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Mismatched Zo Connectors
At risk of being called a Troll, and having little else to do at
present, I copy from another newsgroup the following text. "Reg Edwards" wrote - "The effect of an impedance mis-match at a coaxial connector of ordinary dimensions is practically zero at frequencies up to UHF. Regardless of its other dimensions, the primary requirement of a mismatched connector is that its length should be appreciably less than 1/4-wavelength at the highest working frequency. People are unnecessarily worried at VHF and below. Mix up 50 and 75-ohm connectors, and indeed connectors of unknown Zo, and carry on regardless. For an analysis of performance, download in a few seconds and run immediately program CONNECT from website below." Program CONNECT will calculate the effect on performance of inserting any relatively short length of line, of Zo different from system Zo, into the system. It's less than the inexperienced might imagine from reading frightening magazine and handbook articles about impedance and conjugate mis-matches. If you have a short length of coax lying around, of unknown Zo, just use it! ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
Mismatched Zo Connectors
Reg Edwards wrote:
Regardless of its other dimensions, the primary requirement of a mismatched connector is that its length should be appreciably less than 1/4-wavelength at the highest working frequency. Yes, at HF the reflections from one impedance discontinuity and the reflections from a complimentary impedance discontinuity 3 inches away almost entirely cancel each other. -- 73, Cecil http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
Some of us are so cheeky as to use CATV, RG-6, Rg-8, R8-11, etc., with
no regard as to the supposed 'surge impedence'.. What is the load impedence of a 50 ohm antenna at any frequency removed from its resonance point anyway? If the antenna is 30 ohms or 80 ohms, with some reactance, does the SWR meter notice the inexpensive run of supposed 70 ohm coax that you cadged from the cable tv company? Once in a while I get an antenna that is fed with bits and pieces of this and that, which swears differently back at the shack than it did at the antenna feed point... Inserting another 5 or 10 feet of coax jumper usually cures it... denny / k8do - antenna monger from way back... Another fine myth you've gotten us into, Ollie! |
Mismatched Zo Connectors
Reg Edwards wrote:
Regardless of its other dimensions, the primary requirement of a mismatched connector is that its length should be appreciably less than 1/4-wavelength at the highest working frequency. ====================================== Yes, at HF the reflections from one impedance discontinuity and the reflections from a complimentary impedance discontinuity 3 inches away almost entirely cancel each other. -- 73, Cecil ======================================== Reflections are functions of TIME, not frequency. Oliver Heaviside had the right idea long before the invention of the SWR meter. ----- Reg, G4FGQ. |
Mismatched Zo Connectors
"Denny" wrote If the antenna is 30 ohms or 80 ohms, with some reactance, does the SWR meter notice the inexpensive run of supposed 70 ohm coax that you cadged from the cable tv company? ===================================== Of course it doesn't. But at least it does try. The meter thinks it indicates SWR on the transmission line, whereas it actually indicates SWR on a long, imaginary, non-existent, 50-ohm line between tuner and transmitter. What sort of mess would Laurel & Hardy have found themselves in when trying to disentangle forward from reflected power? =================================== |
Mismatched Zo Connectors
On Tue, 22 Aug 2006 17:28:01 GMT, Cecil Moore
wrote: and the reflections from a complimentary impedance discontinuity What is a "complimentary impedance discontinuity", or even a "complementary impedance discontinuity" if you meant that? Owen -- |
Mismatched Zo Connectors
Cecil Moore wrote:
Reg Edwards wrote: Regardless of its other dimensions, the primary requirement of a mismatched connector is that its length should be appreciably less than 1/4-wavelength at the highest working frequency. Yes, at HF the reflections from one impedance discontinuity and the reflections from a complimentary impedance discontinuity 3 inches away almost entirely cancel each other. What's a "complimentary impedance discontinuity," Cecil? 73, Tom Donaly, KA6RUH |
Mismatched Zo Connectors
"Owen Duffy" wrote in message ... On Tue, 22 Aug 2006 17:28:01 GMT, Cecil Moore wrote: and the reflections from a complimentary impedance discontinuity What is a "complimentary impedance discontinuity", or even a "complementary impedance discontinuity" if you meant that? ======================================= Owen, For the benifit of innocent bystanders, he means the same magnitude discontinuity with the opposite sign. But you knew that of course, didn't you? On the other hand, I'm not sure *I* have described it correctly. It can best be described in terms of the reflection coefficient. There are two reflections, of opposite signs, which do not occur at exactly the same instant in TIME. Whatever it is, Cecil is (im)perfectly correct. ---- Reg. |
Mismatched Zo Connectors
"Reg Edwards" wrote Reflections are functions of TIME, not frequency. Oliver Heaviside had the right idea long before the invention of the SWR meter. ==================================== For "reflections" also read "Echos". ----- Reg, G4FGQ. ==================================== |
Mismatched Zo Connectors
On Wed, 23 Aug 2006 00:54:51 +0100, "Reg Edwards"
wrote: "Reg Edwards" wrote Reflections are functions of TIME, not frequency. Oliver Heaviside had the right idea long before the invention of the SWR meter. ==================================== For "reflections" also read "Echos". Hi Reggie, You are in fact wrong in all accounts. Reflections are functions of distance - as are echoes. This is a phase issue. Time and frequency are always inseparable as Kelvin would instruct you in first principles before another hunk of chalk was winged off your noggin. You may choose to render phase into time, but shift the frequency and the phase shifts, not the distance. Mismatched Zo connectors do not shrink or enlarge with frequency - the effects may, but physical components rarely follow such perturbations.... until an arc-over that is the classic failure mechanism for such mismatches (obviously, and deliberately ignored in this thread). 73's Richard Clark, KB7QHC |
Mismatched Zo Connectors
"Reg Edwards" wrote
Reflections are functions of TIME, not frequency. Oliver Heaviside had the right idea long before the invention of the SWR meter. ==================================== For "reflections" also read "Echos". ==================================== The reason there are so many misunderstandings about SWR is that SWR meters are based on impedance and frequency. Not a simple concept. Whereas reflections (echos) (which according to Cecil are what it's all about) are functions of time and distance. With which we are very familiar. Unfortunately, there does not appear to be a simple measuring instrument which could replace the SWR meter. Any ideas? But we would still need an instrument, a TLI, which indicates whether or not the transmitter is correctly loaded with 50 ohms. So perhaps things are best kept as they are. Just rename the SWR meter! ----- Reg, G4FGQ. ==================================== |
Mismatched Zo Connectors
Ric,
Yet again, like a Catherine Wheel, you are flying off in convoluted tangents. ----- Punchinello |
Mismatched Zo Connectors
On Wed, 23 Aug 2006 02:10:41 +0100, "Reg Edwards"
wrote: Ric, Yet again, like a Catherine Wheel, you are flying off in convoluted tangents. How else to follow your logic? As you can see, facile diversions are easily managed in kind. ;-) If you cannot reconcile distance to reflection, what use is it being preserved in unzipped code? I await your next turn on the highway to avoid this road-kill. To cut the thread short, I recall one of your bedtime fairy tales of how you fought a radar fire aboard an airplane. Cut it anyway you want, but the fire undoubtedly arose from a mismatch. This appears to have marked a trauma in your youth to avoid the discussion of mismatch consequences. Please, in the future, begin your posts with "Once upon a time..." instead of At risk of being called a Troll, You must agree, this particular bait was self-fulfilling; and as always, I am most pleased to serve your bidding. 73's Richard Clark, KB7QHC |
Mismatched Zo Connectors
Owen Duffy wrote:
Cecil Moore wrote: and the reflections from a complimentary impedance discontinuity What is a "complimentary impedance discontinuity", or even a "complementary impedance discontinuity" if you meant that? Sorry about the misspelling. I was trying to us the word "complement" in the sense of "A numerical derived from a given numeral by a specified subtraction rule. Often used to represent the negative of the number represented by the given numeral." Definition from "The IEEE Dictionary". For instance, the reflection coefficient at the second impedance discontinuity can be considered to be the complement of the reflection coefficient at the first impedance discontinuity. --------Z01---x---Z02---y---Z01----------- The physical reflection coefficient at point 'x' would be (Z02-Z01)/(Z01+Z02). The physical reflection coefficient at point 'y' would be (Z01-Z02)/(Z01+Z02). Mathematically, those two reflection coefficients can be considered to be complements of each other. -- 73, Cecil http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
Tom Donaly wrote:
What's a "complimentary impedance discontinuity," Cecil? Sorry my spellchecker didn't catch that. It should have been "complementary", a mathematical term. Please see my reply to Owen. -- 73, Cecil http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
Reg Edwards wrote:
Reflections are functions of TIME, not frequency. Remember that in the (2*pi*frequency*time) term used to describe reflections, frequency is just as important as time. -- 73, Cecil http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
In article , "Reg Edwards"
g4fgq,regp@ZZZbtinternet,com wrote: Reflections are functions of TIME, not frequency. Oliver Heaviside had the right idea long before the invention of the SWR meter. ----- Reg, G4FGQ. Hello, and the present or absence of reflections in the steady-state (no transients as one would see when the system is first energized) is by comparison of an impedance (Zx) at a measurement point to some reference impedance (Zo). This reference impedance can be associated with the characteristic impedance of a transmission line or some other system characteristic. If Zx and/or Zo varies with frequency (has a reactive component) then the RMS amplitude of the voltage/current reflections also varies with frequency. We use this property to match Zx to Zo at some frequency by minimizing the measured reflected voltage (or current or power). In the steady-state there is one voltage/current (as seen by an RF voltmeter or ammeter) placed at the measurement point. We need a directional coupler (part of a Bird model 43) or impedance bridge (referenced to Zo) inserted at the measurment point in order to partition the sampled voltage/current into incident (forward) and reflected waves. I'm not sure exactly what Reg meant. Sincerely, and 73s from N4GGO, John Wood (Code 5550) e-mail: Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 |
Mismatched Zo Connectors
J. B. Wood wrote:
In the steady-state there is one voltage/current (as seen by an RF voltmeter or ammeter) placed at the measurement point. We need a directional coupler (part of a Bird model 43) or impedance bridge (referenced to Zo) inserted at the measurment point in order to partition the sampled voltage/current into incident (forward) and reflected waves. Hi John, one important fact that some people would like to forget is that the reflected wave can indeed be partitioned from the forward wave. Some people on this newsgroup argue that the forward wave and reflected wave are inseparable and that reflected waves contain no rearward traveling energy. However a circulator plus load resistor located at the source will prevent reflected wave energy from being incident upon the source and will heat up that load resistor in the process proving that reflected waves are real and do contain energy. My favorite illustration of such is a one-second lossless transmission line with reflections. The number of watts in the forward wave plus the number of watts in the reflected wave equals the number of joules stored in the line during steady-state. For instance, if Pfor = 200w and Pref = 100w, then 300 joules of RF energy exist in the one-second long lossless line during steady-state. -- 73, Cecil, http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
In article , Cecil Moore
wrote: Hi John, one important fact that some people would like to forget is that the reflected wave can indeed be partitioned from the forward wave. Hello, and it would be more correct to say that the forward and reflected waves are components of a standing wave. However a circulator plus load resistor located at the source will prevent reflected wave energy from being incident upon the source and will heat up that load resistor in the process proving that reflected waves are real and do contain energy. Hmm. Don't quite get that. Say an RF voltage source is located at port A of an ideal 3-port circulator designed for a system (characteristic) impedance of Zo. A load of ZL terminates port B and a load of Zo is attached to port C. Now, incident energy from the source at A is transferred by circulator action to the load at port B. If ZL is not equal to Zo then reflected energy from port B is transferred to port C where it is dissipated in the port C termination. None of the reflected energy originating from port B ever returns to port A in this ideal case (circulator has infinite isolation). Sincerely, John Wood (Code 5550) e-mail: Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 |
Mismatched Zo Connectors
Cecil Moore wrote: Hi John, one important fact that some people would like to forget is that the reflected wave can indeed be partitioned from the forward wave. Some people on this newsgroup argue that the forward wave and reflected wave are inseparable and that reflected waves contain no rearward traveling energy. However a circulator plus load resistor located at the source will prevent reflected wave energy from being incident upon the source and will heat up that load resistor in the process proving that reflected waves are real and do contain energy. Hi Cecil How much energy is "in the reflected wave" without a circulator load resistor? 73, ac6xg |
Mismatched Zo Connectors
Jim Kelley wrote:
How much energy is "in the reflected wave" without a circulator load resistor? There's the same amount of energy in the reflected wave either way, with or without a circulator load resistor. The reflected wave is incapable of looking ahead and using its free will to decide how much energy to contain depending upon its future fate. But that is what some people would have us believe. Does your question imply: A reflected wave that is going to be dissipated in a circulator resistor sometime in the future contains energy but a reflected wave that is going to be dissipated after the power is turned off does not contain energy? In a one second long lossless transmission line, watts equal joules. A forward wave of 200 watts contains 200 joules of energy. A reflected wave of 100 watts contains 100 joules of energy. Under such conditions, the source has supplied exactly 300 joules more than has been delivered to the load, no more and no less. Conservation of energy strikes again. -- 73, Cecil, http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
Cecil Moore wrote:
The reflected wave is incapable of looking ahead and using its free will to decide how much energy to contain depending upon its future fate. But that is what some people would have us believe. Those are the bad people, evidently. Does your question imply: A reflected wave that is going to be dissipated in a circulator resistor sometime in the future contains energy but a reflected wave that is going to be dissipated after the power is turned off does not contain energy? The question implies that there are issues regarding the flow of energy which you continue to misunderstand. Your answer confirms this. In a one second long lossless transmission line, watts equal joules. A forward wave of 200 watts contains 200 joules of energy. A reflected wave of 100 watts contains 100 joules of energy. Under such conditions, the source has supplied exactly 300 joules more than has been delivered to the load, no more and no less. Is your claim that the above describes the system with, or without, the circulator load? 73, ac6xg |
Mismatched Zo Connectors
Jim Kelley wrote:
The question implies that there are issues regarding the flow of energy which you continue to misunderstand. Your answer confirms this. So please enlighten me. How does a wave know whether to carry energy or not depending upon its future fate? It is my understanding that the power in an EM wave is ExH no matter what its future fate. Does a laser beam reflected from an ideal mirror carry any less energy than the forward beam just because it has been reflected? If so, how does that not violate the conservation of energy principle? In a one second long lossless transmission line, watts equal joules. A forward wave of 200 watts contains 200 joules of energy. A reflected wave of 100 watts contains 100 joules of energy. Under such conditions, the source has supplied exactly 300 joules more than has been delivered to the load, no more and no less. Is your claim that the above describes the system with, or without, the circulator load? Yes, in both cases the voltage reflection coefficient at the load is 0.707 making the power reflection coefficient = 0.5, i.e. half the power incident upon the load is reflected. The system with the circulator load at the signal generator has the signal generator supplying 200 watts and the circulator load resistor dissipating 100 watts. 'SGCR' stands for a signal generator equipped with a circulator and circulator load resistor equal to the Z0 of the feedline. There's 300 joules of energy in the feedline during steady-state. 100 watts is dissipated in the load. 200W SGCR-----one second long feedline-------load Pfor=200W-- --Pref=100W The system without the circulator and load consists of a 100 watt source feeding an ideal autotuner tied to the transmission line. In this case all reflected energy is re-reflected by the Z0-matched autotuner. 'SGAT' stands for a signal generator equipped with an ideal autotuner. There's 300 joules of energy in the feedline during steady-state. 100 watts is dissipated in the load. 100W SGAT-----one second long feedline-------load Pfor=200W-- --Pref=100W -- 73, Cecil, http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
Cecil Moore wrote:
How does a wave know whether to carry energy or not depending upon its future fate? Does a laser beam reflected from an ideal mirror carry any less energy than the forward beam just because it has been reflected? What can be said other than; these questions appear to have been posed by someone who is struggling to understand some pretty simple concepts. In a one second long lossless transmission line, watts equal joules. A forward wave of 200 watts contains 200 joules of energy. A reflected wave of 100 watts contains 100 joules of energy. Under such conditions, the source has supplied exactly 300 joules more than has been delivered to the load, no more and no less. Is your claim that the above describes the system with, or without, the circulator load? Yes, in both cases the voltage reflection coefficient at the load is 0.707 making the power reflection coefficient = 0.5, i.e. half the power incident upon the load is reflected. But, is the latter really more than a mathematical convenience? (You may recall that 'power' isn't something which actually moves in physical systems. And being a scalar, it can be tricky to do a proper vector analysis.) How energy moves is dependent upon factors throughout the entire system - not just at the load. The system with the circulator load at the signal generator has the signal generator supplying 200 watts and the circulator load resistor dissipating 100 watts. 'SGCR' stands for a signal generator equipped with a circulator and circulator load resistor equal to the Z0 of the feedline. There's 300 joules of energy in the feedline during steady-state. 100 watts is dissipated in the load. 200W SGCR-----one second long feedline-------load Pfor=200W-- --Pref=100W The system without the circulator and load consists of a 100 watt source feeding an ideal autotuner tied to the transmission line. In this case all reflected energy is re-reflected by the Z0-matched autotuner. 'SGAT' stands for a signal generator equipped with an ideal autotuner. There's 300 joules of energy in the feedline during steady-state. 100 watts is dissipated in the load. 100W SGAT-----one second long feedline-------load Pfor=200W-- --Pref=100W Very inventive. The question was posed without a load on the circulator, not without a circulator. You still haven't answered that question. Perhaps you wouldn't mind just considering one system at a time. No sense changing the variables just to make the solution come out the way we want. Don't they teach you that you're not supposed to change horses in the middle of a stream out there in Texas? ;-) So, since we've obviously been talking about the steady state, what's with all the weird questions about 'how the wave knows' what's going to happen in the future? 73, ac6xg |
Mismatched Zo Connectors
Jim Kelley wrote:
Cecil Moore wrote: What can be said other than; these questions appear to have been posed by someone who is struggling to understand some pretty simple concepts. Actually, I am struggling to understand your concepts which you appear somewhat incapable of putting into words, hence the total absence of anything technical in your posting. Is energy-passing-a-point "power" as defined by the IEEE Dictionary? Does an EM wave possesses ExH amount of power as the technical references assert? So, since we've obviously been talking about the steady state, what's with all the weird questions about 'how the wave knows' what's going to happen in the future? Steady-state had a beginning and it will have an end. It cannot be analyzed without knowing what happened in the beginning and what will happen in the end. Steady-state is the rug under which you and others try to sweep the laws of physics including the conservation of energy principle. I'm doing what I can to call your bluff. -- 73, Cecil http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
On Thu, 24 Aug 2006 14:22:24 -0700, Jim Kelley
wrote: Cecil Moore wrote: How does a wave know whether to carry energy or not depending upon its future fate? Hi Jim, I don't know how you can pass up all these tarnished jewels. Energy at the speed of light has no time dimension (Lorenz law) and as such there is no futurity. No future, no fate - presumptions aside (or galore, depending upon the source). Does a laser beam reflected from an ideal mirror carry any less energy than the forward beam just because it has been reflected? Of course it does. Jim, your question was: How much energy is "in the reflected wave" without a circulator load resistor? and we find, after having gone down the primrose path: Yes, in both cases the voltage reflection coefficient at the load is 0.707 making the power reflection coefficient = 0.5, i.e. half the power incident upon the load is reflected. The common finding of an unterminated circulator load would offer reflections from that port passing back to the apparent source, the original mismatched load. Hence, that load sees more than 0.707 (whatever) - now from two "sources." There is one way to prevent this, but Cecil doesn't have enough experience at the linear bench to come up with that solution. Certainly I can anticipate his fog of vectors and SWR mechanics with 1 second transmission lines blossoming in the swamp - but a real bench tech could whip out the solution and make it work with less effort and certainly not have to cobble up a phonebook thick stack of Xeroxed proofs. Very inventive. The question was posed without a load on the circulator, not without a circulator. You were expecting something else? ;-) 73's Richard Clark, KB7QHC |
Mismatched Zo Connectors
Richard Clark wrote:
There is one way to prevent this, but Cecil doesn't have enough experience at the linear bench to come up with that solution. Probably true but I am not looking to solve that non-problem. The question to be answered is: Is the power in an EM wave equal to ExH as the textbooks say, or is it zero until dissipated? Jim obviously has his own personal definition of "power" that disagrees with The IEEE Dictionary. That is what he is basing his entire argument on - simple semantics using special definitions of words. That's why my argument involves one second long transmission lines in which power in watts = energy in joules. That's an argument that is very difficult to sweep under the rug. The number of joules in a transmission line *ALWAYS* equals the number of joules not lost to radiation, I^2R, and dielectric and not yet delivered to the load. And it is *ALWAYS* equivalent to the sum of the forward and reflected powers in that particular length of transmission line. -- 73, Cecil http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
Cecil Moore wrote:
Is energy-passing-a-point "power" as defined by the IEEE Dictionary? Does an EM wave possesses ExH amount of power as the technical references assert? Nothing the IEEE says counters the fact that the mathematical product of two physical quantities does not and can not physically propagate through a transmission line. It can also not reflect, refract, diffract, superpose, or interfere constructively or destructively. Waves propagate and energy moves. Power is simply the rate at which energy is transferred or changes form. It is the rate at which 'electric smoke' is liberated from one's aerial so to speak. Steady-state had a beginning and it will have an end. It cannot be analyzed without knowing what happened in the beginning and what will happen in the end. But there's no dispute about what happens in the beginning or at the end. It's entirely about what you claim is happening in the steady state. Steady-state is the rug under which you and others try to sweep the laws of physics including the conservation of energy principle. The steady-state condition isn't something which contradicts nature - it IS nature. Clearly, the only one needing to sweep the laws of physics under the rug around here is you, Cecil. 73, ac6xg |
Mismatched Zo Connectors
Cecil Moore wrote:
[snip] Steady-state had a beginning and it will have an end. It cannot be analyzed without knowing what happened in the beginning and what will happen in the end. Steady-state is the rug under which you and others try to sweep the laws of physics including the conservation of energy principle. I'm doing what I can to call your bluff. Cecil, Countless mathematicians and scientists would disagree with your characterization of steady state. Perhaps even a few engineers as well. 8-) This sort of stuff is thoroughly covered in differential equations courses and in any physics or engineering course that look at electrical or mechanical response to impulses and other stimuli. Surely they dealt with such matters at TAMU. If you refuse to accept standard technical conventions, then there is little hope of getting others to agree with you. 73, Gene W4SZ |
Mismatched Zo Connectors
Jim Kelley wrote:
Nothing the IEEE says counters the fact that the mathematical product of two physical quantities does not and can not physically propagate through a transmission line. Once again you make a statement with which no one has disagreed. Has anybody in the world said otherwise? I certainly have not, so your statement appears to be just another one of your straw men. Energy flowing past a point is defined as *power* at that fixed point even if it is reflected energy! The fact that you are forced to misrepresent what I have said speaks volumes. But there's no dispute about what happens in the beginning or at the end. It's entirely about what you claim is happening in the steady state. Exactly what is my claim about what is happening in the steady- state? In case you misunderstood, here it is again. What I have said is happening during steady-state is that the source has supplied exactly the amount of energy contained in the measured forward wave and the measured reflected wave. That energy has been delivered to the system by the source but has not yet reached the load. Occam's razor says that exact amount of energy is most likely contained in the forward and reflected waves, not magically somewhere else, e.g. sloshing around between standing wave nodes as W7EL asserts. I say the ExH watts exist in the forward wave and the reflected wave just as the textbooks assert. You seem to be saying that it isn't there. If it isn't there, where did it go? Conservation of energy strikes again. -- 73, Cecil http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
Gene Fuller wrote:
If you refuse to accept standard technical conventions, then there is little hope of getting others to agree with you. Gene, have you stopped beating your wife? Your usual ad hominem attack completely devoid of any technical content is duly noted. In a one second long lossless transmission line where the forward power is 200W and the reflected power is 100W, it can be proved that the source has supplied 300 joules that have not been accepted by the load. If those joules are not contained in the forward and reflected waves, where are they? -- 73, Cecil http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
Gene Fuller wrote:
If you refuse to accept standard technical conventions, then there is little hope of getting others to agree with you. I am advocating the wave reflection model as explained in: Johnson's, "Transmission Lines and Networks", 1st Edition Ramo/Whinnery's, "Fields and Waves in Modern Radio", 2nd Edition Hecht's, "Optics", 4th Edition Maxwell's, "Reflections" and "Reflections II" "The ARRL Antenna Book", 15th Edition I am also advocating the conservation of energy principle. I hope that one doesn't need references. Exactly what is it about the wave reflection model and the conservation of energy principle with which you disagree? -- 73, Cecil http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
John,
I would like to reply to your question (if that's what it is) but I am unable to understand what you are saying. So I leave it to Cecil and Co. to add further to the complications and confusion. It's really all very simple. ---- Reg. |
Mismatched Zo Connectors
In article , "Reg Edwards"
g4fgq,regp@ZZZbtinternet,com wrote: John, I would like to reply to your question (if that's what it is) but I am unable to understand what you are saying. So I leave it to Cecil and Co. to add further to the complications and confusion. It's really all very simple. ---- Reg. Hello, Reg. What I didn't understand was your statement "Reflections are functions of TIME, not frequency." That statement immediately invited conflict with the info contained in my electromagnetics and transmission line theory texts lining my office bookshelf. I attempted to provide some clarification and hopefully not insult anyone's intelligence. Sincerely, John Wood (Code 5550) e-mail: Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 |
Mismatched Zo Connectors
Reg Edwards wrote:
So I leave it to Cecil and Co. to add further to the complications and confusion. Reg, how about these statements from a recent QEX article? "Contrary to popular views, the forward and reverse waves on a transmission line are not separate fields." "I wish to emphasize the fact that the forward and reverse waves really do not exist separately, ..." "Dual Directional Wattmeters", Eric von Valtier, K8LV, _QEX_, May/June 2006. The article obviously rejects the wave reflection model for transmission lines as presented by Ramo/Whinnery, Johnson, etc. If forward and reverse waves do not exist separately, how is it possible for a circulator to separate them? -- 73, Cecil http://www.qsl.net/w5dxp |
Mismatched Zo Connectors
Cecil,
I think you are conflating models with nature, and trying to champion one correct model over another correct model! It's confusing to onlookers and boring. There is NO inconsistency between saying "there's only one electromagnetic field in a transmission line" and "a circulator seperates the forward wave from the reflected wave" if you've suitably defined what all those terms mean and you do the correct math. The electromagnetic field as a function of space and time in the coaxial transmission line is a three-dimensional time dependent field. There's a description wherein one single vector valued function E(r,phi,z, t) describes the electric field and another describes the magnetic field, and of course, you can get one from the other, so in some sense, all you need to describe what's going on is E(r,phi,z,t). Now, in the coaxial TEM mode the radial and azimuthal dependence of the fields becomes trivial, and you're just left with some function E'(z,t) to describe the electric field, and one B'(z,t) for the magnetic field (once again, you can of course, get one from the other) It turns out that mathematically you can represent this function as a superposition of other functions, forward and reverse traveling waves. It's just a DIFFERENT WAY OF WRITING IT DOWN. A circulator *doesn't know math*. Its operation may have a simple description in the language of forward and reverse waves, but it does what it does no matter what model you use to describe it. If you get different answers using a forward and reflected wave description than some other description, then one or both of your descriptions are wrong. The conversion of one mathematical description of the electromagnetic field into a series of statements in English and the argument based on those words never gets you anywhere on this topic. Why not pick up a copy of Jackson's Electrodynamics and write down what you're trying to say mathematically. If you're right, everyone will have to be convinced. 73, Dan |
Mismatched Zo Connectors
Hello, Reg. What I didn't understand was your statement "Reflections are functions of TIME, not frequency." That statement immediately invited conflict with the info contained in my electromagnetics and transmission line theory texts lining my office bookshelf. I attempted to provide some clarification and hopefully not insult anyone's intelligence. Sincerely, John Wood (Code 5550) e-mail: Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 =================================== Hi John, Your comments were perfectly inoffensive to anyone. Sorry if I gave you the impression that I thought so. I don't agree that my statement about Time and Reflections is in conflict with transmission line theory as described in the books (bibles) lining your office shelves. We diverge because my education was probably altogether different to yours and so we don't speak the same language. Time is represented in Phase Shift. Reflections are echos. Line Length = Distance. Propagation Velocity = Distance vs Time. ---- Reg. |
Mismatched Zo Connectors
The fundamental partial differential equations of transmission lines
are - - dv/dz = R + L*di/dz - di/dz = G + C*dv/dz where volts v and current i are incremental functions of distance and time, and z is incremental distance along line. Everything else follows. Similar equations can be written in terms of frequency. It is often easier to think in terms of Time and Distance rather than Frequency and Impedance. ---- Reg. |
Mismatched Zo Connectors
"Cecil Moore" wrote
If forward and reverse waves do not exist separately, how is it possible for a circulator to separate them? ========================================= Cec, You forgot to allow TIME into the argument. The two waves do NOT, and cannot, exist seperately in time. The circulator merely divides the STEADY STATE, instantaneous, at the same time, power in the wave into two parts according to what the operator, or by design, has set it to do. When the generator is switched off both parts disappear simultaneously. I know this won't satisfy you. ---- Reg. |
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