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An antenna question--43 ft vertical
On 7/10/2015 4:10 PM, Ian Jackson wrote:
In message , writes Ian Jackson wrote: Even when the only transmission line consists the output connector of the SWR meter, and maybe an inch of internal coax, there will still BE a standing wave - but it will only be a tiny portion of longer one. There will NOT be standing waves and there will not be a voltage maximum and a voltage minimum unless there is a transmission line. Are you saying that for a standing wave to qualify as a standing wave, the transmission line needs to be long enough for there to be a voltage maximum a voltage minimum? It seems to be very much like watching a train wreck. We are fascinated by the event even though it is terrible to watch. I'm starting to get a bit tired of it though. I can only watch the train run off the track so many times. -- Rick |
An antenna question--43 ft vertical
Ian Jackson wrote:
In message , writes Ian Jackson wrote: Even when the only transmission line consists the output connector of the SWR meter, and maybe an inch of internal coax, there will still BE a standing wave - but it will only be a tiny portion of longer one. There will NOT be standing waves and there will not be a voltage maximum and a voltage minimum unless there is a transmission line. Are you saying that for a standing wave to qualify as a standing wave, the transmission line needs to be long enough for there to be a voltage maximum a voltage minimum? I am saying that if the connection between the two things of interest is short enough in terms of wavelengths at the frequency of interest, the connection no longer functions as a transmission line, there are no standing waves, but the measurment we call SWR still exists. -- Jim Pennino |
An antenna question--43 ft vertical
On 7/10/2015 4:28 PM, wrote:
rickman wrote: On 7/10/2015 2:34 PM, wrote: rickman wrote: On 7/10/2015 1:39 PM, wrote: standing waves are a consequence of a VSWR greater than 1:1 on a transmission line. Did you really write that? The standing waves are a consequence of a standing wave ratio of greater than 1:1? An IMPEDANCE mismatch on a TRANSMISSION LINE results in standing waves. First you say the standing waves are a result of the SWR being greater than 1:1, now you say it is a result of the impedance mismatch. I'm *so* confused.... :( Are you serious? SWR is a measure of impedance match. A SWR greater than 1:1 indicates an impedance mismatch. An impedance mismatch results in standing waves on a transmission line. What is so difficult to understand about that or are you fixated on the "SW" standing for "standing wave" in the name of the measurement? I'm getting the impression you are being water boarded and will say anything you think will make it end! Give us a location and we will save you! I'm getting the impression you are playing stupid just for the sake of arguing. Guilty as charged. How about you? -- Rick |
An antenna question--43 ft vertical
rickman wrote:
On 7/10/2015 4:10 PM, Ian Jackson wrote: In message , writes Ian Jackson wrote: Even when the only transmission line consists the output connector of the SWR meter, and maybe an inch of internal coax, there will still BE a standing wave - but it will only be a tiny portion of longer one. There will NOT be standing waves and there will not be a voltage maximum and a voltage minimum unless there is a transmission line. Are you saying that for a standing wave to qualify as a standing wave, the transmission line needs to be long enough for there to be a voltage maximum a voltage minimum? It seems to be very much like watching a train wreck. We are fascinated by the event even though it is terrible to watch. I'm starting to get a bit tired of it though. I can only watch the train run off the track so many times. Yes, it looks like a train wreck to me also. A very big problem is people fixated on the term "standing wave". Another is people who do not understand what a transmission line is. To function as a transmission line, the conductors have to be a significant fraction of a wavelength long. The general rule of thumb is that the connection must be greater than 1/10 of a wavelength at the frequency of interest to be regarded as a transmission line. A 10 mm wire carrying a 1 MHz signal is NOT a transmission line even if the wire is RG-8 coaxial cable. A transmission line carries the electromagnetic energy in the electromagnetic field between the conductors that make up the line, not in the conductors. A very short connection can not generate an internal electomagnetic field. This is true for ALL transmission lines, whether they be parallel lines. coaxial lines, or wave guides. Standing waves only occur on transmission lines. SWR is a measurement of impedance and only depends on the impedances of the connection, be it a wire or a transmission line. -- Jim Pennino |
An antenna question--43 ft vertical
rickman wrote:
On 7/10/2015 4:28 PM, wrote: rickman wrote: On 7/10/2015 2:34 PM, wrote: rickman wrote: On 7/10/2015 1:39 PM, wrote: standing waves are a consequence of a VSWR greater than 1:1 on a transmission line. Did you really write that? The standing waves are a consequence of a standing wave ratio of greater than 1:1? An IMPEDANCE mismatch on a TRANSMISSION LINE results in standing waves. First you say the standing waves are a result of the SWR being greater than 1:1, now you say it is a result of the impedance mismatch. I'm *so* confused.... :( Are you serious? SWR is a measure of impedance match. A SWR greater than 1:1 indicates an impedance mismatch. An impedance mismatch results in standing waves on a transmission line. What is so difficult to understand about that or are you fixated on the "SW" standing for "standing wave" in the name of the measurement? I'm getting the impression you are being water boarded and will say anything you think will make it end! Give us a location and we will save you! I'm getting the impression you are playing stupid just for the sake of arguing. Guilty as charged. How about you? At least I know what a transmission line actually is while you obviously do not. -- Jim Pennino |
An antenna question--43 ft vertical
In message ,
writes Ian Jackson wrote: In message , writes Ian Jackson wrote: Even when the only transmission line consists the output connector of the SWR meter, and maybe an inch of internal coax, there will still BE a standing wave - but it will only be a tiny portion of longer one. There will NOT be standing waves and there will not be a voltage maximum and a voltage minimum unless there is a transmission line. Are you saying that for a standing wave to qualify as a standing wave, the transmission line needs to be long enough for there to be a voltage maximum a voltage minimum? I am saying that if the connection between the two things of interest is short enough in terms of wavelengths at the frequency of interest, the connection no longer functions as a transmission line, there are no standing waves, but the measurment we call SWR still exists. Pray tell me exactly (in wavelengths) when something which is too short to be a transmission line suddenly changes into something which IS long enough to be a transmission line. -- Ian |
An antenna question--43 ft vertical
Ian Jackson wrote:
In message , writes Ian Jackson wrote: In message , writes Ian Jackson wrote: Even when the only transmission line consists the output connector of the SWR meter, and maybe an inch of internal coax, there will still BE a standing wave - but it will only be a tiny portion of longer one. There will NOT be standing waves and there will not be a voltage maximum and a voltage minimum unless there is a transmission line. Are you saying that for a standing wave to qualify as a standing wave, the transmission line needs to be long enough for there to be a voltage maximum a voltage minimum? I am saying that if the connection between the two things of interest is short enough in terms of wavelengths at the frequency of interest, the connection no longer functions as a transmission line, there are no standing waves, but the measurment we call SWR still exists. Pray tell me exactly (in wavelengths) when something which is too short to be a transmission line suddenly changes into something which IS long enough to be a transmission line. Sure. A transmission line is distinguished from a wire by the fact that a transmission line carries the energy in the form of an electromagnetic field contained by the structure of the transmission line while a wire carries the energy in the form of conduction in the wire. This is true for all transmission lines, be they parallel, coaxial, wave guide, microstrip, stripline, or any other type of transmission line. A conducting structure becomes a transmission line when it's length in wavelengths becomes long enough to allow the establishment of an electromagnetic field within it's structure. The general rule of thumb is that the dividing point is about 1/10 of a wavelength. For the pendatic, this does NOT mean that at exactly 1/10 of a wave length things suddenly change, it means that in general transmission line effects become negligable below 1/10 of a wave length. A piece of coax will not function as a transmission line at 1/100 of a wavelength even though it is constructed to be a transmission line because it is too small to establish an electromagnetic field between the center conductor and the shield. Note: This is a slightly simplified explaination, for details and mathematical derivations: https://en.wikipedia.org/wiki/Transmission_line http://www.antenna-theory.com/tutori...ine.php#txline http://www.ece.uci.edu/docs/hspice/h...001_2-269.html http://www.allaboutcircuits.com/text...mission-lines/ Standing waves only occur on a transmission line and are due to reflections on the line. If the line length is too short to act as a transmission line, there can be no reflections and no standing waves. -- Jim Pennino |
An antenna question--43 ft vertical
On 7/10/2015 4:10 PM, Ian Jackson wrote:
In message , writes Ian Jackson wrote: Even when the only transmission line consists the output connector of the SWR meter, and maybe an inch of internal coax, there will still BE a standing wave - but it will only be a tiny portion of longer one. There will NOT be standing waves and there will not be a voltage maximum and a voltage minimum unless there is a transmission line. Are you saying that for a standing wave to qualify as a standing wave, the transmission line needs to be long enough for there to be a voltage maximum a voltage minimum? Ian, It's been very interesting to follow the stupid posting of some who claim to know the laws of physics. But then nothing I've have seen in this thread has surprised me in the least. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
An antenna question--43 ft vertical
In message ,
writes Ian Jackson wrote: In message , writes Ian Jackson wrote: In message , writes Ian Jackson wrote: Even when the only transmission line consists the output connector of the SWR meter, and maybe an inch of internal coax, there will still BE a standing wave - but it will only be a tiny portion of longer one. There will NOT be standing waves and there will not be a voltage maximum and a voltage minimum unless there is a transmission line. Are you saying that for a standing wave to qualify as a standing wave, the transmission line needs to be long enough for there to be a voltage maximum a voltage minimum? I am saying that if the connection between the two things of interest is short enough in terms of wavelengths at the frequency of interest, the connection no longer functions as a transmission line, there are no standing waves, but the measurment we call SWR still exists. Pray tell me exactly (in wavelengths) when something which is too short to be a transmission line suddenly changes into something which IS long enough to be a transmission line. Sure. A transmission line is distinguished from a wire by the fact that a transmission line carries the energy in the form of an electromagnetic field contained by the structure of the transmission line while a wire carries the energy in the form of conduction in the wire. This is true for all transmission lines, be they parallel, coaxial, wave guide, microstrip, stripline, or any other type of transmission line. A conducting structure becomes a transmission line when it's length in wavelengths becomes long enough to allow the establishment of an electromagnetic field within it's structure. The general rule of thumb is that the dividing point is about 1/10 of a wavelength. For the pendatic, this does NOT mean that at exactly 1/10 of a wave length things suddenly change, it means that in general transmission line effects become negligable below 1/10 of a wave length. A piece of coax will not function as a transmission line at 1/100 of a wavelength even though it is constructed to be a transmission line because it is too small to establish an electromagnetic field between the center conductor and the shield. Note: This is a slightly simplified explaination, for details and mathematical derivations: https://en.wikipedia.org/wiki/Transmission_line http://www.antenna-theory.com/tutori...ine.php#txline http://www.ece.uci.edu/docs/hspice/h...001_2-269.html http://www.allaboutcircuits.com/text...nt/chpt-14/lon g-and-short-transmission-lines/ Standing waves only occur on a transmission line and are due to reflections on the line. If the line length is too short to act as a transmission line, there can be no reflections and no standing waves. I haven't checked those references yet, but regardless of what they may say, if that 10' of coax between my TX and my 160m ATU is NOT a transmission line - just what IS it? Do different laws of physics apply? -- Ian |
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