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Revisiting the Power Explanation
On Sun, 25 Mar 2007 22:20:25 GMT, Walter Maxwell
wrote: Richard, assume a mismatched load has produced both voltage and current refleftions on the line that result in a particular reactive impedance at the line input. The line input is connected to the output of the transceiver that has a pi-network output coupling circuit. I call this condition 1. It exhibits a mismatch and it exhibits the probability of the reflected energy being absorbed by the source to the degree of the phase relationships. When the network has been adjusted to deliver all the available power into the line the output source impedance is the complex conjugate of the line input impedance. I call this condition 2. It exhibits just what you describe: In this condition the reflected voltage and current waves are totally re-reflected back into the line, while adding in phase to the voltage and current waves from the source, respectively. Consequently, the reflected waves do not pass rearward through the network to be incident on the plate. Only if the network is mistuned, such as being connected to the reactive input of the line without being retuned to resonance, in which case the excessive plate current due to being mistuned will result in an inordinate amount of heating of the plate. It seems to me that in your initial post in the original thread (that was largely ignored for comment) you made mention of injecting a signal from an external source into the mouth of the dragon for the purposes of measuring the source Z. Am I wrong? Yes, you are wrong here, because I made no mention of the 'mouth of a dragon'. That comment must have come from another poster, twarn't I. From March 14: "2. The amplifier is now powered down and the load resistance RL is measured across the input terminals of the resonant pi-network tank circuit (from plate to ground) with an HP-4815 Vector Impedance Meter." Richard, try this on for size and then determine whether you believe RF understands the function of the phasing in impedance matching: .... Now, when adjusting the output network of a tube-type transceiver to deliver all the available power into a line having reflections, the adjustment of the network accomplishes the same function as the stub on the line in the above discussion. Consequently, this is the reason why the reflected power is totally re-reflected at the output terminals of the network, and is never seen at the plate of the amp to cause heating. If you follow my separation of arguments above, you will find it demands that the source MUST have the intervention of an outside agent to resolve its probability of facing destructive energy. In the arts, this is called Deus ex Machina. In the world of science, we would have to say that the source is extremely non-linear when its internal state of Z (a distinctly non-Thevenin characteristic) changes to follow the load. In short, of course no energy finds its way in, we twisted knobs to make that a self-fulfilling prophecy. Without this intervention reflected energies present the real probability of destruction by heat. This is the concept I believe Richard Fry is not appreciating. If I'm wrong on this I hope he'll straighten me out. I will let him speak for himself. 73's Richard Clark, KB7QHC |
Revisiting the Power Explanation
On Mon, 26 Mar 2007 00:35:46 GMT, Cecil Moore
wrote: Richard Clark wrote: Correct but "disputed." Hmmm. i.e. 92% correct. Correct but "debatable." Hmmm. i.e. 85% correct. This is from someone who's experience an orgasm in the 80 percentile? Now we venture into almost pregnancies. |
Revisiting the Power Explanation
Gene Fuller wrote:
Cecil Moore wrote: *** 1 *** If reflected energy is not dissipated, it undergoes destructive interference and is redirected back toward the load as constructive interference instead of being incident upon the source. Why are you having difficulty with that concept from page 388 of "Optics", by Hecht, 4th edition? *** 2 *** Again, reflected power doesn't flow so it doesn't go anywhere. Until you understand that simple fact of physics, further discussion is unlikely to yield valid results. "Reflected power that goes" is only one of your many conceptual flaws. So your first logical step would be proving that reflected power actually flows. After you do that, we can continue to your other conceptual flaws. Paragraphs 1 and 2 appear to declare exactly the opposite behavior for energy (power). Paragraph 1 is about energy and doesn't mention power at all. Paragraph 2 is about power and doesn't mention energy at all. Energy is as different from power as length is different from velocity. Do you also get length and velocity confused? Is there some subtle re-definition going on to allow "redirected back toward the load" and "it doesn't go anywhere" in the same message? Here's a quote from my web page: "The term "power flow" has been avoided in favor of "energy flow". Power is a measure of that energy flow per unit time through a plane." The dimensions of power flow would be watts/sec. I'm not sure what quantity watts/sec would represent or where it would go. -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
Richard Clark wrote:
This is from someone who's experience an orgasm in the 80 percentile? At my age, I wish it was up to 80%. :-) -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
Cecil Moore wrote in
: Owen Duffy wrote: Considering only the attenuator case, you suggest in such a general statement that reflected power always increases the dissipation in a real source that includes an attenuator for the purpose of constraining the equivalent source impedance. Owen, why do you feel compelled to lie about what I said? You are not being paranoid here are you Cecil? If the reflected energy is dissipated within the source, it increases the dissipation. If the reflected energy is not dissipated within the source, it does not increase the dissipation. Why is that so hard for you to understand? Cecil, I can understand the above paragraph ok, it is self defining though so I don't consider it to be any great advance of the art. Whilst I can understand the paragraph, the content is so trivial I can't understand why you felt it necessary to state it. Owen |
Revisiting the Power Explanation
Owen Duffy wrote:
You are not being paranoid here are you Cecil? The word would be inebriated to the point of poor judgment. It was a rough day loading and unloading a full 6x12 U-Haul trailer all by myself. I apologize. If the reflected energy is dissipated within the source, it increases the dissipation. If the reflected energy is not dissipated within the source, it does not increase the dissipation. Why is that so hard for you to understand? Cecil, I can understand the above paragraph ok, it is self defining though so I don't consider it to be any great advance of the art. Didn't say it was an advance. It is my position that you questioned and it really seems obvious to me. Whilst I can understand the paragraph, the content is so trivial I can't understand why you felt it necessary to state it. It was apparently necessary to get you to understand my position. Wherever the circulator load resistor is located is where the dissipation of the energy in the reflected wave will occur. It can be either inside the source box or outside the source box. -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
Cecil Moore wrote:
Gene Fuller wrote: Cecil Moore wrote: *** 1 *** If reflected energy is not dissipated, it undergoes destructive interference and is redirected back toward the load as constructive interference instead of being incident upon the source. Why are you having difficulty with that concept from page 388 of "Optics", by Hecht, 4th edition? *** 2 *** Again, reflected power doesn't flow so it doesn't go anywhere. Until you understand that simple fact of physics, further discussion is unlikely to yield valid results. "Reflected power that goes" is only one of your many conceptual flaws. So your first logical step would be proving that reflected power actually flows. After you do that, we can continue to your other conceptual flaws. Paragraphs 1 and 2 appear to declare exactly the opposite behavior for energy (power). Paragraph 1 is about energy and doesn't mention power at all. Paragraph 2 is about power and doesn't mention energy at all. Energy is as different from power as length is different from velocity. Do you also get length and velocity confused? Is there some subtle re-definition going on to allow "redirected back toward the load" and "it doesn't go anywhere" in the same message? Here's a quote from my web page: "The term "power flow" has been avoided in favor of "energy flow". Power is a measure of that energy flow per unit time through a plane." The dimensions of power flow would be watts/sec. I'm not sure what quantity watts/sec would represent or where it would go. Cecil, I understand the physics quite well, thank you. What I neglected to fully pick up was the silly semantic game you were playing. We all know that "power flow" is a bit of an oxymoron, but it still is widely used as an equivalent to "energy flow". I was just trying to understand the phase of the moon in Texas for this particular thread. 73, Gene W4SZ |
Revisiting the Power Explanation
On Mar 25, 3:48 am, Ian White GM3SEK wrote:
Ian Jackson wrote: In message , Cecil Moore writes Richard Clark wrote: Cecil Moore wrote: your analysis is correct but moot Is he stealing your style? "Moot" is an interesting word, Richard. From Webster's - "moot - 1. a: debatable, b: disputed" Have a look here. http://en.wikipedia.org/wiki/Moot_hall I remember 'Moot Hall' from my days at primary school (some 60 years ago), learning about the Anglo-Saxons. I guess the word may possibly be associated with 'meet', ie a meeting hall where things were debated. However, my Anglo-Saxon is a bit rusty (not much call for it these days). Cecil was using "moot" in its legal sense: that a point had become irrelevant, or no longer needed to be decided because of a change in circumstances. Or at least, Cecil tried to claim that a point made by Keith had become moot. But Keith disputed that... and so it rumbles on. -- 73 from Ian GM3SEK Rumbles, yes indeed. But does it retain any entertainment value, or has it simply gotten painful to watch? Cheers, Tom |
Revisiting the Power Explanation
Gene Fuller wrote:
We all know that "power flow" is a bit of an oxymoron, but it still is widely used as an equivalent to "energy flow". From your last posting it was not readily apparent that you knew the difference between energy and power. There is no reflected power wave but there is a reflected RF energy traveling wave, the power of which can be measured at a fixed point. A Bird directional wattmeter indirectly senses the reflected power at the fixed location of the Bird. -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
On Sun, 25 Mar 2007 19:14:07 -0800, Richard Clark wrote:
On Sun, 25 Mar 2007 22:20:25 GMT, Walter Maxwell wrote: Richard, assume a mismatched load has produced both voltage and current refleftions on the line that result in a particular reactive impedance at the line input. The line input is connected to the output of the transceiver that has a pi-network output coupling circuit. I call this condition 1. It exhibits a mismatch and it exhibits the probability of the reflected energy being absorbed by the source to the degree of the phase relationships. Richard, although it exhibits a mismatch, and thus detunes the source, the probability of the reflected energy being absorbed by the source is zero. The additional power dissipated in the source is due to lowered impedance of the network resulting from off-resonance operation, thus increasing the plate current. The reflected energy does not enter the network, but only results in a decrease in the power delivered relative to that when the reactance in the load is cancelled by correct retuning of the source network. When the network has been adjusted to deliver all the available power into the line the output source impedance is the complex conjugate of the line input impedance. I call this condition 2. It exhibits just what you describe: In this condition the reflected voltage and current waves are totally re-reflected back into the line, while adding in phase to the voltage and current waves from the source, respectively. Consequently, the reflected waves do not pass rearward through the network to be incident on the plate. Only if the network is mistuned, such as being connected to the reactive input of the line without being retuned to resonance, in which case the excessive plate current due to being mistuned will result in an inordinate amount of heating of the plate. It seems to me that in your initial post in the original thread (that was largely ignored for comment) you made mention of injecting a signal from an external source into the mouth of the dragon for the purposes of measuring the source Z. Am I wrong? Yes, you are wrong here, because I made no mention of the 'mouth of a dragon'. That comment must have come from another poster, twarn't I. From March 14: "2. The amplifier is now powered down and the load resistance RL is measured across the input terminals of the resonant pi-network tank circuit (from plate to ground) with an HP-4815 Vector Impedance Meter." Richard, try this on for size and then determine whether you believe RF understands the function of the phasing in impedance matching: ... Now, when adjusting the output network of a tube-type transceiver to deliver all the available power into a line having reflections, the adjustment of the network accomplishes the same function as the stub on the line in the above discussion. Consequently, this is the reason why the reflected power is totally re-reflected at the output terminals of the network, and is never seen at the plate of the amp to cause heating. If you follow my separation of arguments above, you will find it demands that the source MUST have the intervention of an outside agent to resolve its probability of facing destructive energy. In the arts, this is called Deus ex Machina. In the world of science, we would have to say that the source is extremely non-linear when its internal state of Z (a distinctly non-Thevenin characteristic) changes to follow the load. In short, of course no energy finds its way in, we twisted knobs to make that a self-fulfilling prophecy. Without this intervention reflected energies present the real probability of destruction by heat. Twisting the knobs is what adjusts the output impedance of the network to the complex conjugate of the load. But without this intervention the real probability of destruction by heat is not resulting from the reflected energy reaching the plate--it is only that the reflected energy detuned the network, causing the plate current to rise because the network is off resonance. This is the concept I believe Richard Fry is not appreciating. If I'm wrong on this I hope he'll straighten me out. I will let him speak for himself. OK, Richard F, speak up. 73's Richard Clark, KB7QHC |
Revisiting the Power Explanation
Cecil Moore wrote:
Gene Fuller wrote: We all know that "power flow" is a bit of an oxymoron, but it still is widely used as an equivalent to "energy flow". From your last posting it was not readily apparent that you knew the difference between energy and power. There is *** no reflected power wave*** but there is a *** reflected RF energy traveling wave*** , the power of which can be measured at a fixed point. A Bird directional wattmeter indirectly senses the *** reflected power*** at the fixed location of the Bird. Cecil, It was late, but I did not think I was dreaming. You do indeed use energy and power interchangeably and randomly. I will try to keep that flexibility in mind in the future. 8-) 73, Gene W4SZ |
Revisiting the Power Explanation
Gene Fuller wrote:
There is *** no reflected power wave*** but there is a *** reflected RF energy traveling wave*** , the power of which can be measured at a fixed point. A Bird directional wattmeter indirectly senses the *** reflected power*** at the fixed location of the Bird. It was late, but I did not think I was dreaming. You do indeed use energy and power interchangeably and randomly. I see you are still confused. Waves flow. Power doesn't flow. Energy flows. Does your Bird wattmeter move while it's indicating power or does it stand still while indicating joules of energy passing a fixed point in one second? -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
Cecil Moore wrote:
Gene Fuller wrote: There is *** no reflected power wave*** but there is a *** reflected RF energy traveling wave*** , the power of which can be measured at a fixed point. A Bird directional wattmeter indirectly senses the *** reflected power*** at the fixed location of the Bird. It was late, but I did not think I was dreaming. You do indeed use energy and power interchangeably and randomly. I see you are still confused. Waves flow. Power doesn't flow. Energy flows. Does your Bird wattmeter move while it's indicating power or does it stand still while indicating joules of energy passing a fixed point in one second? Cecil, Keep on babbling, but remember, when you are in a hole stop digging. 73, Gene W4SZ |
Revisiting the Power Explanation
"Cecil Moore" wrote in message .. . Gene Fuller wrote: There is *** no reflected power wave*** but there is a *** reflected RF energy traveling wave*** , the power of which can be measured at a fixed point. A Bird directional wattmeter indirectly senses the *** reflected power*** at the fixed location of the Bird. It was late, but I did not think I was dreaming. You do indeed use energy and power interchangeably and randomly. I see you are still confused. Waves flow. Power doesn't flow. Energy flows. Does your Bird wattmeter move while it's indicating power or does it stand still while indicating joules of energy passing a fixed point in one second? -- 73, Cecil http://www.w5dxp.com none of them flow. electrons move, this is called CURRENT. a current causes a voltage which is related to it by an impedance. that is all you need to know. power flow, energy flow, birds flying, those are all secondary effects calculated from the fundamental elements of current, impedance, and voltage. nothing else is necessary, everything else is confusing since important details get lost when most people do calculations of power or energy. stick with the basics and it will all become clear! |
Revisiting the Power Explanation
On Mon, 26 Mar 2007 19:56:02 GMT, Walter Maxwell
wrote: I call this condition 1. It exhibits a mismatch and it exhibits the probability of the reflected energy being absorbed by the source to the degree of the phase relationships. Richard, although it exhibits a mismatch, and thus detunes the source, the probability of the reflected energy being absorbed by the source is zero. The additional power dissipated in the source is due to lowered impedance of the network resulting from off-resonance operation, thus increasing the plate current. The reflected energy does not enter the network, but only results in a decrease in the power delivered relative to that when the reactance in the load is cancelled by correct retuning of the source network. Hi Walt, Examples of separable energies in lines abound. We needn't have to go into circulators, isolators, directional couplers (the real ones, not the Bruene variety) and the rest, which all exhibit classic separation to achieve many design goals. Hence, it follows that reverse energy is real. The longer you pour energy into a mismatch, the longer it will reflect it back. Longer brings time into the discussion and hence power. Power is directly correlateable to heat. Now, the amount of heat is directly correlateable to phase relations. If they are aligned at one of the cardinal points, heat will drive up. If they are aligned at the other cardinal point (180 degrees away) heat will fall. Heat is positive proof of resistance. Being hot or cold is sensation, not heat per se. That is, if the source cools, this is not proof of the source not exhibiting a source resistance - phase does not create nor diminish resistance. Or to put it another way, source resistance is not a function of phase. There is a continuum of phase relationships expressed in angles between 0 and 360. Half will tend to heat, half will tend to cool. Energy is dissipated for the full 360 degrees. When that reverse energy arrives by transmission line, it sees a load. Complex as it is, it must resolve to find itself within this continuum of response. Examples of plate incandescence or arcing are not trivial parlor tricks. You can force the situation with a lumped equivalent, but a lumped equivalent will not prove any invalidity of the transmission line model it replaces (which, on the face of it, is an ironic appeal). This can be simply proven in that a lumped equivalent does not exhibit ALL the characteristics of energy storage in a long line. Some (others than you, Walt) may be tempted to trot out the ghosts in the TV line proof. That is certainly one characteristic that a lumped equivalent can never exhibit (and yet the equivalent acts like the line to an amazing degree for many considerations). No, I won't delve into the endless debate about transient vs. steady state. This is an argument about as insipid as can be offered (by others than you, Walt) as if it made any difference. Rather, a resonant line will exhibit identical properties of resonance at harmonics - a lumped equivalent will not. It is quite obvious that a lumped equivalent is not wholly equivalent, except for a highly constrained example. To say (by others than you, Walt) it supports a general solution that invalidates the line's reality is as absurd a notion as any that are trotted around the track here. In short, if a line exhibits itself as a source of energy for any example, no equivalent can negate that physical truth in a proof for other use. Hence, it follows that: 1. reflected energy is real and consequential; 2. sources exhibit resistance to energy flow; 3. 1 & 2 combine by their phase to result in a change of heat - dissipation; 4. the operator of either a tube or transistorized rig can adjust the phase of 1 through the intermediary of tuning (or conjugating); 5. absolutely no intervention impacts 2, except by degree; 6. successful/unsuccessful intervention still proves 3. 73's Richard Clark, KB7QHC |
Revisiting the Power Explanation
Dave wrote:
none of them flow. electrons move, this is called CURRENT. a current causes a voltage which is related to it by an impedance. that is all you need to know. power flow, energy flow, birds flying, those are all secondary effects calculated from the fundamental elements of current, impedance, and voltage. Sorry Dave, the essence of an EM wave is its electromagnetic energy. Voltage and current are the secondary effects of the photons encountering a conductor. What happens when one doesn't have a conductor? What's the voltage and current in the light from Alpha Centauri? Optical physicists have known for decades what is the essence of EM waves and they don't use voltage and current except for some esoteric calculation. -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
"Richard Clark" wrote in message ... On Mon, 26 Mar 2007 19:56:02 GMT, Walter Maxwell wrote: I call this condition 1. It exhibits a mismatch and it exhibits the probability of the reflected energy being absorbed by the source to the degree of the phase relationships. Richard, although it exhibits a mismatch, and thus detunes the source, the probability of the reflected energy being absorbed by the source is zero. The additional power dissipated in the source is due to lowered impedance of the network resulting from off-resonance operation, thus increasing the plate current. The reflected energy does not enter the network, but only results in a decrease in the power delivered relative to that when the reactance in the load is cancelled by correct retuning of the source network. Hi Walt, Examples of separable energies in lines abound. We needn't have to go into circulators, isolators, directional couplers (the real ones, not the Bruene variety) and the rest, which all exhibit classic separation to achieve many design goals. Hence, it follows that reverse energy is real. The longer you pour energy into a mismatch, the longer it will reflect it back. Longer brings time into the discussion and hence power. Power is directly correlateable to heat. Now, the amount of heat is directly correlateable to phase relations. If they are aligned at one of the cardinal points, heat will drive up. If they are aligned at the other cardinal point (180 degrees away) heat will fall. Heat is positive proof of resistance. Being hot or cold is sensation, not heat per se. That is, if the source cools, this is not proof of the source not exhibiting a source resistance - phase does not create nor diminish resistance. Or to put it another way, source resistance is not a function of phase. There is a continuum of phase relationships expressed in angles between 0 and 360. Half will tend to heat, half will tend to cool. Energy is dissipated for the full 360 degrees. When that reverse energy arrives by transmission line, it sees a load. Complex as it is, it must resolve to find itself within this continuum of response. Examples of plate incandescence or arcing are not trivial parlor tricks. You can force the situation with a lumped equivalent, but a lumped equivalent will not prove any invalidity of the transmission line model it replaces (which, on the face of it, is an ironic appeal). This can be simply proven in that a lumped equivalent does not exhibit ALL the characteristics of energy storage in a long line. Some (others than you, Walt) may be tempted to trot out the ghosts in the TV line proof. That is certainly one characteristic that a lumped equivalent can never exhibit (and yet the equivalent acts like the line to an amazing degree for many considerations). No, I won't delve into the endless debate about transient vs. steady state. This is an argument about as insipid as can be offered (by others than you, Walt) as if it made any difference. Rather, a resonant line will exhibit identical properties of resonance at harmonics - a lumped equivalent will not. It is quite obvious that a lumped equivalent is not wholly equivalent, except for a highly constrained example. To say (by others than you, Walt) it supports a general solution that invalidates the line's reality is as absurd a notion as any that are trotted around the track here. In short, if a line exhibits itself as a source of energy for any example, no equivalent can negate that physical truth in a proof for other use. Hence, it follows that: 1. reflected energy is real and consequential; 2. sources exhibit resistance to energy flow; 3. 1 & 2 combine by their phase to result in a change of heat - dissipation; 4. the operator of either a tube or transistorized rig can adjust the phase of 1 through the intermediary of tuning (or conjugating); 5. absolutely no intervention impacts 2, except by degree; 6. successful/unsuccessful intervention still proves 3. 73's Richard Clark, KB7QHC I wish somone would convince my boss reverse power isnt real. Then he wouldnt be so angry about the power meter head I blew up because I forgot to put an attnuator on it. Even with the -20db of the coupler ther is still 20 watts peak on the reverse side. |
Revisiting the Power Explanation
Cecil, W5DXP wrote:
"Others use the term 'power wave', but I DO NOT, so please stop accusing me of something I am not guilty." Power waves are respectable but a writer chooses his own words. Searching the web on topic: "power reflection on mismatched line" yielded 12,778 hits. First two were from the physics department of the University of Queensland in Australia. No qualms about the word "power" are shown and sample problems are worked. Here is one statement: "Note that the power reflection coefficient is equal to the square of the voltage (or current) coefficient because forward or reflected waves are in rhe same impedance." Remarkable or not, that is the seesnce of what the Bird Electronic Corporation says in instructions for its "Thruline Wattmeter". Power is acceptable and accepted. Why avoid the term? Best regards, Richard Harrison, KB5WZI |
Revisiting the Power Explanation
On Mon, 26 Mar 2007 20:41:42 -0400, "Jimmie D" wrote:
I wish somone would convince my boss reverse power isnt real. Then he wouldnt be so angry about the power meter head I blew up because I forgot to put an attnuator on it. Even with the -20db of the coupler ther is still 20 watts peak on the reverse side. Jimmie, are you stating your belief that reverse, or reflected power isn't REAL power? Ya gotta be kidding! Listen to your boss, he's right! Walt, W2DU |
Revisiting the Power Explanation
Walter Maxwell, W2DU wrote:
"When the matching is accomplished the phase relationship between the forward and reflected voltages can either be 0 degrees or 180 degrees, resulting in a total re-reflection of the voltage. If the resultant voltage is 0 degrees, then the resultant current is 180 degrees, thus voltage sees a virtual open circuit and the current sees a virtual sees a virtual short circuit. The result is that the reflected voltage and current are totally re-reflected IN PHASE with the source voltage and current. This is the reason the forward power in the line is greater than the source power when the line is mismatched at the load, but where the matching device has re-reflected the reflected waves." Eloquently stated and significant because there are many who would swear that a properly matched transmitter re-reflects the reflected waves, but don`t have a clue as to why. Best regards, Richard Harrison, KB5WZI |
Revisiting the Power Explanation
"Walter Maxwell" wrote in message ... On Mon, 26 Mar 2007 20:41:42 -0400, "Jimmie D" wrote: I wish somone would convince my boss reverse power isnt real. Then he wouldnt be so angry about the power meter head I blew up because I forgot to put an attnuator on it. Even with the -20db of the coupler ther is still 20 watts peak on the reverse side. Jimmie, are you stating your belief that reverse, or reflected power isn't REAL power? Ya gotta be kidding! Listen to your boss, he's right! Walt, W2DU If reflected power wasnt real I wouldnt be in trouble or at least on the shame list. I picked up 30 db pad to put on the pwer meter some body started talking to me and I forgot to put the thing on before I took the reading. In other words my origional reply was a kind of tongue in cheek raz to anyone who doesnt believe reflected power is real. Jimmie |
Revisiting the Power Explanation
Richard Harrison wrote:
Power is acceptable and accepted. Why avoid the term? Jim Kelley, AC6XG, has convinced me to make the distinction between the nature of EM energy and the nature of EM power. Power is what exists at a point or plane. Energy is what is moving past the point or through the plane. Reflected power is measured at a point. Reflected energy is what is doing the moving past that point. In addition, there's the difference in definitions between the fields of RF engineering and the field of physics. In physics, zero work implies zero power. I am not avoiding power. I am avoiding "power waves" and "power flow". The dimensions of power flowing past a point would be watts/second. I don't know what physical quantity that would represent. -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
Walter Maxwell wrote:
"Jimmie D" wrote: I wish somone would convince my boss reverse power isnt real. Ya gotta be kidding! Yep, he is kidding. -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
Richard Clark, KB7QHC wrote:
"There is a continuum of phase relationships expressed in degrees between 0 and 360." We are discussing transmission lines and assuming near perfection. Indeed the phase of the wave depends on that of the generator when it was launched and the phase of the generator continues to advance with time, but a good line enforces its Zo, a resistance. Terman says on page 85 of his 1955 opus: "The incident wave on the transmission line can therefore be described as a voltage accompanied by a current that is everywhere in phase with and proportional to, the voltage and dropping back uniformly in phase as the load is approached." The transmission line treats the wave reflected from a discontinuity exactly the same as it does the incident wave. The reflected wave is identical with the incident wave except that it is traveling toward the generator. At an open circuit or high-impedance load, there is tto much line current for the high-impedance to accept gven the limited voltage. The surplus current must reverse phase and the wave must travel back toward the generator. There is no change in the phase of the voltage. At a short circuit or low-impedance load, there is too much line voltage for the low-impedance to accept, given the limited current. The surlus voltage must reverse phase and the wave must travel back toward the generator. There is no change in the phase of the current. There are two phasing conditions between the voltage and current on an ideal transmission line, 0 degrees and 180 degrees. Best regards, Richard Harrison, KB5WZI |
Revisiting the Power Explanation
Cecil Moore wrote:
Richard Harrison wrote: Power is acceptable and accepted. Why avoid the term? Jim Kelley, AC6XG, has convinced me to make the distinction between the nature of EM energy and the nature of EM power. Power is what exists at a point or plane. Energy is what is moving past the point or through the plane. Reflected power is measured at a point. Reflected energy is what is doing the moving past that point. In addition, there's the difference in definitions between the fields of RF engineering and the field of physics. In physics, zero work implies zero power. I am not avoiding power. I am avoiding "power waves" and "power flow". The dimensions of power flowing past a point would be watts/second. I don't know what physical quantity that would represent. Cecil, Utter nonsense. Jim was pulling your chain, and I guess you fell for it. I have been a professional physicist for nearly 40 years. Real physicists fully understand the difference between power as work and power as energy transport. Both definitions are used as needed. I would hazard a guess that most engineers understand and use both definitions as well. All of your ramblings about the difference between energy and power, as well as joules and watts, add nothing but noise to the discussion. It is highly likely that everyone reading this group understands the concept of time. 73, Gene W4SZ |
Revisiting the Power Explanation
Gene Fuller, W4SZ wrote:
"Utter nonsense." Cecil knows as well as anybody the difference between energy and power, Power is the rate of doing work. The electrical unit is the watt (joule/second). It is also the rate of transmission from source to load. A wattmeter keeps track of the rate of energy flow, and the watt-hour meter measures the integral of active power during the integration interval. The power company bills you for the energy consumed during an interval determined by successive watt-hour meter readings. Best regards, Richard Harrison, KB5WZI |
Revisiting the Power Explanation
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Revisiting the Power Explanation
On Mar 25, 8:23 pm, Cecil Moore wrote:
You are not allowed to deny the existence of the 450 ohm real world load while asserting that it still exists. If it exists, it dissipates the reflected energy. If it doesn't exist, it reflects the reflected energy. Please choose one or the other - obviously, you cannot have both at the same time. [snip] If reflected energy is not dissipated, it undergoes destructive interference and is redirected back toward the load as constructive interference instead of being incident upon the source. I like these two paragraphs. They describe exactly what I would expect the relationships to be were "reflected energy" to represent real energy. More importantly, they describe an expectation that is sufficiently precise to be falsifiable. But just to be sure I understand the meaning, let me restate them algebraically: Energy.reflected = Energy.dissipated + Energy.re-reflected If this is not what you meant, then please read no further until you correct my misinterpretataion. ---- Oh good. The interpretation is accepted. So let us call this "Cecil's Hypothesis": "If reflected energy is not dissipated, it is redirected back toward the load." Expressed as an equality: Energy.reflected = Energy.dissipated + Energy.re-reflected And for convenience, its power form: Preflected = Pdissipated + Pre-reflected Now all we need is a single example for which the equality does not hold and "Cecil's Hypothesis" will be disproved. Let us start with the example previously offerred: - Generator with 450 Ohm output impedance - connected directly to a 1000 foot line with 450 Ohm characteristic impedance - connected to a load with 75 Ohm input impedance. And to simplify computation and produce a numerical result, we add a few more details: - The generator is 2 Amp current source in parallel with a 450 Ohm resistor - The line is 31 wavelengths long Let the experiment begin: - The generator is off. - All currents, voltages, energies and powers are zero. - Turn on the current source. - The current source pushes 2 Amps. - This is divided equally between the 450 Ohm generator resistor and the 450 Ohm line. - The generator output voltage is 450 Volts. - The generator output current is 1 Amp. - 450 Watts is being put out by the generator - 450 Watts is being dissipated in the generator resistor - A real wattmeter (one that measures voltage and current) shows 450 Joules/s flowing down the line. (Is it okay to say that "450 Watts are flowing"?) - A directional wattmeter indicates that the "forward power" is 450 Watts and the "reflected power" is 0 Watts. - Vfwd is 450 Volts - Ifwd is 1 Amp - The load is happily oblivious to the oncoming onslaught. - 31 cycles later, the voltage, current and energy reach the load. - But there is an impedance discontinuity which creates a voltage reflection coefficient of -0.714 so the load refuses to accept all the incoming energy. - The voltage across the load is 128.6 Volts - The current into the load is 1.714 Amps - The power dissipated in the load is 220.4 Watts - Vref is -321.5 Volts - Iref is 0.714 Amps - Vfwd is still 450 Volts (the line is lossless for this example) - Ifwd is still 1 Amp - "Forward power" is 450 Watts - "Reflected power" is 229.6 Watts - 220.4 = 450 - 229.6 which is as expected and demonstrates the usefullness of a directional wattmeter for computing actual power transferred (or is it energy?). - Encountering the reflection has caused a change in the voltage and current and this change is now propagating back towards the generator. - 31 cycles later, this change in line conditions reaches the generator. - The conditions at the generator terminals are now the same as the load since it is an integral number of wavelengths from the load. - The voltage at the generator terminals is 128.6 Volts - The current out of the generator is 1.714 Amps - The "forward power" is still 450 Watts. - The "reflected power" has changed from 0 to 229.6 Watts. - There is 128.6 volts across the 450 Ohm generator resistor. - There is 0.286 Amps flowing in the 450 Ohm generator resistor - Because the 0.286 Amps in the 450 Ohm generator resistor plus the 1.714 Amps flowing into the line is 2 Amps, exactly the output of the current source, the system has now settled after one round trip. There is no re-reflection at the generator terminals (and no ghosts). - The power into the line is 220.4 Watts - The power into the 450 Ohm generator resistor is 38.6 Watts - 229.6 Watts of "reflected power" has reduced the dissipation in the generator resistor by 413.4 Watts. - Substituting into the hypothetical equality Preflected = Pdissipated + Pre-reflected 229.6 = -413.4 + 0 - The equality does not hold, thus disproving "Cecil's Hypothesis". It is instructive to also consider the case with a generator constructed as a 900 Volt voltage source connected to a 450 Ohm output resistor. In this case the 450 Watts dissipated for the first 62 cycles increases by 872 Watts to 1322 Watts when the reflection arrives. Similar to above there is no re-reflection or ghosts. Once again the hypothetical equality Preflected = Pdissipated + Pre-reflected 229.6 = 872 + 0 does not hold. But the principle of "conservation of energy" should hold whenever real energies are involved. Since it does not hold in this case, we can only conclude that the numbers computed for "forward and reverse power" do not represent any real energy flows but are merely conveniences to facilitate other computations. ....Keith |
Revisiting the Power Explanation
On 20 Mar, 08:37, Walter Maxwell wrote:
One of the issues discussed in this thread that Owen originated concerned whether or not reflected power enters the power amp and dissipates as heat in the plates of the amp. Some of the posters apparently are unable to appreciate that the reflected power does not cause heating of the amp, unless the reflected power detunes the amp and the amp is left detuned from resonance, which of course is not the correct manner of operating the amp. In the last post of the original thread I presented the details of an experiment I performed (one of many using the same procedure) on a Kenwood TS-830S transceiver that proves how and why reflected power in no way causes heating of the amp when the amp is properly adjusted in the presence of the reflected power. Usually, such a presentation as in the last post in that thread evokes a great deal of response, as for example, Art Unwin's. So I'm somewhat surprised, and a little disappointed that my post has resulted in total silence. Have my efforts in helping to solve the problem gone for naught? Walt, W2DU Walt you got your wish, over 100 posts and still coming. How many postings is it going to take to not only read what you said and also the hard part understand what you are saying? Only you can answer whether your help to solve the problem has gone for naught. Maybe at 200 postings you will feel a bit better about things but I doubt it. But I must thank you as you have greatly decreased the number ugly postings in my direction so please keep it up. Regards Art Art |
Revisiting the Power Explanation
Richard Clatk, WB7QHC wrote:
"This is, of course, contingent only when the line is terminated in its characteristic Z." Lines terminated in Zo don`t produce a reflection at the load. I did not make up the fact that the line forces the current to be exactlly in-phase or exactly out-of-phase with the voltage across the transmission line. I got it from Terman. On page 86 of his 1955 opus: "---This differs from Eqn (4-8) (Zo seen by the incident wave) only by the negative sign, which arises from the fact that the current in the reflected wave travels toward the generator whereas the current in the incident wave travels toward the load. Zo is a RESISTANCE. In a resistance, current is in-phase with its associated voltage. Waves traveling in either direction on a line see the same Zo. Best regards, Richard Harrison, KB5WZI |
Revisiting the Power Explanation
Cecil Moore wrote: So you need to go off and argue with Jim over the definition of "power". Instead of talking about power, Jim has convinced me to talk about watts or joules/sec which he says are not necessarily power. The confusion comes from the field of physics, not from me. While you are talking to Jim, get him to explain the definition of "transfer". For a thorough understanding of the physical meaning that word, I suggest working a few rigorous thermodynamics problems. 73, ac6xg |
Revisiting the Power Explanation
On Mar 25, 4:23 pm, Cecil Moore wrote:
If reflected energy is not dissipated, it undergoes destructive interference and is redirected back toward the load as constructive interference instead of being incident upon the source. Why are you having difficulty with that concept from page 388 of "Optics", by Hecht, 4th edition? Hi Cecil, Dissipation and interference are not interdependent phenomena. Moreover, destructive interference does not "redirect" or otherwise cause anything to happen. Intereference is nothing more than a means for describing the result of the superposition of waves. 73, ac6xg |
Revisiting the Power Explanation
Richard Harrison wrote: Walter Maxwell, W2DU wrote: "When the matching is accomplished the phase relationship between the forward and reflected voltages can either be 0 degrees or 180 degrees, resulting in a total re-reflection of the voltage. If the resultant voltage is 0 degrees, then the resultant current is 180 degrees, thus voltage sees a virtual open circuit and the current sees a virtual sees a virtual short circuit. The result is that the reflected voltage and current are totally re-reflected IN PHASE with the source voltage and current. This is the reason the forward power in the line is greater than the source power when the line is mismatched at the load, but where the matching device has re-reflected the reflected waves." Eloquently stated and significant because there are many who would swear that a properly matched transmitter re-reflects the reflected waves, but don`t have a clue as to why. Best regards, Richard Harrison, KB5WZI Walt doesn't actually indicate 'why' here, either. He is reciting a set of well known circumstances, and implying that one set of facts results in another. While the facts are obviously correct, any cause and effect relationship between them must be inferred. It is not demonstrated. The fact that every time a visitor stands at my front door the bell rings is not proof that standing at my front door *causes* the bell to ring. The behavior of electromagnetic waves and their interaction with matter as described by JC Maxwell and others already provides satisfactory and sufficient explanation for the phenomenon of reflectivity. That should not be overlooked here. 73, ac6xg |
Revisiting the Power Explanation
Gene Fuller wrote:
Utter nonsense. Jim was pulling your chain, and I guess you fell for it. Perhaps your argument is with Jim. -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
Keith Dysart wrote:
Now all we need is a single example for which the equality does not hold and "Cecil's Hypothesis" will be disproved. Cecil's hypothesis is that the conservation of energy principle is valid. All you need is a single example for which the conservation of energy principle does not hold. Remember, the magnitude of energy in a transmission line is *EXACTLY* the amount of energy needed to support the forward joules/sec and the reflected joules/sec. -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
Jim Kelley wrote:
Moreover, destructive interference does not "redirect" or otherwise cause anything to happen. May I direct you to page 388 of "Optics" by Hecht where he asserts that total destructive interference must be matched by an equal magnitude of total constructive interference. Since there are only two possible directions in a transmission line, total destructive interference in one direction must be matched by an equal magnitude of total constructive interference in the opposite direction. From my energy analysis article, a reference: http://micro.magnet.fsu.edu/primer/j...ons/index.html "... when two waves of equal amplitude and wavelength that are 180-degrees ... out of phase with each other meet, they are not actually annihilated, ... All of the photon energy present in these waves must somehow be recovered or redistributed in a new direction, according to the law of energy conservation ... Instead, upon meeting, the photons are redistributed to regions that permit constructive interference, ..." This is a very tough question: In a transmission line with only two directions reckon what "redistributed in a new direction" would necessarily mean? :-) -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
Jim Kelley wrote:
For a thorough understanding of the physical meaning that word, I suggest working a few rigorous thermodynamics problems. What is your response for Gene's assertion that you are pulling my leg about all of this? -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
Jim Kelley wrote:
Walt doesn't actually indicate 'why' here, either. He is reciting a set of well known circumstances, and implying that one set of facts results in another. While the facts are obviously correct, any cause and effect relationship between them must be inferred. From his writings in "Reflections" and his postings here, Walt obviously understands destructive and constructive interference and the fact that (from the Florida State University site): "... All of the photon energy present in these (cancelled) waves must somehow be recovered or redistributed in a new direction, according to the law of energy conservation ..." In a transmission line we have two directions. 1. Toward the load 2. Toward the source When the "photon energy" is "redistributed in a new direction" in a transmission line, I'll bet it goes in exactly the direction that Walt says it goes. -- 73, Cecil http://www.w5dxp.com |
Revisiting the Power Explanation
Cecil Moore wrote in news:ZbBOh.19326$uo3.18213
@newssvr14.news.prodigy.net: Remember, the magnitude of energy in a transmission line is *EXACTLY* the amount of energy needed to support the forward joules/sec and the reflected joules/sec. Cecil, If you go beyond your (unqualified) average view of the world and drilled down on the fields in the line as a function of time and position, and their relationship with steady state real and reactive energy flow at each end of the line in the general case, it may provide you with a more correct view of the tranmission line and its load and source in your favoured energy context. Owen |
Revisiting the Power Explanation
Cecil Moore wrote in news:1qBOh.19329$uo3.12743
@newssvr14.news.prodigy.net: What is your response for Gene's assertion that you are pulling my leg about all of this? The games people play. Wasn't this one called something like 'lets you and him have a fight'. Owen |
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