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#11
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Reg Edwards wrote:
Jim, To measure SWR on the line it is necessary to place the SWR meter at the antenna end of the line. Even then it gives the correct answer only when the line impedance is 50 ohms. Well, duh. Anyone that doesn't know that SWR is with reference to a stated impedance or that SWR is influenced by the characteristics of a real transmission line just isn't paying attention. But the SWR meter is always placed immediately adjacent to the transmitter. Whatever the meter indicates it is not SWR because there is no line on which to measure it. The meter is telling lies. Errr, no, the meter is telling what it sees at the point of measurement. If the measurer is so opaque that he/she doesn't take line influences into account, it is hardly the fault of the measuring instrument that what is reported is not the SWR of the antenna at the specified impedance. The meter indicates only whether or not the transmitter is loaded with a resistance of 50 ohms. Which is ALL you want to know. It tells you nothing more and nothing less. Basically true given the stated conditions, and all that is probably of interest for the average ham. This is, of course, a very valuable function of the instrument. But it is NOT behaving as an SWR meter. Its name should be changed to Transmitter Loading Indicator (TLI). Uttern nonsense; the instrument is still behaving as a SWR meter but the user is not applying it per spec and not correcting measurement error caused by line position. By this logic we have a lot of names to change. For starters: PAM has to change the name of their cooking spray to: Teenage looser get high in a can. Screwdriver manufacturers have to change the name of their product to: General prying instrument and paint can lid removal tool. You may add others. To use the name "SWR meter" and to imagine it is actually measuring an SWR is seriously misleading and is a source of confusion about what is really going on. Nonsense, the meter is always measuring SWR but the user is obviously not measuring the SWR that would be seen at the end of the line. You can't fault the instrument for it's misuse by the ignorant. What would you call a low impedance voltmeter used by some nimrod to measure voltage in a high impedance circuit? It is why there are perpetual arguments and misunderstandings about SWR, tuners and related matters on this newsgroup and in every other place. That is probably true since most people are opaque as to what goes on on a real transmission line, but not everyone is. Change the name to TLI, which is what it really does. Novices will not be lead astray, clear thinking will prevail, false ideas will not take root to remain embedded for the remainder of one's radio career. Clear thinking would demand that the influences of a real line on the observered SWR at an arbitrary point be explained. Air pressure indicators instead of airspeedometers are OK because air pressure actually exists. Non sequitur; SWR actually exists. Getting an accurate measurment is another issue and a matter of education. SWR meters are NOT OK because there is no line for SWR to exist on. (At least not where the meter is imagined or supposed to measure it.) Nonsense. Makes a change from cavity magnetrons. More nonsense and not even a sentence. About the only difference between microwave and HF is that it is a lot easier to build a line, i.e. waveguide, that approximates a theoretical ideal lossless transmission line for reasonable distances at microwave than it is to build lossless coax as commonly used at HF. All the theory remains the same. Personally, I have never had any problem with understanding what it is that a SWR meter displays. ---- Reg. -- Jim Pennino Remove .spam.sux to reply. |
#12
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Ah, Reggie & Richie.
I tried SWRing once. My mother washed my mouth out with soap & water! |
#13
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Errr, no, the meter is telling what it sees at the point of
measurement. ===================================== But the meter is not seeing an SWR because an SWR does not exist. Where is the 50-ohm transmission line on which the SWR is imagined or supposed to lie? As you are unable to answer that question, the remainder of your argument (which, as I say, arises because of the SWR meter misleading misnomer) falls flat on its face. You are an intelligent person. I don't doubt you have no problems with understanding what the so-called SWR meter really indicates. But you didn't learn this from observations of the SWR meter - as you already know it tells lies! Just to reiterate, the so-called SWR meter indicates only whether or not the load on the transmitter is a resistive 50 ohms. If it is not 50 ohms it will not tell you what it actually is. Not that you need to know what it actually is because you will readjust your tuner, without thinking about it, to make it equal to 50 ohms. Which corresponds to no deflection of the meter needle. The TLI is a very useful and valuable device. It does not lead novices and old-wives (who ought to know better) into false ideas, or cause confusion and misunderstandings within the amateur fraternity. Professionals dismiss SWR for what it is worth anyway. Goodby to SWR except on lines where it matters and where it can be measured. Which, in practice, are very few. --- Reg, G4FGQ. |
#14
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Reg Edwards wrote:
Where is the 50-ohm transmission line on which the SWR is imagined or supposed to lie? On my system, there's a 50 ohm cable from the transceiver to the input of the SWR meter and another 50 ohm cable from the output of the SWR meter to the balun. Each of these cables forces the ratio of the voltage to current in each of the traveling waves to a value of 50 ohms. I have an in-line Autek WM-1 and no tuner. -- 73, Cecil http://www.qsl.net/w5dxp |
#15
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Reg Edwards wrote:
Errr, no, the meter is telling what it sees at the point of measurement. ===================================== But the meter is not seeing an SWR because an SWR does not exist. Nonsense. Where is the 50-ohm transmission line on which the SWR is imagined or supposed to lie? In my personal case, there is 50 Ohm transmission line between the transceiver and the SWR meter, then a length of line to a coax switch, then several lines out to antennas. You seem fixated on haveing some magical length of transmission line being necessary for a SWR to exist. This is nonsense. As you are unable to answer that question, the remainder of your argument (which, as I say, arises because of the SWR meter misleading misnomer) falls flat on its face. You are an intelligent person. I don't doubt you have no problems with understanding what the so-called SWR meter really indicates. But you didn't learn this from observations of the SWR meter - as you already know it tells lies! Babble. A SWR meter indicates what is. Knowing what the reading really means is a matter of education, not veracity. Just to reiterate, the so-called SWR meter indicates only whether or not the load on the transmitter is a resistive 50 ohms. If it is not 50 ohms it will not tell you what it actually is. Not that you need to know what it actually is because you will readjust your tuner, without thinking about it, to make it equal to 50 ohms. Which corresponds to no deflection of the meter needle. With some education and multiple measurements, you can caluclate the actual impedance if one desires. What tuner? What makes you believe everyone has a tuner? The TLI is a very useful and valuable device. It does not lead novices and old-wives (who ought to know better) into false ideas, or cause confusion and misunderstandings within the amateur fraternity. Professionals dismiss SWR for what it is worth anyway. The only one I see confused is you and professionals use SWR all the time and in many systems it is extremely important. Goodby to SWR except on lines where it matters and where it can be measured. Which, in practice, are very few. If one knows what they are doing, SWR can always be measured. --- Reg, G4FGQ. -- Jim Pennino Remove .spam.sux to reply. |
#16
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Jim wrote,
If one knows what they are doing, SWR can always be measured. =================================== NOT on a line which isn't there. QED. --- Reg. |
#17
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On Mon, 26 Sep 2005 16:20:14 +0000 (UTC), "Reg Edwards"
wrote: Jim wrote, If one knows what they are doing, SWR can always be measured. NOT on a line which isn't there. QED. Hi Reg, Which only proves Jim is correct, in that you reject the facility to do it with a line. My SWR meters do in fact have a 50 Ohm line transiting from the gozinta to the comesouta. Your poor choice of vendor, or poor solution implemented in design is your own problem, not that of the world's. I see that you still enjoy its mutilated discussion to the obvious neglect of magnetrons. Much better than flogging Kelvinator, I suppose. Now there's an image, you going nose to nose with him. He'd send you back to lower 6th for missing the bloody obvious. 73's Richard Clark, KB7QHC |
#18
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Reg Edwards wrote: Jim wrote, If one knows what they are doing, SWR can always be measured. =================================== NOT on a line which isn't there. QED. --- Reg. Perhaps this is a dumb question Reg, but if the transmission line isn't there, how does RF get from the transmitter to the antenna? Thanks, ac6xg |
#19
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Reg Edwards wrote:
Errr, no, the meter is telling what it sees at the point of measurement. ===================================== But the meter is not seeing an SWR because an SWR does not exist. Where is the 50-ohm transmission line on which the SWR is imagined or supposed to lie? Why do you keep insisting that SWR can only exhist on a 50-ohm transmission line. There are a multitude of impedances in transmission lines that are other than 50-ohms. SWR is present on every and any transmission line that doesn't match the transmission element perfectly. Dave WD9BDZ As you are unable to answer that question, the remainder of your argument (which, as I say, arises because of the SWR meter misleading misnomer) falls flat on its face. You are an intelligent person. I don't doubt you have no problems with understanding what the so-called SWR meter really indicates. But you didn't learn this from observations of the SWR meter - as you already know it tells lies! Just to reiterate, the so-called SWR meter indicates only whether or not the load on the transmitter is a resistive 50 ohms. If it is not 50 ohms it will not tell you what it actually is. Not that you need to know what it actually is because you will readjust your tuner, without thinking about it, to make it equal to 50 ohms. Which corresponds to no deflection of the meter needle. The TLI is a very useful and valuable device. It does not lead novices and old-wives (who ought to know better) into false ideas, or cause confusion and misunderstandings within the amateur fraternity. Professionals dismiss SWR for what it is worth anyway. Goodby to SWR except on lines where it matters and where it can be measured. Which, in practice, are very few. --- Reg, G4FGQ. |
#20
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