter equations for a lumped circuit vs an impedance discontinuity are nothing alike. Even the IEEE definitions for the two different types of impedances are different. The interference conditions at the impedance discontinuity can be proven to be different than for the lumped circuit replacement. That's all. It's simple. Quoting Einstein again: "Everything should be made as simple as possible, but no simpler." :-) When you switch to the lumped-circuit model, you are agreeing to faster than light signal speeds, NO superposition of signals, zero interference, zero phase shifts through coils, identical current everywhere, etc. How the heck can you assert and prove there is zero interference inside a source when reflected energy is flowing through it? -- 73, Cecil, w5dxp.com |
Transmitter Output Impedance
On 5/18/2011 5:58 PM, Cecil Moore wrote:
On May 18, 5:42 pm, John wrote: So, we are saying that the load at the line input can be viewed as a lumped circuit. So now we have a transmitter loaded with a lumped circuit for further analysis. It doesn't quite work that well. I gave an earlier example where Wim got the the s11 parameter wrong by an infinite percentage. The s- parameter equations for a lumped circuit vs an impedance discontinuity are nothing alike. Even the IEEE definitions for the two different types of impedances are different. The interference conditions at the impedance discontinuity can be proven to be different than for the lumped circuit replacement. That's all. It's simple. Quoting Einstein again: "Everything should be made as simple as possible, but no simpler." :-) When you switch to the lumped-circuit model, you are agreeing to faster than light signal speeds, NO superposition of signals, zero interference, zero phase shifts through coils, identical current everywhere, etc. How the heck can you assert and prove there is zero interference inside a source when reflected energy is flowing through it? -- 73, Cecil, w5dxp.com So, you're saying that the Smith chart is wrong? |
Transmitter Output Impedance
On May 18, 3:42*pm, John KD5YI wrote:
.... I'm not speaking for Wim, but I think we are both saying the following: * You have a known load * You have a transmission line with known characteristics * Is is possible to use a Smith chart to get the impedance at the input to the transmission line. * We now know the load applied to the transmitter. All we need to know we get from the chart. We admit that reflections are responsible for the impedance transformation from load to line input. But, we don't need to know anything about the reflection details, energy content of the line, nor how light would like it. So, we are saying that the load at the line input can be viewed as a lumped circuit. So now we have a transmitter loaded with a lumped circuit for further analysis. That's all. It's simple. John Exactly so, John. Good summary. So long as the transmitter's bandwidth is small enough that you are always operating practically at steady-state conditions, the transmitter can't tell the difference between whatever assembly of transmission lines and lumped loads distributed along those lines you want, and a simple lumped circuit that presents the same impedance as the steady-state value of the jumble of transmission lines out there. (For very narrow-band loads, you might want to use a lumped equivalent that presents sensibly the same impedance as the load across the whole transmitted bandwidth, not just at one point.) It is NOT that anyone is assuming "faster than speed of light," it's that we're recognizing that the (HF voice-bandwidth) transmitter is slower than molasses relative to the propagation times involved in a couple hundred feet of coax, or probably even a couple thousand feet. The attenuation per foot of the lines we use is high enough that it's just about impossible to deviate significantly from steady-state conditions for the bandwidths we use. That's certainly not true for pulsed radar signals, or for fast-scan TV, or for other wideband signals. In those cases, you'll probably find it pays to insure the line is matched to the load so there aren't significant reflections, and you may want to arrange the source (PA/ transmitter) to have an output impedance close to the line impedance so it absorbs any reflections that do happen at the load end of the line. (If you want to get fancy, you might use a circulator to insure dissipation of such returning signals.) Cheers, Tom |
Transmitter Output Impedance
On 19 mayo, 00:58, Cecil Moore wrote:
On May 18, 5:42*pm, John KD5YI wrote: So, we are saying that the load at the line input can be viewed as a lumped circuit. So now we have a transmitter loaded with a lumped circuit for further analysis. It doesn't quite work that well. I gave an earlier example where Wim got the the s11 parameter wrong by an infinite percentage. The s- parameter equations for a lumped circuit vs an impedance discontinuity are nothing alike. Hello Cecil, Would you please remind me to the example where I was completely wrong with S11? Even the IEEE definitions for the two different types of impedances are different. The interference conditions at the impedance discontinuity can be proven to be different than for the lumped circuit replacement. That's all. It's simple. Quoting Einstein again: "Everything should be made as simple as possible, but no simpler." :-) When you switch to the lumped-circuit model, you are agreeing to faster than light signal speeds, NO superposition of signals, zero interference, zero phase shifts through coils, identical current everywhere, etc. How the heck can you assert and prove there is zero interference inside a source when reflected energy is flowing through it? Did you ever DESIGNED some serious electronic hardware? I am not pointing to using a recipe book or troubleshooting/repair. -- 73, Cecil, w5dxp.com Regarding your helical; I don't have Eznec. Maybe you can use some screenshots from it, put some comment to it and put that on website, so we can view it. Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
On 19 mayo, 11:05, Wimpie wrote:
On 19 mayo, 00:58, Cecil Moore wrote: On May 18, 5:42*pm, John KD5YI wrote: So, we are saying that the load at the line input can be viewed as a lumped circuit. So now we have a transmitter loaded with a lumped circuit for further analysis. It doesn't quite work that well. I gave an earlier example where Wim got the the s11 parameter wrong by an infinite percentage. The s- parameter equations for a lumped circuit vs an impedance discontinuity are nothing alike. Hello Cecil, Would you please remind me to the example where I was completely wrong with S11? Even the IEEE definitions for the two different types of impedances are different. The interference conditions at the impedance discontinuity can be proven to be different than for the lumped circuit replacement. That's all. It's simple. Quoting Einstein again: "Everything should be made as simple as possible, but no simpler." :-) When you switch to the lumped-circuit model, you are agreeing to faster than light signal speeds, NO superposition of signals, zero interference, zero phase shifts through coils, identical current everywhere, etc. How the heck can you assert and prove there is zero interference inside a source when reflected energy is flowing through it? Did you ever DESIGNED some serious electronic hardware? I am not pointing to using a recipe book or troubleshooting/repair. -- 73, Cecil, w5dxp.com Regarding your helical; I don't have Eznec. Maybe you can use some screenshots from it, put some comment to it and put that on website, so we can view it. Wim PA3DJS www.tetech.nl remove ED from designed.... Wim |
Transmitter Output Impedance
On May 18, 6:13*pm, John KD5YI wrote:
So, you're saying that the Smith chart is wrong? The Smith Chart is a tool - a blank graph. How could it be wrong? Like any tool, it has limitations and can be abused. On May 19, 4:05 am, Wimpie wrote: Would you please remind me to the example where I was completely wrong with S11? ----50 ohm--+--1/4WL Z0=100--200 ohm load s11 is 0.3333 at point '+'. Put it in a box and s11 magically becomes 0.0? The first s11 is a physical reflection coefficient, the second s11 is a virtual reflection coefficient. The virtual 50 ohm impedance is lossless. All the power is dissipated in the 200 ohm resistor at a reflection coefficient of 0.3333. Did you ever DESIGNED some serious electronic hardware? No, but being a good designer has nothing to do with the present academic exercise. W8JI is a good designer yet concepts like yours led him to "measure" a 3 ns delay through a 100 uH air-core 80m loading coil when the actual delay time is closer to 21.5 ns. That's what happens when one relies on the lumped-circuit model and ignores reflected energy. The relative phase of a standing wave doesn't change with length which gives the illusion that the signal is traveling faster than the speed of light, i.e. zero phase delay. I will turn the coil example into a brainteaser and post it to my web page. -- 73, Cecil, w5dxp.com |
Transmitter Output Impedance
On May 19, 4:05*am, Wimpie wrote:
Regarding your helical; I don't have Eznec. Maybe you can use some screenshots from it, put some comment to it and put that on website, so we can view it. Here it is: http://www.w5dxp.com/teaser2.JPG -- 73, Cecil, w5dxp.com |
Transmitter Output Impedance
On 19 mayo, 15:04, Cecil Moore wrote:
On May 19, 4:05*am, Wimpie wrote: Regarding your helical; I don't have Eznec. Maybe you can use some screenshots from it, put some comment to it and put that on website, so we can view it. Here it is:http://www.w5dxp.com/teaser2.JPG -- 73, Cecil, w5dxp.com Hello Cecil, Your circuit (lumped inductance example) with 100V input into 72uH with 2570 Ohms load): From lumped circuit simulation (Beige Bag PSPICE, version 4 professional): I_source = 32mA, -35 degrees I_load = 32mA, -35 degrees This agrees with hand calculation, all phase with respect to input voltage. From simulation, but now a pi filter C=6pF, L=72u, C=6pF, load = 2570 Ohms Simulation carried out with same PSPICE package without using transmission line sections: I_source = 38mA, -1.5 degrees I_load = 38mA, -44 degrees. Total required time for setting up the simulations and guessing the parasitic components to simulate the actual inductor behavior: about 15 minutes. As you can see good agreement without using any of the photons, speed of light, momentum and other issues, just lumped circuit simulation where some parasitics are added. Of course a can make a better match, but this doesn't contribute to the discussion. I hope that some followers or contributors will do the same simulation in a lumped circuit simulator, so that we don't arrive in a discussion that I am cheating. Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
On 19 mayo, 14:03, Cecil Moore wrote:
On May 18, 6:13*pm, John KD5YI wrote: So, you're saying that the Smith chart is wrong? The Smith Chart is a tool *- a blank graph. How could it be wrong? Like any tool, it has limitations and can be abused. On May 19, 4:05 am, Wimpie wrote: Would you please remind me to the example where I was completely wrong with S11? ----50 ohm--+--1/4WL Z0=100--200 ohm load s11 is 0.3333 at point '+'. Put it in a box and s11 magically becomes 0.0? The first s11 is a physical reflection coefficient, the second s11 is a virtual reflection coefficient. The virtual 50 ohm impedance is lossless. All the power is dissipated in the 200 ohm resistor at a reflection coefficient of 0.3333. Cecil, It is very simple, the 1/4 lamba line (100 Ohms) looks into a 200 Ohms load, so seen from that line, VSWR = 2, hence resulting in RC=0.3333. The 50 Ohms source looks into a 50 Ohms load (you can use the quarter wave formula). This equals VSWR=1, so RC=0. I think I wasn't wrong! As mentioned before, a source (whether PA or small signal) doesn't see the difference between a lumped 50 Ohms load or your quarter wave line with 200 Ohms load. Whether or not it is "physical" or "virtual" is also not relevant, just the complex V/I ratio (we call that impedance) counts. The RC inside the line is of no relevance for the PA. Did you ever DESIGNED some serious electronic hardware? No, but being a good designer has nothing to do with the present academic exercise. It may be of importance w.r.t. selecting the right model to solve technical problems. A good example what can happen when selecting over-the-top approaches is this thread. W8JI is a good designer yet concepts like yours led him to "measure" a 3 ns delay through a 100 uH air-core 80m loading coil when the actual delay time is closer to 21.5 ns. That's what happens when one relies on the lumped-circuit model and ignores reflected energy. The relative phase of a standing wave doesn't change with length which gives the illusion that the signal is traveling faster than the speed of light, i.e. zero phase delay. I will turn the coil example into a brainteaser and post it to my web page. -- 73, Cecil, w5dxp.com Wim PA3DJS www.tetech.nl |
Transmitter Output Impedance
Hello Cecil,
I would like to return back to the topic with a brainteaser also. You posted links to some document written by Walt. The first reference (QEX, May-June 2001, http://www.w2du.com/QEXMayJun01.pdf ) shows some measuring results using load pulling in table one. I have a source 100Vp, 4 MHz, sinusoidal, in series with a capacitance of 796 pF (that is a capacitive reactance of 50 Ohms). Would you be so kind to determine the output impedance of this source using load pulling (for example using 51.2 Ohms and 44.6 Ohms). Of course I have no problems if you (or somebody else) use a simulator to save time. If you (or somebody else) feel uncomfortable with a zero ohm voltage source, you may add 1 Ohms in series with the capacitor. Did you (or somebody else) expect the calculated result based on load pulling? With kind regards, Wim PA3DJS www.tetech.nl |
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