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"Richard Clark" wrote in message ... On 23 May 2004 19:02:20 -0700, (alhearn) wrote: Hank: Aren't you confusing the reflections that a TV signal experiences when it bounces off nearby buildings and structures (causing ghosts) with transmission line refections -- two entirely different things. Al Hi Al, No, he has it correct. There is no material difference between the two except for the velocity constant (which has no bearing on the matter). 73's Richard Clark, KB7QHC There is a third case, which will cause the same results. Namely, the effect of passing the signal through a filter with a nonlinear phase characteristic. Tam/WB2TT |
Dave wrote:
no, only that you ignored the body of the message and answered what you wanted to discuss instead of what was asked. Yes, I did. I didn't know anything about the original question so I kindly offered to discuss something I know something about. If that is against netnews guidelines, could you show me where it says so? nope, that is a real world situation, but not the one under discussion. A 1/4WL matching section is not a "real world situation"? Since when? Everything I post is a real-world situation except for the obvious, e.g. one-second long lossless transmission lines. so which is it, in phase or 180 degrees out of phase??? It depends upon which signal we are talking about and whether the impedance discontinuity steps-up or steps-down. Assuming the generated forward wave (a1) has the voltage and current in phase at zero degrees: For a step-up impedance discontinuity, the s11(a1) reflection term will have the voltage at zero degrees (and the current at 180 degrees). For a Z0-match, b1 will be zero so s12(a2) must be equal magnitude and opposite phase to s11(a1). That puts the reflection from the load with voltage at 180 degrees (and current at zero degrees). All interference at port1 is totally destructive for a Z0-match. The s21(a1) term has voltage at zero degrees (and current at zero degrees). All interference at port2 is constructive so s22(a2) also has the voltage at zero degrees (and current at zero degrees). For a step-down impedance discontinuity associated with a Z0-match, the phases of the reflected voltages and currents are shifted by 180 degrees and b1 still equals zero. The above is exactly what happens at the match point at the input of a tuner. ***Therefore, the great majority of ham radio antenna systems have the voltages and currents either in-phase or 180 degrees out of phase at the tuner match point.*** In fact, all a tuner does is shift the magnitude and phase of the reflected waves from a mismatched antenna to be equal in magnitude and 180 degrees out of phase with the reflections from the match point. Therefore, all reflections are canceled at the match point but not between the match point and the antenna. This was all explained 64 years ago (when I was two years old) by J. C. Slater in _Microwave_Transmission_. Why do I have to explain it all over again? -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Cecil Moore wrote: the rearward-traveling momentum energy in those two waves is conserved by changing direction to become part of a forward-traveling wave. Yeeesh. You had it on, dog, up until that. And don't try to tell me (again) that I'm lying that you said it. (Remember when you wrote this? "If reflected energy makes its way back into the final amp, it was never generated in the first place, by definition." Hint: apply the same idea to your "rearward-traveling momentum" and you'll have it.) 73, Jim AC6XG |
Henry Kolesnik wrote:
SWR ghosts are usually smear because the transmission line is short and the displacement fo the image is small compared to object reflection shost which have a greater image displacement becasue the reflected signal travels over a greater distance. If reflected waves don't make a round trip back toward the source and get re-reflected, how can there be ghosts? :-) -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
On Mon, 24 May 2004 12:49:39 -0500, Cecil Moore
wrote: I didn't know anything about the original question Stock answer. This was all explained 64 years ago (when I was two years old) by J. C. Slater in _Microwave_Transmission_. Why do I have to explain it all over again? Possibly because you so ill understood it then as now? |
Richard Fry wrote:
TV Ghosting (quotes below) To elaborate, the visibility of a ghost image in analog TV systems is related to the magnitude, phase and time displacement of the RF reflection that produced it as compared to the original, or non-reflected waveform. The round-trip transit time from the TV tx output to the mismatch in its antenna system will determine the time displacement of the ghost, at the rate of 1 microsecond of displacement per ~490 feet of distance between the tx and the reflection plane (vp = 0.997c). Richard, you know you are going against the conventional wisdom on this newsgroup. Ghosting cannot exist during steady-state so if ghosting exists it simply means that you are still in the transient state and the steady-state doesn't exist (yet). -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Richard Clark wrote:
wrote: This was all explained 64 years ago (when I was two years old) by J. C. Slater in _Microwave_Transmission_. Why do I have to explain it all over again? Possibly because you so ill understood it then as now? Well Richard, here's your chance. Please enlighten us on J.C. Slater's meaning of: "The method of eliminating reflections is based on the interference between waves. ... The fundamental principle behind the elimination of reflections is then to have each reflected wave canceled by another wave of equal amplitude and opposite phase." -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
"Cecil Moore" wrote in message ... Dave wrote: no, only that you ignored the body of the message and answered what you wanted to discuss instead of what was asked. Yes, I did. I didn't know anything about the original question so I kindly offered to discuss something I know something about. If that is against netnews guidelines, could you show me where it says so? of course it is against guidelines. you were starting a new thread without changing the subject. in effect hijacking the thread for your own discussion. nope, that is a real world situation, but not the one under discussion. A 1/4WL matching section is not a "real world situation"? Since when? Everything I post is a real-world situation except for the obvious, e.g. one-second long lossless transmission lines. i said it was real world, but it is not what the original thread was about. |
Cecil Moore wrote: Jim Kelley wrote: Cecil Moore wrote: rearward-traveling momentum energy in those two waves is conserved by changing direction to become part of a forward-traveling wave. Yeeesh. You had it on, dog, up until that. And don't try to tell me (again) that I'm lying that you said it. (Remember when you wrote this? "If reflected energy makes its way back into the final amp, it was never generated in the first place, by definition." Hint: apply the same idea to your "rearward-traveling momentum" and you'll have it.) Egads Jim, exactly how much of reality do you think I am capable of ignoring? You're evidently capable of ignoring at least some, Cecil. I *don't* agree with that definition above and your implication that momentum and energy don't need to be conserved is simply metaphysics in action. We both know that momentum and energy must be conserved. We just disagree agree on how nature chooses to do that. And, because of that disagreement, I'm forced to endure your beligerant rhetoric. 73, Jim AC6XG |
"Cecil Moore" wrote in message ... Richard Fry wrote: TV Ghosting (quotes below) To elaborate, the visibility of a ghost image in analog TV systems is related to the magnitude, phase and time displacement of the RF reflection that produced it as compared to the original, or non-reflected waveform. The round-trip transit time from the TV tx output to the mismatch in its antenna system will determine the time displacement of the ghost, at the rate of 1 microsecond of displacement per ~490 feet of distance between the tx and the reflection plane (vp = 0.997c). Richard, you know you are going against the conventional wisdom on this newsgroup. Ghosting cannot exist during steady-state so if ghosting exists it simply means that you are still in the transient state and the steady-state doesn't exist (yet). -- 73, Cecil http://www.qsl.net/w5dxp Looking for the smiley face. It is probably fair to say that in the *general case* there is no steady reflection in video transmission, unless the round trip delay is N horizontal lines. BTW, weirdest case I saw came when the dog chewed through the cable. Now I was seeing the main signal coming from the cable, plus a ghost that was picked up directly from the transmitter. The ghost was to the left and above the main signal. Tam/WB2TT |
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