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An antenna question--43 ft vertical
Jeff wrote:
The SWR has to be the same at any point on the coax or transmission line minus the loss in the line. A simple swr meter may show some differance because of the way that kind of meter works. By changing the length of the line , the apparent SWR may be differant at that point. There is no such thing as apparent SWR. It is what it is in a given place. By 'apparent SWR' he means as indicated SWR on the meter, and yes it can change at various point on the line due to inadequacies in the meter; the 'real' VSWR will of course remain the same at any point on a lossless line. Jeff Nope, it changes in the real world due to various line losses and in the theoretical, lossless line world it can change for several reasons. Ever heard of a transmission line impedance transformer, which is multiple sections of transmission lines with differing impedance? Ever heard of a tapered impedance transmission line which is also used to transform impedances? The SWR at any location in a system is what it is. Bringing up equipment errors is a straw man. -- Jim Pennino |
An antenna question--43 ft vertical
Ralph Mowery wrote:
"Jeff" wrote in message ... The SWR has to be the same at any point on the coax or transmission line minus the loss in the line. A simple swr meter may show some differance because of the way that kind of meter works. By changing the length of the line , the apparent SWR may be differant at that point. There is no such thing as apparent SWR. It is what it is in a given place. By 'apparent SWR' he means as indicated SWR on the meter, and yes it can change at various point on the line due to inadequacies in the meter; the 'real' VSWR will of course remain the same at any point on a lossless line. Jeff That is what I mean Jeff. If there is any SWR, by changing the length of the line, the voltage/current changes in such a maner that at certain points you may get a 50 ohm match at that point. What do you mean "if"? There is ALWAYS a SWR in a transmission line system. -- Jim Pennino |
An antenna question--43 ft vertical
rickman wrote:
On 7/9/2015 9:14 AM, Ralph Mowery wrote: "Jeff" wrote in message ... The SWR has to be the same at any point on the coax or transmission line minus the loss in the line. A simple swr meter may show some differance because of the way that kind of meter works. By changing the length of the line , the apparent SWR may be differant at that point. There is no such thing as apparent SWR. It is what it is in a given place. By 'apparent SWR' he means as indicated SWR on the meter, and yes it can change at various point on the line due to inadequacies in the meter; the 'real' VSWR will of course remain the same at any point on a lossless line. Jeff That is what I mean Jeff. If there is any SWR, by changing the length of the line, the voltage/current changes in such a maner that at certain points you may get a 50 ohm match at that point. https://en.wikipedia.org/wiki/Standi...dance_matching "if there is a perfect match between the load impedance Zload and the source impedance Zsource=Z*load, that perfect match will remain if the source and load are connected through a transmission line with an electrical length of one half wavelength (or a multiple of one half wavelengths) using a transmission line of any characteristic impedance Z0." This wiki article has a lot of good info in it. I have seen a lot of stuff posted here that this article directly contradicts.... I wonder who is right? It has been my observation that when the subject matter is long established science, such as transmission line theory, wiki is normally correct. -- Jim Pennino |
An antenna question--43 ft vertical
Jeff wrote:
you may get a 50 ohm match at that point. https://en.wikipedia.org/wiki/Standi...dance_matching "if there is a perfect match between the load impedance Zload and the source impedance Zsource=Z*load, that perfect match will remain if the source and load are connected through a transmission line with an electrical length of one half wavelength (or a multiple of one half wavelengths) using a transmission line of any characteristic impedance Z0." This wiki article has a lot of good info in it. I have seen a lot of stuff posted here that this article directly contradicts.... I wonder who is right? That is a very specific case where the source is not at the system impedance and happens to be equal to the load impedance, there will also be standing waves on the transmission line and associated losses as the VSWR on the line will be equal to the magnitude of the mismatch between the transmission line impedance and the load impedance. Jeff Most people take the source impdedance to be the system impedance, i.e. the impedance for which everything else is designed for. To put it another way, do we design transmitters to match the antenna and feed line or design antennas and feedline to match the transmitter? -- Jim Pennino |
An antenna question--43 ft vertical
Jeff wrote:
By 'apparent SWR' he means as indicated SWR on the meter, and yes it can change at various point on the line due to inadequacies in the meter; the 'real' VSWR will of course remain the same at any point on a lossless line. Jeff That is what I mean Jeff. If there is any SWR, by changing the length of the line, the voltage/current changes in such a maner that at certain points you may get a 50 ohm match at that point. Absolutely NOT. By changing the length of a transmission you will NEVER create the situation where you get a 50 ohm match from an initial mismatch. How about a section of transmission line with one impedance of some length attached to a section of transmission line with a different impedance of random length? -- Jim Pennino |
An antenna question--43 ft vertical
Jeff wrote:
On 09/07/2015 17:03, Ralph Mowery wrote: "Jeff" wrote in message ... By 'apparent SWR' he means as indicated SWR on the meter, and yes it can change at various point on the line due to inadequacies in the meter; the 'real' VSWR will of course remain the same at any point on a lossless line. Jeff That is what I mean Jeff. If there is any SWR, by changing the length of the line, the voltage/current changes in such a maner that at certain points you may get a 50 ohm match at that point. Absolutely NOT. By changing the length of a transmission you will NEVER create the situation where you get a 50 ohm match from an initial mismatch. This is clearly demonstrable on a Smith chart. Take any starting point other than a pure 50 ohms and add a length of transmission line. What you will find is that as you increase the length of line your point will merely rotate around the chart at a fixed radius (known as a constant VSWR circle), it will never spiral into the centre which is 50 ohms and where it must be for a perfect match. The only time that it will start to spiral inwards is if the line is lossy, but you will need a very long length, and the spiralling inwards is due to the loss in the coax NOT any matching characteristics due to the length of line. If such an effect as you are talking about is observed it is merely due to the finite, and often poor, directivity of the SWR meter giving you a false reading. Also it is worth noting that achieving 50 ohms as a magnitude |Z| of the complex impedance (Sqrt(R^2+X^2)) is not the same as getting a good match with 50 ohms resistive. Even if |Z| = 50 ohms it will have a VSWR greater than 1 if Z0. Again, plot the point on a Smith chart and you will see that it can never be in the centre of the chart. Jeff That is easy to disprove Jeff. If I have a 50 ohm load and use a 1/2 wave of any impedance line other than 50 ohms, the swr will be greater than 1:1, except at 1/2 wave multiplies of the line. At this point there will be a 50 ohm match. The swr of the line will not actually be 1:1 but some greater value. That is correct, but not the situation that we are discussing, we are talking about matching a load to a 50 ohm transmission line. In that case changing the length of line will NEVER result in a match. Using a *different impedance* length of coax as a transmission line transformer is a totally different case, and as you say will result is a standing wave on the line and associated losses. Jeff So you are only interested in special cases? -- Jim Pennino |
An antenna question--43 ft vertical
Jeff wrote:
No. It is defined as Vmax/Vmin on the line. Show an equation that defines SWR as the matching of the source to the line. OK, since you insist, one more time: SWR = (1 + |r|)/(1 - |r|) Where r = reflection coefficient. r = (Zl - Zo)/(Zl + Zo) Where Zl = complex load impedance and Zo = complex source impedance. https://en.wikipedia.org/wiki/Reflection_coefficient http://www.antenna-theory.com/tutori...nsmission3.php And once more time, the formula linking VSWR to Reflection coefficient uses ONLY the MAGNITUDE of the Reflection Coefficient |r|, taking the magnitude removes the phase component. The magnitude DEPENDS on the phase component. Secondly the formula linking VSWR to Reflection Coefficient is NOT a definition of VSWR, it is merely a formula that links 2 related quantities. So is power P=EI or P=E^2/R? Which is the "official" definition? -- Jim Pennino |
An antenna question--43 ft vertical
On 7/9/2015 1:46 PM, wrote:
rickman wrote: On 7/8/2015 7:43 PM, wrote: Ralph Mowery wrote: wrote in message ... Ralph Mowery wrote: Can you show any place where the SWR definition mentions the Source impedance ? I have several times now, but once again: SWR = (1 + |r|)/(1 - |r|) Where r = reflection coefficient. r = (Zl - Zo)/(Zl + Zo) Where Zl = complex load impedance and Zo = complex source impedance. https://en.wikipedia.org/wiki/Reflection_coefficient http://www.antenna-theory.com/tutori...nsmission3.php You might check that again. I don't see Zo being defined as the complex source impedance, but rather as the transmission line characteristic impedance... not the same thing at all. YOu have just proven my point. Read carefully from your refernce to Wikipedia : "The reflection coefficient of a load is determined by its impedance and the impedance toward the source." Notice it says TOWARD and not THE SOURCE. Notice it actually says "the impedance toward the source". From the second referaence notice that it says load impedance and impedance of the transmission line. Nothing mentions the source at all: What the hell do you think the transmission line is in this case if not the source? "The reflection coefficient is usually denoted by the symbol gamma. Note that the magnitude of the reflection coefficient does not depend on the length of the line, only the load impedance and the impedance of the transmission line. Also, note that if ZL=Z0, then the line is "matched". In this case, there is no mismatch loss and all power is transferred to the load." Perhaps you would like the second link better as it has pictures. Of maybe this one that explains it all starting with lumped equivelant circuits. http://www.maximintegrated.com/en/ap...dex.mvp/id/742 Notice that ALL the links talk about the source impedance. How about this one? https://en.wikipedia.org/wiki/Standi...dance_matching I think this has some very interesting analysis, very specifically referring to "purely resistive load impedance". So what? A purely resistive anything is a special case of the general problem. So? -- Rick |
An antenna question--43 ft vertical
On 7/9/2015 1:58 PM, wrote:
rickman wrote: On 7/9/2015 9:14 AM, Ralph Mowery wrote: "Jeff" wrote in message ... The SWR has to be the same at any point on the coax or transmission line minus the loss in the line. A simple swr meter may show some differance because of the way that kind of meter works. By changing the length of the line , the apparent SWR may be differant at that point. There is no such thing as apparent SWR. It is what it is in a given place. By 'apparent SWR' he means as indicated SWR on the meter, and yes it can change at various point on the line due to inadequacies in the meter; the 'real' VSWR will of course remain the same at any point on a lossless line. Jeff That is what I mean Jeff. If there is any SWR, by changing the length of the line, the voltage/current changes in such a maner that at certain points you may get a 50 ohm match at that point. https://en.wikipedia.org/wiki/Standi...dance_matching "if there is a perfect match between the load impedance Zload and the source impedance Zsource=Z*load, that perfect match will remain if the source and load are connected through a transmission line with an electrical length of one half wavelength (or a multiple of one half wavelengths) using a transmission line of any characteristic impedance Z0." This wiki article has a lot of good info in it. I have seen a lot of stuff posted here that this article directly contradicts.... I wonder who is right? It has been my observation that when the subject matter is long established science, such as transmission line theory, wiki is normally correct. Why do you ignore it when it says Zo is the impedance of the transmission line and not the source? -- Rick |
An antenna question--43 ft vertical
rickman wrote:
On 7/9/2015 1:27 PM, wrote: rickman wrote: On 7/8/2015 9:07 PM, John S wrote: On 7/8/2015 4:48 PM, wrote: John S wrote: On 7/8/2015 12:47 PM, wrote: John S wrote: So, at 1Hz the law has changed, eh? What new law do I need to use? To be pendatic, there is only one set of physical laws that govern electromagnetics. However for DC all the complex parts of those laws have no effect and all the equations can be simplified to remove the complex parts. In the real, practical world people look upon this as two sets of laws, one for AC and one for DC. A good example of this is the transmission line which does not exist at DC; at DC a transmission line is nothing more than two wires with some resistance that is totally and only due to the ohmic resistance of the material that makes up the wires. So, is .01Hz AC or DC, Jim? How about 1Hz? 10Hz? Where does AC begin and DC end? It is called a limit. If there is NO time varying component, it is DC, otherwise it is AC. Are you playing devil's advocate or are you really that ignorant? Then there is no such thing as DC because even a battery looses voltage over a period of time. DC voltage sources have noise. Are just being argumentative or are you really that ignorant? Even if you have a theoretical voltage source, there are no circuits (other than imaginary) that have been on since before the big bang and will be on for all time in the future. So what? Is there some point to all this other than to be argumentative? How long before someone brings up the fact that a resistor generates AC signals as some kind of straw man objection to DC theory? The point is that separating DC and AC as being ruled by separate "laws" is pointless. Just discuss the topic of interest rather than digressing onto pointless diversions. Actually separating DC and AC is extremely practical which is why it is done in the real world. -- Jim Pennino |
An antenna question--43 ft vertical
rickman wrote:
On 7/9/2015 1:44 PM, wrote: Wayne wrote: wrote in message ... John S wrote: On 7/8/2015 7:27 PM, Wayne wrote: "John S" wrote in message ... On 7/7/2015 1:44 PM, wrote: Ian Jackson wrote: In message , Jerry Stuckle writes Sure, there is ALWAYS VSWR. It may be 1:1, but it's always there. If there's no reflection, there can be no standing wave. So, being pedantic, there's no such thing as an SWR of 1:1! Despite the name, VSWR is defined in terms of complex impedances and wavelengths, not "waves" of any kind. Actually, VSWR is defined as the ratio of Vmax/Vmin. That's also my understanding of the definition. In fact since SWR is defined as the maximum to minimum voltage ratio, the "V" in VSWR is redundant. Sort of. There is also ISWR but it is not used frequently. # Not sort of, but is. # There is also PSWR. And both go back to the Vmax/Vmin definition. The PSWR is a tricky one because you can end up with a power ratio instead of a voltage ratio. Actually, no, PSWR has nothing to do with power ratios as in RF power, rather it has to do with power ratios as in values raised to the second power. Lol! "The term power standing wave ratio (PSWR) is sometimes referred to, and defined as the square of the voltage standing wave ratio." "In other words, there are no actual powers being compared." https://en.wikipedia.org/wiki/Standing_wave_ratio -- Jim Pennino |
An antenna question--43 ft vertical
On 7/9/2015 4:29 AM, Roger Hayter wrote:
Jeff wrote: On 08/07/2015 19:14, wrote: John S wrote: On 7/7/2015 1:44 PM, wrote: Ian Jackson wrote: In message , Jerry Stuckle writes Sure, there is ALWAYS VSWR. It may be 1:1, but it's always there. If there's no reflection, there can be no standing wave. So, being pedantic, there's no such thing as an SWR of 1:1! Despite the name, VSWR is defined in terms of complex impedances and wavelengths, not "waves" of any kind. Actually, VSWR is defined as the ratio of Vmax/Vmin. Actually, VSWR can be defined several ways, one of which is: (1 + |r|)/(1 - |r|) Where r is the reflection coefficient which can be defined a: (Zl - Zo)/(Zl + Zo) Where Zl is the complex load impedance and Zo is the complex source impedance. Note that a complex impedance has a frequency dependant part. Note the the definition of VSWR uses the magnitude of the reflection coefficient, |r|, which removes the phase and frequency dependant parts. Jeff The magnitude remains frequency dependent. VSWR is the RATIO of the magnitudes Vmax/Vmin regardless of frequency. |
An antenna question--43 ft vertical
On 7/9/2015 12:40 PM, wrote:
Jeff wrote: On 08/07/2015 19:14, wrote: John S wrote: On 7/7/2015 1:44 PM, wrote: Ian Jackson wrote: In message , Jerry Stuckle writes Sure, there is ALWAYS VSWR. It may be 1:1, but it's always there. If there's no reflection, there can be no standing wave. So, being pedantic, there's no such thing as an SWR of 1:1! Despite the name, VSWR is defined in terms of complex impedances and wavelengths, not "waves" of any kind. Actually, VSWR is defined as the ratio of Vmax/Vmin. Actually, VSWR can be defined several ways, one of which is: (1 + |r|)/(1 - |r|) Where r is the reflection coefficient which can be defined a: (Zl - Zo)/(Zl + Zo) Where Zl is the complex load impedance and Zo is the complex source impedance. Note that a complex impedance has a frequency dependant part. Note the the definition of VSWR uses the magnitude of the reflection coefficient, |r|, which removes the phase and frequency dependant parts. Jeff The magnitude DEPENDS on the frequency dependant parts. But the ratio of Vmax/Vmin does not. |
An antenna question--43 ft vertical
rickman wrote:
On 7/9/2015 1:58 PM, wrote: rickman wrote: On 7/9/2015 9:14 AM, Ralph Mowery wrote: "Jeff" wrote in message ... The SWR has to be the same at any point on the coax or transmission line minus the loss in the line. A simple swr meter may show some differance because of the way that kind of meter works. By changing the length of the line , the apparent SWR may be differant at that point. There is no such thing as apparent SWR. It is what it is in a given place. By 'apparent SWR' he means as indicated SWR on the meter, and yes it can change at various point on the line due to inadequacies in the meter; the 'real' VSWR will of course remain the same at any point on a lossless line. Jeff That is what I mean Jeff. If there is any SWR, by changing the length of the line, the voltage/current changes in such a maner that at certain points you may get a 50 ohm match at that point. https://en.wikipedia.org/wiki/Standi...dance_matching "if there is a perfect match between the load impedance Zload and the source impedance Zsource=Z*load, that perfect match will remain if the source and load are connected through a transmission line with an electrical length of one half wavelength (or a multiple of one half wavelengths) using a transmission line of any characteristic impedance Z0." This wiki article has a lot of good info in it. I have seen a lot of stuff posted here that this article directly contradicts.... I wonder who is right? It has been my observation that when the subject matter is long established science, such as transmission line theory, wiki is normally correct. Why do you ignore it when it says Zo is the impedance of the transmission line and not the source? I don't; The transmission line in this case IS the source. The SWR in a system, any kind of system, is measured at a point in a system. One side of that point is the source and the other side of that point is the load. It also does not matter which side you declare the source and which side you declare the load. A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source and a 50 Ohm load. By convention the load side is normally taken as the side which, when the system is powered, the power is desired to be dissipated. -- Jim Pennino |
An antenna question--43 ft vertical
On 7/9/2015 1:16 PM, wrote:
rickman wrote: On 7/9/2015 1:27 PM, wrote: rickman wrote: On 7/8/2015 9:07 PM, John S wrote: On 7/8/2015 4:48 PM, wrote: John S wrote: On 7/8/2015 12:47 PM, wrote: John S wrote: So, at 1Hz the law has changed, eh? What new law do I need to use? To be pendatic, there is only one set of physical laws that govern electromagnetics. However for DC all the complex parts of those laws have no effect and all the equations can be simplified to remove the complex parts. In the real, practical world people look upon this as two sets of laws, one for AC and one for DC. A good example of this is the transmission line which does not exist at DC; at DC a transmission line is nothing more than two wires with some resistance that is totally and only due to the ohmic resistance of the material that makes up the wires. So, is .01Hz AC or DC, Jim? How about 1Hz? 10Hz? Where does AC begin and DC end? It is called a limit. If there is NO time varying component, it is DC, otherwise it is AC. Are you playing devil's advocate or are you really that ignorant? Then there is no such thing as DC because even a battery looses voltage over a period of time. DC voltage sources have noise. Are just being argumentative or are you really that ignorant? Even if you have a theoretical voltage source, there are no circuits (other than imaginary) that have been on since before the big bang and will be on for all time in the future. So what? Is there some point to all this other than to be argumentative? How long before someone brings up the fact that a resistor generates AC signals as some kind of straw man objection to DC theory? The point is that separating DC and AC as being ruled by separate "laws" is pointless. Just discuss the topic of interest rather than digressing onto pointless diversions. Actually separating DC and AC is extremely practical which is why it is done in the real world. Sure, but separating the real and imaginary parts of impedance is SOMETIMES practical which is why it is done in the real world. |
An antenna question--43 ft vertical
On 7/9/2015 3:03 PM, John S wrote:
On 7/9/2015 12:40 PM, wrote: Jeff wrote: On 08/07/2015 19:14, wrote: John S wrote: On 7/7/2015 1:44 PM, wrote: Ian Jackson wrote: In message , Jerry Stuckle writes Sure, there is ALWAYS VSWR. It may be 1:1, but it's always there. If there's no reflection, there can be no standing wave. So, being pedantic, there's no such thing as an SWR of 1:1! Despite the name, VSWR is defined in terms of complex impedances and wavelengths, not "waves" of any kind. Actually, VSWR is defined as the ratio of Vmax/Vmin. Actually, VSWR can be defined several ways, one of which is: (1 + |r|)/(1 - |r|) Where r is the reflection coefficient which can be defined a: (Zl - Zo)/(Zl + Zo) Where Zl is the complex load impedance and Zo is the complex source impedance. Note that a complex impedance has a frequency dependant part. Note the the definition of VSWR uses the magnitude of the reflection coefficient, |r|, which removes the phase and frequency dependant parts. Jeff The magnitude DEPENDS on the frequency dependant parts. But the ratio of Vmax/Vmin does not. Huh? I'm pretty sure the VSWR is a function of frequency. A great deal about the impedances *and* the voltages change with frequency. -- Rick |
An antenna question--43 ft vertical
John S wrote:
On 7/9/2015 1:16 PM, wrote: rickman wrote: On 7/9/2015 1:27 PM, wrote: rickman wrote: On 7/8/2015 9:07 PM, John S wrote: On 7/8/2015 4:48 PM, wrote: John S wrote: On 7/8/2015 12:47 PM, wrote: John S wrote: So, at 1Hz the law has changed, eh? What new law do I need to use? To be pendatic, there is only one set of physical laws that govern electromagnetics. However for DC all the complex parts of those laws have no effect and all the equations can be simplified to remove the complex parts. In the real, practical world people look upon this as two sets of laws, one for AC and one for DC. A good example of this is the transmission line which does not exist at DC; at DC a transmission line is nothing more than two wires with some resistance that is totally and only due to the ohmic resistance of the material that makes up the wires. So, is .01Hz AC or DC, Jim? How about 1Hz? 10Hz? Where does AC begin and DC end? It is called a limit. If there is NO time varying component, it is DC, otherwise it is AC. Are you playing devil's advocate or are you really that ignorant? Then there is no such thing as DC because even a battery looses voltage over a period of time. DC voltage sources have noise. Are just being argumentative or are you really that ignorant? Even if you have a theoretical voltage source, there are no circuits (other than imaginary) that have been on since before the big bang and will be on for all time in the future. So what? Is there some point to all this other than to be argumentative? How long before someone brings up the fact that a resistor generates AC signals as some kind of straw man objection to DC theory? The point is that separating DC and AC as being ruled by separate "laws" is pointless. Just discuss the topic of interest rather than digressing onto pointless diversions. Actually separating DC and AC is extremely practical which is why it is done in the real world. Sure, but separating the real and imaginary parts of impedance is SOMETIMES practical which is why it is done in the real world. On rare occasions, but in the real world the DC analysis and the AC analysis are ALWAYS done seperately. A real world example: in the analysis of a circuit containing active components, first a DC analysis is done to establish the operating point of the circuit, then the AC analysis is done. -- Jim Pennino |
An antenna question--43 ft vertical
John S wrote:
On 7/9/2015 4:29 AM, Roger Hayter wrote: Jeff wrote: On 08/07/2015 19:14, wrote: John S wrote: On 7/7/2015 1:44 PM, wrote: Ian Jackson wrote: In message , Jerry Stuckle writes Sure, there is ALWAYS VSWR. It may be 1:1, but it's always there. If there's no reflection, there can be no standing wave. So, being pedantic, there's no such thing as an SWR of 1:1! Despite the name, VSWR is defined in terms of complex impedances and wavelengths, not "waves" of any kind. Actually, VSWR is defined as the ratio of Vmax/Vmin. Actually, VSWR can be defined several ways, one of which is: (1 + |r|)/(1 - |r|) Where r is the reflection coefficient which can be defined a: (Zl - Zo)/(Zl + Zo) Where Zl is the complex load impedance and Zo is the complex source impedance. Note that a complex impedance has a frequency dependant part. Note the the definition of VSWR uses the magnitude of the reflection coefficient, |r|, which removes the phase and frequency dependant parts. Jeff The magnitude remains frequency dependent. VSWR is the RATIO of the magnitudes Vmax/Vmin regardless of frequency. See above. Nowhere is it written in stone that the Vmax/Vmin is the one, true, only and holy definition of SWR. -- Jim Pennino |
An antenna question--43 ft vertical
On 7/9/2015 3:05 PM, wrote:
rickman wrote: On 7/9/2015 1:58 PM, wrote: rickman wrote: On 7/9/2015 9:14 AM, Ralph Mowery wrote: "Jeff" wrote in message ... The SWR has to be the same at any point on the coax or transmission line minus the loss in the line. A simple swr meter may show some differance because of the way that kind of meter works. By changing the length of the line , the apparent SWR may be differant at that point. There is no such thing as apparent SWR. It is what it is in a given place. By 'apparent SWR' he means as indicated SWR on the meter, and yes it can change at various point on the line due to inadequacies in the meter; the 'real' VSWR will of course remain the same at any point on a lossless line. Jeff That is what I mean Jeff. If there is any SWR, by changing the length of the line, the voltage/current changes in such a maner that at certain points you may get a 50 ohm match at that point. https://en.wikipedia.org/wiki/Standi...dance_matching "if there is a perfect match between the load impedance Zload and the source impedance Zsource=Z*load, that perfect match will remain if the source and load are connected through a transmission line with an electrical length of one half wavelength (or a multiple of one half wavelengths) using a transmission line of any characteristic impedance Z0." This wiki article has a lot of good info in it. I have seen a lot of stuff posted here that this article directly contradicts.... I wonder who is right? It has been my observation that when the subject matter is long established science, such as transmission line theory, wiki is normally correct. Why do you ignore it when it says Zo is the impedance of the transmission line and not the source? I don't; The transmission line in this case IS the source. No, the source is the source. Even if you wish to consider transmission line as the source in some example, the page clearly says Zo is the impedance of the transmission line, without any context where you can say it is a source or a load. https://en.wikipedia.org/wiki/Charac...ion_line_model The SWR in a system, any kind of system, is measured at a point in a system. You mean a system that includes a source, a transmission line and a load? One side of that point is the source and the other side of that point is the load. It also does not matter which side you declare the source and which side you declare the load. In that case the antenna is Zo? I don't think so. A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source and a 50 Ohm load. By convention the load side is normally taken as the side which, when the system is powered, the power is desired to be dissipated. I don't know why you dig your heels in on every little point. Sometimes you are just wrong and need to acknowledge that so the discussion can move on. Zo (or Z0) is used to represent the characteristic impedance of a transmission line. Zs (or Zsource) is used for the source. ZL (or Zload) is used for the load. Read the wiki quote above and the many other *clear* examples. -- Rick |
An antenna question--43 ft vertical
John S wrote:
On 7/9/2015 12:40 PM, wrote: Jeff wrote: On 08/07/2015 19:14, wrote: John S wrote: On 7/7/2015 1:44 PM, wrote: Ian Jackson wrote: In message , Jerry Stuckle writes Sure, there is ALWAYS VSWR. It may be 1:1, but it's always there. If there's no reflection, there can be no standing wave. So, being pedantic, there's no such thing as an SWR of 1:1! Despite the name, VSWR is defined in terms of complex impedances and wavelengths, not "waves" of any kind. Actually, VSWR is defined as the ratio of Vmax/Vmin. Actually, VSWR can be defined several ways, one of which is: (1 + |r|)/(1 - |r|) Where r is the reflection coefficient which can be defined a: (Zl - Zo)/(Zl + Zo) Where Zl is the complex load impedance and Zo is the complex source impedance. Note that a complex impedance has a frequency dependant part. Note the the definition of VSWR uses the magnitude of the reflection coefficient, |r|, which removes the phase and frequency dependant parts. Jeff The magnitude DEPENDS on the frequency dependant parts. But the ratio of Vmax/Vmin does not. So what? P=E^2/R; does that mean current is irrelevant to power? There is no one, true, written in stone, official and holy definition of SWR. All the definitions are equally valid. -- Jim Pennino |
An antenna question--43 ft vertical
rickman wrote:
On 7/9/2015 3:03 PM, John S wrote: On 7/9/2015 12:40 PM, wrote: Jeff wrote: On 08/07/2015 19:14, wrote: John S wrote: On 7/7/2015 1:44 PM, wrote: Ian Jackson wrote: In message , Jerry Stuckle writes Sure, there is ALWAYS VSWR. It may be 1:1, but it's always there. If there's no reflection, there can be no standing wave. So, being pedantic, there's no such thing as an SWR of 1:1! Despite the name, VSWR is defined in terms of complex impedances and wavelengths, not "waves" of any kind. Actually, VSWR is defined as the ratio of Vmax/Vmin. Actually, VSWR can be defined several ways, one of which is: (1 + |r|)/(1 - |r|) Where r is the reflection coefficient which can be defined a: (Zl - Zo)/(Zl + Zo) Where Zl is the complex load impedance and Zo is the complex source impedance. Note that a complex impedance has a frequency dependant part. Note the the definition of VSWR uses the magnitude of the reflection coefficient, |r|, which removes the phase and frequency dependant parts. Jeff The magnitude DEPENDS on the frequency dependant parts. But the ratio of Vmax/Vmin does not. Huh? I'm pretty sure the VSWR is a function of frequency. A great deal about the impedances *and* the voltages change with frequency. A simple fact that totally eludes him. SWR is a quality of an impedance match at a specified point in a system and at a specified frequency. -- Jim Pennino |
An antenna question--43 ft vertical
"rickman" wrote in message ... The magnitude DEPENDS on the frequency dependant parts. But the ratio of Vmax/Vmin does not. Huh? I'm pretty sure the VSWR is a function of frequency. A great deal about the impedances *and* the voltages change with frequency. -- Rick The SWR is measured at a fixed frequency , so the formular is frequency independant. Each time you change frequencies , the SWR will usually change. I guess that it all depends on how you look at it. You can use a sweep generator and spectrum analizer to get a SWR curve over a frequency range. If you feed a dummy load of pure resistance, it will not mater what frequency you use, the swr will stay the same. If the load has an impedance that is not constant at all frequencies, then the swr will change as the frequency changes. |
An antenna question--43 ft vertical
"rickman" wrote in message ... Why do you ignore it when it says Zo is the impedance of the transmission line and not the source? I don't; The transmission line in this case IS the source. No, the source is the source. Even if you wish to consider transmission line as the source in some example, the page clearly says Zo is the impedance of the transmission line, without any context where you can say it is a source or a load. https://en.wikipedia.org/wiki/Charac...ion_line_model The SWR in a system, any kind of system, is measured at a point in a system. You mean a system that includes a source, a transmission line and a load? One side of that point is the source and the other side of that point is the load. It also does not matter which side you declare the source and which side you declare the load. In that case the antenna is Zo? I don't think so. A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source and a 50 Ohm load. By convention the load side is normally taken as the side which, when the system is powered, the power is desired to be dissipated. I don't know why you dig your heels in on every little point. Sometimes you are just wrong and need to acknowledge that so the discussion can move on. Zo (or Z0) is used to represent the characteristic impedance of a transmission line. Zs (or Zsource) is used for the source. ZL (or Zload) is used for the load. Read the wiki quote above and the many other *clear* examples. -- Rick I think that is his problem. The source does not mater . It is just there to provide power to the load. The swr is stated TOWARD the SOURCE. It does not have anything to do with the actual source impedance. As someone said eairler you measure the swr, then put any value resistor in parallel with the transmitter (source) and measuer the swr. It will still be the same if nothing else changes. Jimp just can not seem to get it in his head the impedance of the transmitter (source) does not matter. It seems to me he thinks the coax is the source. I just don't see the coax generating any power outside of a very minute random power depending on the temperature that would be in the micro watts or less that is way out of the scope of the swr discussion. |
An antenna question--43 ft vertical
rickman wrote:
On 7/9/2015 3:05 PM, wrote: rickman wrote: On 7/9/2015 1:58 PM, wrote: rickman wrote: On 7/9/2015 9:14 AM, Ralph Mowery wrote: "Jeff" wrote in message ... The SWR has to be the same at any point on the coax or transmission line minus the loss in the line. A simple swr meter may show some differance because of the way that kind of meter works. By changing the length of the line , the apparent SWR may be differant at that point. There is no such thing as apparent SWR. It is what it is in a given place. By 'apparent SWR' he means as indicated SWR on the meter, and yes it can change at various point on the line due to inadequacies in the meter; the 'real' VSWR will of course remain the same at any point on a lossless line. Jeff That is what I mean Jeff. If there is any SWR, by changing the length of the line, the voltage/current changes in such a maner that at certain points you may get a 50 ohm match at that point. https://en.wikipedia.org/wiki/Standi...dance_matching "if there is a perfect match between the load impedance Zload and the source impedance Zsource=Z*load, that perfect match will remain if the source and load are connected through a transmission line with an electrical length of one half wavelength (or a multiple of one half wavelengths) using a transmission line of any characteristic impedance Z0." This wiki article has a lot of good info in it. I have seen a lot of stuff posted here that this article directly contradicts.... I wonder who is right? It has been my observation that when the subject matter is long established science, such as transmission line theory, wiki is normally correct. Why do you ignore it when it says Zo is the impedance of the transmission line and not the source? I don't; The transmission line in this case IS the source. No, the source is the source. Even if you wish to consider transmission line as the source in some example, the page clearly says Zo is the impedance of the transmission line, without any context where you can say it is a source or a load. No, in THIS case the transmission is the source. If you connect a transmitter to a power amplifier with cable so short the transmission line effects are negliable, you STILL have a SWR at the point between the two. It is numerically irrelevant which end you designate the source and which end you designate the load; the SWR at that point is the same either way. https://en.wikipedia.org/wiki/Charac...ion_line_model The SWR in a system, any kind of system, is measured at a point in a system. You mean a system that includes a source, a transmission line and a load? I mean ANY system. From a practical point of view, there is not much point in calculating a SWR anywhere if there is not a source of energy somewhere that eventually winds up in a load to be dissipated, but it is still a perfectly valid calculation. Here's an example of a more complex system one can actually find in an Amateur station: A transmitter is connected to a power amplifier through a coas transmission line. The amplifier is connected through a coax transmission line to a unbalanced to balanced transformer. The transmformer is connected to a balanced transmission line to an antenna. There is no SWR for the system. The SWR is meansured at a POINT in the system. One side of that point is the source and the other side of that point is the load. It also does not matter which side you declare the source and which side you declare the load. In that case the antenna is Zo? I don't think so. Too bad; you are wrong. A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source and a 50 Ohm load. By convention the load side is normally taken as the side which, when the system is powered, the power is desired to be dissipated. I don't know why you dig your heels in on every little point. Sometimes you are just wrong and need to acknowledge that so the discussion can move on. Zo (or Z0) is used to represent the characteristic impedance of a transmission line. Zs (or Zsource) is used for the source. ZL (or Zload) is used for the load. Read the wiki quote above and the many other *clear* examples. The source impedance is USUALLY a transmission line, but does not HAVE to be. The source impdedance could be the output of a matching section made of lumped components. WHAT the source and WHAT the load is physically does not matter. If you are using a VNA to measure SWR, the source is whatever you connect to the source port and the load is whatever you connect to the load port. -- Jim Pennino |
An antenna question--43 ft vertical
On 7/9/2015 3:50 PM, Ralph Mowery wrote:
"rickman" wrote in message ... The magnitude DEPENDS on the frequency dependant parts. But the ratio of Vmax/Vmin does not. Huh? I'm pretty sure the VSWR is a function of frequency. A great deal about the impedances *and* the voltages change with frequency. -- Rick The SWR is measured at a fixed frequency , so the formular is frequency independant. Each time you change frequencies , the SWR will usually change. I think that is the definition of "frequency dependent". I guess that it all depends on how you look at it. You can use a sweep generator and spectrum analizer to get a SWR curve over a frequency range. If you feed a dummy load of pure resistance, it will not mater what frequency you use, the swr will stay the same. If the load has an impedance that is not constant at all frequencies, then the swr will change as the frequency changes. I'm not going to debate the fine details of the subject. Anyone can believe anything they wish. But the bottom line is that the SWR depends on the components used in the system which, in any useful SWR measurement, will give you a frequency dependent value. The SWR using a dummy (purely resistive) load will not depend on frequency, but it also won't tell you a thing about your antenna system. -- Rick |
An antenna question--43 ft vertical
On 7/9/2015 4:00 PM, Ralph Mowery wrote:
"rickman" wrote in message ... Why do you ignore it when it says Zo is the impedance of the transmission line and not the source? I don't; The transmission line in this case IS the source. No, the source is the source. Even if you wish to consider transmission line as the source in some example, the page clearly says Zo is the impedance of the transmission line, without any context where you can say it is a source or a load. https://en.wikipedia.org/wiki/Charac...ion_line_model The SWR in a system, any kind of system, is measured at a point in a system. You mean a system that includes a source, a transmission line and a load? One side of that point is the source and the other side of that point is the load. It also does not matter which side you declare the source and which side you declare the load. In that case the antenna is Zo? I don't think so. A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source and a 50 Ohm load. By convention the load side is normally taken as the side which, when the system is powered, the power is desired to be dissipated. I don't know why you dig your heels in on every little point. Sometimes you are just wrong and need to acknowledge that so the discussion can move on. Zo (or Z0) is used to represent the characteristic impedance of a transmission line. Zs (or Zsource) is used for the source. ZL (or Zload) is used for the load. Read the wiki quote above and the many other *clear* examples. -- Rick I think that is his problem. The source does not mater . It is just there to provide power to the load. The swr is stated TOWARD the SOURCE. It does not have anything to do with the actual source impedance. As someone said eairler you measure the swr, then put any value resistor in parallel with the transmitter (source) and measuer the swr. It will still be the same if nothing else changes. Jimp just can not seem to get it in his head the impedance of the transmitter (source) does not matter. It seems to me he thinks the coax is the source. So he is agreeing with you that the source is not relevant. What is relevant is the transmission line impedance. I just don't see the coax generating any power outside of a very minute random power depending on the temperature that would be in the micro watts or less that is way out of the scope of the swr discussion. Then don't bother to talk about it. I know I won't. -- Rick |
An antenna question--43 ft vertical
In article ,
wrote: So what? P=E^2/R; does that mean current is irrelevant to power? There is no one, true, written in stone, official and holy definition of SWR. All the definitions are equally valid. "SWR is a little tweeting bird chirping in a meadow. SWR is a wreath of flowers which smell BAD. Are you sure your circuits are registering properly? Your ears are green." (Spock, "I, Mudd", 1967) (slightly misquoted) |
An antenna question--43 ft vertical
Ralph Mowery wrote:
"rickman" wrote in message ... Why do you ignore it when it says Zo is the impedance of the transmission line and not the source? I don't; The transmission line in this case IS the source. No, the source is the source. Even if you wish to consider transmission line as the source in some example, the page clearly says Zo is the impedance of the transmission line, without any context where you can say it is a source or a load. https://en.wikipedia.org/wiki/Charac...ion_line_model The SWR in a system, any kind of system, is measured at a point in a system. You mean a system that includes a source, a transmission line and a load? One side of that point is the source and the other side of that point is the load. It also does not matter which side you declare the source and which side you declare the load. In that case the antenna is Zo? I don't think so. A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source and a 50 Ohm load. By convention the load side is normally taken as the side which, when the system is powered, the power is desired to be dissipated. I don't know why you dig your heels in on every little point. Sometimes you are just wrong and need to acknowledge that so the discussion can move on. Zo (or Z0) is used to represent the characteristic impedance of a transmission line. Zs (or Zsource) is used for the source. ZL (or Zload) is used for the load. Read the wiki quote above and the many other *clear* examples. -- Rick I think that is his problem. The source does not mater . It is just there to provide power to the load. The swr is stated TOWARD the SOURCE. It does not have anything to do with the actual source impedance. As someone said eairler you measure the swr, then put any value resistor in parallel with the transmitter (source) and measuer the swr. It will still be the same if nothing else changes. Jimp just can not seem to get it in his head the impedance of the transmitter (source) does not matter. It seems to me he thinks the coax is the source. I just don't see the coax generating any power outside of a very minute random power depending on the temperature that would be in the micro watts or less that is way out of the scope of the swr discussion. Nope. SWR is a measure of the impedance match at a point in a system. It does not matter what the physical ends are. One end could be an unbalanced to balanced transformation network and the other end a length of parallel transmission line. If the impedance of the tranmitter does not matter, than connect YOUR transmitter to a length of 95 Ohm coax which is terminated in a square loop with an impedance of 110 Ohms. What is the SWR at the point between the coax and loop? What is the source and what is the load? What is the SWR at the point beteen the transmitter and the coax? What is the source and what is the load? -- Jim Pennino |
An antenna question--43 ft vertical
rickman wrote:
On 7/9/2015 4:00 PM, Ralph Mowery wrote: "rickman" wrote in message ... Why do you ignore it when it says Zo is the impedance of the transmission line and not the source? I don't; The transmission line in this case IS the source. No, the source is the source. Even if you wish to consider transmission line as the source in some example, the page clearly says Zo is the impedance of the transmission line, without any context where you can say it is a source or a load. https://en.wikipedia.org/wiki/Charac...ion_line_model The SWR in a system, any kind of system, is measured at a point in a system. You mean a system that includes a source, a transmission line and a load? One side of that point is the source and the other side of that point is the load. It also does not matter which side you declare the source and which side you declare the load. In that case the antenna is Zo? I don't think so. A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source and a 50 Ohm load. By convention the load side is normally taken as the side which, when the system is powered, the power is desired to be dissipated. I don't know why you dig your heels in on every little point. Sometimes you are just wrong and need to acknowledge that so the discussion can move on. Zo (or Z0) is used to represent the characteristic impedance of a transmission line. Zs (or Zsource) is used for the source. ZL (or Zload) is used for the load. Read the wiki quote above and the many other *clear* examples. -- Rick I think that is his problem. The source does not mater . It is just there to provide power to the load. The swr is stated TOWARD the SOURCE. It does not have anything to do with the actual source impedance. As someone said eairler you measure the swr, then put any value resistor in parallel with the transmitter (source) and measuer the swr. It will still be the same if nothing else changes. Jimp just can not seem to get it in his head the impedance of the transmitter (source) does not matter. It seems to me he thinks the coax is the source. So he is agreeing with you that the source is not relevant. What is relevant is the transmission line impedance. Place a lumped component matching network between the transmission line and the antenna. What is the source at the point between the line and the network? What is the source at the point between the network and the antenna? -- Jim Pennino |
An antenna question--43 ft vertical
On 7/9/2015 5:11 PM, wrote:
rickman wrote: On 7/9/2015 4:00 PM, Ralph Mowery wrote: "rickman" wrote in message ... Why do you ignore it when it says Zo is the impedance of the transmission line and not the source? I don't; The transmission line in this case IS the source. No, the source is the source. Even if you wish to consider transmission line as the source in some example, the page clearly says Zo is the impedance of the transmission line, without any context where you can say it is a source or a load. https://en.wikipedia.org/wiki/Charac...ion_line_model The SWR in a system, any kind of system, is measured at a point in a system. You mean a system that includes a source, a transmission line and a load? One side of that point is the source and the other side of that point is the load. It also does not matter which side you declare the source and which side you declare the load. In that case the antenna is Zo? I don't think so. A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source and a 50 Ohm load. By convention the load side is normally taken as the side which, when the system is powered, the power is desired to be dissipated. I don't know why you dig your heels in on every little point. Sometimes you are just wrong and need to acknowledge that so the discussion can move on. Zo (or Z0) is used to represent the characteristic impedance of a transmission line. Zs (or Zsource) is used for the source. ZL (or Zload) is used for the load. Read the wiki quote above and the many other *clear* examples. -- Rick I think that is his problem. The source does not mater . It is just there to provide power to the load. The swr is stated TOWARD the SOURCE. It does not have anything to do with the actual source impedance. As someone said eairler you measure the swr, then put any value resistor in parallel with the transmitter (source) and measuer the swr. It will still be the same if nothing else changes. Jimp just can not seem to get it in his head the impedance of the transmitter (source) does not matter. It seems to me he thinks the coax is the source. So he is agreeing with you that the source is not relevant. What is relevant is the transmission line impedance. Place a lumped component matching network between the transmission line and the antenna. What is the source at the point between the line and the network? What is the source at the point between the network and the antenna? Deep thoughts.... What is the sound of one hand clapping? -- Rick |
An antenna question--43 ft vertical
wrote in message ... Wayne wrote: wrote in message ... John S wrote: On 7/8/2015 7:27 PM, Wayne wrote: "John S" wrote in message ... On 7/7/2015 1:44 PM, wrote: Ian Jackson wrote: In message , Jerry Stuckle writes Sure, there is ALWAYS VSWR. It may be 1:1, but it's always there. If there's no reflection, there can be no standing wave. So, being pedantic, there's no such thing as an SWR of 1:1! Despite the name, VSWR is defined in terms of complex impedances and wavelengths, not "waves" of any kind. Actually, VSWR is defined as the ratio of Vmax/Vmin. That's also my understanding of the definition. In fact since SWR is defined as the maximum to minimum voltage ratio, the "V" in VSWR is redundant. Sort of. There is also ISWR but it is not used frequently. # Not sort of, but is. # There is also PSWR. And both go back to the Vmax/Vmin definition. The PSWR is a tricky one because you can end up with a power ratio instead of a voltage ratio. # Actually, no, PSWR has nothing to do with power ratios as in RF power, # rather it has to do with power ratios as in values raised to the second # power. What I'm getting at is that the ratio of forward to reflected power needs a bit more math to get to VSWR. |
An antenna question--43 ft vertical
wrote:
Ralph Mowery wrote: "rickman" wrote in message ... Why do you ignore it when it says Zo is the impedance of the transmission line and not the source? I don't; The transmission line in this case IS the source. No, the source is the source. Even if you wish to consider transmission line as the source in some example, the page clearly says Zo is the impedance of the transmission line, without any context where you can say it is a source or a load. https://en.wikipedia.org/wiki/Charac...nsmission_line _model The SWR in a system, any kind of system, is measured at a point in a system. You mean a system that includes a source, a transmission line and a load? One side of that point is the source and the other side of that point is the load. It also does not matter which side you declare the source and which side you declare the load. In that case the antenna is Zo? I don't think so. A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source and a 50 Ohm load. By convention the load side is normally taken as the side which, when the system is powered, the power is desired to be dissipated. I don't know why you dig your heels in on every little point. Sometimes you are just wrong and need to acknowledge that so the discussion can move on. Zo (or Z0) is used to represent the characteristic impedance of a transmission line. Zs (or Zsource) is used for the source. ZL (or Zload) is used for the load. Read the wiki quote above and the many other *clear* examples. -- Rick I think that is his problem. The source does not mater . It is just there to provide power to the load. The swr is stated TOWARD the SOURCE. It does not have anything to do with the actual source impedance. As someone said eairler you measure the swr, then put any value resistor in parallel with the transmitter (source) and measuer the swr. It will still be the same if nothing else changes. Jimp just can not seem to get it in his head the impedance of the transmitter (source) does not matter. It seems to me he thinks the coax is the source. I just don't see the coax generating any power outside of a very minute random power depending on the temperature that would be in the micro watts or less that is way out of the scope of the swr discussion. Nope. SWR is a measure of the impedance match at a point in a system. No it is not. You don't get standing waves on 10mm of wire. (At HF anyway). It is a property of a driven transmission line and depends on the network at the far end. It is directional and does *not* depend on the impedance of the source. (If you put a signal source at the far end, in parallel with the existing load or replacing it, then you would get a potentially quite different SWR due to the impedance of what was the source. Because you would not have matched the source impedance to the tansmission line impedance. In the general case, a network which matches the impedance looking into the tansmission line to the impedance desired by the source for a satisfactory working point willl *not* match the source impadance to the transmission line characteristic impedance. In the general case it will be impossible to match impedances in both directions, and in pracitce we don't even try. It does not matter what the physical ends are. One end could be an unbalanced to balanced transformation network and the other end a length of parallel transmission line. If the impedance of the tranmitter does not matter, than connect YOUR transmitter to a length of 95 Ohm coax which is terminated in a square loop with an impedance of 110 Ohms. What is the SWR at the point between the coax and loop? What is the source and what is the load? What is the SWR at the point beteen the transmitter and the coax? What is the source and what is the load? -- Roger Hayter |
An antenna question--43 ft vertical
Wayne wrote:
wrote in message ... Wayne wrote: wrote in message ... John S wrote: On 7/8/2015 7:27 PM, Wayne wrote: "John S" wrote in message ... On 7/7/2015 1:44 PM, wrote: Ian Jackson wrote: In message , Jerry Stuckle writes Sure, there is ALWAYS VSWR. It may be 1:1, but it's always there. If there's no reflection, there can be no standing wave. So, being pedantic, there's no such thing as an SWR of 1:1! Despite the name, VSWR is defined in terms of complex impedances and wavelengths, not "waves" of any kind. Actually, VSWR is defined as the ratio of Vmax/Vmin. That's also my understanding of the definition. In fact since SWR is defined as the maximum to minimum voltage ratio, the "V" in VSWR is redundant. Sort of. There is also ISWR but it is not used frequently. # Not sort of, but is. # There is also PSWR. And both go back to the Vmax/Vmin definition. The PSWR is a tricky one because you can end up with a power ratio instead of a voltage ratio. # Actually, no, PSWR has nothing to do with power ratios as in RF power, # rather it has to do with power ratios as in values raised to the second # power. What I'm getting at is that the ratio of forward to reflected power needs a bit more math to get to VSWR. Yes, in terms of power: VSWR = (1 + sqrt(Pr/Pf))/(1 - (sqrt(Pr/Pf)) Where Pf = forward power, Pr = reflected power. -- Jim Pennino |
An antenna question--43 ft vertical
rickman wrote:
On 7/9/2015 5:11 PM, wrote: rickman wrote: On 7/9/2015 4:00 PM, Ralph Mowery wrote: "rickman" wrote in message ... Why do you ignore it when it says Zo is the impedance of the transmission line and not the source? I don't; The transmission line in this case IS the source. No, the source is the source. Even if you wish to consider transmission line as the source in some example, the page clearly says Zo is the impedance of the transmission line, without any context where you can say it is a source or a load. https://en.wikipedia.org/wiki/Charac...ion_line_model The SWR in a system, any kind of system, is measured at a point in a system. You mean a system that includes a source, a transmission line and a load? One side of that point is the source and the other side of that point is the load. It also does not matter which side you declare the source and which side you declare the load. In that case the antenna is Zo? I don't think so. A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source and a 50 Ohm load. By convention the load side is normally taken as the side which, when the system is powered, the power is desired to be dissipated. I don't know why you dig your heels in on every little point. Sometimes you are just wrong and need to acknowledge that so the discussion can move on. Zo (or Z0) is used to represent the characteristic impedance of a transmission line. Zs (or Zsource) is used for the source. ZL (or Zload) is used for the load. Read the wiki quote above and the many other *clear* examples. -- Rick I think that is his problem. The source does not mater . It is just there to provide power to the load. The swr is stated TOWARD the SOURCE. It does not have anything to do with the actual source impedance. As someone said eairler you measure the swr, then put any value resistor in parallel with the transmitter (source) and measuer the swr. It will still be the same if nothing else changes. Jimp just can not seem to get it in his head the impedance of the transmitter (source) does not matter. It seems to me he thinks the coax is the source. So he is agreeing with you that the source is not relevant. What is relevant is the transmission line impedance. Place a lumped component matching network between the transmission line and the antenna. What is the source at the point between the line and the network? What is the source at the point between the network and the antenna? Deep thoughts.... What is the sound of one hand clapping? Try this: SWR like voltage is determined by two points. In the case of voltage, the "other" point is usually ground, but can be anything. In the case of SWR, the "other" point is usually a transmission line, but can be anything. -- Jim Pennino |
An antenna question--43 ft vertical
Roger Hayter wrote:
wrote: Ralph Mowery wrote: "rickman" wrote in message ... Why do you ignore it when it says Zo is the impedance of the transmission line and not the source? I don't; The transmission line in this case IS the source. No, the source is the source. Even if you wish to consider transmission line as the source in some example, the page clearly says Zo is the impedance of the transmission line, without any context where you can say it is a source or a load. https://en.wikipedia.org/wiki/Charac...nsmission_line _model The SWR in a system, any kind of system, is measured at a point in a system. You mean a system that includes a source, a transmission line and a load? One side of that point is the source and the other side of that point is the load. It also does not matter which side you declare the source and which side you declare the load. In that case the antenna is Zo? I don't think so. A 50 Ohm source and a 100 Ohm load has the same SWR as a 100 Ohm source and a 50 Ohm load. By convention the load side is normally taken as the side which, when the system is powered, the power is desired to be dissipated. I don't know why you dig your heels in on every little point. Sometimes you are just wrong and need to acknowledge that so the discussion can move on. Zo (or Z0) is used to represent the characteristic impedance of a transmission line. Zs (or Zsource) is used for the source. ZL (or Zload) is used for the load. Read the wiki quote above and the many other *clear* examples. -- Rick I think that is his problem. The source does not mater . It is just there to provide power to the load. The swr is stated TOWARD the SOURCE. It does not have anything to do with the actual source impedance. As someone said eairler you measure the swr, then put any value resistor in parallel with the transmitter (source) and measuer the swr. It will still be the same if nothing else changes. Jimp just can not seem to get it in his head the impedance of the transmitter (source) does not matter. It seems to me he thinks the coax is the source. I just don't see the coax generating any power outside of a very minute random power depending on the temperature that would be in the micro watts or less that is way out of the scope of the swr discussion. Nope. SWR is a measure of the impedance match at a point in a system. No it is not. You don't get standing waves on 10mm of wire. (At HF anyway). It is a property of a driven transmission line and depends on the network at the far end. In the case where you have a transmission line, but only where you have a transmission line. Connect an Amateur transmitter directly to one end of an SWR meter and the other end of the meter to a 100 Ohm resitor. The frequency is the bottom end of the 160 M band. The SWR meter reads 2:1. Where are the standing waves? -- Jim Pennino |
An antenna question--43 ft vertical
On 7/9/2015 12:32 AM, wrote:
John S wrote: On 7/8/2015 4:48 PM, wrote: John S wrote: On 7/8/2015 12:47 PM, wrote: John S wrote: So, at 1Hz the law has changed, eh? What new law do I need to use? To be pendatic, there is only one set of physical laws that govern electromagnetics. However for DC all the complex parts of those laws have no effect and all the equations can be simplified to remove the complex parts. In the real, practical world people look upon this as two sets of laws, one for AC and one for DC. A good example of this is the transmission line which does not exist at DC; at DC a transmission line is nothing more than two wires with some resistance that is totally and only due to the ohmic resistance of the material that makes up the wires. So, is .01Hz AC or DC, Jim? How about 1Hz? 10Hz? Where does AC begin and DC end? It is called a limit. If there is NO time varying component, it is DC, otherwise it is AC. Are you playing devil's advocate or are you really that ignorant? Then there is no such thing as DC because even a battery looses voltage over a period of time. DC voltage sources have noise. An ideal battery doesn't. Where can one be purchased? |
An antenna question--43 ft vertical
On 7/9/2015 12:58 PM, wrote:
rickman wrote: On 7/9/2015 9:14 AM, Ralph Mowery wrote: "Jeff" wrote in message ... The SWR has to be the same at any point on the coax or transmission line minus the loss in the line. A simple swr meter may show some differance because of the way that kind of meter works. By changing the length of the line , the apparent SWR may be differant at that point. There is no such thing as apparent SWR. It is what it is in a given place. By 'apparent SWR' he means as indicated SWR on the meter, and yes it can change at various point on the line due to inadequacies in the meter; the 'real' VSWR will of course remain the same at any point on a lossless line. Jeff That is what I mean Jeff. If there is any SWR, by changing the length of the line, the voltage/current changes in such a maner that at certain points you may get a 50 ohm match at that point. https://en.wikipedia.org/wiki/Standi...dance_matching "if there is a perfect match between the load impedance Zload and the source impedance Zsource=Z*load, that perfect match will remain if the source and load are connected through a transmission line with an electrical length of one half wavelength (or a multiple of one half wavelengths) using a transmission line of any characteristic impedance Z0." This wiki article has a lot of good info in it. I have seen a lot of stuff posted here that this article directly contradicts.... I wonder who is right? It has been my observation that when the subject matter is long established science, such as transmission line theory, wiki is normally correct. Wiki is subject to the same errors you make because the information is usually supplied by people like you. |
An antenna question--43 ft vertical
On 7/9/2015 1:01 PM, wrote:
Jeff wrote: you may get a 50 ohm match at that point. https://en.wikipedia.org/wiki/Standi...dance_matching "if there is a perfect match between the load impedance Zload and the source impedance Zsource=Z*load, that perfect match will remain if the source and load are connected through a transmission line with an electrical length of one half wavelength (or a multiple of one half wavelengths) using a transmission line of any characteristic impedance Z0." This wiki article has a lot of good info in it. I have seen a lot of stuff posted here that this article directly contradicts.... I wonder who is right? That is a very specific case where the source is not at the system impedance and happens to be equal to the load impedance, there will also be standing waves on the transmission line and associated losses as the VSWR on the line will be equal to the magnitude of the mismatch between the transmission line impedance and the load impedance. Jeff Most people take the source impdedance to be the system impedance, i.e. the impedance for which everything else is designed for. Most *engineers* take the source impedance to be the impedance of the *generator*. In fact, perhaps the rest of us should call it the generator rather than the source so that we can communicate with you on your level. |
An antenna question--43 ft vertical
John S wrote:
On 7/9/2015 12:32 AM, wrote: John S wrote: On 7/8/2015 4:48 PM, wrote: John S wrote: On 7/8/2015 12:47 PM, wrote: John S wrote: So, at 1Hz the law has changed, eh? What new law do I need to use? To be pendatic, there is only one set of physical laws that govern electromagnetics. However for DC all the complex parts of those laws have no effect and all the equations can be simplified to remove the complex parts. In the real, practical world people look upon this as two sets of laws, one for AC and one for DC. A good example of this is the transmission line which does not exist at DC; at DC a transmission line is nothing more than two wires with some resistance that is totally and only due to the ohmic resistance of the material that makes up the wires. So, is .01Hz AC or DC, Jim? How about 1Hz? 10Hz? Where does AC begin and DC end? It is called a limit. If there is NO time varying component, it is DC, otherwise it is AC. Are you playing devil's advocate or are you really that ignorant? Then there is no such thing as DC because even a battery looses voltage over a period of time. DC voltage sources have noise. An ideal battery doesn't. Where can one be purchased? At the ideal battery store. -- Jim Pennino |
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