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Reflected power ?
I know that any power not dissipated by an antenna is reflected back to the
transmitter. Then the transmitter "reflects" this reflection back to antenna, ad nauseum until its all gone. I also know that a short or an open is required to reflect power and I'm searching for which it is, an open or a short. I'm inclined to think it's a virtual open but I'm at a loss to understand that and I wonder if someone has a good explanation or analogy and some math wouldn't hurt. tnx Hank WD5JFR |
On Sun, 23 May 2004 02:07:13 GMT, "Henry Kolesnik"
wrote: I know that any power not dissipated by an antenna is reflected back to the transmitter. Then the transmitter "reflects" this reflection back to antenna, ad nauseum until its all gone. I also know that a short or an open is required to reflect power and I'm searching for which it is, an open or a short. I'm inclined to think it's a virtual open but I'm at a loss to understand that and I wonder if someone has a good explanation or analogy and some math wouldn't hurt. tnx Hank WD5JFR Hi Hank, What you describe as reflection and re-reflection occurs between the mismatched antenna and the tuner that has been adjusted to minimize power returned to the transmitter. The sole function of the tuner is to keep this power from being dissipated by the transmitter (common experience of arcing, denoting a voltage reflection, or thermal runaway, denoting a current reflection). The "virtual" reflection (offered by the tuner) is generally know as the complex conjugate of the remote load, seen at the near end of the line through which it is returning. This means that the line transforms the phase and amplitude of the reflection, and the tuner's job is to invert that relationship to counteract it, and return it to the antenna. There are both wave descriptions of this process, and lumped circuit equivalents. Both work, and both describe the same process from different points of view. One does not negate the other's validity (unless, of course, you attempt to mix the points of view and demand consistency in terms - a frequent rhetorical trap here). There will no doubt be a flurry of denials to this simple example with contortions of logic to match. As for the math, you will find it by the reams, once you've been overwhelmed with the arcana of hyperbolic descriptions of a novel physics that have to proceed its proof. Keep your eye on how your literal points in your question go abandoned with these arcane theories. 73's Richard Clark, KB7QHC |
"Richard Clark" wrote: What you describe as reflection and re-reflection occurs between the mismatched antenna and the tuner that has been adjusted to minimize power returned to the transmitter. The sole function of the tuner is to keep this power from being dissipated by the transmitter (common experience of arcing, denoting a voltage reflection, or thermal runaway, denoting a current reflection). The "virtual" reflection (offered by the tuner) is generally know as the complex conjugate of the remote load, seen at the near end of the line through which it is returning. This means that the line transforms the phase and amplitude of the reflection, and the tuner's job is to invert that relationship to counteract it, and return it to the antenna. There are both wave descriptions of this process, and lumped circuit equivalents. Both work, and both describe the same process from different points of view. One does not negate the other's validity (unless, of course, you attempt to mix the points of view and demand consistency in terms - a frequent rhetorical trap here). There will no doubt be a flurry of denials to this simple example with contortions of logic to match. As for the math, you will find it by the reams, once you've been overwhelmed with the arcana of hyperbolic descriptions of a novel physics that have to proceed its proof. Keep your eye on how your literal points in your question go abandoned with these arcane theories. 73's Richard Clark, KB7QHC ==================================== Dear Richard, you are confusing the matter even further, if that were possible. The only saving grace about your tedius message is that you yourself eventually realise what a load of overcomplicated nonsense it is. Reflected power is a mere fiction. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. All the power which leaves the transmiter is radiated except for that which is lost in the line. It has nowhere else to go! But for the existence of so-called SWR meters, the words 'forward and reflected power' would never enter people's vocabularies. For the few who become involved with such matters, the misleading fiction also appears in the language of mathematics. Names have to be invented in order to discuss mathematical equations in plain English. But there's no reason why they should be propagated, just to confuse, into the real World. The sole purpose of an SWR meter is to indicate whether or not the transmitter is loaded with 50 ohms. ---- Reg, G4FGQ |
On Sun, 23 May 2004 05:57:28 +0000 (UTC), "Reg Edwards"
wrote: Dear Richard, you are confusing the matter even further, if that were possible. Old Son, Have I stolen your thunder? Like the pendulum with a dull and meagre swing, your predictable observations on this subject return to an unremarkable SWR, a topic never raised without the old wife discovering it under her bed.... Does the following strike a bell? A QUOTATION: "When you can measure what you are speaking about and express it in numbers you know something about it. But when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. It may be the beginning of knowledge but you have scarcely in your thoughts advanced to the state of science." You have never offered a scintilla of quantized discussion to the matter. If you can summon up a respectable treatise that would make lord kelvinator proud, then maybe we would have something of actual substance to discuss. We can start with any of a number of my own - if, of course, you want to advance to the state of science. Forgive this last bit of presumption if you are simply trolling again. That, too, has its own entertainment merit and I am glad to correspond in kind. :-) 73's Richard Clark, KB7QHC |
Richard Clark wrote:
There are both wave descriptions of this process, and lumped circuit equivalents. Both work, and both describe the same process from different points of view. One does not negate the other's validity I agree with that last statement - and we can take it a step further. Each description can do things that the other one can't; no argument about that. But in cases where both descriptions should be valid, then they *must* agree. This is a basic cross-check that should always be applied... but regrettably isn't. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Reg Edwards wrote:
Reflected power is a mere fiction. Fiction may not be the right word, but reflected power is certainly a *useless* thing to calculate. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. Agreed. After the first microsecond the transmitter is operating into a steady-state load impedance. The only *useful* question then is: "Given that particular value of load impedance, how much power can my transmitter generate?" But that isn't an antenna/transmission-line problem at all - the answer lies in the transmitter, and *only* the transmitter. As far as the transmitter is concerned, it doesn't matter how that particular value of load impedance was created. There are several ways to create a specified value of (R +/-jX), and whichever way it's done, the transmitter will deliver exactly the power. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
"Reg Edwards" wrote in message ... Reflected power is a mere fiction. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. but, but, but, i can SEE reflected power! it shows on my TDR, i can see ghosts in video from it, i can measure it, i can catch it in a circulator! how can it be fiction?!?!?! |
Reg:
Consider a signal generator connected through a circulator to the input of a slotted line. The circulator provides a constant impedance to the signal generator no matter what impedance is connected to the output port of the circulator. Now, if your quote below is true, please explain the standing wave pattern measured via the slotted line probe whenever the slotted line itself is terminated in other than its characteristic impedance. Also ponder this scenario. A transmitter is adjusted to deliver the maximum output power of which it is capable (limited by its power supply) into a 50 ohm transmission line several wavelengths long, terminated in a 50 ohm antenna. The transmission line is just barely rated to handle the power delivered by the transmitter under these conditions. Now something fails within the antenna, and its input Z rises to 2000 ohms. If the transmitter has no protective circuits to shut it down, it will continue to generate power, and the transmission line will arc/burn. Of course, so might the tx output circuits, but let's say they are "very robust," and the tx continues to operate. What is the source of the additional power causing the line failure? The tx already was delivering all the power it could before the failure, so it isn't coming from there. RF Visit http://rfry.org for FM broadcast RF system papers. ____________________ "Reg Edwards" wrote Reflected power is a mere fiction. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. |
Dave wrote:
"Reg Edwards" wrote in message ... Reflected power is a mere fiction. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. but, but, but, i can SEE reflected power! it shows on my TDR, i can see ghosts in video from it, i can measure it, i can catch it in a circulator! how can it be fiction?!?!?! You aren't being literal-minded enough. When you claim to "see" and "measure" reflected power, you're applying theories that assume it exists. You are not proving that it does exist. What shows on your TDR, as ghosts on your TV, and also on a slotted line, is the interaction between forward and reflected voltage waves. Likewise a circulator (or a directional coupler) processes the voltage and current waves. I've yet to see a fully detailed functional explanation of any of those devices in terms of power waves alone. That is because "forward and reflected power waves" is a derivative concept. It depends on concepts of voltage and current waves for its existence; but it doesn't add anything useful that we didn't already know. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
"Ian White, G3SEK" wrote in message ... Dave wrote: "Reg Edwards" wrote in message ... Reflected power is a mere fiction. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. but, but, but, i can SEE reflected power! it shows on my TDR, i can see ghosts in video from it, i can measure it, i can catch it in a circulator! how can it be fiction?!?!?! You aren't being literal-minded enough. When you claim to "see" and "measure" reflected power, you're applying theories that assume it exists. You are not proving that it does exist. What shows on your TDR, as ghosts on your TV, and also on a slotted line, is the interaction between forward and reflected voltage waves. Likewise a circulator (or a directional coupler) processes the voltage and current waves. I've yet to see a fully detailed functional explanation of any of those devices in terms of power waves alone. That is because "forward and reflected power waves" is a derivative concept. It depends on concepts of voltage and current waves for its existence; but it doesn't add anything useful that we didn't already know. i know that, i was just trying to get in all the bogus arguments before anyone else did. 'power waves' are a concept invented to simplify some concepts, but instead they just hide the important details. we have been over and over that on here in the past and always end up in the same place, i was just hoping to skip right to the end. |
"Dave" wrote in message ... "Ian White, G3SEK" wrote in message ... Dave wrote: "Reg Edwards" wrote in message ... Reflected power is a mere fiction. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. but, but, but, i can SEE reflected power! it shows on my TDR, i can see ghosts in video from it, i can measure it, i can catch it in a circulator! how can it be fiction?!?!?! You aren't being literal-minded enough. When you claim to "see" and "measure" reflected power, you're applying theories that assume it exists. You are not proving that it does exist. What shows on your TDR, as ghosts on your TV, and also on a slotted line, is the interaction between forward and reflected voltage waves. Likewise a circulator (or a directional coupler) processes the voltage and current waves. I've yet to see a fully detailed functional explanation of any of those devices in terms of power waves alone. That is because "forward and reflected power waves" is a derivative concept. It depends on concepts of voltage and current waves for its existence; but it doesn't add anything useful that we didn't already know. i know that, i was just trying to get in all the bogus arguments before anyone else did. 'power waves' are a concept invented to simplify some concepts, but instead they just hide the important details. we have been over and over that on here in the past and always end up in the same place, i was just hoping to skip right to the end. maybe if i had learned to use smileys it would have helped.... what is the sarcastic one?? something like ;-^ or something like that?? |
If this old mind recalls correctly a TV station with an undesireable SWR
will not transmit a clear image to its viewers because the delayed re-reflection arrives at the TV set later and casues a ghost or smear. Could you please explain the "Reflected power is a mere fiction." and the smear or ghost? tnx Hank WD5JFR "Reg Edwards" wrote in message ... "Richard Clark" wrote: What you describe as reflection and re-reflection occurs between the mismatched antenna and the tuner that has been adjusted to minimize power returned to the transmitter. The sole function of the tuner is to keep this power from being dissipated by the transmitter (common experience of arcing, denoting a voltage reflection, or thermal runaway, denoting a current reflection). The "virtual" reflection (offered by the tuner) is generally know as the complex conjugate of the remote load, seen at the near end of the line through which it is returning. This means that the line transforms the phase and amplitude of the reflection, and the tuner's job is to invert that relationship to counteract it, and return it to the antenna. There are both wave descriptions of this process, and lumped circuit equivalents. Both work, and both describe the same process from different points of view. One does not negate the other's validity (unless, of course, you attempt to mix the points of view and demand consistency in terms - a frequent rhetorical trap here). There will no doubt be a flurry of denials to this simple example with contortions of logic to match. As for the math, you will find it by the reams, once you've been overwhelmed with the arcana of hyperbolic descriptions of a novel physics that have to proceed its proof. Keep your eye on how your literal points in your question go abandoned with these arcane theories. 73's Richard Clark, KB7QHC ==================================== Dear Richard, you are confusing the matter even further, if that were possible. The only saving grace about your tedius message is that you yourself eventually realise what a load of overcomplicated nonsense it is. Reflected power is a mere fiction. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. All the power which leaves the transmiter is radiated except for that which is lost in the line. It has nowhere else to go! But for the existence of so-called SWR meters, the words 'forward and reflected power' would never enter people's vocabularies. For the few who become involved with such matters, the misleading fiction also appears in the language of mathematics. Names have to be invented in order to discuss mathematical equations in plain English. But there's no reason why they should be propagated, just to confuse, into the real World. The sole purpose of an SWR meter is to indicate whether or not the transmitter is loaded with 50 ohms. ---- Reg, G4FGQ |
Henry Kolesnik wrote:
I know that any power not dissipated by an antenna is reflected back to the transmitter. Then the transmitter "reflects" this reflection back to antenna, ad nauseum until its all gone. I also know that a short or an open is required to reflect power and I'm searching for which it is, an open or a short. I'm inclined to think it's a virtual open but I'm at a loss to understand that and I wonder if someone has a good explanation or analogy and some math wouldn't hurt. Hank, EM reflections are covered on this web page. http://www.mellesgriot.com/products/optics/oc_2_1.htm In particular: "Clearly, if the wavelength of the incident light and the thickness of the film are such that a phase difference exists between reflections of p, then reflected wavefronts interfere destructively, and overall reflected intensity is a minimum. If the two reflections are of equal amplitude, then this amplitude (and hence intensity) minimum will be zero." "In the absence of absorption or scatter, the principle of conservation of energy indicates all "lost" reflected intensity will appear as enhanced intensity in the transmitted beam. The sum of the reflected and transmitted beam intensities is always equal to the incident intensity. This important fact has been confirmed experimentally." In order for (rearward-traveling) "reflected intensity" to "appear as (forward-traveling) enhanced intensity in the transmitted beam", the momentum of that (rearward-traveling) intensity must change directions. Thus, it appears that total destructive interference between two rearward- traveling reflected waves in a transmission line will reverse the direction of momentum of the energy in those canceled reflected waves. We need to change a few of your statements: Any power not dissipated or radiated by an antenna is reflected back. "Dissipation" means EM energy transformed into heat, according to the IEEE Dictionary. The transmitter/tuner end will not re-reflect 100% of the reflected energy unless there exists a short, open, pure reactance, or "total destructive interference" as explained in _Optics_, by Hecht. Besides a short or an open, a purely reactive impedance will cause 100% energy reflection. Apparently, so will "total destructive interference". Quoting from _Microwave_Transmission_, by J. C. Slater: "The method of eliminating reflections is based on the interference between waves. ... The fundamental principle behind the elimination of reflections is then to have each reflected wave canceled by another wave of equal amplitude and opposite phase." That's pretty clear. We get one set of rearward-traveling reflections at the match point. We get another set of rearward-traveling reflections at the antenna. If these two sets of reflections are equal in magnitude and opposite in phase at the match point, they cancel each other and the rearward-traveling momentum energy in those two waves is conserved by changing direction to become part of a forward-traveling wave. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
"Dave" wrote in message ... "Reg Edwards" wrote in message ... Reflected power is a mere fiction. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. but, but, but, i can SEE reflected power! it shows on my TDR, i can see ghosts in video from it, i can measure it, i can catch it in a circulator! how can it be fiction?!?!?! Clearly there is reflected power. Just don't take the SWR meter too literally. It does not actually measure power, but the scale has been fudged so it indicates the correct power if the load is equal to some design value. I can see a long thread here. Tam/WB2TT |
Richard Clark wrote:
As for the math, you will find it by the reams, once you've been overwhelmed with the arcana of hyperbolic descriptions of a novel physics that have to proceed its proof. A scattering parameter analysis, described in HP Application Note 95-1 (available on the web) is ideal for analyzing what happens at a match point in a typical ham radio antenna system. b1 = s11(a1) + s12(a2) b2 = s21(a1) + s22(a2) b1 is the net forward voltage, b2 is the net reflected voltage a1 is the incident forward voltage, a2 is the incident reflected voltage Quoting from HP AN 95-1: Another advantage of s-parameters springs from the simple relationship between the variables a1, a2, b1, and b2, and various power waves: |a1|^2 = Power incident on the input of the network. (forward power incident on the match point) |a2|^2 = Power reflected from the load. |b1|^2 = Power reflected from the input port of the network. (power reflected from the match point back toward the source) |b2|^2 = Power incident on the load. The previous four equations show that s-parameters are simply related to power gain and mismatch loss, quantities which are often of more interest than the corresponding voltage functions. |s11|^2 = Power reflected from the network input divided by power incident on the network input |s22|^2 = Power reflected from the network output divided by power incident on the network output |s21|^2 = Power delivered to a Z0 load divided by power available from a Z0 source |s12|^2 = Reverse transducer power gain with Z0 load and source End quote. b2 is the voltage reflected back toward the source and b2 = s21(a1) + s22(a2) It should be obvious that b2 cannot be zero unless there exists total destructive interference between s21(a1) and s22(a2), i.e. s21(a1) is equal in magnitude and opposite in phase to s22(a2). -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
"Tam/WB2TT" wrote in message ... Clearly there is reflected power. Just don't take the SWR meter too literally. It does not actually measure power, but the scale has been fudged so it indicates the correct power if the load is equal to some design value. I can see a long thread here. see my last replies to this thread... i'm done... cecil and reg are back and will undoubtedly re-hash optical methods and conjugate matches till the server dies... as for me, this thread is now over. |
Reg Edwards wrote:
Reflected power is a mere fiction. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. Therefore, radar cannot work since it relies upon reflected joules/second. Mirrors also cannot work since there is an ExB amount of power in those reflections. Reg, for a 291.5 ohm antenna to accept 100 watts requires the forward power to the antenna to be 200 watts. 100 watts is accepted by the antenna and 100 watts is rejected by the antenna. 200 watts to the antenna is routinely accomplished by a 100 watt ham transmitter and a Z0-match provided by a tuner. This is exactly like a partially silvered mirror that reflects half the irradiance and allows half the irradiance through. Assume a one second long lossless unterminated transmission line. Pour 1000 watts into it for one second. During the next second, we disconnect the line from the source and you grab the two wires, one in each hand. Then tell us whether reflected power exists or not. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Dave wrote:
That is because "forward and reflected power waves" is a derivative concept. It depends on concepts of voltage and current waves for its existence; but it doesn't add anything useful that we didn't already know. i know that, i was just trying to get in all the bogus arguments before anyone else did. Oh... in that case: "Well done - a noble effort, sir!" (You forgot to mention the slotted line, which mercifully saved you from a perfect score :-) 'power waves' are a concept invented to simplify some concepts, but instead they just hide the important details. we have been over and over that on here in the past and always end up in the same place, i was just hoping to skip right to the end. What, in this newsgroup? maybe if i had learned to use smileys it would have helped.... what is the sarcastic one?? something like ;-^ or something like that?? Sorry I missed the deliberate irony on your part, Dave, but the same things have often been said here in total seriousness. And here we go again... -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Ian White, G3SEK wrote:
After the first microsecond the transmitter is operating into a steady-state load impedance. The only *useful* question then is: "Given that particular value of load impedance, how much power can my transmitter generate?" But that isn't an antenna/transmission-line problem at all - the answer lies in the transmitter, and *only* the transmitter. Using 200 ft. of unterminated RG-58 on 440 MHz, the transmitter sees close to 50 ohms and can deliver its full rated power into the coax with no antenna. Therefore, I seriously doubt that your question above is the "only *useful* question". -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
"Cecil Moore" wrote in message ... Henry Kolesnik wrote: I know that any power not dissipated by an antenna is reflected back to the transmitter. Then the transmitter "reflects" this reflection back to antenna, ad nauseum until its all gone. I also know that a short or an open is required to reflect power and I'm searching for which it is, an open or a short. I'm inclined to think it's a virtual open but I'm at a loss to understand that and I wonder if someone has a good explanation or analogy and some math wouldn't hurt. Hank, EM reflections are covered on this web page. http://www.mellesgriot.com/products/optics/oc_2_1.htm In particular: "Clearly, if the wavelength of the incident light and the thickness of the film are such that a phase difference exists between reflections of p, then reflected wavefronts interfere destructively, and overall reflected intensity is a minimum. If the two reflections are of equal amplitude, then this amplitude (and hence intensity) minimum will be zero." "In the absence of absorption or scatter, the principle of conservation of energy indicates all "lost" reflected intensity will appear as enhanced intensity in the transmitted beam. The sum of the reflected and transmitted beam intensities is always equal to the incident intensity. This important fact has been confirmed experimentally." In order for (rearward-traveling) "reflected intensity" to "appear as (forward-traveling) enhanced intensity in the transmitted beam", the momentum of that (rearward-traveling) intensity must change directions. Thus, it appears that total destructive interference between two rearward- traveling reflected waves in a transmission line will reverse the direction of momentum of the energy in those canceled reflected waves. We need to change a few of your statements: Any power not dissipated or radiated by an antenna is reflected back. "Dissipation" means EM energy transformed into heat, according to the IEEE Dictionary. The transmitter/tuner end will not re-reflect 100% of the reflected energy unless there exists a short, open, pure reactance, or "total destructive interference" as explained in _Optics_, by Hecht. Besides a short or an open, a purely reactive impedance will cause 100% energy reflection. Apparently, so will "total destructive interference". Quoting from _Microwave_Transmission_, by J. C. Slater: "The method of eliminating reflections is based on the interference between waves. ... The fundamental principle behind the elimination of reflections is then to have each reflected wave canceled by another wave of equal amplitude and opposite phase." That's pretty clear. We get one set of rearward-traveling reflections at the match point. We get another set of rearward-traveling reflections at the antenna. If these two sets of reflections are equal in magnitude and opposite in phase at the match point, they cancel each other and the rearward-traveling momentum energy in those two waves is conserved by changing direction to become part of a forward-traveling wave. -- 73, Cecil http://www.qsl.net/w5dxp Cecil, I am not quite sure what you are saying. But, I ran a SPICE simulation of the following: 1V 1MHz source with resistor R0 feeding a 50 Ohm 250 ns transmission line shorted at the far end. Independent of R0, in steady state the voltage at the input end of the transmission line will be 1V. The effect of R0 is to limit how long it takes to reach steady state. For R0 = 50 Ohms, it is one cycle; for R0 = 500 Ohms, it is about 8 cycles, as eyeballed off the waveform display. |
Henry wrote,
I know that any power not dissipated by an antenna is reflected back to the transmitter. Then the transmitter "reflects" this reflection back to antenna, ad nauseum until its all gone. I also know that a short or an open is required to reflect power and I'm searching for which it is, an open or a short. I'm inclined to think it's a virtual open but I'm at a loss to understand that and I wonder if someone has a good explanation or analogy and some math wouldn't hurt. tnx Hank WD5JFR This post is guaranteed to get Cecil revivified. Here's a hint: quit thinking solely in terms of power, that's for fellows who want to explain how it all works without going into any of the complicated details. Get an undergraduate physics text that discusses waves, and read it, or, better yet, take a class. Take all explanations you read in amateur publications with a grain of salt. After you've done this, you still won't be able to argue with Cecil, because that requires an extensive knowledge of the moronic, unfair, and downright pathalogical debating techniques of which Cecil is a master. But, it will be harder for you to fall for some of the crackpot ideas you're liable to read on this newsgroup, and it will give you something to think about when sipping your after-dinner port. 73, Tom Donaly, KA6RUH |
Tam/WB2TT wrote:
I am not quite sure what you are saying. But, I ran a SPICE simulation of the following: 1V 1MHz source with resistor R0 feeding a 50 Ohm 250 ns transmission line shorted at the far end. Independent of R0, in steady state the voltage at the input end of the transmission line will be 1V. The effect of R0 is to limit how long it takes to reach steady state. For R0 = 50 Ohms, it is one cycle; for R0 = 500 Ohms, it is about 8 cycles, as eyeballed off the waveform display. Does SPICE report the steady-state forward and reflected waves or just the superposition of those two waves? We all know what they look like when superposed. The question is whether the identity of the forward and reflected waves disappear after they are superposed. To the best of my knowledge, the very existence of standing waves requires the existence of a forward- traveling wave and a rearward-traveling wave. I have asked for examples of standing waves void of rearward- traveling waves and none has been forthcoming. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Tdonaly wrote:
This post is guaranteed to get Cecil revivified. Here's a hint: quit thinking solely in terms of power, that's for fellows who want to explain how it all works without going into any of the complicated details. Like Hewlett Packard in their AN 95-1 publication? "Another advantage of the s-parameters springs from the simple relationship between the variables a1, a2, b1, and b2, and *various power waves*. ... The previous four equations show that s-parameters are simply related to power gain and mismatch loss, quantities which are often of more interest than the corresponding voltage functions." -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
I just want to know the reflection physics in the Tx, no antenna tuner, just
a mismatched antenna. I recall no pysics book that tell me how the reflection sees the transmitter. 73 Hank WD5JFR There are no stupid questions, just stupid people asking! "Tdonaly" wrote in message ... Henry wrote, I know that any power not dissipated by an antenna is reflected back to the transmitter. Then the transmitter "reflects" this reflection back to antenna, ad nauseum until its all gone. I also know that a short or an open is required to reflect power and I'm searching for which it is, an open or a short. I'm inclined to think it's a virtual open but I'm at a loss to understand that and I wonder if someone has a good explanation or analogy and some math wouldn't hurt. tnx Hank WD5JFR This post is guaranteed to get Cecil revivified. Here's a hint: quit thinking solely in terms of power, that's for fellows who want to explain how it all works without going into any of the complicated details. Get an undergraduate physics text that discusses waves, and read it, or, better yet, take a class. Take all explanations you read in amateur publications with a grain of salt. After you've done this, you still won't be able to argue with Cecil, because that requires an extensive knowledge of the moronic, unfair, and downright pathalogical debating techniques of which Cecil is a master. But, it will be harder for you to fall for some of the crackpot ideas you're liable to read on this newsgroup, and it will give you something to think about when sipping your after-dinner port. 73, Tom Donaly, KA6RUH |
Henry Kolesnik wrote:
I just want to know the reflection physics in the Tx, no antenna tuner, just a mismatched antenna. I recall no pysics book that tell me how the reflection sees the transmitter. The reflected waves obey the laws of physics. The kicker is that we don't know (and apparently cannot directly measure) the source impedance. What the reflections can do is modify the designed-for load line through superposition of the forward and reflected waves. Modification of the designed-for load line is not desirable and, if unprotected, can cause over-voltage, over-current, or phase problems. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
OK, if we shine a flashlight at a mirror the light bounces back and what
ever is caught by the reflector will be reflected. Take away the reflector and the reflection just keeps going. If someone can tell me what the hot filament does perhaps I can understand what happens in the finals, or whatever. tnx Hank WD5JFR "Cecil Moore" wrote in message ... Henry Kolesnik wrote: I just want to know the reflection physics in the Tx, no antenna tuner, just a mismatched antenna. I recall no pysics book that tell me how the reflection sees the transmitter. The reflected waves obey the laws of physics. The kicker is that we don't know (and apparently cannot directly measure) the source impedance. What the reflections can do is modify the designed-for load line through superposition of the forward and reflected waves. Modification of the designed-for load line is not desirable and, if unprotected, can cause over-voltage, over-current, or phase problems. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Henry Kolesnik wrote:
OK, if we shine a flashlight at a mirror the light bounces back and what ever is caught by the reflector will be reflected. Take away the reflector and the reflection just keeps going. If someone can tell me what the hot filament does perhaps I can understand what happens in the finals, or whatever. The hot filament provides a source of electrons. How many electrons are emitted depends on the instantaneous voltages on the other elements, the plate and grids. Reflected waves have an effect on those instantaneous voltages but IMO, there's not much sense in pursuing the "filament" line of reasoning. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
It's true in the case of transmission lines that there are standing
waves and reflections but, unfortunately, this concept has somehow come to dominate and confuse the concept of matching a tranmitter to an antenna -- a generator to a load. Like in many areas of science, mathematicians and scientists often find convenient ways to mathematically describe and predict physical phenomenon that hinders, even misleads, the understanding of how it actually works. If you leave out the complex part of impedences for the moment and think of 100 volt generator that has a 50 ohm internal impedance driving a 50 ohm load, current is 1 amp and the power dissipated by the load is 50 watts. There is also 50 watts dissipated by the generator's internal impedance, for a total of 100 watts dissipated by the entire system. Therefore, the "available" power for this generator is 50 watts. Maximum available I^2*R power only occurs when the load impedance is equal to the generator's characteristic impedance, 50 ohms (do the math). Any load impedance higher or lower, ALWAYS produces less "available" power. Herein lies one of the big problems with the "reflection" definition, conceptually. The generator (transmitter) is not a constant-power device. When a manufacturer says that it's XYZ transmitter produces 100 watts, it only produces (has available) 100 watts (after internal dissipation) into a 50 ohm load. Any other load *always* produces less available power, due to simple I^2*R laws. It has nothing to do with reflections or standing waves, although, mathmatically, reflection formulas accurately describe it. A couple of examples using a 100 volt constant voltage generator and an internal impedance (RG) of 50 ohms: 1) Load (RL) = 50 ohms. Current = 100 / (50 + 50) = 1 amp Power dissipated in RL (PL) = (1)^2*50 = 50 watts Power dissipated in RG (PG) = (1)^2*50 = 50 watts SWR = RL/RG = PL/PG = 1:1 2) Load (RL) = 100 ohms. Current = 100 / (50 + 100) = .667 amp Power dissipated in RL (PL) = (.667)^2*100 = 44.5 watts Power dissipated in RG (PG) = (.667)^2*50 = 22.25 watts SWR = RL/RG = PL/PG = 2:1 3) Load (RL) = 25 ohms. Current = 100 / (50 + 25) = 1.34 amp Power dissipated in RL (PL) = (1.34)^2*25 = 44.9 watts Power dissipated in RG (PG) = (1.34)^2*50 = 89.8 watts SWR = RG/RL = PG/PL = 2:1 Notice that the total power dissipated in all three examples is different. The transmitter is NOT a constant-power source, but it's also not a unlimited power source and has operational limits. Therefore, what is commonly called "reflected power" is power that never leaves the transmitter and is dissipated as heat by the transmitter's internal 50 ohm impedance (if the transmitter's design doesn't prematurely shut down first). Al "Henry Kolesnik" wrote in message ... I know that any power not dissipated by an antenna is reflected back to the transmitter. Then the transmitter "reflects" this reflection back to antenna, ad nauseum until its all gone. I also know that a short or an open is required to reflect power and I'm searching for which it is, an open or a short. I'm inclined to think it's a virtual open but I'm at a loss to understand that and I wonder if someone has a good explanation or analogy and some math wouldn't hurt. tnx Hank WD5JFR |
alhearn wrote:
Herein lies one of the big problems with the "reflection" definition, conceptually. That's why I often resort to a signal generator with a circulator/load to illustrate my point. That signal generator *is* a constant power source. Therefore, what is commonly called "reflected power" is power that never leaves the transmitter and is dissipated as heat by the transmitter's internal 50 ohm impedance (if the transmitter's design doesn't prematurely shut down first). You can mount an argument that if the source doesn't see its source impedance, then there is a reflection at that internal mismatch. But that's not what is commonly called reflected power. When we talk about reflected power on this newsgroup, we are usually referring to the forward power rejected by a mismatch between the transmission line Z0 and the antenna impedance (associated with mismatch loss). In a typical ham radio antenna system, the "lost" reflected power is forced to engage in destructive interference at the tuner and thus joins the forward power wave. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
I thought filaments produced photons/light waves as well. You took me to
light now you want to leave! Come on I just want a good basic understand on what it is the the Tx reflects the power , how it does it and a little simple math. My dad used to say if you can't explain something you think you know to someone else it might because you don't understand it yourself or lack command of the language. In this case for me it's both. 73 Hank WD5JFR "Cecil Moore" wrote in message ... Henry Kolesnik wrote: OK, if we shine a flashlight at a mirror the light bounces back and what ever is caught by the reflector will be reflected. Take away the reflector and the reflection just keeps going. If someone can tell me what the hot filament does perhaps I can understand what happens in the finals, or whatever. The hot filament provides a source of electrons. How many electrons are emitted depends on the instantaneous voltages on the other elements, the plate and grids. Reflected waves have an effect on those instantaneous voltages but IMO, there's not much sense in pursuing the "filament" line of reasoning. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
On Sun, 23 May 2004 10:06:15 -0500, Cecil Moore
wrote: Richard Clark wrote: As for the math, you will find it by the reams, once you've been overwhelmed with the arcana of hyperbolic descriptions of a novel physics that have to proceed its proof. A scattering parameter analysis,... arcana deleted as an obviously fulfilled prophecy. |
On Sun, 23 May 2004 09:31:10 +0100, "Ian White, G3SEK"
wrote: This is a basic cross-check that should always be applied... but regrettably isn't. Hi Ian, Perhaps in this immediate thread. However, I have demonstrated both sides coming to the same conclusions several many times, and one example as recently as within this last week. This issue is not about being right, it is about ego foremost else why all the debate? Hank has asked a fairly straightforward question with rather simple terms he could accept as a compelling case. To this point (some 22 entries) that has been largely abandoned with each scribbler answering their own imagining of how to discover the philosopher's stone. 73's Richard Clark, KB7QHC |
Henry Kolesnik wrote:
I thought filaments produced photons/light waves as well. You took me to light now you want to leave! Well, the light emitted by tube filaments is irrelevant to the RF function. I use light examples because light and RF are both EM waves and a lot more is known about light than about RF. Come on I just want a good basic understand on what it is the the Tx reflects the power , how it does it and a little simple math. My dad used to say if you can't explain something you think you know to someone else it might because you don't understand it yourself or lack command of the language. In this case for me it's both. What I am trying to say is that I don't know what happens inside a transmitter. Under Z0-matched conditions, as with a tuner, I believe that what happens inside a transmitter is pretty much irrelevant. The transmitter sees its designed-for impedance and that is essentially all that matters. What I am willing to discuss in detail is what happens at a Z0-match point (x) in an antenna system with reflections - something like the following: XMTR---51.5 ohm line---x---1/4WL 300 ohm line---1749 ohm load 100W -- 200W -- -- 0W -- 100W For these typical conditions, all voltages and currents are either in-phase or 180 degrees out of phase at the match point (x), which makes a power analysis the most simple analysis of all. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Richard Clark wrote:
wrote: A scattering parameter analysis,... arcana deleted as an obviously fulfilled prophecy. Richard, you are the only technical person I know of who ever considered s-paramater analysis to be a secret or mystery. It is one of the more technically popular methods of analysis, ideally suited to transmission line analysis. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
On Sun, 23 May 2004 02:07:13 GMT, "Henry Kolesnik"
wrote: I know that any power not dissipated by an antenna is reflected back to the transmitter. Then the transmitter "reflects" this reflection back to antenna, ad nauseum until its all gone. I also know that a short or an open is required to reflect power and I'm searching for which it is, an open or a short. I'm inclined to think it's a virtual open but I'm at a loss to understand that and I wonder if someone has a good explanation or analogy and some math wouldn't hurt. tnx Hank WD5JFR Hi Hank, Round Two. A short or an open certainly reflects. However, as you have observed through your question, so does a poorly matched antenna; thus you must agree that it presents neither a short nor an open. As such, reflection is not confined to these two conditions. We can display a condition where we have a 2:1 mismatch. This is fairly commonplace as a consideration, if not as a reality. Here, the reflected power is less than the total applied (some 12% if dead reckoning is correct). That is, if the antenna presents a 2:1 mismatch to the power applied to it, nearly 90% of that power will proceed to be radiated with a trivial portion returned to the source (or the tuner). If we boost that mismatch to 10:1, that increases the reflection substantially (let's call it 90% in this spirit of dead reckoning) and naturally less is radiated. The math is quite as simple as a balance ledger. 10:1 for a 50 Ohm source would mean either the load presents a Z of 500 Ohms, or 5 Ohms. From this you can see that we are approaching either an open (hi-Z) or a short (lo-Z) and either perform the same job of reflection - short of total reflection. As such, there is no distinction to the power whether it encounters either, the reflection ensues by virtue of the simple mismatch, not by the literal condition. The computation of mismatch defines how reflective the interface is. 73's Richard Clark, KB7QHC |
"Cecil Moore" wrote in message ... What I am willing to discuss in detail is what happens at a Z0-match point (x) in an antenna system with reflections - something like the following: what you are willing to discuss is irrelevent as it has nothing to do with the original topic which was about what happens in the transmitter. For these typical conditions, all voltages and currents are either in-phase or 180 degrees out of phase at the match point (x), which makes a power analysis the most simple analysis of all. that should read "For these specific conditions", those conditions are hardly 'typical', they are a very exactly contrived example which makes it easy to compare powers. thus making the proper analysis of currents or voltages seem unnecessary. taking simple cases like this and improperly generalizing them is what leads to the worst mis-conceptions and circular arguments in this group. |
Richard Clark wrote: On Sun, 23 May 2004 05:57:28 +0000 (UTC), "Reg Edwards" wrote: Dear Richard, you are confusing the matter even further, if that were possible. Old Son, Have I stolen your thunder? Like the pendulum with a dull and meagre swing, your predictable observations on this subject return to an unremarkable SWR, a topic never raised without the old wife discovering it under her bed.... Does the following strike a bell? A QUOTATION: "When you can measure what you are speaking about and express it in numbers you know something about it. But when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. It may be the beginning of knowledge but you have scarcely in your thoughts advanced to the state of science." You have never offered a scintilla of quantized discussion to the matter. We had a pet scintilla when I was a kid. Cutest sarn thing you ever saw, like a cross between a rabbit and a squirrel! 8^) hehe, - Mike KB3EIA - |
Cecil Moore wrote:
Richard Clark wrote: As for the math, you will find it by the reams, once you've been overwhelmed with the arcana of hyperbolic descriptions of a novel physics that have to proceed its proof. A scattering parameter analysis, described in HP Application Note 95-1 (available on the web) is ideal for analyzing what happens at a match point in a typical ham radio antenna system. b1 = s11(a1) + s12(a2) b2 = s21(a1) + s22(a2) b1 is the net forward voltage, b2 is the net reflected voltage a1 is the incident forward voltage, a2 is the incident reflected voltage Quoting from HP AN 95-1: Another advantage of s-parameters springs from the simple relationship between the variables a1, a2, b1, and b2, and various power waves: |a1|^2 = Power incident on the input of the network. (forward power incident on the match point) |a2|^2 = Power reflected from the load. |b1|^2 = Power reflected from the input port of the network. (power reflected from the match point back toward the source) |b2|^2 = Power incident on the load. The previous four equations show that s-parameters are simply related to power gain and mismatch loss, quantities which are often of more interest than the corresponding voltage functions. |s11|^2 = Power reflected from the network input divided by power incident on the network input |s22|^2 = Power reflected from the network output divided by power incident on the network output |s21|^2 = Power delivered to a Z0 load divided by power available from a Z0 source |s12|^2 = Reverse transducer power gain with Z0 load and source End quote. b2 is the voltage reflected back toward the source and b2 = s21(a1) + s22(a2) It should be obvious that b2 cannot be zero unless there exists total destructive interference between s21(a1) and s22(a2), i.e. s21(a1) is equal in magnitude and opposite in phase to s22(a2). -- 73, Cecil http://www.qsl.net/w5dxp Richard is right, There is the first ream! Sorry, I'm a bit pippish today.......... - Mike KB3EIA - |
Dave wrote:
"Cecil Moore" wrote: What I am willing to discuss in detail is what happens at a Z0-match point (x) in an antenna system with reflections - something like the following: what you are willing to discuss is irrelevent as it has nothing to do with the original topic which was about what happens in the transmitter. Uhhhh Dave, the original topic is the Subject: line. If anything, what happens inside a transmitter is the irrelevant subject since appreciable reflections hardly ever reach the typical ham transmitter. For these typical conditions, all voltages and currents are either in-phase or 180 degrees out of phase at the match point (x), which makes a power analysis the most simple analysis of all. that should read "For these specific conditions", those conditions are hardly 'typical', they are a very exactly contrived example which makes it easy to compare powers. No, those are typical conditions, where the ham radio antenna system is tuned to a Z0-match by a tuner, either external or internal. It is not a "very exactly contrived example" at all. It is absolutely typical of any ham radio installation where the final amp sees close to a 1:1 SWR and that is the great majority. At the Z0-match point at the input of every properly tuned transmatch, the voltages and currents are either in phase or 180 degrees out of phase. If you don't know that, it is no wonder that you label my power analysis stuff as "contrived". -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
On Sun, 23 May 2004 17:18:52 GMT, "Henry Kolesnik"
wrote: OK, if we shine a flashlight at a mirror the light bounces back and what ever is caught by the reflector will be reflected. Take away the reflector and the reflection just keeps going. If someone can tell me what the hot filament does perhaps I can understand what happens in the finals, or whatever. tnx Hank WD5JFR Hi Hank, Well I see in correspondence following this as "replies," that they are far from satisfactory. All part of the arcana that precedes the convolutions of math you would have had to endure. The abandonment of this lead is simply a matter of Cecil's lack of experience in the metaphor of light. To answer your question above. Removing the reflector is unnecessary as it is part of the initial condition and has nothing to do with it serving as the correlative to a tuner that you want to remove from the argument (which is a perfectly acceptable imposition of conditions). Your question also goes to the heart of the matter. We begin with a hot filament which emits radiation (and yes, no reflector is required so we will skip that as one of your conditions). The amount of radiation is directly correlated to the amount of heat. This will simplify matters, but in the end it will yield a failure of metaphors (which always occur if you cannot bridge the logic). The radiation strikes a reflection (immaterial whether complete or partial) and that portion which returns, impinges upon the filament, the source. The filament absorbs the power, which in turn raises its temperature (everyday experience proves the heat of such radiation). This will, in turn, cause a higher radiation (given the quid-pro-quo of heat and radiation). In a sense, this means the reflected power is re-radiated. The confirmation of this is that if you achieved full reflection, you then define total insulation of the radiation (no heat escapes) and temperature rises accordingly, and this may lead to catastrophic failure of the filament (a very bright illumination if you could see it, and consequent fusing current - electric kilns use this principle but tolerate the current by under rating the source). You can imagine the correlative to transmitter failure for the same conditions. The failure of the metaphor? RF is not heat (common light is) and the return of power to be rendered into heat does not result in a higher RF output. I will anticipate the sophomore's comments that RF reflections do not become heat, in and of itself: The returned power (either through wave mechanics or lumped circuitry) must result in either a higher potential across the source, or a higher current through it. Elevated potentials yield the everyday experience of an arc (heat). Elevated currents yield the everyday experience of current density through the same element (much like the filament of our metaphor - heat). One failure mode comes with the peak power snap, followed by the muttering of "Oh ****!" Or it comes through the more progressive thermal runaway, followed by the muttering of "what's that funny smell?" 73's Richard Clark, KB7QHC |
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