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Analyzing Stub Matching with Reflection Coefficients
Cecil Moore wrote:
x a1=10----| |----s21(a1)=5 toward the load s11(a1)=5----| For those of you who are unfamiliar with the way s-parameter voltages are normalized, here are the *actual measured* voltages at the impedance discontinuity at t=0 + delta-t. All three voltages can easily be seen on an o'scope a short time after t=0. During the buildup to steady- state Vref1 goes from 50V to 0V. How that is possible without interaction is the question for ac6xg. x Vfor1=70.7V----| |----120.7V=Vfor2 toward the load Vref1=50V----| rho1-- | --tau2(Vref2)=0 The corresponding equation used by RF engineers is: Vref1 = rho1(Vfor1) + tau2(Vref2) In this t=0 case, Vref2=0, so Vref1 = rho1(Vfor1) at t=0 -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
Cecil Moore wrote:
Gene Fuller wrote: You don't believe in superposition, do you? It is discussed in lots of books if you want to understand. Do you believe Jim's argument that two coherent EM waves of equal magnitudes and opposite phases traveling collinearly in the same direction in a transmission line can never be canceled? If Jim is right, we can toss the s-parameter analysis in the garbage can and join Roy in calling it gobbledigook (sic). Cecil, Never is a long time. And I am sure you would slip away from free space or a linear medium to provide some counter example as soon as I agreed. I agree with Jim and Roy, and most of the rest of the world. Electromagnetic waves, or photons if you prefer, simply do not interact without the assistance of interfaces, discontinuities, or a non-linear medium. Interference is a result from linear superposition. No waves are harmed in the process. At interfaces and discontinuities lots of things can happen. There are well-established techniques for analyzing those things. There is no law of "conservation of waves", however. There is also no law that says all of the individual component waves you may choose to create need to have some sort of detailed energy balance. I have explained several times how the conservation of energy law works, but you seem to disbelieve me. (Hint: I did not make this stuff up. I gave you direct quotes from very reliable sources.) Since you keep bringing up s-parameters, with the implication that they provide some new truth, perhaps you might go back and re-read AN-95-1. From page 7 of the slide version: "If other independent and dependent variables had been chosen, the network would have been described, as before, by two linear equations similar to equations 1 and 2, except that the variables and the parameters describing their relationships would be different. However, all parameter sets contain the same information about a network, and it is always possible to calculate any set in terms of any other set." The other variables described earlier in the note include voltage and current. Again, we come to my old standby, mathematical convenience. S-parameters are very useful, but they bring nothing new to the physical reality. 73, Gene W4SZ |
Analyzing Stub Matching with Reflection Coefficients
Cecil Moore wrote:
Cecil Moore wrote: x a1=10----| |----s21(a1)=5 toward the load s11(a1)=5----| For those of you who are unfamiliar with the way s-parameter voltages are normalized, here are the *actual measured* voltages at the impedance discontinuity at t=0 + delta-t. All three voltages can easily be seen on an o'scope a short time after t=0. During the buildup to steady- state Vref1 goes from 50V to 0V. How that is possible without interaction is the question for ac6xg. x Vfor1=70.7V----| |----120.7V=Vfor2 toward the load Vref1=50V----| rho1-- | --tau2(Vref2)=0 The corresponding equation used by RF engineers is: Vref1 = rho1(Vfor1) + tau2(Vref2) In this t=0 case, Vref2=0, so Vref1 = rho1(Vfor1) at t=0 Cecil, I am impressed! That's a pretty fancy o'scope you got. Measurement of voltages to four significant digits at t = 0 + delta-t is definitely world-class. That 291.4 ohm line is pretty special as well. Is there some non-standard definition of *actual measured* that we should consider to help interpret your results? 8-) 73, Gene W4SZ |
Analyzing Stub Matching with Reflection Coefficients
Gene Fuller wrote:
Never is a long time. Waves never interact *is* a long time. I agree with Jim and Roy, and most of the rest of the world. Electromagnetic waves, or photons if you prefer, simply do not interact without the assistance of interfaces, discontinuities, or a non-linear medium. Interference is a result from linear superposition. No waves are harmed in the process. "No waves are harmed in the process" implies that waves can never be canceled. Yet, all the textbooks and all the web pages say that when two coherent collinear waves of equal magnitudes and opposite phases meet, they only appear to be destroyed but their energy components are actually "redistributed" in different directions. That's exactly what happens to reflected waves toward the source when a Z0-match is achieved. The energy components in the reflected waves, s11(a1) and s12(a2), are redistributed back toward the load. How does b1 ever go permanently to zero without s11(a1) and s12(a2) canceling each other? There is also no law that says all of the individual component waves you may choose to create need to have some sort of detailed energy balance. Yes, there is, Gene. It is called the conservation of energy principle. You cannot create energy in one place, have it destroyed in another place, and then argue that everything is all right because the net energy balance remains the same. "If other independent and dependent variables had been chosen, the network would have been described, as before, by two linear equations similar to equations 1 and 2, except that the variables and the parameters describing their relationships would be different. However, all parameter sets contain the same information about a network, and it is always possible to calculate any set in terms of any other set." The other variables described earlier in the note include voltage and current. Again, we come to my old standby, mathematical convenience. S-parameters are very useful, but they bring nothing new to the physical reality. Then why are you so afraid to discuss an s-parameter analysis? Please respond to my example posting. How does s11(a1) go from 5 to 0 without interacting with something? -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
On Apr 16, 8:35 pm, Cecil Moore wrote:
No they don't. If the waves themselves changed, then their resultant superposition would also change. It's a completely unfounded notion, If what you say is true, then if we measure field strengths far enough away from an antenna to get outside the range of interference, then all antennas are isotropic. "Outside the range of interference"? Yes, please call NASA and tell them about that. :-) ac6xg |
Analyzing Stub Matching with Reflection Coefficients
Gene Fuller wrote:
I am impressed! That's a pretty fancy o'scope you got. Measurement of voltages to four significant digits at t = 0 + delta-t is definitely world-class. That 291.4 ohm line is pretty special as well. Your non-technical diversions are noted. How about discussing the technical question that was posed? The voltages can be viewed on an o'scope. Their magnitudes agree with the above calculated magnitudes. Do you know of any reason that those voltages would not obey the rules of the reflection model? When does a reflection coefficient of 0.707 not reflect 0.707 of the incident voltage? The 291.4 ohm line is chosen to make rho=s11=0.707. My "450" ohm ladder-line measures to be actually 380 ohms. Nothing special about 291.4 ohms except that: (291.4-50)/(291.4+50) = 0.707 We could actually design a feedline with Z0 = 291.4 ohms. Want me to show you how? :-) If you don't like that value, use 300 ohms and 51.5 ohms for the coax. I'm sure between the choices of 50 ohm coax and 52 ohm coax, there must be a 51.5 ohm coax in there somewhere. -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
Jim Kelley wrote:
"Outside the range of interference"? Yes, please call NASA and tell them about that. :-) You said that EM waves cannot be perfectly collinear. Therefore, there has to exist a distance where they diverge and stop interfering. Your words, not mine. -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
On Apr 16, 9:20 pm, Cecil Moore wrote:
Do you believe Jim's argument that two coherent EM waves of equal magnitudes and opposite phases traveling collinearly in the same direction in a transmission line can never be canceled? I asked you to show me the two waves of equal magnitude and opposite phase travelling in the same direction in a transmission line. Show me the waves, Cecil. AC6XG |
Analyzing Stub Matching with Reflection Coefficients
On Apr 17, 8:30 am, Cecil Moore wrote:
You said that EM waves cannot be perfectly collinear. Therefore, there has to exist a distance where they diverge and stop interfering. Your words, not mine. You are mistaken. In order to prevent errors of this sort in the future, please quote the words you intend to refer to. ac6xg |
Analyzing Stub Matching with Reflection Coefficients
Cecil Moore wrote:
Gene Fuller wrote: I am impressed! That's a pretty fancy o'scope you got. Measurement of voltages to four significant digits at t = 0 + delta-t is definitely world-class. That 291.4 ohm line is pretty special as well. Your non-technical diversions are noted. How about discussing the technical question that was posed? The voltages can be viewed on an o'scope. Their magnitudes agree with the above calculated magnitudes. Do you know of any reason that those voltages would not obey the rules of the reflection model? When does a reflection coefficient of 0.707 not reflect 0.707 of the incident voltage? The 291.4 ohm line is chosen to make rho=s11=0.707. My "450" ohm ladder-line measures to be actually 380 ohms. Nothing special about 291.4 ohms except that: (291.4-50)/(291.4+50) = 0.707 We could actually design a feedline with Z0 = 291.4 ohms. Want me to show you how? :-) If you don't like that value, use 300 ohms and 51.5 ohms for the coax. I'm sure between the choices of 50 ohm coax and 52 ohm coax, there must be a 51.5 ohm coax in there somewhere. Cecil, You rarely reply directly to anything, and this is no exception. I was commenting on the *actual measurement* that you claimed. You added the emphasis, not me. Perhaps it was a *virtual measurement* instead? Do you find that you can achieve the desired results more often with such measurements? 8-) 73, Gene W4SZ |
Analyzing Stub Matching with Reflection Coefficients
Cecil Moore wrote:
Jim Kelley wrote: Cecil Moore wrote: Jim Kelley wrote: I said it because waves do not, according to the definition of the word, 'act upon one another'. But they can act upon one another, Jim. The Florida State web page says so. The Melles-Groit web page says so. No they don't. If the waves themselves changed, then their resultant superposition would also change. It's a completely unfounded notion, Cecil. Here's an example of that "unfounded notion". Please point out my error. The error is not in the superposition of waves. The error is in your beliefs about the superposition of waves. Let's take the Florida State example that you like. If I recall correctly it illustrates how two waves traveling in the same direction combine and interfere. Now if one of the waves at its peak has an amplitude of 1.0, while at that same instant the other wave has a peak amplitude of -0.5, the resultant wave will have a peak amplitude of 0.5. I hope we agree so far. Now, according to you, this process effects a change on each of the individual waves. If that is so, then please describe each of the waves after they have superposed, and detail the process by which that change took place. Only interactions with matter can alter the characteristics of waves. That's what Maxwells equations tell us. The argument for wave-wave "interaction" is the same as the argument for reflection from virtual impedance discontinuities. ac6xg |
Analyzing Stub Matching with Reflection Coefficients
Richard Harrison wrote: At a short or an open on a line , it is the current or voltage the discontinuity generates which turns the wave around. That is more or less true. But the claim being disputed here is the other way around; that voltages and currents generate discontinuities. If a virtual condition can generate the energy surge or escalation needed for a reversal in direction, it is as acceptable as a real discontinuity, in my opinion. If it can do that it is acceptable as a miracle, in my opinion. :-) 73, Jim AC6XG |
Analyzing Stub Matching with Reflection Coefficients
Cecil Moore wrote:
"No waves are harmed in the process" implies that waves can never be canceled. No. The fact that waves do not have an effect on other waves does not mean that their fields don't superpose. Superposition is a mathematical as well as physical operation. You maintain that the process of adding x to y must somehow change x and y. You insist that superposing x and y means that x effects change to y, and y effects change to x. But the process of superposing x and y does not have an effect on either x or y. The only effect is we now have the algebraic sum of x and y. ac6xg |
Analyzing Stub Matching with Reflection Coefficients
On Apr 17, 12:09 pm, Jim Kelley wrote:
Richard Harrison wrote: At a short or an open on a line , it is the current or voltage the discontinuity generates which turns the wave around. That is more or less true. But the claim being disputed here is the other way around; that voltages and currents generate discontinuities. If a virtual condition can generate the energy surge or escalation needed for a reversal in direction, it is as acceptable as a real discontinuity, in my opinion. If it can do that it is acceptable as a miracle, in my opinion. :-) 73, Jim AC6XG Since it's easy in a lab to set up situations that clearly demonstrate that there is no echo of a transient off a "virtual short" or "virtual open", even if you could show me that miracle, it's not a miracle I could rely on. I'd forever know that I can demonstrate situations where the miracle does not occur. Mind you, if you did show such a miracle, I'd very much want resolution between the line equations based on however far back you want to go toward Maxwell's equations (J. C. Maxwell in this case) and the "newly discovered phenomenon." In my opinion, which probably matches pretty closely with Jim's here, the fundamental line equations I know specifically disallow such a happening; at the very least we'd have to add a nonlinearity to the system. (Imagine a spark gap across the line, set off by voltage over a certain level...) The fundamental line equations have always given me acceptable results when I deal with transmission lines. It's certainly possible that they are flawed, just as Newtonian physics is flawed. But just as we continue to use Newtonian physics in areas where we know we won't be running into, or even close to its "speed of light" or "tiny quanta of energy" limitations, I suspect we'll continue using the fundamental line equations to solve line problems in our real world. Since we have computers to handle the calculations for us easily, it seems to me there's not much reason to OVER-simplify the models we abstract from the real world problems we're trying to solve. I see a lot of value to simplifications that let us visualize problems more clearly. I see a lot of value to modifying, or even throwing out, "classic" equations and models if we move to new ground and discover those classic models fail. But I don't see any value in throwing out details that are easy to let a computer handle for me--in other words, in possibly simplifying a model until it is no longer accurate. Cheers, Tom |
Analyzing Stub Matching with Reflection Coefficients
Gene Fuller wrote:
"Interference is a result from linear superposition. No waves are harmed in the process." Yes. Thomas Young demonstrated the constructive and destructive interference berween two slits of light in 1801. The rest is all commentary. Best regards, Richard Harrison, KB5WZI |
Analyzing Stub Matching with Reflection Coefficients
Alan Peake wrote: Hi Jim, That is more or less true. But the claim being disputed here is the other way around; that voltages and currents generate discontinuities. Actually, the claim was there is reflection from a virtual discontinuity. Almost the same thing? Good point. Let's say it's virtually the same thing. ;-) 73, Jim AC6XG |
Analyzing Stub Matching with Reflection Coefficients
Hi Jim,
That is more or less true. But the claim being disputed here is the other way around; that voltages and currents generate discontinuities. Actually, the claim was there is reflection from a virtual discontinuity. Almost the same thing? I agree that there isn't in the sense that an open 1/4 wave stub looks like a short but the reflections which appear to have come the short actually come from the open end, but how can you introduce a stub without also introducing a physical discontinuity which will give a real reflection (such reflection of course, not being that which would come from a short)? Alan |
Analyzing Stub Matching with Reflection Coefficients
If you get this twice, blame it on the strange behaviour of the
google groups UI. On Apr 16, 8:18 am, Cecil Moore wrote: Keith Dysart wrote: So, out of curiosity, what do you think the outcome of my experiment would be? With an IC-706? I don't know. Others have tried it with varying results. Do 10 cent resistors ever work? Or is a circulator always needed to prevent re-reflections? Your 10 cent resistor can be thought of as a low dB pad of sorts. It will attenuate but not eliminate re-reflection. Remembering that this conversation was about realizing mistakes, it would be highly valuable if you were to 'realize' that you are in error about this. If the generator output impedance is the same as the characteristic impedance of the line, then a wave incident upon the generator is not reflected at all. Zero. With regards to Icom equipment, there is no dispute of the above fact, but rather, there is dispute about whether the output impedance of the transmitter can be characterized. Leaving transmitters aside, it is easy to characterize the output impedance of a generator constructed as a voltage source in series with a resistor. The output impedance is the value of the resistor. Again, let me remind you of Ramo & Whinnery's warning not to attach importance to what is calculated to happen inside an equivalent source. Ramo and Whinnery's warning must be taken seriously but applies only with reference to an equivalent circuit. If the actual circuit is as described, then the caution does not apply. There are models available for virtually any amplifier you might choose but I don't know how those models handle reflections. It is well understood in all the literature how the generator described above handles reflections. If the output impedance is the same as the characteristic impedance, then there is no reflection. This follows from the superposition principle and its application to generators. You have indicated some reluctance to accept this, but I get the feeling you are more convinced by measurement than by theory. So I propose we continue with the experiment so that you can 'realize' that for linear generators, superposition does apply and there is no reflection from a generator whose output impedance is the same as the characteristic impedance of the line. But we need an experiment. I have a slightly better one than previously described that you can easily replicate to convince yourself. This way you do not need to take my word for the results. Begin by creating two files in the same directory with the content included below my signature. Then download and install LTspice from Linear Technology: http://www.linear.com/designtools/so...witchercad.jsp Double click on "TLsuperposition.asc", one of the files previously created. You will see a schematic with 3 transmission lines. The top transmission line, 'bidirectional', has two generators attached to it; one on the left and one on the right. The TL has a 50 Ohm characteristic impedance and the two generators have 50 Ohm output impedances, easily seen from the schematic. The source in the left generator creates a 5 V, 2 MHz sine wave. The source in the right generator creates a 7 V, 3 MHz sine wave. Thus two waves are sent towards each other across the transmission line. The second transmission line is connected to a similar generator on the left but is terminated by a resistor on the right. The third transmission line is connected to a similar generator on the right and terminated by a resistor on the left. If superposition holds, the observed signals at the two ends of the 'bidirectional' line will be sums of the signals at the corresponding ends of the 'left-to-right' and 'right-to-left' line. So click Run to get some observations. Some traces appear. The first 10 microseconds are recorded and displayed. The top pane shows the outputs of the left and right sources. The middle pane shows the signals at the left and right ends of the bidirectional transmission line as well as the sum of the signals at the left end of the l-to-r and r-to-l lines, and the sum of the signals at the right end of the l-to-r and r-to-l lines. Since some of these traces are on top of each other, click on the signal name to bring the desired trace to the top. They are on top of each other because they have the same values, as expected. The third pane shows the difference between the left end of the bidirectional line and the sum of the left end of the other two lines, and the same for the right. Note that the maximum difference is around 500 nanovolts. This is not bad. Theory says it should be zero, but given the limitations of simulation 500 nV is close enough. If this experiment were conducted with real parts, it would be impossible to get that close. So we have run an experiment that demonstrates the results I expected, but results that are not consistent with your contention. So I claim superposition holds at generators as well as loads. Reflections do not occur even when the source is energized. You may like to experiment. Try different frequencies. Try different waveshapes. Try a different length of line. Try different source and terminating resistors. (Just remember that you have to change the appropriate items on both the bidirectional line and the other two for the sums to be correct). So what is the probability that you now 'realize' you were wrong and '10 cent' resistors actually do eliminate reflections. I can not emphasize enough how important this result is to you. It will allow you to use superposition to analyze the behaviour at the generator end and a whole class of problems which you could not previously solve will now be solvable. ....Keith PS - Any questions? Just ask ---- Place the following data into "TLsuperposition.asc" Version 4 SHEET 1 1276 756 WIRE -464 96 -512 96 WIRE 544 96 496 96 WIRE -336 112 -352 112 WIRE -112 112 -128 112 WIRE 128 112 112 112 WIRE 352 112 336 112 WIRE -464 144 -464 96 WIRE -352 144 -352 112 WIRE -352 144 -464 144 WIRE -256 144 -352 144 WIRE -128 144 -128 112 WIRE -128 144 -176 144 WIRE -16 144 -128 144 WIRE 112 144 112 112 WIRE 112 144 80 144 WIRE 224 144 112 144 WIRE 336 144 336 112 WIRE 336 144 304 144 WIRE 496 144 496 96 WIRE 496 144 336 144 WIRE -16 176 -512 176 WIRE 544 176 80 176 WIRE -512 192 -512 176 WIRE 544 192 544 176 WIRE -464 224 -512 224 WIRE -112 240 -128 240 WIRE 128 240 112 240 WIRE -464 272 -464 224 WIRE -256 272 -464 272 WIRE -128 272 -128 240 WIRE -128 272 -176 272 WIRE -16 272 -128 272 WIRE 112 272 112 240 WIRE 112 272 80 272 WIRE 224 272 112 272 WIRE 336 272 304 272 WIRE -16 304 -512 304 WIRE 336 304 336 272 WIRE 336 304 80 304 WIRE -512 320 -512 304 WIRE 336 320 336 304 WIRE 544 352 496 352 WIRE -112 368 -128 368 WIRE 128 368 112 368 WIRE -256 400 -288 400 WIRE -128 400 -128 368 WIRE -128 400 -176 400 WIRE -16 400 -128 400 WIRE 112 400 112 368 WIRE 112 400 80 400 WIRE 224 400 112 400 WIRE 496 400 496 352 WIRE 496 400 304 400 WIRE -288 432 -288 400 WIRE -16 432 -288 432 WIRE 544 432 80 432 WIRE -288 448 -288 432 WIRE 544 448 544 432 FLAG -512 192 0 FLAG -112 112 Vleft FLAG 128 112 Vright FLAG 352 112 VsrcR FLAG -336 112 VsrcL FLAG -288 448 0 FLAG -112 368 VloadR FLAG -112 240 VgenL FLAG 128 240 VloadL FLAG 544 192 0 FLAG 336 320 0 FLAG 544 448 0 FLAG -512 320 0 FLAG 128 368 VgenR SYMBOL voltage -512 80 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 0 35 41 Left 0 WINDOW 3 24 115 Left 0 SYMATTR InstName VbidirL SYMATTR Value SINE(0 5 2e6) SYMBOL voltage 544 80 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 0 36 55 Left 0 WINDOW 3 9 99 Left 0 SYMATTR InstName VbidirR SYMATTR Value SINE(0 7 3e6) SYMBOL tline 32 160 R0 WINDOW 0 -32 -35 Left 0 WINDOW 3 -78 34 Left 0 SYMATTR InstName Tbidir SYMATTR Value Td=1.1e-6 Z0=50 SYMBOL res 320 128 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 19 86 VTop 0 SYMATTR InstName Rright SYMATTR Value 50 SYMBOL res -272 160 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 11 28 VBottom 0 SYMATTR InstName Rleft SYMATTR Value 50 SYMBOL tline 32 288 R0 WINDOW 0 -23 -34 Left 0 WINDOW 3 -95 35 Left 0 SYMATTR InstName Tltor SYMATTR Value Td=1.1e-6 Z0=50 SYMBOL tline 32 416 M0 WINDOW 0 -25 -36 Left 0 WINDOW 3 -92 38 Left 0 SYMATTR InstName Trtol SYMATTR Value Td=1.1e-6 Z0=50 SYMBOL res -272 288 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 12 26 VBottom 0 SYMATTR InstName RgenL SYMATTR Value 50 SYMBOL res 320 384 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 18 86 VTop 0 SYMATTR InstName RgenR SYMATTR Value 50 SYMBOL res 208 288 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 12 25 VBottom 0 SYMATTR InstName RloadL SYMATTR Value 50 SYMBOL res -160 384 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 19 83 VTop 0 SYMATTR InstName RloadR SYMATTR Value 50 SYMBOL voltage 544 336 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 0 36 55 Left 0 WINDOW 3 7 99 Left 0 SYMATTR InstName VsrcR SYMATTR Value SINE(0 7 3e6) SYMBOL voltage -512 208 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 0 35 41 Left 0 WINDOW 3 24 115 Left 0 SYMATTR InstName VsrcL SYMATTR Value SINE(0 5 2e6) TEXT -496 416 Left 0 !.tran 10e-6 ---- The above line was the last one to go into "TLsuperposition.asc" ---- Place the following data into "TLsuperposition.plt" [Transient Analysis] { Npanes: 3 Active Pane: 2 { traces: 2 {524296,0,"V(vleft)-(V(vgenl)+V(vloadr))"} {524294,0,"V(vright)-(V(vgenr)+V(vloadl))"} X: ('µ',0,0,1e-006,1e-005) Y[0]: ('n',0,-5.4e-007,9e-008,4.5e-007) Y[1]: ('_',0,1e+308,0,-1e+308) Volts: ('n',0,0,0,-5.4e-007,9e-008,4.5e-007) Log: 0 0 0 }, { traces: 4 {268959756,0,"V(vleft)"} {268959751,0,"V(vright)"} {524291,0,"V(vgenl)+V(vloadr)"} {524292,0,"V(vgenr)+V(vloadl)"} X: ('µ',0,0,1e-006,1e-005) Y[0]: (' ',0,-6,1,6) Y[1]: ('n',0,1e+308,2e-009,-1e+308) Volts: (' ',0,0,0,-6,1,6) Log: 0 0 0 }, { traces: 2 {524293,0,"V(vsrcl)"} {524290,0,"V(vsrcr)"} X: ('µ',0,0,1e-006,1e-005) Y[0]: (' ',0,-7,1,7) Y[1]: ('_',0,1e+308,0,-1e+308) Volts: (' ',0,0,0,-7,1,7) Log: 0 0 0 } } ---- The above line was the last one to go into "TLsuperposition.plt" Now what is the chance that this makes it all through without any carriage return and line feed issues? I suppose I get to try when it comes back. |
Analyzing Stub Matching with Reflection Coefficients
On 17 Apr 2007 20:04:26 -0700, Keith Dysart wrote:
PS - Any questions? Just ask SPICE Error: Trtol: transmission line Z0 must be given Circuit: * D:\Program Files\LTC\SwCADIII\examples\newsgroup\TLsuperposit ion.asc Error on line 4 : tbidir vleft 0 vright 0 td=3d1.1e-6 z0=3d50 Unknown parameter "-6" Error on line 7 : tltor vgenl 0 vloadl 0 td=3d1.1e-6 z0=3d50 Unknown parameter "-6" Error on line 8 : trtol vgenr 0 vloadr 0 td=3d1.1e-6 z0=3d50 Unknown parameter "-6" Fatal Error: Trtol: transmission line Z0 must be given 73's Richard Clark, KB7QHC |
Analyzing Stub Matching with Reflection Coefficients
On Apr 17, 11:33 pm, Richard Clark wrote:
On 17 Apr 2007 20:04:26 -0700, Keith Dysart wrote: PS - Any questions? Just ask SPICE Error: Trtol: transmission line Z0 must be given Circuit: * D:\Program Files\LTC\SwCADIII\examples\newsgroup\TLsuperposit ion.asc Error on line 4 : tbidir vleft 0 vright 0 td=3d1.1e-6 z0=3d50 Unknown parameter "-6" Error on line 7 : tltor vgenl 0 vloadl 0 td=3d1.1e-6 z0=3d50 Unknown parameter "-6" Error on line 8 : trtol vgenr 0 vloadr 0 td=3d1.1e-6 z0=3d50 Unknown parameter "-6" Fatal Error: Trtol: transmission line Z0 must be given 73's Richard Clark, KB7QHC Ouch. In TLsuperposition.asc, there are three lines that define the transmission lines: SYMATTR Value Td=1.1e-6 Z0=50 SYMATTR Value Td=1.1e-6 Z0=50 SYMATTR Value Td=1.1e-6 Z0=50 Looks to me like whatever technique you used to save the file substituted '=3d' for '='. '3d' is the ascii encoding for '=' so maybe '=' is treated specially. Since these are the only '='s in the file, perhaps manually editting the '3d's out will fix the problem. What tools did you use to recover and save the text? ....Keith |
Analyzing Stub Matching with Reflection Coefficients
Jim Kelley wrote:
I asked you to show me the two waves of equal magnitude and opposite phase travelling in the same direction in a transmission line. Show me the waves, Cecil. b1 = s11(a1) + s12(a2) = 0 -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
Jim Kelley wrote:
In order to prevent errors of this sort in the future, please quote the words you intend to refer to. You have absolutely refused to extend that courtesy to me so no, not until you do the same. If waves don't diverge somewhere out there, your argument is wrong. If they do diverge somewhere out there, they cease to superpose. You cannot have it both ways. -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
Gene Fuller wrote:
You rarely reply directly to anything, and this is no exception. I was commenting on the *actual measurement* that you claimed. Uhhhh Gene, actual measurements are made to ascertain the s-parameters. Shirley, you should know that. -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
Jim Kelley wrote:
Only interactions with matter can alter the characteristics of waves. I'm not sure what that means. Are the reflections at an impedance discontinuity "interactions with matter"? If so, I don't disagree. -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
Jim Kelley wrote:
Superposition is a mathematical as well as physical operation. You maintain that the process of adding x to y must somehow change x and y. Absolutely false, Jim. Please produce my posting that said that superposition of x and Y *must* somehow change x and y. I have said just the opposite. -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
Keith Dysart wrote:
If the generator output impedance is the same as the characteristic impedance of the line, then a wave incident upon the generator is not reflected at all. Zero. Sorry, that statement is theoretical and has been proved untrue for real-world generators unless heroic measures are taken, e.g. circulators. With regards to Icom equipment, there is no dispute of the above fact, but rather, there is dispute about whether the output impedance of the transmitter can be characterized. Yes, real world generators have a habit of not abiding by theory. Ramo and Whinnery's warning must be taken seriously but applies only with reference to an equivalent circuit. If the actual circuit is as described, then the caution does not apply. But Keith, you have *never* described an actual circuit. All you have described are equivalent circuits. What tube do you use? What transistor do you use? What tank circuit do you use? What load line do you use? Where the heck is your schematic? It is well understood in all the literature how the generator described above handles reflections. Please give us a schematic of the described generator. -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
On Apr 18, 1:35 am, Cecil Moore wrote:
Keith Dysart wrote: If the generator output impedance is the same as the characteristic impedance of the line, then a wave incident upon the generator is not reflected at all. Zero. Sorry, that statement is theoretical and has been proved untrue for real-world generators unless heroic measures are taken, e.g. circulators. With regards to Icom equipment, there is no dispute of the above fact, but rather, there is dispute about whether the output impedance of the transmitter can be characterized. Yes, real world generators have a habit of not abiding by theory. Ramo and Whinnery's warning must be taken seriously but applies only with reference to an equivalent circuit. If the actual circuit is as described, then the caution does not apply. But Keith, you have *never* described an actual circuit. All you have described are equivalent circuits. What tube do you use? What transistor do you use? What tank circuit do you use? What load line do you use? Where the heck is your schematic? It is well understood in all the literature how the generator described above handles reflections. Please give us a schematic of the described generator. -- 73, Cecil http://www.w5dxp.com The person who desires to not realize can always build road blocks to prevent realization. So sad. ....Keith |
Analyzing Stub Matching with Reflection Coefficients
On Apr 17, 11:55 am, Jim Kelley wrote:
On Apr 16, 9:20 pm, Cecil Moore wrote: Do you believe Jim's argument that two coherent EM waves of equal magnitudes and opposite phases traveling collinearly in the same direction in a transmission line can never be canceled? I asked you to show me the two waves of equal magnitude and opposite phase travelling in the same direction in a transmission line. Show me the waves, Cecil. May I offer an example for Cecil. Two signal generators, each with an output (source) impedance of 50 Ohms, each connected to 0.25 wavelength of 50 Ohm line. Let us call them North and South with their output lines heading towards each other. The two output lines are connected in parallel to a 3rd 50 Ohm line heading east that is 0.5 wavelengths long terminated in 50 Ohms. The generators are constructed in the Thevenin style with a very low impedance voltage source connected in series with a 50 Ohm resistor. Turn on the voltage source in the North generator. The wave leaves the generator, arriving at the joint 0.25 cycles later. Some of this wave is reflected and for the wave that goes through, half of it goes east towards the load and reaches the load 0.5 cycles later, while the other half continues south towards the South generator which it reaches 0.25 cycles after reaching the joint. Since everything is terminated in 50 Ohms, there are no reflections and the system is in steady state 0.75 cycles after the North voltage source is turned on. Turn on the South voltage source which, for interest, is 180 degrees out of phase with the North. Heading towards the joint is a new wave which, when it reaches the joint, some is reflected and the rest goes through splitting between north and east. The east wave is 180 degrees out of phase with the pre-existing wave from the North generator and cancels completely on the East line. The other half of the wave from the South generator heads north where it reaches the North generator after 0.25 cycles. Again, since all lines are terminated in 50 Ohms, there are no reflections. 0.75 cycles after the South source is turned on there is no energy left in the East line. Where did it go? Drained by load, it was. 0.5 cycles after the South source is turned on, the North generator stops supplying energy to the line because the voltage wave from the South is in phase with output from the North and no current flows. 0.5 cycles after the South source is turned on, it stops supplying energy to the line since the orignal wave from the north plus the reflection from the joint is always equal to the source voltage so no current flows. 0.75 cycles after the South source is turned on, the system is in steady state. The last thing that happens is that energy finishes draining from the East line. So it appears that two waves in the line going east are 180 degrees out of phase and cancelling. Call this Explanation A. Let us do the experiment in a slightly different order... Connect only the lines going north and south, leave the line going east disconnected. Turn on the two sources and let the system stabilize. At the joint between north and south will be voltage null where the voltage is always 0. Now connect the east line to this voltage null. Since there is 0 voltage here, there will be no waves sent down the line so there can not be any cancellation. Call this Explanation B. |
Analyzing Stub Matching with Reflection Coefficients
Keith Dysart wrote:
The person who desires to not realize can always build road blocks to prevent realization. e.g. like refusing to provide a schematic for the source. :-) -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
Keith Dysart wrote:
Some may argue that a perfect generator can not be constructed, but really that is a matter of cash; with enough cash one can construct a generator that is arbitrarily close to perfect. But bears no resemblance to the average amateur radio transmitter. The *goal* is to explain what happens with the average amateur radio transmitter. We already have signal generators with circulator loads that will do what you are trying to do. So why bother trying to reinvent the wheel? -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
On Apr 18, 8:45 am, Cecil Moore wrote:
Keith Dysart wrote: The person who desires to not realize can always build road blocks to prevent realization. e.g. like refusing to provide a schematic for the source. :-) -- 73, Cecil http://www.w5dxp.com So sad Cecil. If you had just popped open LTspice, you would have seen the schematic under consideration. But when you don't want to take a chance on learning, you can refuse to jump over the bar no matter how low it is, claiming it is too high. So sad. ....Keith |
Analyzing Stub Matching with Reflection Coefficients
Keith Dysart wrote:
Cecil Moore wrote: Keith Dysart wrote: The person who desires to not realize can always build road blocks to prevent realization. e.g. like refusing to provide a schematic for the source. :-) So sad Cecil. If you had just popped open LTspice, you would have seen the schematic under consideration. I may have missed it, but to the best of my knowledge, this is the first time you have mentioned the LTspice reference. I apologize but I'm retired without access to spice. Is that schematic available anywhere on the web? If not, how about emailing me a .jpg copy of it? -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
On Apr 18, 8:57 am, Cecil Moore wrote:
Keith Dysart wrote: Some may argue that a perfect generator can not be constructed, but really that is a matter of cash; with enough cash one can construct a generator that is arbitrarily close to perfect. But bears no resemblance to the average amateur radio transmitter. The *goal* is to explain what happens with the average amateur radio transmitter. We already have signal generators with circulator loads that will do what you are trying to do. So why bother trying to reinvent the wheel? You give yourself the perfect out, don't you. You won't study the simple circuits that can be understand (for which, by the way a circulator is not required, thus indicating that you do not yet understand them) because they are not complicated enough to represent an average amateur radio transmitter, and you can't study an average amateur radio transmitter because it is too complicated to be understood. Conclusion: No need to study. Life is good. No need to understand. So sad. ....Keith |
Analyzing Stub Matching with Reflection Coefficients
Keith Dysart wrote:
You give yourself the perfect out, don't you. You won't study the simple circuits that can be understand (for which, by the way a circulator is not required, thus indicating that you do not yet understand them) because they are not complicated enough to represent an average amateur radio transmitter, and you can't study an average amateur radio transmitter because it is too complicated to be understood. I'm willing to study them if you will only send me a schematic. But I'm not going to waste a lot of time on something that is of very limited usefulness. We already have a model that will eliminate reflections, i.e. a signal generator equipped with a circulator, but we don't use such for amateur radio transmitters. Why invent something else that we don't use for amateur radio transmitters? Why not choose an actual amateur radio transmitter to try to understand what happens with amateur radio transmitters? That seems like a no-brainer to me. -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
On Apr 18, 9:52 am, Cecil Moore wrote:
Keith Dysart wrote: You give yourself the perfect out, don't you. You won't study the simple circuits that can be understand (for which, by the way a circulator is not required, thus indicating that you do not yet understand them) because they are not complicated enough to represent an average amateur radio transmitter, and you can't study an average amateur radio transmitter because it is too complicated to be understood. I'm willing to study them if you will only send me a schematic. But I'm not going to waste a lot of time on something that is of very limited usefulness. We already have a model that will eliminate reflections, i.e. a signal generator equipped with a circulator, but we don't use such for amateur radio transmitters. Why invent something else that we don't use for amateur radio transmitters? Why not choose an actual amateur radio transmitter to try to understand what happens with amateur radio transmitters? That seems like a no-brainer to me. Why? You say. Because if one does not understand how the simple circuits behave, there is no hope for understanding how something as complex as an amateur radio transmitter behaves. Amateur transmitters do not have circulators. If you don't have the tools to figure out what happens when a wave is incident on the simplest of generators (an ideal voltage source in series with a resistor), there is no way you can figure it out for a more complicated transmitter. Start simple, then extend. To learn what happens with the simplest of generators, look in any textbook on the subject or google '"lattice diagram" reflection'. The LTspice simulation I previously offerred can be used to confirm the results of analysis. ....Keith PS - The schematic for the generator is as described above. They are connected to each end of a transmission line as described in a previous post. Compute how much of the incident wave is reflected at each end. Choose any frequency, line length, voltage and waveshape you find convenient for the generators. |
Analyzing Stub Matching with Reflection Coefficients
Keith Dysart wrote:
Start simple, then extend. I'm not stopping you from doing that. Please feel free to post whatever you choose to post. -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
On Apr 18, 11:27 am, Cecil Moore wrote:
Keith Dysart wrote: Start simple, then extend. I'm not stopping you from doing that. Please feel free to post whatever you choose to post. It is unfortunate, but you are back where you started; choosing not to learn. Opportunity squandered. ....Keith PS - If you change your mind, do feel free to ask. |
Analyzing Stub Matching with Reflection Coefficients
On Apr 18, 5:40 am, Keith Dysart wrote:
,,, Of course the same holds for the ideal transmission lines and the terminators. The lack of absolute perfection does not obviate the value of the thought experiment for furthering understanding. Actually, Keith, one of the beauties of your proposed experiment is that the line connecting the generators does NOT have to be lossless. It need only be uniform. The N-S section does not even have to be exactly 1/2 wave long; it just needs to be tapped in the center. The E-W section can be virtually any length, and it doesn't even have to have the same impedance or loss characteristics as the N-S section. The generators can be a far cry from perfect; they could just as well be ideal voltage sources, or ideal current sources, or even ICOM transmitters; they just need to be the same, and have some way to be driven out-of-phase. Using line with loss results in the sources having to deliver a small amount of power, of course, and having the N- S section differ slightly from 1/2 wavelength just means that the sources will see a slightly reactive load. And of course, the value of your experiment is what goes on in the lines, and has nothing to do with the sources driving them. It's a beautifully simple experiment that can be produced easily on the bench, or in a simulator (like the free LTSpice or even RFSim99). Thanks for offering it, Keith. Cheers, Tom Still waiting for someone to send me an ICOM 706 or whatever that was so I can measure the source impedance seen at the output terminals while it's delivering its nominally rated power to the recommended load... |
Analyzing Stub Matching with Reflection Coefficients
Keith Dysart wrote:
It is unfortunate, but you are back where you started; choosing not to learn. Opportunity squandered. Sorry Keith, From your already lengthy postings, I simply don't perceive that you have anything new to offer, at least not to me now in my 8th decade. But I could be wrong, as could you, so please proceed. -- 73, Cecil http://www.w5dxp.com |
Analyzing Stub Matching with Reflection Coefficients
Cecil Moore wrote:
Jim Kelley wrote: Superposition is a mathematical as well as physical operation. You maintain that the process of adding x to y must somehow change x and y. Absolutely false, Jim. Please produce my posting that said that superposition of x and Y *must* somehow change x and y. I'm sorry. I must have misunderstood what you meant when you angrily insisted that waves interact. Must be one of those semantics things again. I know. Let's agree on a definition. How about the one in Merriam Websters Collegiate Dictionary, Tenth Edition: interact: to act upon one another I have said just the opposite. I must admit to not having seen that post. On the other hand I do recall seeing some where you ruthlessly insulted other people who maintained that position. I believe those are still on Google groups if you'd like to have a look back. 73, Jim AC6XG |
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