|
"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 |
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? Obviously, not as much as you. Why not just say, "God is the cause of everything I (Jim) cannot explain or understand."? The meaning would be virtually identical to your present positions. 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. You can argue against energy conservation all you want. *Conservation of Momentum* has got you over a barrel in this argument whether you realize it or not. Somehow, the momentum in the wave reflected from a mismatched load is reversed. Please explain how that happens without changing directions. Somehow, the energy in the wave reflected from a mismatched load changes directions. Please enlighten us on exactly the mechanism involved. Hint: J.C.Slater explained it all in _Microwave_Transmissions_ before you were born. -- 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 13:19:41 -0500, Cecil Moore
wrote: Well Richard, here's your chance. Please enlighten us on J.C. What was the original question? [accredited stock response] |
Dave wrote:
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. Of course, it is not against the guidelines as the subject was "Reflected Power". I simply continued to talk about reflected power, the subject of the thread. That's a broad subject. Perhaps the originator erred in choosing that broad of a subject but he chose that subject nevertheless. All of my postings to this thread have been about reflected power, including this one, in defense of my postings about reflected power. i said it was real world, but it is not what the original thread was about. The original thread was about "Reflected Power". My example was about reflected power. I might not even have read the text of the original posting. It would be interesting to know why your agenda requires diverting the issue away from "reflected power"? What are you afraid of? -- 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! =----- |
Tam/WB2TT wrote:
"Cecil Moore" wrote: 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). Looking for the smiley face. Is there a smiley face that means, "sad but true"? Many otherwise intelligent, knowledgeable, educated engineers have attempted to force their metaphysical "steady-state" agenda on uninitiated and unsuspecting victims. One is saddened by such an event and one wonders why. Does a steady-state religion or creed exist within amateur radio? If so, what are its purpose and goals? -- 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! =----- |
Jim Kelley wrote:
We both know that momentum and energy must be conserved. We just disagree agree on how nature chooses to do that. Well then, please enlighten us, Jim. How does nature choose to reverse the momentum in the wave reflected from a mismatched source? It is obvious that the wave reflected from a mismatched source has momentum in the rearward direction. Exactly what reverses that momentum? Please be specific. Remember that standing waves prove that the rearward-traveling wave exists in reality and thus possesses energy and momentum in the rearward direction, both of which must be conserved. Maybe you should read _Microwave_Transmission_ by J. C. Slater before you continue? -- 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 quote below & 'steady state'
The transmitter is continuously generating incident power, which is continuously subject to reflection(s) by any mismatch in the antenna system. Given the right magnitude, phase and time displacement, each reflection will produce a continuous ghost on the TV screen. These ghosts can be seen (continuously) in/on the output waveform of a TV demodulator connected at the output of the transmitter -- both in time domain on an oscilloscope, and visually on a monitor. I've seen these continuous reflections scores of times at TV tx sites all over the US as a field engineer for RCA Broadcast Division. "Conventional wisdom" on this NG may say otherwise, but hopefully some may learn the reality from this exchange. - RF ____________________ "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). |
Richard Clark wrote:
wrote: Well Richard, here's your chance. Please enlighten us on J.C. What was the original question? [accredited stock response] When totally ignorant, divert the issue as long as possible. Why am I not surprised? -- 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:
Well then, please enlighten us, Jim. How does nature choose to reverse the momentum in the wave reflected from a mismatched source? It is obvious that the wave reflected from a mismatched source has momentum in the rearward direction. Typo: please change "source" to "load" in the above. Sorry. -----= 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 14:06:28 -0500, Cecil Moore
wrote: What was the original question? [accredited stock response] When totally ignorant, divert the issue as long as possible. Why am I not surprised? Are you sure this is the original question? [accredited stock response] |
Henry Kolesnik wrote:
I know that any power not dissipated by an antenna is reflected back to the transmitter. Then the transmitter "reflects" this reflection back to antenna, ad nauseum until its all gone. I also know that a short or an open is required to reflect power and I'm searching for which it is, an open or a short. I'm inclined to think it's a virtual open but I'm at a loss to understand that and I wonder if someone has a good explanation or analogy and some math wouldn't hurt. tnx Hank WD5JFR Hi Hank, Here's a link which talks about (and illustrates) the physics of waves at a boundary. http://www.physicsclassroom.com/Class/waves/U10L3a.html It shows what happens at the two extremes for transverse waves along a string - not unlike electromagnetic waves in a transmission line in some ways. In one instance, the string is fastened directly to the boundary - a rod in this case. This is analogous to a short across a transmission line. It will be seen that a reflection occurs, and that the wave becomes inverted upon reflecting. In the other case, the string is fastened to a ring which can slide freely up and down the rod. This case is analogous to an unterminated, or open transmission line. It can be seen that this too causes a reflection, only this time the wave is reflected back without a phase reversal. The amplitude of the reflected wave in both these cases equals the amplitude of the incident wave. Now imagine that some friction between the sliding ring and the rod can be added in varying amounts. This friction would be proportional to the conductance in an electrical circuit, and would be infinite at one extreme and zero at the other. The greater the friction, the greater the conductance (and the lower the electrical resistance). As we begin to increase the friction (conductance) from zero, the amplitude of the inverted, reflected wave begins to decrease. The decrease in amplitude continues with increasing friction until the amplitude of the reflected wave becomes zero. It could be said that this value is equal to the Z0 of the transmission line. As the amount of friction is increased still further, a small reflection once again begins to appear. Only now the phase is opposite from what it was before. Further increases in friction produce further increases in reflection amplitude until the amplitude of the reflected wave once again equals the amplitude of the incident wave. What we noticed in the exercise is that there is some value of friction (conductance or resistance) for which no reflection occurs. The exact value depends on the medium through which the wave is propagating. All other values produced a reflection. There is no perfect explanation, and this certainly isn't a perfect analogy but I hope that it will at least help give you a little more of a feel for the idea. 73, Jim AC6XG |
Cecil Moore wrote: Jim Kelley wrote: We both know that momentum and energy must be conserved. We just disagree agree on how nature chooses to do that. How does nature choose to reverse the momentum in the wave reflected from a mismatched source? The definition is accurate as well as descriptive. As I've explained at least a dozen times, energy only moves in the direction of transfer. 73, Jim AC6XG |
"Cecil Moore" wrote in message ... Dave wrote: 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. Of course, it is not against the guidelines as the subject was "Reflected Power". I simply continued to talk about reflected power, the subject of the thread. That's a broad subject. Perhaps the originator erred in choosing that broad of a subject but he chose that subject nevertheless. All of my postings to this thread have been about reflected power, including this one, in defense of my postings about reflected power. then obviously you just struck on the convenient subject line and ignored the original question, subverting the whole thread for your own twisted use... including the argument that you were not taking over the discussion. this obviously just raises the noise floor and does nothing to help the original poster who by now is likely heading for his local library if he is smart. |
Richard Clark wrote:
Are you sure this is the original question? I am sure that our solar system and homo sapiens didn't exist when the original question was asked. -----= 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! =----- |
Jim Kelley wrote:
It shows what happens at the two extremes for transverse waves along a string - not unlike electromagnetic waves in a transmission line in some ways. Where are the E and H fields in the string response? -- 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 15:28:40 -0500, Cecil Moore
wrote: I am sure that our solar system and homo sapiens didn't exist when the original question was asked. So the question is which came first, the homo or the solar system? |
Jim Kelley wrote:
The definition is accurate as well as descriptive. As I've explained at least a dozen times, energy only moves in the direction of transfer. Energy moves in whatever direction energy moves. According to you, if we reflect light energy from Alpha Centauri back to Alpha Centauri, no energy movement has occurred. Never mind that it takes 20 years to accomplish that energy movement. Your "no work equals no energy" concept is as bogus as it possibly can be. Joules of energy passing a point in delta- time is power, by IEEE definition. -- 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! =----- |
Dave wrote:
then obviously you just struck on the convenient subject line and ignored the original question, ... Nope, you must have missed the posting where I said I didn't possess sufficient knowledge to answer the original question but I was willing to discuss something related to the subject line for which I do possess sufficient knowledge. Why all the logical diversions? What are you afraid of? -- 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: I am sure that our solar system and homo sapiens didn't exist when the original question was asked. So the question is which came first, the homo or the solar system? For what it is worth, I believe that the first homo sapien originated about a quarter of a million years ago and was a female with dominant genes. -- 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 16:17:13 -0500, Cecil Moore
wrote: For what it is worth, I believe that the first homo sapien originated about a quarter of a million years ago and was a female with dominant genes. Strange belief for a creation of barely 5000 years old. What has this to do with Reflected Power? |
Cecil Moore wrote:
According to you, if we reflect light energy from Alpha Centauri back to Alpha Centauri, no energy movement has occurred. Cecil, unless you can simply express your views, and let me be the one to express my views, the exchange becomes degraded to ascii mud wrestling. I have no interest in that. Please make your point without speaking on 'my behalf'. 73, Jim AC6XG |
"Richard Fry" wrote in message ... Concept below However this is not an accurate model of a transmitter. For an example, take an old Heathkit DX-100 generating a measured 180 watts of CW RF into a matched 50 ohm load. To do this, it does NOT also dissipate 180 watts of RF into some "virtual" internal RF load in the DX-100. In fact, the PAs and power supply in the DX-100 could not produce a total RF output power of 360 watts without exceeding their ratings. The dissipation in the PA is essentially related only the DC to RF conversion efficiency of the PA, which in this case probably is about 75%, max (Class C). So a PA input power of about 240 watts DC is required to produce 180 watts of RF output power. The other 60 watts of plate input power is converted to heat by the PA tube anodes. The entire RF output generated by the PA stage is applied virtually 100% to the output connector. How much of that is absorbed by the load connected there is a function of load SWR and system losses. Finally someone who is getting closer to the flaw in the way many mis-interpret the maximum power transfer theorm concept. -- Steve N, K,9;d, c. i My email has no u's. |
"Tam/WB2TT" wrote in message ... "Richard Fry" wrote in message ......................... ............................... Concept below However this is not an accurate model of a transmitter. For an example, take an old Heathkit DX-100 generating a measured 180 watts of CW RF into a matched 50 ohm load. To do this, it does NOT also dissipate 180 watts of RF into some "virtual" internal RF load in the DX-100. In fact, the PAs and power supply in the DX-100 could not produce a total RF output power of 360 watts without exceeding their ratings. The dissipation in the PA is essentially related only the DC to RF conversion efficiency of the PA, which in this case probably is about 75%, max (Class C). So a PA input power of about 240 watts DC is required to produce 180 watts of RF output power. The other 60 watts of plate input power is converted to heat by the PA tube anodes. The entire RF output generated by the PA stage is applied virtually 100% to the output connector. How much of that is absorbed by the load connected there is a function of load SWR and system losses. - RF There is a Motorola ap note that agrees with what Richard is saying. To paraphrase it, if the the DX100 had an output impedance of 50 Ohms, then the overall efficiency would be 37.5%. Unfortunately I can't read all the digressions in the thread. I skim by author... This is an interesting twist, Tam. I think if this were the case, then there would be MORE power dissipated in the Tx than Mr. Fry is saying - making the situation worse. By that, I mean, getting further from what is going on. I think this goes in the wrong direction. I believe the flaw is believing that the Rs=RL must exist for the transmitter. -- Steve N, K,9;d, c. i My email has no u's. |
Cecil Moore wrote:
snip For what it is worth, I believe that the first homo sapien originated about a quarter of a million years ago and was a female with dominant genes. -- 73, Cecil http://www.qsl.net/w5dxp My wife has me convinced that ALL women have the dominant genes!!!! Deacon Dave |
The first ghost is the most visible and the offspring become less and less
visible. Ghosts of ghosts are hard to see. If you're a whiteman you haven't seen any skinwalkers, aka Navajo ghosts.. -- 73 Hank WD5JFR "Cecil Moore" wrote in message ... 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! =----- |
If the anser were at the library I'd already have it and wouldn't be here.
-- 73 Hank WD5JFR "Dave" wrote in message ... "Cecil Moore" wrote in message ... Dave wrote: 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. Of course, it is not against the guidelines as the subject was "Reflected Power". I simply continued to talk about reflected power, the subject of the thread. That's a broad subject. Perhaps the originator erred in choosing that broad of a subject but he chose that subject nevertheless. All of my postings to this thread have been about reflected power, including this one, in defense of my postings about reflected power. then obviously you just struck on the convenient subject line and ignored the original question, subverting the whole thread for your own twisted use... including the argument that you were not taking over the discussion. this obviously just raises the noise floor and does nothing to help the original poster who by now is likely heading for his local library if he is smart. |
Richard Clark wrote:
Strange belief for a creation of barely 5000 years old. Wow, religious dogma in both your fields of religion and electronics? What has this to do with Reflected Power? You asked - I answered. -----= 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! =----- |
Jim Kelley wrote:
... the exchange becomes degraded to ascii mud wrestling. That's exactly why you are in my email kill file. Please find someone else with which to enjoy that favorite sadistic sport of yours. -- 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! =----- |
Thanks, I knew this but what I don't know is why a final doesn't dissipate
the reflected wave but just reflects 100% I assume. Transistor and tube finals dissipate a bunch producing the RF but what is the mirror, check valve or diode that keeps it reflecting -- 73 Hank WD5JFR "Jim Kelley" wrote in message ... Henry Kolesnik wrote: I know that any power not dissipated by an antenna is reflected back to the transmitter. Then the transmitter "reflects" this reflection back to antenna, ad nauseum until its all gone. I also know that a short or an open is required to reflect power and I'm searching for which it is, an open or a short. I'm inclined to think it's a virtual open but I'm at a loss to understand that and I wonder if someone has a good explanation or analogy and some math wouldn't hurt. tnx Hank WD5JFR Hi Hank, Here's a link which talks about (and illustrates) the physics of waves at a boundary. http://www.physicsclassroom.com/Class/waves/U10L3a.html It shows what happens at the two extremes for transverse waves along a string - not unlike electromagnetic waves in a transmission line in some ways. In one instance, the string is fastened directly to the boundary - a rod in this case. This is analogous to a short across a transmission line. It will be seen that a reflection occurs, and that the wave becomes inverted upon reflecting. In the other case, the string is fastened to a ring which can slide freely up and down the rod. This case is analogous to an unterminated, or open transmission line. It can be seen that this too causes a reflection, only this time the wave is reflected back without a phase reversal. The amplitude of the reflected wave in both these cases equals the amplitude of the incident wave. Now imagine that some friction between the sliding ring and the rod can be added in varying amounts. This friction would be proportional to the conductance in an electrical circuit, and would be infinite at one extreme and zero at the other. The greater the friction, the greater the conductance (and the lower the electrical resistance). As we begin to increase the friction (conductance) from zero, the amplitude of the inverted, reflected wave begins to decrease. The decrease in amplitude continues with increasing friction until the amplitude of the reflected wave becomes zero. It could be said that this value is equal to the Z0 of the transmission line. As the amount of friction is increased still further, a small reflection once again begins to appear. Only now the phase is opposite from what it was before. Further increases in friction produce further increases in reflection amplitude until the amplitude of the reflected wave once again equals the amplitude of the incident wave. What we noticed in the exercise is that there is some value of friction (conductance or resistance) for which no reflection occurs. The exact value depends on the medium through which the wave is propagating. All other values produced a reflection. There is no perfect explanation, and this certainly isn't a perfect analogy but I hope that it will at least help give you a little more of a feel for the idea. 73, Jim AC6XG |
Henry Kolesnik wrote:
Thanks, I knew this but what I don't know is why a final doesn't dissipate the reflected wave but just reflects 100% I assume. Transistor and tube finals dissipate a bunch producing the RF but what is the mirror, check valve or diode that keeps it reflecting There is none! The definition is the problem. It is simply a copout. Sources can dissipate reflected energy. The amount is unknown. -- 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 17:01:44 -0500, Cecil Moore
wrote: Richard Clark wrote: Strange belief for a creation of barely 5000 years old. Wow, religious dogma in both your fields of religion and electronics? Nice to see you accede. What has this to do with Reflected Power? You asked - I answered. Did you? What was the original question? [accredited stock response] |
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