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Computer model experiment
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Computer model experiment
"tom" wrote in message t... On 5/10/2010 3:12 PM, wrote: As Clint said in the wonderful old movie, "A man's gotta know his limits". For antenna modelers it should read, "A man's gotta know the program's limits". Of course, Art thinks things have changed and the computer modelers have a better grasp upon reality than the ones even he calls "the masters". He is an example of the blind man leading himself. tom K0TAR The computer program should know its limits. Anytine a program allows the data entered to be too large or small for the calculations, it should be flagged as being out of range. Also many computer programs will use simplified formulars that can mast the true outcome. Usually it is not very much, but as all errors start to add up the end results may be way off. I often enter data that I know will be difficult for programs to use. If the program gives an answer then I usually don't use that program expecting a exect answer. Back in the Windows 3.1 and 3.11 days the simple calculator would give wrong answers to simple problems. I think if you entered 3.11 and subtracted 3.1 from it you got the wrong answer. That program was not corrected by Microsoft. |
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Computer model experiment
On 5/10/2010 9:34 PM, Ralph Mowery wrote:
The computer program should know its limits. Anytine a program allows the data entered to be too large or small for the calculations, it should be flagged as being out of range. Also many computer programs will use simplified formulars that can mast the true outcome. Usually it is not very much, but as all errors start to add up the end results may be way off. I often enter data that I know will be difficult for programs to use. If the program gives an answer then I usually don't use that program expecting a exect answer. Back in the Windows 3.1 and 3.11 days the simple calculator would give wrong answers to simple problems. I think if you entered 3.11 and subtracted 3.1 from it you got the wrong answer. That program was not corrected by Microsoft. I disagree. The program cannot "know" its limits if the problem it's modeling is complex enough. So the user must understand the program and especially the math related to what the program is modeling. Blaming the program for giving you the "wrong" answer is like blaming the tires for hitting the guard rail because you exceeded their limits. Those limits are not the same under varying conditions and must be filtered by experience and understanding. tom K0TAR |
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Computer model experiment
On May 10, 7:45*pm, tom wrote:
On 5/10/2010 9:34 PM, Ralph Mowery wrote: The computer program should know its limits. *Anytine a program allows the data entered to be too large or small for the calculations, it should be flagged as being out of range. *Also many computer programs will use simplified formulars that can mast the true outcome. *Usually it is not very much, but as all errors start to add up the end results may be way off. I often enter data that I know will be difficult for programs to use. *If the program gives an answer then I usually don't use that program expecting a exect answer. Back in the Windows 3.1 and 3.11 days the simple calculator would give wrong answers to simple problems. *I think if you entered 3.11 and subtracted 3.1 from it you got the wrong answer. *That program was not corrected by Microsoft. I disagree. *The program cannot "know" its limits if the problem it's modeling is complex enough. *So the user must understand the program and especially the math related to what the program is modeling. Blaming the program for giving you the "wrong" answer is like blaming the tires for hitting the guard rail because you exceeded their limits. * Those limits are not the same under varying conditions and must be filtered by experience and understanding. tom K0TAR I've found it in my best interest to check the consistency of results in various ways, whenever I can. Often there's more than one way to think about a problem, and if the answers I get differ, I want to know why. Until I can resolve the differences, I distrust both (or all...) answers. I also like to have an idea about the tolerance on the answers, and many programs (and formulas you use to calculate answers for yourself) don't give much of a clue about the tolerance. Some are "exact," and some should be considered only approximations, but often they don't bother to tell you which. One example is formulas for calculating the impedance of TEM transmission lines; it's common to see, for air-dielectric two-wire line, Z0=276*log10(2D/d), but this is an approximation whose error becomes significant as d approaches D. Even the better formula, Z0=120invcosh(D/d), is not exact: the 120 isn't exactly correct, there's no consideration of finite conductor resistance (and resulting skin depth), and there's no consideration of the atmospheric pressure and relative humidity... I mostly agree with Tom: don't expect the program, or formula, to know how you are going to misapply it. Try to be aware of what the answers you get imply. Learn the limits of your tools (programs; formulas), and apply them wisely so they will serve you well. Do I get stung by my own foolishness in not paying proper attention to things like this? You bet I do! Just last night, I entered a coil into the Hamwaves inductance calculator and it was happy to give me an answer. The coil? Ten turns of 1mm wire in a coil 10mm diameter and 10mm long... Duh, that's a 1mm winding pitch and the turns will short together. I didn't think to check that at first. The calculator complains and won't give you an answer if the pitch is less than the wire diameter, but not if it's just equal. Considering the same very useful inductance calculator, I've learned to ignore the answer for the effective shunt stray capacitance: it in general doesn't come close to matching the value calculated from the self-resonance and the inductance. To see what I mean, try entering D=10mm, N=10, len.=20mm, d=1mm, and check what C(L,p) is reported. Now try changing D in 1mm increments up and down. OK, so I don't trust the reported C(L,p) value, but because I've checked several cases of all the other reported values against measurements of actual coils and against one or two other programs I use, I've learned to trust those other reported values, within some tolerance (that's a lot looser than the reported precision in the calculator!). -- I don't mean to pick on that inductance calculator, just to use it to illustrate what applies to pretty much all calculation programs and formulas. Cheers, Tom |
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Computer model experiment
On May 12, 12:58*pm, K7ITM wrote:
.... To see what I mean, try entering D=10mm, N=10, len.=20mm, d=1mm, and check what C(L,p) is reported. *Now try changing D in 1mm increments up and down. *OK, so I don't trust the reported C(L,p) value, ... OK, it also helps to RTFM. The text down below the inductance calculator explains about this some. Also, I should have said that you need to set the "design frequency" to something low (e.g. 10MHz) to see the effect. However, the text suggests that C(L,p) value would be larger than expected...and I've also seen it for some coils to be considerably smaller. So I end up, then, not finding the lumped model including C(L,p) being very useful for the things I do, where I want a model that gives me _decent_ agreement over a broader frequency range, rather than perhaps more exact agreement over a very limited frequency range (as happens when the reported value of C(L,p) gets very large; try "design frequency" = 1MHz for that coil). Cheers, Tom |
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Computer model experiment
On May 12, 3:16*pm, K7ITM wrote:
On May 12, 12:58*pm, K7ITM wrote: ... To see what I mean, try entering D=10mm, N=10, len.=20mm, d=1mm, and check what C(L,p) is reported. *Now try changing D in 1mm increments up and down. *OK, so I don't trust the reported C(L,p) value, ... OK, it also helps to RTFM. *The text down below the inductance calculator explains about this some. *Also, I should have said that you need to set the "design frequency" to something low (e.g. 10MHz) to see the effect. *However, the text suggests that C(L,p) value would be larger than expected...and I've also seen it for some coils to be considerably smaller. *So I end up, then, not finding the lumped model including C(L,p) being very useful for the things I do, where I want a model that gives me _decent_ agreement over a broader frequency range, rather than perhaps more exact agreement over a very limited frequency range (as happens when the reported value of C(L,p) gets very large; try "design frequency" = 1MHz for that coil). Cheers, Tom Remember, I have always specified that one does not go beyond the units supplied by Maxwell, Maxwell did not use lumped loads. It is stipulated that equilibrium is paramount as soon as you see the "=" sign. Thus I can say I am persueing exactnes or accuracy and not fudging.It was when Maxwell followed the edict of the "equal" sign that he was forced to add the particle elevation vector by the addition of displacement current even tho he could not describe the addition. To him it was a mathematical equation and nothing else and without explanation of the process. Art |
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Computer model experiment
On May 12, 3:16*pm, K7ITM wrote:
On May 12, 12:58*pm, K7ITM wrote: ... To see what I mean, try entering D=10mm, N=10, len.=20mm, d=1mm, and check what C(L,p) is reported. *Now try changing D in 1mm increments up and down. *OK, so I don't trust the reported C(L,p) value, ... OK, it also helps to RTFM. *The text down below the inductance calculator explains about this some. *Also, I should have said that you need to set the "design frequency" to something low (e.g. 10MHz) to see the effect. *However, the text suggests that C(L,p) value would be larger than expected...and I've also seen it for some coils to be considerably smaller. *So I end up, then, not finding the lumped model including C(L,p) being very useful for the things I do, where I want a model that gives me _decent_ agreement over a broader frequency range, rather than perhaps more exact agreement over a very limited frequency range (as happens when the reported value of C(L,p) gets very large; try "design frequency" = 1MHz for that coil). Cheers, Tom Again I state. If you are using Maxwell equations you cannot stray from the units supplied.Hams do not follow the rules with respect to antennas so approximations are literally garranteed. Using Maxwells equations alone you have the presence of point radiation. With a single point radiation the rules of physics state that radiation limits is in the form of a sphere. If one states you cannot have a sphere of radiation they are breaking all the laws of physics and I certainly had no part in the making of the rules. Regards Art |
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Computer model experiment
On May 12, 4:49*pm, Art Unwin wrote:
On May 12, 3:16*pm, K7ITM wrote: On May 12, 12:58*pm, K7ITM wrote: ... To see what I mean, try entering D=10mm, N=10, len.=20mm, d=1mm, and check what C(L,p) is reported. *Now try changing D in 1mm increments up and down. *OK, so I don't trust the reported C(L,p) value, ... OK, it also helps to RTFM. *The text down below the inductance calculator explains about this some. *Also, I should have said that you need to set the "design frequency" to something low (e.g. 10MHz) to see the effect. *However, the text suggests that C(L,p) value would be larger than expected...and I've also seen it for some coils to be considerably smaller. *So I end up, then, not finding the lumped model including C(L,p) being very useful for the things I do, where I want a model that gives me _decent_ agreement over a broader frequency range, rather than perhaps more exact agreement over a very limited frequency range (as happens when the reported value of C(L,p) gets very large; try "design frequency" = 1MHz for that coil). Cheers, Tom Again I state. *If you are using Maxwell *equations you cannot stray from the units supplied.Hams do not follow the rules with respect to antennas so approximations are literally garranteed. Using Maxwells equations alone you have the presence of point radiation. With a single point radiation the rules of physics state that radiation limits is in the form of a sphere. If one states you cannot have a sphere of radiation they are breaking all the laws of physics and I certainly had no part in the making of the rules. Regards Art- Hide quoted text - - Show quoted text - you can have a spherically symetric static electric field as is easily shown by gauss's law. but in order to have 'radiation' (implying em wave propagating through space) you must have movement of some kind, that immediately removes the spherical symetry by creating an axis defined by the direction of movement. this is why even the theoretical infinitesimal dipole still produces a doughnut shaped field in free space. |
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Computer model experiment
On May 12, 3:49*pm, Art Unwin wrote:
Again I state. *If you are using Maxwell *equations you cannot stray from the units supplied.Hams do not follow the rules with respect to antennas so approximations are literally garranteed. Maybe this is good.. I have noticed my antennas tend to actually work as radiators of RF, where as most of yours seem to prefer to turn it to heat. :/ I think Maxwell must be taking you for a big ride. I bet he's up there is the land of the big RF just laughing his head off at all this silly jibber jabber you keep blaming him for. Using Maxwells equations alone you have the presence of point radiation. With a single point radiation the rules of physics state that radiation limits is in the form of a sphere. If one states you cannot have a sphere of radiation they are breaking all the laws of physics and I certainly had no part in the making of the rules. Regards Art How many cases of a single point of radiation have you seen in the real world, using real world antennas? This is not a trick question. |
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Computer model experiment
On 5/12/2010 3:49 PM, Art Unwin wrote:
Again I state. If you are using Maxwell equations you cannot stray from the units supplied.Hams do not follow the rules with respect "stray from the units"? How can one stray? All the units we are talking about here are freely convertible. Is this now religion? tom K0TAR |
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