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A short 160M antenna
Jeff wrote in :
On 08/11/2014 17:46, gareth wrote: "Brian Reay" wrote in message ... He isn't the first fool to think he could generate an EM wave breaking Maxwell's laws. You continue to be the one who originates ths abuse that you seek to lay at others' door, and you continue to misunderstand Maxwell. The changing magnetic field cause by rotating a magent at such a speed that it would cease to be a short antennae will create a changing electric field, as described by Maxwell For once have to agree with Gareth, a rotating magnet will cause EM radiation. Jeff *silently munches popcorn, waits for picture to start* |
A short 160M antenna
Jeff wrote in :
For once have to agree with Gareth, a rotating magnet will cause EM radiation. Ok, maybe so. Is this right...? Suppose a wire is part of a closed circuit, that magnet would certainly induce current. Now, if that wire were NOT closed, but in the form of some antenna, then at an appropriate frequency, in the part of an antenna that normally sees current (at the feedpoint end), you would see a current, thus all the other attributes of an antenna subject to an electromagnetic field would also exist? IF (I'm not stating, just trying to follow a thought based on what you said), IF this is so, then it would mean the EM wave existed with or without the wire, purely because the magnet was spinning. Alternatively, does it just mean that an alternative magnetic field near an antenna feedpoint is as capable of inducing a signal out of the antenna as an electromagnetic wave is? Maybe I should go back to my popcorn. I may not even understand what I see, but I want to watch. |
A short 160M antenna
"Sn!pe" wrote in message
o.uk... What produces the electric component of the EM field? The changing magnetic field. Of course, it should go withour saying that the axis of spin must be between the N and S poles, and not along the axis of the magnet, in case of confusion thereto. |
A short 160M antenna
"Sn!pe" wrote in message
.uk... gareth wrote: "Sn!pe" wrote in message o.uk... What produces the electric component of the EM field? The changing magnetic field. Of course, it should go withour saying that the axis of spin must be between the N and S poles, and not along the axis of the magnet, in case of confusion thereto. I don't understand. Is it not the case that the electric component of the EM field arises from a voltage difference? How does that voltage difference arise, please? I suggest that you go back to an earlier level and think about the dynamo, alternator and transformer, where a changing magnetic field produces an electric field, for it is the same principle. It is unfortunate that matters of electricity are very difficult to understand in full, so we are presented with a series of models (usually starting off with the increasing pressure as the depth of water in a bucket is increased) none of which are absolutely correct, but all of which get us over a hurdle of understanding until along comes the next model. And the biggest partial model that leads to much understanding is that electricity is all about pos and neg charges whereas in fact it is all about the EM fields! |
A short 160M antenna
"Sn!pe" wrote in message
. uk... Do not dynamos, alternators and transformers rely on currents induced into *conductors* by changing magnetic fields? Please see 'Faraday's Law of Induction' regarding the current induced into a conductor. https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction Actually it is explained in the opening remarks of that article where it says that an EMF is produced. |
A short 160M antenna
"Sn!pe" wrote in message
. uk... Where is the conductor in your 'rotating magnet' suggestion? Is it not the case that the current gives rise to the potential difference from which the eletric field arises? It is the current that is directly responsible for the magnetic component, of course. I attempted a partial explanation of your question in the following paragraph ... And the biggest partial model that leads to much MISunderstanding is that electricity is all about pos and neg charges whereas in fact it is all about the EM fields! Perhaps I'm just being dense, I doubt that very much. but I still don't see how the electric component of the propagating EM field arises in your scenario. I have to admit, though, that it's probably 50 years since I last looked at this stuff in (I think) the ARRL Handbook, perhaps my memory is at fault. Well, it is 42 years since I studied all that stuff*****, admittedly in the 3rd year of an electronics course at University, and perhaps therein lies the problem for many people, for unless you have studied differential vector fields then you won't have the backgrund for Maxwell's Equations. By saying that, I do not mean to be condescending and am always willing to help others. Maxwell's equations are the starting point for a real understanding of all matters electrical. ***** apart frm a bit of revision a few years ago to understand the claims made by the Crossed Field Antenna idea. |
A short 160M antenna
On 09/11/14 13:01, Sn!pe wrote:
gareth wrote: "Sn!pe" wrote in message .uk... gareth wrote: "Sn!pe" wrote in message o.uk... What produces the electric component of the EM field? The changing magnetic field. Of course, it should go withour saying that the axis of spin must be between the N and S poles, and not along the axis of the magnet, in case of confusion thereto. I don't understand. Is it not the case that the electric component of the EM field arises from a voltage difference? How does that voltage difference arise, please? I suggest that you go back to an earlier level and think about the dynamo, alternator and transformer, where a changing magnetic field produces an electric field, for it is the same principle. Do not dynamos, alternators and transformers rely on currents induced into *conductors* by changing magnetic fields? Please see 'Faraday's Law of Induction' regarding the current induced into a conductor. https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction Where is the conductor in your 'rotating magnet' suggestion? Is it not the case that the current gives rise to the potential difference from which the eletric field arises? It is the current that is directly responsible for the magnetic component, of course. It is unfortunate that matters of electricity are very difficult to understand in full, so we are presented with a series of models (usually starting off with the increasing pressure as the depth of water in a bucket is increased) none of which are absolutely correct, but all of which get us over a hurdle of understanding until along comes the next model. And the biggest partial model that leads to much understanding is that electricity is all about pos and neg charges whereas in fact it is all about the EM fields! I agree that "It is unfortunate that matters of electricity are very difficult to understand in full". Perhaps I'm just being dense, but I still don't see how the electric component of the propagating EM field arises in your scenario. I have to admit, though, that it's probably 50 years since I last looked at this stuff in (I think) the ARRL Handbook, perhaps my memory is at fault. You are not 'being dense', you are perfectly correct. Waving a magnet will not generate an EM wave, it won't even induce a current unless there is a conductor to hand. Likewise, waving a battery around, won't generate an EM wave either. Maxwell's equations come as a 'set' to generate an EM wave, you can't start with just one. That was one of the flaws in the Cross Field Antenna theory-or the original one, it varied as it was challenged. It had other flaws, eg the idea that the Poynting vector was some 'extra' physical phenomenon which could be 'synthesised', rather than just a mathematical vector representation of the power in the E and M fields. As I pointed out in a previous post, the differential term is zero in the absence of one of the fields so the equations have no, non-trivial, solutions. As I recall, this is one of the standard things you are taught when you attend a lecture on Maxwell's Equations. Perhaps someone missed a lecture (or more),has lost some crucial pages from his notes,or hasn't got a clue. Like all equations, if you apply them correctly, Maxwell's equations do work. However, if you can't understand them, you will mislead yourself. |
A short 160M antenna
Lostgallifreyan wrote in
: IF (I'm not stating, just trying to follow a thought based on what you said), IF this is so, then it would mean the EM wave existed with or without the wire, purely because the magnet was spinning. Ok, scratch that! My own speculation is plain wrong, surely. The earlier point in myearlier post MAY be true, but if so, only because the presence of a nearby antenna feedpoint means that a current carrying wire is actually present. All this, assuming that you can use the current carrying portion of some antenna as if it were a winding in a dynamo, given a magnetic field varying at a rate appropriate for said antenna. Even if this IS possible, it isn't the same as doing an EM wave with no wire at all. That would be magic, no? |
A short 160M antenna
"Brian Reay" wrote in message
... Waving a magnet will not generate an EM wave, it won't even induce a current unless there is a conductor to hand. From Maxwell, del cross E = -dB/dt Maxwell's equations come as a 'set' to generate an EM wave, I regret that you have only part of the story, for Maxwell's Equations describe _ALL_ electrical phenomena. you can't start with just one. I regret that you are not correct there. As I pointed out in a previous post, the differential term is zero in the absence of one of the fields so the equations have no, non-trivial, solutions. That was not what you said before, and now you are attempting to change history in order to save face. You said that for static fields there were no non-zero differential results and you poured scorn not only on my background, but also on Essex University where I studied. As I recall, this is one of the standard things you are taught when you attend a lecture on Maxwell's Equations. Perhaps someone missed a lecture (or more),has lost some crucial pages from his notes,or hasn't got a clue. Well, Brian, M3OSN,Old Chap, you accuse me of making comments as an excuse to originate abuse, but, once again, it is only you who displays the fault that you allege. Like all equations, if you apply them correctly, Maxwell's equations do work. However, if you can't understand them, you will mislead yourself. Do you mean those who ahve not grasped that they apply to _ALL_ electrical phenomena? |
A short 160M antenna
"gareth" wrote in message
... "Brian Reay" wrote in message ... As I pointed out in a previous post, the differential term is zero in the absence of one of the fields so the equations have no, non-trivial, solutions. That was not what you said before, and now you are attempting to change history in order to save face. You said that for static fields there were no non-zero differential results and you poured scorn not only on my background, but also on Essex University where I studied. And here is the evidence of your attempt to rewrite history in order to save face, coupled once again with your uncontrollable urge to make nasty comments in passing (Why do you behave like that?) ... -----ooooo----- "Brian Reay" wrote in message ... Of course, regardless of the day of the week, Maxwell is much good for a static field. (Differential = 0). The appalling lack of mathematical ability shown by some who claim degrees in engineering really makes you wonder at times. Especially as that would have been in a maths qualification required for any decent Uni. entry. |
A short 160M antenna
"Brian Reay" wrote in message
... As I pointed out in a previous post, the differential term is zero in the absence of one of the fields so the equations have no, non-trivial, solutions. You bandy about that some do not understand Maxwell's Equations*****, but it is only you who does not seem to, for in the case of a static magnetic field due to a current, the non-zero differential given by Maxwell's Equations in a vacuum is (off the top of my head, EOE) .. del cross B = Mu0* J B being the Magnetic Field, Mu0 the permeability of free space and J the current density. Brian, M3OSN, Old Chum, why not give up whilst you are still (a long way) behind? ***** Every day, almost every hour, it seems that you originate personal insults. Why do you behave like that? |
A short 160M antenna
Jeff wrote in :
E cross H in mathematical terms. 'Cross product' of E and H? As in, related to 'dot product'? If so that might be my wau in to understanding Maxwell, I've used dot product before, translated myself to find intersections of lines, and saw cross product closely related, documented pretty much beside it a couple of times. |
A short 160M antenna
Jeff wrote:
On 08/11/2014 17:46, gareth wrote: "Brian Reay" wrote in message ... He isn't the first fool to think he could generate an EM wave breaking Maxwell's laws. You continue to be the one who originates ths abuse that you seek to lay at others' door, and you continue to misunderstand Maxwell. The changing magnetic field cause by rotating a magent at such a speed that it would cease to be a short antennae will create a changing electric field, as described by Maxwell For once have to agree with Gareth, a rotating magnet will cause EM radiation. Jeff Nope, a rotating magnet will produce a rotatating magnetic field. A moving magenetic field is a moving magnetic field and nothing more than that. -- Jim Pennino |
A short 160M antenna
Jeff wrote:
Ok, maybe so. Is this right...? Suppose a wire is part of a closed circuit, that magnet would certainly induce current. Now, if that wire were NOT closed, but in the form of some antenna, then at an appropriate frequency, in the part of an antenna that normally sees current (at the feedpoint end), you would see a current, thus all the other attributes of an antenna subject to an electromagnetic field would also exist? IF (I'm not stating, just trying to follow a thought based on what you said), IF this is so, then it would mean the EM wave existed with or without the wire, purely because the magnet was spinning. Alternatively, does it just mean that an alternative magnetic field near an antenna feedpoint is as capable of inducing a signal out of the antenna as an electromagnetic wave is? Maybe I should go back to my popcorn. I may not even understand what I see, but I want to watch. It means that a rotating magnet will produce a radiated EM field, nothing to do with any other piece of wire or antenna in close proximity. Nope. As Garth claims it is inherent in Maxwell's equations that this must happen. Nope. What Maxwell's Equations say is a moving magnet produces a moving magnetic field. A moving magnetic field is not an electromagnetic field. If you want pictures then have a look at: http://www.falstad.com/emwave2/index.html and select rotating magnet and Poynting Vector. Jeff -- Jim Pennino |
A short 160M antenna
Sn!pe wrote:
Sn!pe wrote: Jeff wrote: [...] Run the java applet and in set up (top right) select rotating magnet, and then select Show Poynting vector (or any other filed that you wish to view) Jeff. Thanks, Jeff. It seems that I lack a suitable Java installation, I'll look into it. [later: now done] OK, I've fixed that. I think it's probably time I did a bit of research for myself, I've never heard of Poynting vectors and for the moment I don't understand what I'm seeing. Anyway, thanks again, Jeff. Yes, that is correct, you do not understand what you are seeing. -- Jim Pennino |
A short 160M antenna
gareth wrote:
"Sn!pe" wrote in message o.uk... What produces the electric component of the EM field? The changing magnetic field. Wrong. There is no electric component therefore no electromagnetic field. -- Jim Pennino |
A short 160M antenna
wrote in message
... Nope, a rotating magnet will produce a rotatating magnetic field. A moving magenetic field is a moving magnetic field and nothing more than that. That is so wrong that I will leave it to others, others who perhaps have sided with the redneck previously, to point out his error, and the use of rotating magnets to create electric fields in dynamos and alternators. |
A short 160M antenna
gareth wrote:
"Sn!pe" wrote in message .uk... gareth wrote: "Sn!pe" wrote in message o.uk... What produces the electric component of the EM field? The changing magnetic field. Of course, it should go withour saying that the axis of spin must be between the N and S poles, and not along the axis of the magnet, in case of confusion thereto. I don't understand. Is it not the case that the electric component of the EM field arises from a voltage difference? How does that voltage difference arise, please? I suggest that you go back to an earlier level and think about the dynamo, alternator and transformer, where a changing magnetic field produces an electric field, for it is the same principle. That is not a spinning magnet, that is a changing magnetic field across a conductor which induces a current in the conductor which produces an AC voltage in the conductor, or in other words, a generator. No electormagetic field until you connect the wire with AC voltage to an antenna which converts the AC voltage to an electromagnetic wave. It is unfortunate that matters of electricity are very difficult to understand Especially by babbling gas bags. -- Jim Pennino |
A short 160M antenna
Brian Reay wrote:
snip You are not 'being dense', you are perfectly correct. Waving a magnet will not generate an EM wave, it won't even induce a current unless there is a conductor to hand. Likewise, waving a battery around, won't generate an EM wave either. Maxwell's equations come as a 'set' to generate an EM wave, you can't start with just one. That was one of the flaws in the Cross Field Antenna theory-or the original one, it varied as it was challenged. It had other flaws, eg the idea that the Poynting vector was some 'extra' physical phenomenon which could be 'synthesised', rather than just a mathematical vector representation of the power in the E and M fields. As I pointed out in a previous post, the differential term is zero in the absence of one of the fields so the equations have no, non-trivial, solutions. As I recall, this is one of the standard things you are taught when you attend a lecture on Maxwell's Equations. Perhaps someone missed a lecture (or more),has lost some crucial pages from his notes,or hasn't got a clue. Like all equations, if you apply them correctly, Maxwell's equations do work. However, if you can't understand them, you will mislead yourself. Precisely so; unfortunately most people do not have the math skills to show that Maxwell's Equations say spinning magnets do not produce electromagnetic fields. -- Jim Pennino |
A short 160M antenna
Jeff wrote:
You are not 'being dense', you are perfectly correct. Waving a magnet will not generate an EM wave, it won't even induce a current unless there is a conductor to hand. Likewise, waving a battery around, won't generate an EM wave either. Maxwell's equations come as a 'set' to generate an EM wave, you can't start with just one. That was one of the flaws in the Cross Field Antenna theory-or the original one, it varied as it was challenged. It had other flaws, eg the idea that the Poynting vector was some 'extra' physical phenomenon which could be 'synthesised', rather than just a mathematical vector representation of the power in the E and M fields. As I pointed out in a previous post, the differential term is zero in the absence of one of the fields so the equations have no, non-trivial, solutions. As I recall, this is one of the standard things you are taught when you attend a lecture on Maxwell's Equations. Perhaps someone missed a lecture (or more),has lost some crucial pages from his notes,or hasn't got a clue. Like all equations, if you apply them correctly, Maxwell's equations do work. However, if you can't understand them, you will mislead yourself. Thank you, Brian, I was beginning to doubt myself there. Not having had the benefit of a University education like Gareth I tend to take an empirical approach to this sort of thing. Unfortunately this time Brian is not correct and a rotating magnet will indeed produce an EM wave. The point that you have missed Brian is that the differential term is zero for a static magnetic field, but when the magnetic field is rotating analysis of the equations reveal that there must be an E field produced in order to satisfy the full set of equations. Have a look at the link in my previous post. Jeff Even if true, the presence of an E field and an H field alone is NOT the same thing as an electromagnetic field. -- Jim Pennino |
A short 160M antenna
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A short 160M antenna
gareth wrote:
"Brian Reay" wrote in message ... Waving a magnet will not generate an EM wave, it won't even induce a current unless there is a conductor to hand. From Maxwell, del cross E = -dB/dt Maxwell's equations come as a 'set' to generate an EM wave, I regret that you have only part of the story, for Maxwell's Equations describe _ALL_ electrical phenomena. Nope; disproved mid-20th century. Maxwell's equations are a classical approximation to quantum electrodynamics much like Newtons Laws are a classical approximation to situations much slower than the speed of light. Maxwell's equations do not apply when the particle nature of electromagnetic radiation is concidered or for very strong electric fields, for example. -- Jim Pennino |
A short 160M antenna
wrote in message
... What Maxwell's Equations say is a moving magnet produces a moving magnetic field. Maxwell's Equations say nothing about moving magnets. However, Jimp's equations are a different matter. |
A short 160M antenna
gareth wrote:
wrote in message ... What Maxwell's Equations say is a moving magnet produces a moving magnetic field. Maxwell's Equations say nothing about moving magnets. A moving magnet produces a time varying magnetic field. Are you now saying that Maxwell's equations do not apply to a time varying magnetic field, gas bag? -- Jim Pennino |
A short 160M antenna
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A short 160M antenna
On 09/11/2014 17:55, Jeff wrote:
You are not 'being dense', you are perfectly correct. Waving a magnet will not generate an EM wave, it won't even induce a current unless there is a conductor to hand. Likewise, waving a battery around, won't generate an EM wave either. Maxwell's equations come as a 'set' to generate an EM wave, you can't start with just one. That was one of the flaws in the Cross Field Antenna theory-or the original one, it varied as it was challenged. It had other flaws, eg the idea that the Poynting vector was some 'extra' physical phenomenon which could be 'synthesised', rather than just a mathematical vector representation of the power in the E and M fields. As I pointed out in a previous post, the differential term is zero in the absence of one of the fields so the equations have no, non-trivial, solutions. As I recall, this is one of the standard things you are taught when you attend a lecture on Maxwell's Equations. Perhaps someone missed a lecture (or more),has lost some crucial pages from his notes,or hasn't got a clue. Like all equations, if you apply them correctly, Maxwell's equations do work. However, if you can't understand them, you will mislead yourself. Thank you, Brian, I was beginning to doubt myself there. Not having had the benefit of a University education like Gareth I tend to take an empirical approach to this sort of thing. Unfortunately this time Brian is not correct and a rotating magnet will indeed produce an EM wave. The point that you have missed Brian is that the differential term is zero for a static magnetic field, but when the magnetic field is rotating analysis of the equations reveal that there must be an E field produced in order to satisfy the full set of equations. Have a look at the link in my previous post. Jeff You are confusing a rotating magnetic field with one which is changing due to an alternating current producing it. |
A short 160M antenna
On 09/11/2014 18:07, Lostgallifreyan wrote:
Jeff wrote in : E cross H in mathematical terms. 'Cross product' of E and H? As in, related to 'dot product'? If so that might be my wau in to understanding Maxwell, I've used dot product before, translated myself to find intersections of lines, and saw cross product closely related, documented pretty much beside it a couple of times. A cross product of two vectors is a third vector orthogonal to the first two. In the case of the EM wave, the E and H vectors are orthogonal so the cross product is in the third dimension, the direction of propagation. A dot product is a scalar quantity, ie it has magnitude but no direction. As you say, it is used to find where lines, represented as vectors, intersect. |
A short 160M antenna
"Brian Reay" wrote in message
... You are confusing a rotating magnetic field with one which is changing due to an alternating current producing it. It is a frequent sneer of yours that some subject or other is taught in the first couple of years at secondary school, and yet you are setting yourself up as the target for such a sneer by making comments such as that quoted above. In AC motors you can have both; a rotating magnetic field produced by alternating currents. Magnetic fields are universally the same and do not "care" whatever was the agency that creates them |
A short 160M antenna
On 2014-11-09 20:00:10 +0000, Brian Reay said:
On 09/11/2014 18:07, Lostgallifreyan wrote: Jeff wrote in : E cross H in mathematical terms. 'Cross product' of E and H? As in, related to 'dot product'? If so that might be my wau in to understanding Maxwell, I've used dot product before, translated myself to find intersections of lines, and saw cross product closely related, documented pretty much beside it a couple of times. A cross product of two vectors is a third vector orthogonal to the first two. In the case of the EM wave, the E and H vectors are orthogonal so the cross product is in the third dimension, the direction of propagation. A dot product is a scalar quantity, ie it has magnitude but no direction. As you say, it is used to find where lines, represented as vectors, intersect. Does a rotating magnet in vacuo (no conductors around to carry current) produce an electric field? Sounds a simple question, which has been answered each way by several people. Anyone who is interested but not absolutely sure should go and check this question out, I think. Starting to try to do so illustrates the well-known fact that there is a lot of nonsense on the web. I take it you are firmly in the 'no' camp, Brian? -- Percy Picacity |
A short 160M antenna
Brian Reay wrote in :
A cross product of two vectors is a third vector orthogonal to the first two. In the case of the EM wave, the E and H vectors are orthogonal so the cross product is in the third dimension, the direction of propagation. Ok, thanks. This reminds me of the Flemings 'hand rules', which I have never been taught directly so have failed ot remember and have to look up on the rare occasion I need to. Any relation? Or are those limited to motors and generators? |
A short 160M antenna
"Brian Reay" wrote in message
... The question then is, "is the wire loop necessary to produce RF radiation?" Or something similar, yes. Essentially, the rotating field can cause a current to flow in a conductor, that current will produce another magnetic field. The current is charge movement, therefore you have an electric field. That and the 'new' magnetic field can produce an EM wave. No different to any other coil 'excited' with an AC current- perhaps the method of exciting the coil is a little unconventional ;-) Sometimes I am astounded by the things that you come out with; things that perhaps explains your daily output of bluster and the smokescreen that you attempt to creat with your continual personal abuse? |
A short 160M antenna
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A short 160M antenna
Ian Jackson wrote:
snip If a permanent magnet was oscillated inside a loop of wire, it would produce an oscillating current in the loop. An oscillating current would produce RF radiation (especially if it was tuned with a capacitor to the frequency of the magnet's oscillation). In which case you have a generator producing AC voltage. The question then is, "is the wire loop necessary to produce RF radiation?" The wire loop is necessary to produce an AC voltage. An AC voltage applied to an antenna produces RF radiation. Before tubes were invented, high frequency AC generators were used to generate high frequency AC voltage which was applied to antennas. -- Jim Pennino |
A short 160M antenna
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A short 160M antenna
El 09-11-14 23:01, escribió:
wrote: El 08-11-14 8:03, escribió: In rec.radio.amateur.antenna wrote: "Brian wrote in message ... His whole grasp of antenna theory is flawed. He was trying to (indirectly) argue the other day via his his interpretation of Maxwell's Equations you could generate an EM wave by waving a magnet about. When corrected, he introduced another variation. Well, Brian, M3OSN, Old Chum, as was pointed out to you, all of your posts these days are personal attacks aimed at one or another. Why do you behave like that? Certainly, as I corrected myself, if you wave a magnet about fast enough, say, 1000,000,000 times per second, you will certainly generate an EM wave and no-one has corrected me on that point because that point is true. No, that point is utterly, completely, and absolutely false and goes once again to show you have no clue as to the difference between an electric field, a magnetic field, and an electromagnetic field. Without doing the math, can we be sure that there is no radiation from a rotating magnetic dipole? You could ask someone who understands the math. It is not that I don't understand the math, but I don't want to spend time if we can get an answer by using reciprocity (the part of my text you skipped). Back to reciprocity: When using reciprocity, a permament magnet will rotate in an EM radiation field (produced by an antenna-transmitter combination, far field distance). Of course you need to spin-up the magnet as you don't have a rotating field. Once it is synchronized, you can extract power from it (resulting in a slip angle). So the other way around, using reciprocity, the rotating magnet will generate power in a load connected to the antenna that was used to generate the EM field. If we can't prove that reciprocity (or other assumption) doesn't hold for this case, then the rotating permanent magnet produces EM radiation. -- Wim PA3DJS Please remove abc first in case of PM |
A short 160M antenna
Wimpie wrote:
El 09-11-14 23:01, escribió: wrote: El 08-11-14 8:03, escribió: In rec.radio.amateur.antenna wrote: "Brian wrote in message ... His whole grasp of antenna theory is flawed. He was trying to (indirectly) argue the other day via his his interpretation of Maxwell's Equations you could generate an EM wave by waving a magnet about. When corrected, he introduced another variation. Well, Brian, M3OSN, Old Chum, as was pointed out to you, all of your posts these days are personal attacks aimed at one or another. Why do you behave like that? Certainly, as I corrected myself, if you wave a magnet about fast enough, say, 1000,000,000 times per second, you will certainly generate an EM wave and no-one has corrected me on that point because that point is true. No, that point is utterly, completely, and absolutely false and goes once again to show you have no clue as to the difference between an electric field, a magnetic field, and an electromagnetic field. Without doing the math, can we be sure that there is no radiation from a rotating magnetic dipole? You could ask someone who understands the math. It is not that I don't understand the math, but I don't want to spend time if we can get an answer by using reciprocity (the part of my text you skipped). Back to reciprocity: When using reciprocity, a permament magnet will rotate in an EM radiation field (produced by an antenna-transmitter combination, far field distance). Of course you need to spin-up the magnet as you don't have a rotating field. Once it is synchronized, you can extract power from it (resulting in a slip angle). So the other way around, using reciprocity, the rotating magnet will generate power in a load connected to the antenna that was used to generate the EM field. None of which has a permanet magnet spinning in empty space, which is why I snipped it. If we can't prove that reciprocity (or other assumption) doesn't hold for this case, then the rotating permanent magnet produces EM radiation. And rigously proving any of that is much more complex then F=ma. -- Jim Pennino |
A short 160M antenna
On 11/9/2014 4:09 PM, Wimpie wrote:
El 08-11-14 8:03, escribió: In rec.radio.amateur.antenna wrote: "Brian wrote in message ... His whole grasp of antenna theory is flawed. He was trying to (indirectly) argue the other day via his his interpretation of Maxwell's Equations you could generate an EM wave by waving a magnet about. When corrected, he introduced another variation. Well, Brian, M3OSN, Old Chum, as was pointed out to you, all of your posts these days are personal attacks aimed at one or another. Why do you behave like that? Certainly, as I corrected myself, if you wave a magnet about fast enough, say, 1000,000,000 times per second, you will certainly generate an EM wave and no-one has corrected me on that point because that point is true. No, that point is utterly, completely, and absolutely false and goes once again to show you have no clue as to the difference between an electric field, a magnetic field, and an electromagnetic field. Without doing the math, can we be sure that there is no radiation from a rotating magnetic dipole? When using reciprocity, a permament magnet will rotate in an EM radiation field (produced by an antenna-transmitter combination, far field distance). Of course you need to spin-up the magnet as you don't have a rotating field. Once it is synchronized, you can extract power from it (resulting in a slip angle). So the other way around, using reciprocity, the rotating magnet will generate power in a load connected to the antenna that was used to generate the EM field. I don't follow this at all. I'm not familiar with the principle of reciprocity and so can't say if you are applying it correctly. But consider this. If the rotating magnet were sending out EM waves, it would require energy to do that. But a rotating magnet will rotate indefinitely bar other sources of friction. So clearly it is not emanating EM waves. An example is a magnet suspended over a superconductor. It can be set spinning and will not stop for a long time. -- Rick |
A short 160M antenna
rickman wrote:
snip I don't follow this at all. I'm not familiar with the principle of reciprocity and so can't say if you are applying it correctly. The reciprocity situation has nothing to do with a permanet magnet rotating in isolation. Reciprocity for that would be battery rotating in isolation. But consider this. If the rotating magnet were sending out EM waves, it would require energy to do that. But a rotating magnet will rotate indefinitely bar other sources of friction. So clearly it is not emanating EM waves. An example is a magnet suspended over a superconductor. It can be set spinning and will not stop for a long time. All true and can be trivially verified in an evacuated container. -- Jim Pennino |
A short 160M antenna
El 10-11-14 3:51, rickman escribió:
On 11/9/2014 4:09 PM, Wimpie wrote: El 08-11-14 8:03, escribió: In rec.radio.amateur.antenna wrote: "Brian wrote in message ... His whole grasp of antenna theory is flawed. He was trying to (indirectly) argue the other day via his his interpretation of Maxwell's Equations you could generate an EM wave by waving a magnet about. When corrected, he introduced another variation. Well, Brian, M3OSN, Old Chum, as was pointed out to you, all of your posts these days are personal attacks aimed at one or another. Why do you behave like that? Certainly, as I corrected myself, if you wave a magnet about fast enough, say, 1000,000,000 times per second, you will certainly generate an EM wave and no-one has corrected me on that point because that point is true. No, that point is utterly, completely, and absolutely false and goes once again to show you have no clue as to the difference between an electric field, a magnetic field, and an electromagnetic field. Without doing the math, can we be sure that there is no radiation from a rotating magnetic dipole? When using reciprocity, a permament magnet will rotate in an EM radiation field (produced by an antenna-transmitter combination, far field distance). Of course you need to spin-up the magnet as you don't have a rotating field. Once it is synchronized, you can extract power from it (resulting in a slip angle). So the other way around, using reciprocity, the rotating magnet will generate power in a load connected to the antenna that was used to generate the EM field. I don't follow this at all. I'm not familiar with the principle of reciprocity and so can't say if you are applying it correctly. Just do a search on reciprocity in electronic systems, it isn't difficult. But consider this. If the rotating magnet were sending out EM waves, it would require energy to do that. But a rotating magnet will rotate indefinitely bar other sources of friction. So clearly it is not emanating EM waves. An example is a magnet suspended over a superconductor. It can be set spinning and will not stop for a long time. The reason that you don't need to take magnetic dipole radiation into account in real mechanical systems is because of the radiated power is very low (low RPM in practical mechanical systems). Friction (bearings/air, eddy current, etc) is orders of magnitude more then the "friction" caused by the EM radiation. On an astronomical scale things are different. -- Wim PA3DJS Please remove abc first in case of PM |
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