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On Sat, 20 May 2006 17:39:44 GMT, "Tom Donaly"
wrote: Cecil thinks your simplified ideas are received wisdom. Hi Tom, Is there some suggestion of smoldering bush in this parable? Commandments that are unzipped and ready for immediate entablature? 73's Richard Clark, KB7QHC |
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Cecil Moore wrote:
Reg Edwards wrote: I suppose, Cecil, that if you keep repeating the same old tired line, over and over again, you might find someone who will agree with you. I agreed with Cecil the first time he said it. But I'm only a foreigner. So whatever I say doesn't carry any weight. Or does it? I dug out my linear network theory book and would like to present a few quotes and comments: "The real world is inherently non-linear." Lightning hitting an antenna can cause arcing and melted wires. "Although nature is non-linear, linear approximations over defined ranges of validity are valid representations of non-linear phenomena." Amateur radio antennas are usually confined to that limited linear range. "The necessary and sufficient conditions for a linear system a (1) validity of the principle of superposition; (2) preservation of scale factor. Does doubling the power input to the antenna ~double the radiated power? Does it ~double the non-radiated losses? "Fortunately for the engineer, however, linear systems are frequently excellent approximations to reality and have a wide range of validity in the real world." Maxwell's equations in particular. Textbook equations for traveling waves and standing waves assume linearity. You can still pretend a dipole is a "linear system," as you call it, and still understand that the current envelope is not a simple sine function. The Achilles heel of all your reflection mechanics ideas is the assumption that everything is lossless. (Not to mention the fact that it's supposed to exist in outer space.) You and Reg like to think of a dipole as a transmission line, and Reg can even tell you its characteristic impedance (average). What neither he nor you ever mention is the alpha part of the propagation constant. That's the important part, though, since it signifies radiation, the very thing the antenna was designed to do. By the way, why are you quoting from a network theory book when not too long ago you were ranting and raving about the invalidity of the lumped constant model? 73, Tom Donaly, KA6RUH |
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"Richard Clark" wrote in message ... On Sat, 20 May 2006 12:14:29 -0000, "Dave" wrote: KEEP IT GOING! Dave, your trolling effort is rather a poor substitute for the sense of accomplishment. Too many do it far better, with more flair, and offer more entertainment than this pallid use of the CAPS KEYS. I'm just cheering you on... besides if I'm going to troll I might as well abandon some other parts of decency in the process. And it doesn't seem like anyone cares, even with the obvious thread title it took off all on its own. |
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Tom Donaly wrote:
You can still pretend a dipole is a "linear system," as you call it, and still understand that the current envelope is not a simple sine function. Diverting to a "simple" sine function in the same spirit as diverting to a "small" loading coil? If you were always talking about a perfect sine wave, you should have said so long before now and nobody would have disagreed with you. The Achilles heel of all your reflection mechanics ideas is the assumption that everything is lossless. That's NOT the assumption. The assumption is that lossless systems are easiest to understand so let's understand them first before we move on to something more complex. You guys have proven that you don't even understand the simple lossless condition. (Not to mention the fact that it's supposed to exist in outer space.) You and Reg like to think of a dipole as a transmission line, and Reg can even tell you its characteristic impedance (average). What neither he nor you ever mention is the alpha part of the propagation constant. That's the important part, though, since it signifies radiation, the very thing the antenna was designed to do. Only about 1 dB of the steady-state energy stored in a 1/2WL dipole is radiated so radiation is not the largest effect. The radiation from an antenna can be simulated by using resistance wire to simulate a 1 dB loss in a transmission line. The reason that I have rarely mentioned such is that you guys don't understand enough of the basics to proceed to those more complex examples. By the way, why are you quoting from a network theory book when not too long ago you were ranting and raving about the invalidity of the lumped constant model? The lumped constant model is valid under certain conditions. What I object to is its use under known invalid conditions. The lumped constant model and distributed network model are both *linear systems*. -- 73, Cecil http://www.qsl.net/w5dxp |
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Richard Clark wrote:
On Sat, 20 May 2006 17:39:44 GMT, "Tom Donaly" wrote: Cecil thinks your simplified ideas are received wisdom. Hi Tom, Is there some suggestion of smoldering bush in this parable? Commandments that are unzipped and ready for immediate entablature? 73's Richard Clark, KB7QHC Hi Richard, Yes, but there's some evidence Cecil is about to apostatize. I hope he doesn't end up wandering in the wilderness. 73, Tom Donaly, KA6RUH |
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Richard Harrison wrote:
Richard Clark, KB7QHC wrote: "Who. in your estimation, does qualify to discuss it?" If it`s about antennas, I nominate Kraus. If it`s about mathematics, many marhematicians qualify. In algebra, y = mx + b, (the point slope formula), is called linear because it is the graph of a straight line. . . . But of course you realize that the function y = mx + b doesn't meet the requirements of a linear function when applied to network theory. Roy Lewallen, W7EL |
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Richard Harrison wrote:
Cecil, W5DXP wrote: "Assuming the source signal is a pure sine wave, if the standing wave current "isn`t in general sinusoidally shaped (as Roy said)", then the antenna would have to be introducing harmonic radiation that doesn`t exist in the source signal." . . . Either Cecil is misquoting me, or Richard is misquoting Cecil. Cecil calls the total current the "standing wave current". I never said that the standing wave current isn't sinusoidally shaped. I said that the *envelope* of the standing wave -- that is, a graph of the magnitude of the current on a transmission line as a function of position along the line -- is not sinusoidally shaped except in the special case of a complete reflection. This isn't a personal theory, but a very well established fact which can easily be derived from fundamental equations. (Or it can even be found clearly stated in texts for those unable to understand the derivation.) On antennas, the current distribution (magnitude of current vs position) is generally not sinusoidal either, although it's approximately so on thin wire antennas. Assuming that the transmission line is driven with a pure sine wave, the forward, reverse, and total currents as a function of *time* will be sinusoidal and consequently no harmonics will be generated. (I'm of course neglecting nonlinear effects which might occur in a real transmission line or antenna such as magnetic conductors or nonlinear dielectrics. But in practical terms these will be virtually unmeasurable with ordinary coax or twinlead and amateur power levels.) It's hard to determine whether Cecil's sustained confusion between a time waveform and a graph of amplitude vs distance is intentional or if the concepts are really mixed up for him. It has, in either case, provided a convenient diversion from his basic strange theories at the time it was getting particularly hard for him to continue supporting them. Roy Lewallen, W7EL |
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Roy Lewallen wrote:
Richard Harrison wrote: In algebra, y = mx + b, (the point slope formula), is called linear because it is the graph of a straight line. But of course you realize that the function y = mx + b doesn't meet the requirements of a linear function when applied to network theory. I knew what Richard meant. Quoting "Linear Network Theory", by Ferris: "In the functional relationship, h(t)=kf(t), no matter what h(t) and f(t) represent, the relation h(t)=kf(t) must be linear. ... An elementary concept, then, is that h(t) and f(t) are related by a straight line of the form h(t) = mt + b." -- 73, Cecil http://www.qsl.net/w5dxp |
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Roy Lewallen wrote:
Richard Harrison wrote: Cecil, W5DXP wrote: "Assuming the source signal is a pure sine wave, if the standing wave current "isn`t in general sinusoidally shaped (as Roy said)", then the antenna would have to be introducing harmonic radiation that doesn`t exist in the source signal." Either Cecil is misquoting me, or Richard is misquoting Cecil. Richard quoted me correctly. I did *NOT* quote you. I merely stated what I thought you said. Cecil calls the total current the "standing wave current". That is absolutely false. Total current equals standing wave current plus traveling wave current. Or standing wave current equals total current minus traveling wave current. Subtract out the traveling wave component and a pure standing wave component is left. Note that you did not quote me. You merely stated what you thought I said and you were mistaken. I never said that the standing wave current isn't sinusoidally shaped. I said that the *envelope* of the standing wave -- that is, a graph of the magnitude of the current on a transmission line as a function of position along the line -- is not sinusoidally shaped except in the special case of a complete reflection. The envelope of the standing wave current is the same whether reflection is complete or not since the traveling wave current has been subtracted from the total current. Seems you should have said the total current envelope is not sinusoidal. The standing wave current envelope is obviously sinusoidal since the traveling wave has been subtracted. This isn't a personal theory, but a very well established fact which can easily be derived from fundamental equations. Please provide a reference that says after the traveling wave current has been subtracted from the total current, the resulting standing wave current envelope is not sinusoidal. (Or it can even be found clearly stated in texts for those unable to understand the derivation.) On antennas, the current distribution (magnitude of current vs position) is generally not sinusoidal either, although it's approximately so on thin wire antennas. Just because the scale of the position axis changes with VF doesn't mean things become non-sinusoidal. Assuming that the transmission line is driven with a pure sine wave, the forward, reverse, and total currents as a function of *time* will be sinusoidal and consequently no harmonics will be generated. This statement contradicts what I thought you said before. Seems we are now in agreement. -- 73, Cecil http://www.qsl.net/w5dxp |
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Roy Lewallen, W7EL wrote:
"But of course you realize that the function y = mx + b doesn`t meet the requirements of a linear function when applied to network theory." Works for me. Linear means the graph of the function is a straight line. f(x) = y = mx + b is called linear because its graph is a straight line. A straight line is the shortest distance between two points. In y = mx + b, m is a constant determining the slope of the line. x is is the independent variable. b is the offset or point along the x-axis where the line crosses. y then is a linear function of x because its slope is always mx, but displaced in the x-direction by a constant value, namely b. y is linear the same as IR is linear, or by substitution, E is linear in Ohm`s law where E=IR. For any value of I, voltage = IR and the graph of I versus E is a straight line with a slope equal to R. Resistance is a common factor in network theory. Best regards, Richard Harrison, KB5WZI |
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