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#1
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Jim Kelley wrote:
Refer to a table of sines and observe the two things which vary throughout the period of any sinusoidal wave. One of them is amplitude. What would you prefer I call the other one? Did you not understand what Gene Fuller said? Io*cos(kx) is the amplitude term. If kx=0 then the amplitude is Io. If kx=pi/4, the amplitude is 0.707*Io. If kx=pi/2, the amplitude is zero. cos(wt) does not vary with (x), only with time. At any snapshot in time, e.g. t=0, the phase does not vary at all. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
#2
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Cecil Moore wrote:
Jim Kelley wrote: Refer to a table of sines and observe the two things which vary throughout the period of any sinusoidal wave. One of them is amplitude. What would you prefer I call the other one? Did you not understand what Gene Fuller said? Somebody once made a claim about answering a question with a question. He said that it was a means of diversion. Clearly that is the case. It's no coincidence that the phase of the standing wave varies by 90 degrees along the length of a 90 degree standing wave antenna. ac6xg |
#3
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Jim Kelley wrote:
It's no coincidence that the phase of the standing wave varies by 90 degrees along the length of a 90 degree standing wave antenna. But it doesn't, Jim. Both Kraus and EZNEC agree that standing wave current phase varies by only ~3 degrees over the entire length of a 180 degree wire dipole (referenced to the phase at the feedpoint). If you slide a current probe up and down a 1/2WL wire dipole, you will find that the phase referenced to the phase at the feedpoint barely changes and cannot be used to determine position on the dipole. The position along the dipole is contained in the amplitude. The ARCCOS of the relative amplitude will yield the position along the dipole. Please read what Gene Fuller said: Gene Fuller, W4SZ wrote: In a standing wave antenna problem, such as the one you describe, there is no remaining phase information. Any specific phase characteristics of the traveling waves died out when the startup transients died out. Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be seen again. The only "phase" remaining is the cos (kz) term, which is really an amplitude description, not a phase. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
#4
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Cecil Moore wrote:
Jim Kelley wrote: It's no coincidence that the phase of the standing wave varies by 90 degrees along the length of a 90 degree standing wave antenna. But it doesn't, Jim. Both Kraus and EZNEC agree that standing wave current phase varies by only ~3 degrees over the entire length of a 180 degree wire dipole (referenced to the phase at the feedpoint). You're always trying to drag other people into your messes. So now, in addition to waves of average power and the 4th mechanism of reflection, we have waves that don't change phase. :-) Fine business OM. ac6xg |
#5
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Jim Kelley wrote:
So now, in we have waves that don't change phase. :-) Yes, and w7el has verified that fact either on this newsgroup or another newsgroup. If you have EZNEC, you can easily verify it for yourself - anyone can. Here's what Hecht said in "Optics" regarding standing wave phase: "It (the standing wave phasor) doesn't rotate at all, and the resultant wave it represents doesn't progress through space - its a standing wave." -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
#6
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Cecil Moore wrote:
Jim Kelley wrote: So now, in we have waves that don't change phase. :-) Yes, and w7el has verified that fact either on this newsgroup or another newsgroup. If you have EZNEC, you can easily verify it for yourself - anyone can. It's absurd to talk about waves that don't change phase, Cecil. If 'it' does not change phase in some dimension, then 'it' is not a wave. Again I refer you to a table of sines. Here's what Hecht said in "Optics" regarding standing wave phase: "It (the standing wave phasor) doesn't rotate at all, and the resultant wave it represents doesn't progress through space - its a standing wave." Hecht knew exactly what he was talking about. It's not always evident that you know exactly what Hecht is talking about. ac6xg |
#7
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Jim Kelley wrote:
Cecil Moore wrote: Jim Kelley wrote: So now, in we have waves that don't change phase. :-) Yes, and w7el has verified that fact either on this newsgroup or another newsgroup. If you have EZNEC, you can easily verify it for yourself - anyone can. It's absurd to talk about waves that don't change phase, Cecil. If 'it' does not change phase in some dimension, then 'it' is not a wave. Again I refer you to a table of sines. Here's what Hecht said in "Optics" regarding standing wave phase: "It (the standing wave phasor) doesn't rotate at all, and the resultant wave it represents doesn't progress through space - its a standing wave." Hecht knew exactly what he was talking about. It's not always evident that you know exactly what Hecht is talking about. ac6xg There's not much point in arguing with Cecil, Jim. He won't stop playing the one-note samba until he's too old to whistle the tune. 73, Tom Donaly, KA6RUH |
#8
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Jim Kelley wrote:
It's absurd to talk about waves that don't change phase, Cecil. If 'it' does not change phase in some dimension, then 'it' is not a wave. Yes, my point exactly and that's what a couple of my references say - that standing waves are not waves at all. I'm glad that we agree that a standing wave does not meet the definition of a wave. "College Physics", by Bueche and Hecht: "These ... patterns are called *standing waves*, as compared to the propagating waves considered above. They might better not be called waves at all, since they do not transport energy and momentum." "Electrical Communication", by Albert: "Such a plot of voltage is usually referred to as a *voltage standing wave* or as a *stationary wave*. Neither of these terms is particularly descriptive of the phenomenon. A plot of effective values of voltage, appearing as in Fig. 6(e), *is not a wave* in the usual sense. However, the term "standing wave" is in widespread use." Please contact w7el and ask him if the total current on a 90 degree monopole changes by 90 degrees over its length. Please tell us what he says. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
#9
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Jim Kelley wrote:
So now, in addition to the 4th mechanism of reflection, ... Three years ago, I removed that 4th mechanism of reflection from my energy article in favor of "redistribution" instead of "reflection". About a year ago, I told you that and predicted that you would regurgitate that same old dead horse sometime in the future. Thanks for proving me correct in my prediction. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
#10
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Cecil Moore wrote:
Jim Kelley wrote: So now, in addition to the 4th mechanism of reflection, ... Three years ago, I removed that 4th mechanism of reflection from my energy article in favor of "redistribution" instead of "reflection". About a year ago, I told you that and predicted that you would regurgitate that same old dead horse sometime in the future. Thanks for proving me correct in my prediction. At least you were correct about something - all thanks to me, evidently. :-) ac6xg |
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