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FIGHT! FIGHT! FIGHT!
Roy Lewallen wrote:
As I pointed out some time ago, the envelope of a standing wave isn't in general sinusoidally shaped. Assuming the source signal is sinusoidal, your above assertion would require non-linearity in the antenna. Since antennas are generally considered to be linear systems, would you please explain where the nonlinearity is coming from? -- 73, Cecil http://www.qsl.net/w5dxp |
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Gene Fuller wrote:
I am really puzzled. I cannot see even one inconsistency in my statements, including those you quote. What is the problem? You said there is phase remaining in the cos(kz) term which is contained in the amplitude. Then you said there is no phase information. Those statements contradict each other. In any case, the graph at http://www.qsl.net/w5dxp/travstnd.GIF proves that there is phase information contained in the standing wave current magnitude. The arc-cosine of the standing wave current magnitude is identical to the phase of the traveling wave referenced to the source current. Please note that the "experts" have been strangely silent on the contents of that graph. -- 73, Cecil http://www.qsl.net/w5dxp |
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Cecil Moore wrote:
Roy Lewallen wrote: As I pointed out some time ago, the envelope of a standing wave isn't in general sinusoidally shaped. Assuming the source signal is sinusoidal, your above assertion would require non-linearity in the antenna. Since antennas are generally considered to be linear systems, would you please explain where the nonlinearity is coming from? Additional thought: Assuming the source signal is a pure sine wave, if the standing wave current "isn't in general sinusoidally shaped", then the antenna would have to be introducing harmonic radiation that doesn't exist in the source signal. That fact is easily proved with a Fourier analysis. I wasn't aware that standing wave antennas cause radiation on harmonic frequencies. Any standing wave current waveform that deviates very far from a sinusoid would be illegal. -- 73, Cecil http://www.qsl.net/w5dxp |
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Cecil Moore wrote:
Gene Fuller wrote: I am really puzzled. I cannot see even one inconsistency in my statements, including those you quote. What is the problem? You said there is phase remaining in the cos(kz) term which is contained in the amplitude. Then you said there is no phase information. Those statements contradict each other. Cecil, My exact words, which you quoted, were, The only "phase" remaining is the cos (kz) term, which is really an amplitude description, not a phase. If you interpreted that comment as supporting the existence of a phase in this situation, then I cannot offer any help except to suggest you go back and review the meaning of "not". This has become sillier than I ever imagined possible. I am done with this FIGHT! 73, Gene W4SZ |
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Cecil Moore wrote:
Roy Lewallen wrote: As I pointed out some time ago, the envelope of a standing wave isn't in general sinusoidally shaped. Assuming the source signal is sinusoidal, your above assertion would require non-linearity in the antenna. Since antennas are generally considered to be linear systems, would you please explain where the nonlinearity is coming from? No it wouldn't, Cecil. Even you know better than that. For those who believe Cecil, consider a lossy transmission line terminated in a short, or open. The signal is attenuated as it goes down the line, and also attenuated as it comes back up the line, in an exponential fashion. The envelope is thus not sinusoidal. The signal may be sinusoidal, but the envelope can't possibly be. Cecil's antennas may be lossless, but most of us want our antennas to radiate energy, hopefully, as efficiently as possible, so we have to put up with current distributions that aren't easy either to envision or to calculate. That's why even Cecil uses EZNEC. 73, Tom Donaly, KA6RUH |
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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." Standing waves are produced by forward and reflected traveling soinusoidal waves produced by the same generator. Coherent signals on a transmission line and antenna of the same frequency are correctly represented by phasors. The term phasor is preferred over vector for an arrow which indicates phase separation and magnitude of an electrical unit. Phasors are used to represent sinusoidal voltages and currents. They are also used to represent reactances and impedances. Like vectors, phasors can be "added" by the head-to-tail method or by the component method. If a phasor represents an alternating current: I = Io cos omega t, then the sum of the two phasors representing forward and reflected sinusoidal components is another sinusoid of the same frequency. Point is the components are amenable to phasor representation. All the old authors do it. This amenability is proof the standing wave is a sinusoid too. Best regards, Richard Harrison, KB5WZI |
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Gene Fuller wrote:
The only "phase" remaining is the cos (kz) term, which is really an amplitude description, not a phase. Yes, there it is again, you said there is phase information in the amplitude description and you were right. -- 73, Cecil http://www.qsl.net/w5dxp |
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On Wed, 17 May 2006 16:19:17 GMT, "Tom Donaly"
wrote: Cecil's antennas may be lossless, Hi Tom, Even more amazing is that they are linear transmission lines. 73's Richard Clark, KB7QHC |
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Tom Donaly wrote:
Cecil Moore wrote: Assuming the source signal is sinusoidal, your above assertion would require non-linearity in the antenna. Since antennas are generally considered to be linear systems, would you please explain where the nonlinearity is coming from? No it wouldn't, Cecil. Even you know better than that. For those who believe Cecil, consider a lossy transmission line terminated in a short, or open. The signal is attenuated as it goes down the line, and also attenuated as it comes back up the line, in an exponential fashion. The envelope is thus not sinusoidal. An attenuated (damped) sinusoidal signal is still sinusoidal, Tom. The fact that such a signal doesn't generate harmonics proves that it is sinusoidal. If it were not sinusoidal, it would by definition, be generating harmonics. Are you really asserting that a damped sinusoidal signal generates harmonics? That's the only way to prove it has gone nonsinusoidal. All non-sinusoidal waveforms contain harmonics of the fundamental frequency. Every competent engineer in the world is aware of that technical fact. If the source signal to an antenna is a pure single- frequency sine wave, and if the standing wave current is non- sinusoidal, then the antenna has necessarily introduced harmonics, i.e. the antenna is non-linear. W7EL is simply mistaken when he says the standing wave current waveform is not sinusoidal. If the standing wave current waveform ever was nonsinusoidal, the antenna would, by definition, be non-linear and be generating harmonics not present in the source waveform. Seems you guys need to review your Math 202 course covering Fourier transforms. -- 73, Cecil http://www.qsl.net/w5dxp |
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Richard Harrison wrote:
If a phasor represents an alternating current: I = Io cos omega t, then the sum of the two phasors representing forward and reflected sinusoidal components is another sinusoid of the same frequency. Point is the components are amenable to phasor representation. All the old authors do it. This amenability is proof the standing wave is a sinusoid too. The absence of harmonic frequencies generated by the antenna is also proof that the standing wave is a sinusoid. All nonsinusoidal waveforms contain harmonics. -- 73, Cecil http://www.qsl.net/w5dxp |
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