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Mike Coslo wrote:
Richard is right, There is the first ream! Sorry, I'm a bit pippish today.......... Ignorance of s-parameter analysis, like ignorance of the Smith Chart, is not a mortal sin. -- 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 ... Tam/WB2TT wrote: I am not quite sure what you are saying. But, I ran a SPICE simulation of the following: 1V 1MHz source with resistor R0 feeding a 50 Ohm 250 ns transmission line shorted at the far end. Independent of R0, in steady state the voltage at the input end of the transmission line will be 1V. The effect of R0 is to limit how long it takes to reach steady state. For R0 = 50 Ohms, it is one cycle; for R0 = 500 Ohms, it is about 8 cycles, as eyeballed off the waveform display. Does SPICE report the steady-state forward and reflected waves or just the superposition of those two waves? We all know what they look like when superposed. The question is whether the identity of the forward and reflected waves disappear after they are superposed. To the best of my knowledge, the very existence of standing waves requires the existence of a forward- traveling wave and a rearward-traveling wave. I have asked for examples of standing waves void of rearward- traveling waves and none has been forthcoming. -- 73, Cecil http://www.qsl.net/w5dxp It shows the composite voltage waveform, and the net current. Exactly what a Bird wattmeter would do. Of course the Bird only shows you steady state, Spice (SWCAD) swhows how you got there. Tam/WB2TT |
Cec et al, what have circulators, S-parameters, etc. to do with HF ?
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Tam/WB2TT wrote:
It shows the composite voltage waveform, and the net current. Exactly what a Bird wattmeter would do. That's not what a Bird wattmeter does. A Bird wattmeter possesses a directional coupler. SPICE apparently does not. Is it possible to add a directional coupler to SPICE? If you know the Z0, the net voltage/current magnitudes/phases, it should be possible to use phasor addition/subtraction to obtain the forward and reflected components, just like the Bird wattmeter does. -- 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! =----- |
Not much but neither does much of this thread regarding my original query.
I hope someone that understands the question can answer in a way that my feeble brain can comprehend. At least we're eliminating what's not the answer. 73 Hank WD5JFR "Reg Edwards" wrote in message ... Cec et al, what have circulators, S-parameters, etc. to do with HF ? |
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 ________________ "alhearn" wrote If you leave out the complex part of impedences for the moment and think of 100 volt generator that has a 50 ohm internal impedance driving a 50 ohm load, current is 1 amp and the power dissipated by the load is 50 watts. There is also 50 watts dissipated by the generator's internal impedance, for a total of 100 watts dissipated by the entire system. Therefore, the "available" power for this generator is 50 watts. |
Reg Edwards wrote:
Cec et al, what have circulators, S-parameters, etc. to do with HF ? What does scattering have to do with antenna systems with reflections???? Maybe you should download the HP AN 95-1? It's available at: http://www.sss-mag.com/pdf/hpan95-1.pdf From _Fields_and_Waves_in_Communication_Electronics_ by Ramo, Whinnery, and Van Duzer. "11.09 Scattering and Transmission Coefficients ... This article introduces two of the *most* useful (two-port analysis) forms based on wave quantities." This is a (c)1965 book, a later version of a classic fields and waves (c)1944 book by Ramo & Whinnery. -- 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! =----- |
Henry Kolesnik wrote:
Not much but neither does much of this thread regarding my original query. They have a lot to do with the subject of the thread. :-) I hope someone that understands the question can answer in a way that my feeble brain can comprehend. At least we're eliminating what's not the answer. Back a dozen years ago, or so, Mr. Bruene tried to 'ping' a final amp with a slightly off-frequency signal to ascertain the output impedance of the amp and he published his results in QST. His apparent error was that he didn't do it at the frequency of operation of the amp and he didn't know what the 'Q' of a final amp really is. There has been a running argument ever since, probably best documented in QEX magazine. There are basically two sides to the argument. 1. If load-pulling causes a falloff of power on each side of the operating point, then the system is conjugately matched. That conjugate match includes such things as non-dissipative resistances. 2. Conjugate matches do not exist in a typical amateur system. Brilliant minds have been trying to prove one or the other and both sides (IMO) have failed in that proof. There is no final, definitive proof of either position. If there was such, there would be no argument. That's why we cannot answer your question. The picture is further clouded by a definition. If reflected energy makes its way back into the final amp, it was never generated in the first place, by definition. -- 73, Cecil http://www.qsl.net/w5dxp "Reg Edwards" wrote: Cec et al, what have circulators, S-parameters, etc. to do with HF ? -----= 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! =----- |
Then why can high SWR on a TV Tx cauuse ghosts or smearing on the TV Rx?
Hank WD5JFR "Cecil Moore" wrote in message ... Henry Kolesnik wrote: Not much but neither does much of this thread regarding my original query. They have a lot to do with the subject of the thread. :-) I hope someone that understands the question can answer in a way that my feeble brain can comprehend. At least we're eliminating what's not the answer. Back a dozen years ago, or so, Mr. Bruene tried to 'ping' a final amp with a slightly off-frequency signal to ascertain the output impedance of the amp and he published his results in QST. His apparent error was that he didn't do it at the frequency of operation of the amp and he didn't know what the 'Q' of a final amp really is. There has been a running argument ever since, probably best documented in QEX magazine. There are basically two sides to the argument. 1. If load-pulling causes a falloff of power on each side of the operating point, then the system is conjugately matched. That conjugate match includes such things as non-dissipative resistances. 2. Conjugate matches do not exist in a typical amateur system. Brilliant minds have been trying to prove one or the other and both sides (IMO) have failed in that proof. There is no final, definitive proof of either position. If there was such, there would be no argument. That's why we cannot answer your question. The picture is further clouded by a definition. If reflected energy makes its way back into the final amp, it was never generated in the first place, by definition. -- 73, Cecil http://www.qsl.net/w5dxp "Reg Edwards" wrote: Cec et al, what have circulators, S-parameters, etc. to do with HF ? -----= 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: "Cecil Moore" wrote: What I am willing to discuss in detail is what happens at a Z0-match point (x) in an antenna system with reflections - something like the following: what you are willing to discuss is irrelevent as it has nothing to do with the original topic which was about what happens in the transmitter. Uhhhh Dave, the original topic is the Subject: line. If anything, what happens inside a transmitter is the irrelevant subject since appreciable reflections hardly ever reach the typical ham transmitter. here is the original: 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 obviously not about what is going on at some contrived transmission line joint. For these typical conditions, all voltages and currents are either in-phase or 180 degrees out of phase at the match point (x), which makes a power analysis the most simple analysis of all. that should read "For these specific conditions", those conditions are hardly 'typical', they are a very exactly contrived example which makes it easy to compare powers. No, those are typical conditions, where the ham radio antenna system is tuned to a Z0-match by a tuner, either external or internal. It is not a "very exactly contrived example" at all. It is absolutely typical of any ham radio installation where the final amp sees close to a 1:1 SWR and that is the great majority. At the Z0-match point at the input of every properly tuned transmatch, the voltages and currents are either in phase or 180 degrees out of phase. If you don't know that, it is no wonder that you label my power analysis stuff as "contrived". of course it is contrived. no one uses loads of those exact impedances, or lengths of coax like you do. |
Henry, the trouble is nobody can understand your questions. This is because
a "conjugate match" is not relevant. And that's because the internal impedance of the transmitter is an unknown quantity. The sole purpose of the so-called SWR meter is to indicate whether or not transmitter is loaded with 50 ohms. Can anyone suggest what else it USEFULLY indicates? What else does anyone need to know? ---- Reg, G4FGQ "Henry Kolesnik" wrote Not much but neither does much of this thread regarding my original query. I hope someone that understands the question can answer in a way that my feeble brain can comprehend. At least we're eliminating what's not the answer. 73 Hank WD5JFR "Reg Edwards" wrote in message ... Cec et al, what have circulators, S-parameters, etc. to do with HF ? |
My original question nor any subsequent questions included or even hinted
"conjugate match." SWR was not in the original question either but later as it applies to ghosting or smearing transmitted TV pix. Again is it an open, or short and if not what is it or can't it be explain becasue no one knows? I guess may Sunday is a day of relaxation for minds that know! 73 Hank WD5JFR "Reg Edwards" wrote in message ... Henry, the trouble is nobody can understand your questions. This is because a "conjugate match" is not relevant. And that's because the internal impedance of the transmitter is an unknown quantity. The sole purpose of the so-called SWR meter is to indicate whether or not transmitter is loaded with 50 ohms. Can anyone suggest what else it USEFULLY indicates? What else does anyone need to know? ---- Reg, G4FGQ "Henry Kolesnik" wrote Not much but neither does much of this thread regarding my original query. I hope someone that understands the question can answer in a way that my feeble brain can comprehend. At least we're eliminating what's not the answer. 73 Hank WD5JFR "Reg Edwards" wrote in message ... Cec et al, what have circulators, S-parameters, etc. to do with HF ? |
Henry Kolesnik wrote:
Then why can high SWR on a TV Tx cauuse ghosts or smearing on the TV Rx? Hank, You're preaching to the choir, asking me that question. I don't like that definition but if you poll the gurus on this newsgroup, most will say that reflected power that is incident upon the transmitter was never generated in the first place. (Never mind the ghosting that they can see with their own eyes.) Lots of steady-state ills can be swept under the rug by assuming nothing but fixed frequency sine waves with zero modulation. A guru's answer to you question is that "ghosting is not steady- state". :-) -- 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! =----- |
Quote below
Actually, it depends upon where that high SWR physically is located. A dummy load with a 1.3:1 SWR connected directly at the tx output connector will not produce a visible ghost in the demodulated TV picture. A 1.3:1 antenna SWR at the far end of more than about 500 feet of otherwise matched transmission line connected to that same transmitter WILL produce a visible ghost. -RF __________ "Henry Kolesnik" wrote Then why can high SWR on a TV Tx cauuse ghosts or smearing on the TV Rx? |
Dave wrote:
Cecil wrote: Uhhhh Dave, the original topic is the Subject: line. If anything, what happens inside a transmitter is the irrelevant subject since appreciable reflections hardly ever reach the typical ham transmitter. here is the original: Are you saying that the original subject was wrong? of course it is contrived. no one uses loads of those exact impedances, or lengths of coax like you do. Dave, have you ever heard of an example? What I posted is one easy-to-understand example of virtually an infinite number of possible examples of a Z0-match. If you like, here is another example of a Z0-match: XMTR------tuner---unknown length of feedline---unknown load 100W-- --0W There is a Z0-match at the input of the tuner. All the voltages and all the currents are very close to in-phase or 180 degrees out of phase at the input of the tuner. Do you have the balls to assert that the above configuration is "contrived"? THE GREAT MAJORITY OF AMATEUR RADIO ANTENNA SYSTEMS ACHIEVE CLOSE TO A Z0-MATCH!!! That means all the voltages and currents are close to being in phase or 180 degrees out of phase. I'm sorry that technical fact hairlips you. Since your hidden agenda is hidden, I can only guess what it might be. -- 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! =----- |
Reg Edwards wrote:
Can anyone suggest what else it USEFULLY indicates? It usefully indicates the vector sum of two voltages proportional to the net voltage and net current. It also usefully indicates the vector difference of the two voltages proportional to the net voltage and net current. Those are extremely useful indications for the initiated. I agree it is not very useful for the uninitiated. I trust that doesn't include you. -- 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! =----- |
Henry Kolesnik wrote:
... can't it be explained because no one knows? So far, it cannot be proven one way or another, so I guess you would be safe in assuming that "no one knows for sure". There are many opinions, none of which can be proven (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 Fry wrote:
A dummy load with a 1.3:1 SWR connected directly at the tx output connector will not produce a visible ghost in the demodulated TV picture. Of course, a same-cycle reflection has virtually no effect on ghosting. A 1.3:1 antenna SWR at the far end of more than about 500 feet of otherwise matched transmission line connected to that same transmitter WILL produce a visible ghost. Of course, a different-cycle reflection is what causes ghosting. -- 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! =----- |
Sorry Henry. I confused your query with what's going on in another thread.
Short circuits and open circuits result in reflection coefficients of -1 and +1 respectively. ---- Reg |
Cecil Moore wrote: Reg Edwards wrote: Reflected power is a mere fiction. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. Therefore, radar cannot work since it relies upon reflected joules/second. Mirrors also cannot work since there is an ExB amount of power in those reflections. I made note of this in a thread I just started. Is this a good analogy? Certainly the signal goes out, hits something and then comes back. Wouldn't this scramble the signal by some definable amount in an antenna? Reg, for a 291.5 ohm antenna to accept 100 watts requires the forward power to the antenna to be 200 watts. 100 watts is accepted by the antenna and 100 watts is rejected by the antenna. 200 watts to the antenna is routinely accomplished by a 100 watt ham transmitter and a Z0-match provided by a tuner. This is exactly like a partially silvered mirror that reflects half the irradiance and allows half the irradiance through. Assume a one second long lossless unterminated transmission line. Pour 1000 watts into it for one second. During the next second, we disconnect the line from the source and you grab the two wires, one in each hand. Then tell us whether reflected power exists or not. All we have to do is get an antenna that is 186,347.3233361 miles long. Or would that be 122,989.233401 miles? At any rate, the answer should be pretty easy to verify by using a very long but practical sized antenna. Anyone done that? - Mike KB3EIA - |
Cecil Moore wrote:
Assume a one second long lossless unterminated transmission line. Pour 1000 watts into it for one second. During the next second, we disconnect the line from the source and you grab the two wires, one in each hand. Then tell us whether reflected power exists or not. So if we had an infinitely long antenna, would the power put into it last forever? - Mike KB3EIA - |
It's true that even a simple DC battery circuit can be described in
terms of incident and reflected power, SWR, and reflection coefficients, but that's very unrealistic when trying to conceptually understand what's going on. I suppose a point that I'm making is that understanding how to match a source with a load doesn't have much to do with reflections and standing waves although, again, it can certainly be described (unrealistically) that way. Take the case of a transmitter and an antenna connected together with a two-port black box between them, and that black box happened to contain a transmission line. That unseen transmission line has standing waves and reflections (assuming a mismatched condition), losses, etc. all contained within the box. However, the transmitter only sees a steady state complex impedance when looking into the box (at a single frequency). Obviously there's some conjugate matching that needs to take place for maximum power transfer, but there are no reflections or standing waves involved outside the box -- unless transmission line stubs are used for matching. In short, transmission lines have reflections and standing waves, and as a "black box" they affect how the load is seen by the source. But extending the power reflection concept outside of that black box only confuses things, even though it works mathmatically. Al Cecil Moore wrote in message ... alhearn wrote: Herein lies one of the big problems with the "reflection" definition, conceptually. That's why I often resort to a signal generator with a circulator/load to illustrate my point. That signal generator *is* a constant power source. Therefore, what is commonly called "reflected power" is power that never leaves the transmitter and is dissipated as heat by the transmitter's internal 50 ohm impedance (if the transmitter's design doesn't prematurely shut down first). You can mount an argument that if the source doesn't see its source impedance, then there is a reflection at that internal mismatch. But that's not what is commonly called reflected power. When we talk about reflected power on this newsgroup, we are usually referring to the forward power rejected by a mismatch between the transmission line Z0 and the antenna impedance (associated with mismatch loss). In a typical ham radio antenna system, the "lost" reflected power is forced to engage in destructive interference at the tuner and thus joins the forward power wave. |
Mike Coslo wrote:
Cecil Moore wrote: Therefore, radar cannot work since it relies upon reflected joules/second. Mirrors also cannot work since there is an ExB amount of power in those reflections. I made note of this in a thread I just started. Is this a good analogy? Certainly the signal goes out, hits something and then comes back. Wouldn't this scramble the signal by some definable amount in an antenna? Of course, but the point is that there exists energy as power, ExH, in the reflected wave. If there is no energy in a reflected wave, radar wouldn't work. Anyone who says there is no energy in a reflected wave is just pulling your leg. Assume a one second long lossless unterminated transmission line. Pour 1000 watts into it for one second. During the next second, we disconnect the line from the source and you grab the two wires, one in each hand. Then tell us whether reflected power exists or not. At any rate, the answer should be pretty easy to verify by using a very long but practical sized antenna. Anyone done that? Anyone who has ever used a TDR on a mismatched transmission line. -- 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! =----- |
Mike Coslo wrote:
Cecil Moore wrote: Assume a one second long lossless unterminated transmission line. Pour 1000 watts into it for one second. During the next second, we disconnect the line from the source and you grab the two wires, one in each hand. Then tell us whether reflected power exists or not. So if we had an infinitely long antenna, would the power put into it last forever? It would have a feedpoint impedance of around 600 ohms and I don't know how long it would have to be to eliminate reflections. A terminated rhombic comes close to the characteristics of an infinitely long antenna. -- 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! =----- |
alhearn wrote:
Take the case of a transmitter and an antenna connected together with a two-port black box between them, and that black box happened to contain a transmission line. That unseen transmission line has standing waves and reflections (assuming a mismatched condition), losses, etc. all contained within the box. However, the transmitter only sees a steady state complex impedance when looking into the box (at a single frequency). That's a steady-state shortcut which assumes pure sine waves that don't exist in reality. Please don't confuse steady-state shortcuts with reality. Noise and modulation cause the "steady-state complex impedance" not to be steady-state at all. Many will say it's close enough, but one cannot understand reflections by assuming an un- varying steady-state. In a TV system with ghosting due to reflections, the unvarying steady- state condition doesn't exist. In fact, when you assume steady-state conditions, you eliminate ghosting, at least in your own mind. In reality, steady-state doesn't really exist because of random noise and unpredictable modulation. -- 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 ... ................................. Of course, but the point is that there exists energy as power, ExH, in the reflected wave. If there is no energy in a reflected wave, radar wouldn't work. Anyone who says there is no energy in a reflected wave is just pulling your leg. But its not free. If you tap it, it won't be there to re reflect. So, I think in the steady state you have changed the load impedance. BTW, (not a joke or sarcasm) Have you heard of Zero Point Energy? They calculate there is something like 10**26 Joules in a cubic meter of empty space. Tam/WB2TT |
"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%. ..................................... |
Aviation Week & Space Technology. March 1, 2004. P50.
Tam |
Tam/WB2TT wrote:
"Cecil Moore" wrote: Of course, but the point is that there exists energy as power, ExH, in the reflected wave. If there is no energy in a reflected wave, radar wouldn't work. Anyone who says there is no energy in a reflected wave is just pulling your leg. But its not free. If you tap it, it won't be there to re reflect. So, I think in the steady state you have changed the load impedance. Moral: don't use it up, just use a negligible portion for measurement purposes. A Bird wattmeter consumes very little actual power. BTW, (not a joke or sarcasm) Have you heard of Zero Point Energy? They calculate there is something like 10**26 Joules in a cubic meter of empty space. Yes, some people think that is the energy being measured, off and on, in the cold fusion experiments. The question is: If one taps into the energy being used to support the structure of space itself, what happens to that space structure? IMO, space is the result of the annihilation of matter and anti-matter in the early universe and certainly still contains that annihilation energy. -- 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:
Hi Ian, Perhaps in this immediate thread. However, I have demonstrated both sides coming to the same conclusions several many times, and one example as recently as within this last week. This issue is not about being right, it is about ego foremost else why all the debate? Hank has asked a fairly straightforward question with rather simple terms he could accept as a compelling case. To this point (some 22 entries) that has been largely abandoned with each scribbler answering their own imagining of how to discover the philosopher's stone. 73's Richard Clark, KB7QHC I haven't been here terribly long, maybe 6 weeks, but I have noticed that your comment applies to around half of the threads longer than 4 or so comments. A better ratio than many newsgroups, and people seem to have a sense of humor, which a lot of other newsgroup's participants decidedly do not. So, all in all, it could be worse. tom K0TAR |
Tom Ring wrote: Richard Clark wrote: Hi Ian, Perhaps in this immediate thread. However, I have demonstrated both sides coming to the same conclusions several many times, and one example as recently as within this last week. This issue is not about being right, it is about ego foremost else why all the debate? Hank has asked a fairly straightforward question with rather simple terms he could accept as a compelling case. To this point (some 22 entries) that has been largely abandoned with each scribbler answering their own imagining of how to discover the philosopher's stone. 73's Richard Clark, KB7QHC I haven't been here terribly long, maybe 6 weeks, but I have noticed that your comment applies to around half of the threads longer than 4 or so comments. A better ratio than many newsgroups, and people seem to have a sense of humor, which a lot of other newsgroup's participants decidedly do not. So, all in all, it could be worse. That's very true, Tom. Even with the egos, the civility level is pretty high in here. Of course that is probably why the fringe elements don't hang out here. - Mike KB3EIA - |
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 "Henry Kolesnik" wrote in message om... If this old mind recalls correctly a TV station with an undesireable SWR will not transmit a clear image to its viewers because the delayed re-reflection arrives at the TV set later and casues a ghost or smear. Could you please explain the "Reflected power is a mere fiction." and the smear or ghost? tnx Hank WD5JFR "Reg Edwards" wrote in message ... "Richard Clark" wrote: What you describe as reflection and re-reflection occurs between the mismatched antenna and the tuner that has been adjusted to minimize power returned to the transmitter. The sole function of the tuner is to keep this power from being dissipated by the transmitter (common experience of arcing, denoting a voltage reflection, or thermal runaway, denoting a current reflection). The "virtual" reflection (offered by the tuner) is generally know as the complex conjugate of the remote load, seen at the near end of the line through which it is returning. This means that the line transforms the phase and amplitude of the reflection, and the tuner's job is to invert that relationship to counteract it, and return it to the antenna. There are both wave descriptions of this process, and lumped circuit equivalents. Both work, and both describe the same process from different points of view. One does not negate the other's validity (unless, of course, you attempt to mix the points of view and demand consistency in terms - a frequent rhetorical trap here). There will no doubt be a flurry of denials to this simple example with contortions of logic to match. As for the math, you will find it by the reams, once you've been overwhelmed with the arcana of hyperbolic descriptions of a novel physics that have to proceed its proof. Keep your eye on how your literal points in your question go abandoned with these arcane theories. 73's Richard Clark, KB7QHC ==================================== Dear Richard, you are confusing the matter even further, if that were possible. The only saving grace about your tedius message is that you yourself eventually realise what a load of overcomplicated nonsense it is. Reflected power is a mere fiction. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. All the power which leaves the transmiter is radiated except for that which is lost in the line. It has nowhere else to go! But for the existence of so-called SWR meters, the words 'forward and reflected power' would never enter people's vocabularies. For the few who become involved with such matters, the misleading fiction also appears in the language of mathematics. Names have to be invented in order to discuss mathematical equations in plain English. But there's no reason why they should be propagated, just to confuse, into the real World. The sole purpose of an SWR meter is to indicate whether or not the transmitter is loaded with 50 ohms. ---- Reg, G4FGQ |
It usefully indicates the vector sum of two voltages
proportional to the net voltage and net current. It also usefully indicates the vector difference of the two voltages proportional to the net voltage and net current. Those are extremely useful indications for the initiated. I agree it is not very useful for the uninitiated. I trust that doesn't include you. -- 73, Cecil An SWR meter does NOT usefully indicate the vector sum of two voltages or the vector difference between two voltages. I've never seen a meter with such scales. Even if it did, of what possible use would it be to anyone who is already reliably informed his transmitter is loaded with 50 ohms. ---- Reg, G4FGQ |
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"Cecil Moore" wrote in message ... Tam/WB2TT wrote: It shows the composite voltage waveform, and the net current. Exactly what a Bird wattmeter would do. That's not what a Bird wattmeter does. A Bird wattmeter possesses a directional coupler. Sort of. I have built circuits that subtract out the transmitted signal, leaving the received signal.signal. The Bird is cruder than that. SPICE apparently does not. I was driving it with a sine wave, but did a transient analysis. The whole point is it does not have to know about reflections. It calculates the waveform by using the same rules that are used to derive standing waves and reflections. Is it possible to add a directional coupler to SPICE? I have built a SPICE model of a Kenwood power/SWR meter (Have better schematic than for a Bird). Actually, an idealized version that is not physically realizable; I did this on purpose. Clearly shows what the limitations are. Interesting thing is that there is information present that no SWR meter that I know of displays. For an SWR other than 1:1, you can deduce whether RL is bigger or smaller than Z0 by comparing two voltages. If you know the Z0, the net voltage/current magnitudes/phases, it should be possible to use phasor addition/subtraction to obtain the forward and reflected components, just like the Bird wattmeter does. But there is only one voltage sample, which is the sum of Vf and Vr. There *are* two current samples, but they are exactly the same, only one is 180 degrees out of phase due to looking at the opposite end of the current transformer. Here is what happens. Say you want a meter that shows 100W full scale when feeding a 50 Ohm load. That is 70.7 V and 1.414 A. In the "Forward" direction this leads to 100 = 70.7K1 + 1.414K2 In the "Reverse"direction, we know that Pr=0, so 0 = 70.7K1 - 1.414K2 ( The minus sign comes from reversing the current reading). You have 2 equations, so you can solve for K1 and K2. You know it can't *really* measure power, because there is no multiplier. Just like the Bird, it *adds* (vector wise) voltage and current. -- 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! =----- |
Reg Edwards wrote:
An SWR meter does NOT usefully indicate the vector sum of two voltages or the vector difference between two voltages. I've never seen a meter with such scales. That's the way a Bird wattmeter works. The vector sum of two voltages is the forward power on the scale. The vector difference of those same two voltages is the reflected power on the scale. One voltage is proportional to the net voltage. The other voltage is proportional to the net current. Even if it did, of what possible use would it be to anyone who is already reliably informed his transmitter is loaded with 50 ohms. In addition to my 50 ohm SWR meter, I have 450 ohm and 300 ohm SWR meters, Reg. They indicate the forward/reflected powers and SWR on the antenna side of the tuner which I find most helpful. -- 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:
You have 2 equations, so you can solve for K1 and K2. You know it can't *really* measure power, because there is no multiplier. Just like the Bird, it *adds* (vector wise) voltage and current. Exactly, and if you work out the math, you will find it yields a meter deflection that can be calibrated in watts of forward or reflected power. In your example, assume that 70.7v yields a 5v sample and 1.414a yields a 5v sample. If they are in phase, 10v will indicate 100 watts forward and zero volts will indicate zero watts reflected. If they are not equal and not in phase, their sum still indicates forward watts and their difference still indicates reflected watts. -- 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: Cecil wrote: Uhhhh Dave, the original topic is the Subject: line. If anything, what happens inside a transmitter is the irrelevant subject since appreciable reflections hardly ever reach the typical ham transmitter. here is the original: Are you saying that the original subject was wrong? no, only that you ignored the body of the message and answered what you wanted to discuss instead of what was asked. of course it is contrived. no one uses loads of those exact impedances, or lengths of coax like you do. Dave, have you ever heard of an example? What I posted is one easy-to-understand example of virtually an infinite number of possible examples of a Z0-match. If you like, here is another example of a Z0-match: XMTR------tuner---unknown length of feedline---unknown load 100W-- --0W There is a Z0-match at the input of the tuner. All the voltages and all the currents are very close to in-phase or 180 degrees out of phase at the input of the tuner. Do you have the balls to assert that the above configuration is "contrived"? nope, that is a real world situation, but not the one under discussion. THE GREAT MAJORITY OF AMATEUR RADIO ANTENNA SYSTEMS ACHIEVE CLOSE TO A Z0-MATCH!!! That means all the voltages and currents are close to being in phase or 180 degrees out of phase. I'm sorry that technical fact hairlips you. Since your hidden agenda is hidden, I can only guess what it might be. so which is it, in phase or 180 degrees out of phase??? |
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. 73 Hank WD5JFR "alhearn" wrote in message om... 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 "Henry Kolesnik" wrote in message om... If this old mind recalls correctly a TV station with an undesireable SWR will not transmit a clear image to its viewers because the delayed re-reflection arrives at the TV set later and casues a ghost or smear. Could you please explain the "Reflected power is a mere fiction." and the smear or ghost? tnx Hank WD5JFR "Reg Edwards" wrote in message ... "Richard Clark" wrote: What you describe as reflection and re-reflection occurs between the mismatched antenna and the tuner that has been adjusted to minimize power returned to the transmitter. The sole function of the tuner is to keep this power from being dissipated by the transmitter (common experience of arcing, denoting a voltage reflection, or thermal runaway, denoting a current reflection). The "virtual" reflection (offered by the tuner) is generally know as the complex conjugate of the remote load, seen at the near end of the line through which it is returning. This means that the line transforms the phase and amplitude of the reflection, and the tuner's job is to invert that relationship to counteract it, and return it to the antenna. There are both wave descriptions of this process, and lumped circuit equivalents. Both work, and both describe the same process from different points of view. One does not negate the other's validity (unless, of course, you attempt to mix the points of view and demand consistency in terms - a frequent rhetorical trap here). There will no doubt be a flurry of denials to this simple example with contortions of logic to match. As for the math, you will find it by the reams, once you've been overwhelmed with the arcana of hyperbolic descriptions of a novel physics that have to proceed its proof. Keep your eye on how your literal points in your question go abandoned with these arcane theories. 73's Richard Clark, KB7QHC ==================================== Dear Richard, you are confusing the matter even further, if that were possible. The only saving grace about your tedius message is that you yourself eventually realise what a load of overcomplicated nonsense it is. Reflected power is a mere fiction. Power which is not radiated from an antenna never actually arrives there. In fact it never leaves the transmitter. All the power which leaves the transmiter is radiated except for that which is lost in the line. It has nowhere else to go! But for the existence of so-called SWR meters, the words 'forward and reflected power' would never enter people's vocabularies. For the few who become involved with such matters, the misleading fiction also appears in the language of mathematics. Names have to be invented in order to discuss mathematical equations in plain English. But there's no reason why they should be propagated, just to confuse, into the real World. The sole purpose of an SWR meter is to indicate whether or not the transmitter is loaded with 50 ohms. ---- Reg, G4FGQ |
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). The visible part of a TV image is scanned onto the display screen at a horizontal rate of about 1 line per 50 microseconds.* An internal reflection from a transmit antenna connected to the tx by 1,000 feet of transmission line will create a ghost image ~1 microsecond after the main image -- or ~1/2" to the right side of it in a 25" wide picture. As the narrowest vertical line that can be viewed on a display using a 4MHz video bandwidth is a bit less than 0.35 microseconds wide, a ghost image of it displaced by 1 microsecond is clearly and separately visible on a 25" wide display, and will not appear as a "smear" of the main image. Ghosts also can be produced by external reflections of the radiated TV signal from buildings, large signs, etc. Often these ghosts have much greater displacement from the main image than those that can be transmitted from reflections in the TV transmit antenna system. This is the result of the greater transit time for those reflections w.r.t. the direct ray, that are common for reflecting and scattering surfaces where located in the propagation environment. Reflections with "short" time displacements are more difficult to resolve separately as ghosts, but still affect and limit the visual quality of the TV image. Reflections 40dB or more suppressed from the main image have no practical, visible affect on it -- regardless of their time displacement. R. Fry, RCA Broadcast Field Engineer 1965-1980 *allows for the H&V sync pulse intervals and some overscan _______________________ R. Fry wrote A 1.3:1 antenna SWR at the far end of more than about 500 feet of otherwise matched transmission line connected to that same transmitter WILL produce a visible ghost. "Cecil Moore" responded Of course, a different-cycle reflection is what causes ghosting. |
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