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No antennae radiate all the power fed to them!
Ignoring, for the moment, travelling wave antenna, and restricting
discussion to standing wave antennae ... A wave is launched, and radiates SOME of the power, and suffers both I2R losses and dielectric and permeability losses associated with creating and collapsing the near field. At first, there is no standing wave, until the wave reaches the point of reflection in the antenna and heads back the way it has come (because not all has been radiated*****) On the way back, it againn suffers the losses described above, as well as radiating a bit more. It then reaches the other end and suffers further reflections ad infinitum. An interesting conclusion is, therefore, that the I2R losses are repeated, each tiome with a smaller loss, as the wave decrements. ***** Without the remnants of non-radiated power, there could NOT be a standing wave! |
No antennae radiate all the power fed to them!
On 01/11/14 15:26, gareth wrote:
Ignoring, for the moment, travelling wave antenna, and restricting discussion to standing wave antennae ... A wave is launched, and radiates SOME of the power, and suffers both I2R losses and dielectric and permeability losses associated with creating and collapsing the near field. At first, there is no standing wave, until the wave reaches the point of reflection in the antenna and heads back the way it has come (because not all has been radiated*****) On the way back, it again suffers the losses described above, as well as radiating a bit more. It then reaches the other end and suffers further reflections ad infinitum. An interesting conclusion is, therefore, that the I2R losses are repeated, each time with a smaller loss, as the wave decrements. ***** Without the remnants of non-radiated power, there could NOT be a standing wave! I don't think anybody would dispute what you say here, so what's to discuss? -- ;-) .. 73 de Frank Turner-Smith G3VKI - mine's a pint. .. http://turner-smith.co.uk .. Ubuntu 12.04 Thunderbirds are go. |
No antennae radiate all the power fed to them!
On 01/11/2014 16:17, Frank Turner-Smith G3VKI wrote:
On 01/11/14 15:26, gareth wrote: Ignoring, for the moment, travelling wave antenna, and restricting discussion to standing wave antennae ... A wave is launched, and radiates SOME of the power, and suffers both I2R losses and dielectric and permeability losses associated with creating and collapsing the near field. At first, there is no standing wave, until the wave reaches the point of reflection in the antenna and heads back the way it has come (because not all has been radiated*****) On the way back, it again suffers the losses described above, as well as radiating a bit more. It then reaches the other end and suffers further reflections ad infinitum. An interesting conclusion is, therefore, that the I2R losses are repeated, each time with a smaller loss, as the wave decrements. ***** Without the remnants of non-radiated power, there could NOT be a standing wave! I don't think anybody would dispute what you say here, so what's to discuss? I would dispute the statement "Without the remnants of non-radiated power, there could NOT be a standing wave!" But I'm not as clever as Gareth, so I'll sit at the back of the room with my dunce's cap on and keep quiet :-) |
No antennae radiate all the power fed to them!
gareth wrote:
Ignoring, for the moment, travelling wave antenna, and restricting discussion to standing wave antennae ... An antenna is an antenna. A wave is launched, and radiates SOME of the power, and suffers both I2R losses and dielectric and permeability losses associated with creating and collapsing the near field. Nope, voltage is applied to an antenna causing currents to be created which in turn cause an electromagnetic field to be created. As antennas are made of real materials they have a resistance and the current through that resistance leads to losses. However, in the real world most antennas have an impedance in the tens of Ohms while the resistance is in milliohms, so normally the losses are trivial compared to the radiation. At first, there is no standing wave, until the wave reaches the point of reflection in the antenna and heads back the way it has come (because not all has been radiated*****) On the way back, it againn suffers the losses described above, as well as radiating a bit more. Pure nonsense. It then reaches the other end and suffers further reflections ad infinitum. Pure nonsense. An interesting conclusion is, therefore, that the I2R losses are repeated, each tiome with a smaller loss, as the wave decrements. A nonsense conclusion based on a nonsense assumption. ***** Without the remnants of non-radiated power, there could NOT be a standing wave! Sigh. -- Jim Pennino |
No antennae radiate all the power fed to them!
|
No antennae radiate all the power fed to them!
"gareth" wrote in message
... Ignoring, for the moment, travelling wave antenna, and restricting discussion to standing wave antennae ... A wave is launched, and radiates SOME of the power, and suffers both I2R losses and dielectric and permeability losses associated with creating and collapsing the near field. Of course, it goes without saying that the wave was already travelling up the feeder and it diffracts along the elements of the antenna, rather than being launched from the feedpoint! |
No antennae radiate all the power fed to them!
"Lostgallifreyan" wrote in message
. .. Eh? |
No antennae radiate all the power fed to them!
On Sat, 01 Nov 2014 18:10:45 +0000, gareth wrote:
"Lostgallifreyan" wrote in message . .. Eh? He thinks your writing style is deranged and your theories are total nonsense. He also pleased that someone is willing to take the time to expose your posts for the idiotic nonsense that they are, because leaving you to post that sort of guff unchallenged could give a casual reader the mistaken impression that you are in any way correct in your bizarre assertions. |
No antennae radiate all the power fed to them!
wrote:
gareth wrote: Ignoring, for the moment, travelling wave antenna, and restricting discussion to standing wave antennae ... An antenna is an antenna. A wave is launched, and radiates SOME of the power, and suffers both I2R losses and dielectric and permeability losses associated with creating and collapsing the near field. Nope, voltage is applied to an antenna causing currents to be created which in turn cause an electromagnetic field to be created. As antennas are made of real materials they have a resistance and the current through that resistance leads to losses. However, in the real world most antennas have an impedance in the tens of Ohms while the resistance is in milliohms, so normally the losses are trivial compared to the radiation. At first, there is no standing wave, until the wave reaches the point of reflection in the antenna and heads back the way it has come (because not all has been radiated*****) On the way back, it againn suffers the losses described above, as well as radiating a bit more. Pure nonsense. It then reaches the other end and suffers further reflections ad infinitum. Pure nonsense. An interesting conclusion is, therefore, that the I2R losses are repeated, each tiome with a smaller loss, as the wave decrements. A nonsense conclusion based on a nonsense assumption. ***** Without the remnants of non-radiated power, there could NOT be a standing wave! Sigh. He is confusing the current and voltage distribution plots for waves. Plus, an RF wave has a magnetic component. That can't exist IN the antenna element as it is conductor. |
No antennae radiate all the power fed to them!
Frank Turner-Smith G3VKI wrote:
On 01/11/14 15:26, gareth wrote: Ignoring, for the moment, travelling wave antenna, and restricting discussion to standing wave antennae ... A wave is launched, and radiates SOME of the power, and suffers both I2R losses and dielectric and permeability losses associated with creating and collapsing the near field. At first, there is no standing wave, until the wave reaches the point of reflection in the antenna and heads back the way it has come (because not all has been radiated*****) On the way back, it again suffers the losses described above, as well as radiating a bit more. It then reaches the other end and suffers further reflections ad infinitum. An interesting conclusion is, therefore, that the I2R losses are repeated, each time with a smaller loss, as the wave decrements. ***** Without the remnants of non-radiated power, there could NOT be a standing wave! I don't think anybody would dispute what you say here, so what's to discuss? It is nonsense, they can be no wave in the element due to it being a conductor. He is confusing the I and V plots for waves. |
No antennae radiate all the power fed to them!
Bernie wrote in :
He thinks your writing style is deranged and your theories are total nonsense. He also pleased that someone is willing to take the time to expose your posts for the idiotic nonsense that they are, because leaving you to post that sort of guff unchallenged could give a casual reader the mistaken impression that you are in any way correct in your bizarre assertions. Concise. :) Which I can do, at times, but this wasn't one of them. Looks like I was at leasi intelligible because you got it. :) Just one point though... it's not aimed at Gareth, it's specifically aimed at supporting the countering move. Not the same thing, because as I explained, there are several other aspects of life where this matters. |
No antennae radiate all the power fed to them!
On Sat, 01 Nov 2014 13:52:06 -0500, Lostgallifreyan wrote:
Bernie wrote in : He thinks your writing style is deranged and your theories are total nonsense. He also pleased that someone is willing to take the time to expose your posts for the idiotic nonsense that they are, because leaving you to post that sort of guff unchallenged could give a casual reader the mistaken impression that you are in any way correct in your bizarre assertions. Concise. :) Which I can do, at times, but this wasn't one of them. Looks like I was at leasi intelligible because you got it. :) Just one point though... it's not aimed at Gareth, it's specifically aimed at supporting the countering move. Not the same thing, because as I explained, there are several other aspects of life where this matters. I kept it short as I was worried about 'putting words in your mouth'. I didn't mention the Chopin, either - doesn't matter how many times I hear it, I never tire of Berceuse : http://www.youtube.com/watch?v=8TQ-AXJZqtg |
No antennae radiate all the power fed to them!
Bernie wrote in :
I never tire of Berceuse Nice. I bet Satie knew that, there seems to be a link in his sound. For me it's mainly the Etudes and Preludes that work best... Not sure why, and not all either, mostly the lyrical Schubert-like ones, rather than the purely virtuosic stuff, I remember watching my mum playing once, I just stood there, and my mind got strongly influenced by that, it mixed a fascination for many more things, all related, organs, synthesisers, looms, typeriters like my dad used, computers, logic arrays, the things Babbage built... It's all related, and to me all such machines are living, or a direct extension of life. It's a slow Saturday night, but I'll stop there, it's strayed a bit from antennas, though if (and only if) a good and specific reason arises, I'll say why I think antennas of all things have gathered such an acrimonius history in Usenet dicussions, but otherwise I'll keep that bit of philosphy to myself. It's not a complex thought, just a deep and entirely untechnical one... |
No, antennae radiate all the power fed to them!
On 11/1/2014 11:26 AM, gareth wrote:
Ignoring, for the moment, travelling wave antenna, and restricting discussion to standing wave antennae ... A wave is launched, and radiates SOME of the power, and suffers both I2R losses and dielectric and permeability losses associated with creating and collapsing the near field. At first, there is no standing wave, until the wave reaches the point of reflection in the antenna and heads back the way it has come (because not all has been radiated*****) On the way back, it againn suffers the losses described above, as well as radiating a bit more. It then reaches the other end and suffers further reflections ad infinitum. An interesting conclusion is, therefore, that the I2R losses are repeated, each tiome with a smaller loss, as the wave decrements. ***** Without the remnants of non-radiated power, there could NOT be a standing wave! I think the subject says it all. -- Rick |
No antennae radiate all the power fed to them!
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No antennae radiate all the power fed to them!
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No antennae radiate all the power fed to them!
rickman wrote in :
Hmm, what? I'm sorry, I was looking out the window for a moment. Were you saying something? Nope. writing. |
No antennae radiate all the power fed to them!
On Sat, 1 Nov 2014 15:26:52 -0000, "gareth"
wrote: ***** Without the remnants of non-radiated power, there could NOT be a standing wave! That's quite true. Standing waves require a transmission line. If all the RF has been radiated, and there are no "remnants" left in the transmission line, there can be no standing waves because there is no RF. Think about the other boundary conditions. If you unplug the coax cable and antenna, and then transmit into an open circuit, there are no standing waves. All the RF power is converted to heat in the output stage. There's no transmission line upon which to produce standing waves and there's no antenna to radiate. Without a transmission line or antenna, there can be no radiation and therefore, not standing waves. The other extreme is also true. If you have an infinitely long lossless coaxial cable, with either an open, short, or black hole at the far end, there are no reflections because the wave will never quite reach the open or short to produce a reflection. Without a reflection, there can be no standing waves. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
No antennae radiate all the power fed to them!
Jeff Liebermann wrote in
: Without a reflection, there can be no standing waves. That's the one bit that comes naturally to my own understanding, such as it is. How far does this parallel with an optical laser cavity? I'd find it easier to understand if someone here who knows both can point out a few essential similarotes and differences. Also, in the ringing of a resonant audio filter (or any electronic filter), there seem to be parallels there too. After all you can only have ringing, a note produced, while energy remains in the system. |
No antennae radiate all the power fed to them!
On 2014-11-01 20:44:55 +0000, Jeff Liebermann said:
On Sat, 1 Nov 2014 15:26:52 -0000, "gareth" wrote: ***** Without the remnants of non-radiated power, there could NOT be a standing wave! That's quite true. Standing waves require a transmission line. If all the RF has been radiated, and there are no "remnants" left in the transmission line, there can be no standing waves because there is no RF. Think about the other boundary conditions. If you unplug the coax cable and antenna, and then transmit into an open circuit, there are no standing waves. All the RF power is converted to heat in the output stage. There's no transmission line upon which to produce standing waves and there's no antenna to radiate. Without a transmission line or antenna, there can be no radiation and therefore, not standing waves. The other extreme is also true. If you have an infinitely long lossless coaxial cable, with either an open, short, or black hole at the far end, there are no reflections because the wave will never quite reach the open or short to produce a reflection. Without a reflection, there can be no standing waves. However, this does not change the fact that standing waves do not 'use up' any of the power fed to the aerial (in principle, increased current intensity increases resistive losses, but this loss can be made arbitrarily low by having a lower wire resistance). Standing waves do not in principle use 'power' at all and certainly do not dissipate energy that otherwise would be radiated. They require a signal to be applied to the transmission line but, whether the power is radiated at the other end or the signal merely meets a mismatch, say an open circuit, the standing wave does not affect, or need to use, any of the power that leaves the other end. Indeed they work just as well if no power whatever is used, as in the open circuit case. -- Percy Picacity |
No antennae radiate all the power fed to them!
Percy Picacity wrote in
: However, this does not change the fact that standing waves do not 'use up' any of the power fed to the aerial Is that like potential vs kinetic energy? After all, a filter could be said to 'store' energy in an eternal oscillation if it had no losses, and nothign drawing output from it. The moment you do, you lose energy, the 'note' fades. Given that if you produce a standing wave in a tank of liquid such that one bulge exists above the rim, the standing wave can be considered a form of storage (potential energy), because that tank will hold more liquid that it would if brim full without the wave. |
No antennae radiate all the power fed to them!
gareth wrote:
"gareth" wrote in message ... Ignoring, for the moment, travelling wave antenna, and restricting discussion to standing wave antennae ... A wave is launched, and radiates SOME of the power, and suffers both I2R losses and dielectric and permeability losses associated with creating and collapsing the near field. Of course, it goes without saying that the wave was already travelling up the feeder and it diffracts along the elements of the antenna, rather than being launched from the feedpoint! Nope; there is an electric field in a feed line (other than wave guide) but no electromagnetic field. As a problem for the student, how big would a wave guide have to be to be able to transfer 7 Mhz? About the only antenaa where a "wave is launched" is a dielectric lens antenna with a wave guide feed. Of course, at the other end of the wave guide is an antenna to which voltage is applied, which causes current flow in the antenna, which causes an electromagnetic field to be created in the wave guide which then flows to the antenna. -- Jim Pennino |
No antennae radiate all the power fed to them!
On Sat, 01 Nov 2014 16:05:53 -0500, Lostgallifreyan
wrote: Jeff Liebermann wrote in : Without a reflection, there can be no standing waves. That's the one bit that comes naturally to my own understanding, such as it is. How far does this parallel with an optical laser cavity? I'd find it easier to understand if someone here who knows both can point out a few essential similarotes and differences. Sigh... topic drift again. The parallel with a longitudinal mode laser cavity is fairly close. http://en.wikipedia.org/wiki/Longitudinal_mode The transmission line is some multiple of 1/2 wavelength long. The signal bounces back and forth between the ends, reinforcing itself with every bounce, until it spews forth from from one end or edge. Obviously, without reflections, there would not be any laser action. Also, in the ringing of a resonant audio filter (or any electronic filter), there seem to be parallels there too. After all you can only have ringing, a note produced, while energy remains in the system. Not quite. If you apply energy to a resonant circuit (electrical or mechanical), that then remove the input, you'll get a damped wave (i.e. exponential decay) output where the rate of decay is determined by the losses in the system. You could build a transmission line oscillator, which would exhibit some rather small damped wave output when turned off, but in most cases, there's no connection with reflected or standing waves because there is usually no transmission line. Might as well be part of the problem. What I do in my spare time. I recorded these in about 1998. Please forgive my screwups, plagerism, lack of coherent style, sloppy fingering, etc: http://802.11junk.com/jeffl/music/ -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
No antennae radiate all the power fed to them!
"Brian Reay" wrote in message
... He is confusing the current and voltage distribution plots for waves. No, there is no confusion on my part. Please explain why you think that, for I fear that there may be confusion on your part. Plus, an RF wave has a magnetic component. Well, i think we all knew that. That can't exist IN the antenna element as it is conductor. Yes, and no, for it is the magnetic componentry in the wire that causes the skin effect. |
No antennae radiate all the power fed to them!
"Brian Reay" wrote in message
... It is nonsense, they can be no wave in the element due to it being a conductor. You seem to be unaware that a travelling wave around a wire is what causes the wave to move along the wire, and not the electrons inside, which only oscillate a very short distance about their mean. He is confusing the I and V plots for waves. There is no confusion on my part. Perhaps you could explain where you think I am confused, for I had not mentioned the separated I and V waveforms. Perhaps you are confused yourself, perhaps, by the current maximum at the centre of a dipole, for it is not a DC maximum but rises and falls in magnitude? |
No antennae radiate all the power fed to them!
On Sat, 1 Nov 2014 21:14:48 +0000, Percy Picacity
wrote: However, this does not change the fact that standing waves do not 'use up' any of the power fed to the aerial (in principle, increased current intensity increases resistive losses, but this loss can be made arbitrarily low by having a lower wire resistance). Standing waves do not in principle use 'power' at all and certainly do not dissipate energy that otherwise would be radiated. They require a signal to be applied to the transmission line but, whether the power is radiated at the other end or the signal merely meets a mismatch, say an open circuit, the standing wave does not affect, or need to use, any of the power that leaves the other end. Indeed they work just as well if no power whatever is used, as in the open circuit case. I'll make it even easier. An RF signal can only do three things: - Radiate (as in an antenna) - Conduct (pass through as in a transmission line) - Dissipate (convert to heat) Real transmission line and antenna systems involve combinations of these three mechanisms. If you run into something that doesn't quite fit into one or more of these mechanisms, it's probably wrong. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
No antennae radiate all the power fed to them!
gareth wrote:
"Brian Reay" wrote in message ... It is nonsense, they can be no wave in the element due to it being a conductor. You seem to be unaware that a travelling wave around a wire is what causes the wave to move along the wire, and not the electrons inside, which only oscillate a very short distance about their mean. You seem to be unaware that current is the total, net movement of all the electrons in a wire, not just a single electron. He is confusing the I and V plots for waves. There is no confusion on my part. Perhaps you could explain where you think I am confused, for I had not mentioned the separated I and V waveforms. Yeah, right. Perhaps you are confused yourself, perhaps, by the current maximum at the centre of a dipole, for it is not a DC maximum but rises and falls in magnitude? Only a very confused individual would babble on about the instantaneous current or voltage. -- Jim Pennino |
No antennae radiate all the power fed to them!
On 2014-11-01 22:02:48 +0000, Jeff Liebermann said:
On Sat, 1 Nov 2014 21:14:48 +0000, Percy Picacity wrote: However, this does not change the fact that standing waves do not 'use up' any of the power fed to the aerial (in principle, increased current intensity increases resistive losses, but this loss can be made arbitrarily low by having a lower wire resistance). Standing waves do not in principle use 'power' at all and certainly do not dissipate energy that otherwise would be radiated. They require a signal to be applied to the transmission line but, whether the power is radiated at the other end or the signal merely meets a mismatch, say an open circuit, the standing wave does not affect, or need to use, any of the power that leaves the other end. Indeed they work just as well if no power whatever is used, as in the open circuit case. I'll make it even easier. An RF signal can only do three things: - Radiate (as in an antenna) - Conduct (pass through as in a transmission line) - Dissipate (convert to heat) Real transmission line and antenna systems involve combinations of these three mechanisms. If you run into something that doesn't quite fit into one or more of these mechanisms, it's probably wrong. If 'conduct' includes the case where the signal goes to the other end of the transmission line but does not go beyond it to any other component, I'll agree with you. In that case, neglecting losses, no power is used (apart from a truly tiny amount transiently as the wave builds up and energy is stored in the first few microseconds) -- Percy Picacity |
No antennae radiate all the power fed to them!
gareth wrote:
"Brian Reay" wrote in message ... He is confusing the current and voltage distribution plots for waves. No, there is no confusion on my part. Please explain why you think that, for I fear that there may be confusion on your part. Plus, an RF wave has a magnetic component. Well, i think we all knew that. That can't exist IN the antenna element as it is conductor. Yes, and no, for it is the magnetic componentry in the wire that causes the skin effect. Magnetic fields can exist in a conductor. Electromagnetic fields can not exist in a conductor. -- Jim Pennino |
No antennae radiate all the power fed to them!
On 11/1/2014 5:31 PM, wrote:
rickman wrote: On 11/1/2014 1:03 PM, wrote: gareth wrote: Ignoring, for the moment, travelling wave antenna, and restricting discussion to standing wave antennae ... An antenna is an antenna. Deep thoughts... A wave is launched, and radiates SOME of the power, and suffers both I2R losses and dielectric and permeability losses associated with creating and collapsing the near field. Nope, voltage is applied to an antenna causing currents to be created which in turn cause an electromagnetic field to be created. As antennas are made of real materials they have a resistance and the current through that resistance leads to losses. I thought there were *real* materials with no resistance. Isn't that what a superconductor is? Well, to be pendatic, there are no real materials with zero resistance that can be used to build antennas. Why can't you build an antenna with a superconductor? As all the current existing superconductors require a bunch of supporting equipment to keep them cold, they can't be used for antennas. Really? What is the problem? There are super conductors at liquid nitrogen temperatures and you can have that sitting in a flask on your desk. Why couldn't that cool an antenna? Once you remove the I*R losses, you don't even have to worry about the radiated power heating the N2. I think you are confusing need with practicality. There is nothing to stop you from making a superconducting antenna. There just isn't a need for it unless you live in Gareth's world. Hmmm... wasn't that a movie? Gareth's World? If room temperature superconductors are ever invented... However, those are like a cure for the common cold, practical fusion power, and peace in the Middle East, all just around the corner for the past half century or so. I've never heard anyone say either a cure for the common cold or fusion was "around" the corner. I've never heard anyone say at all that peace is expected in the middle east. I believe there are rather cold temperatures in space. A superconducting antenna could be used there with *no* supporting "apparatus". -- Rick |
No antennae radiate all the power fed to them!
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No antennae radiate all the power fed to them!
On 11/1/2014 5:23 PM, Lostgallifreyan wrote:
Percy Picacity wrote in : However, this does not change the fact that standing waves do not 'use up' any of the power fed to the aerial Is that like potential vs kinetic energy? After all, a filter could be said to 'store' energy in an eternal oscillation if it had no losses, and nothign drawing output from it. The moment you do, you lose energy, the 'note' fades. Given that if you produce a standing wave in a tank of liquid such that one bulge exists above the rim, the standing wave can be considered a form of storage (potential energy), because that tank will hold more liquid that it would if brim full without the wave. What? For a wave to have a "bulge" above the top of the tank means there is a trough well below the top of the tank. The amount of liquid does not change because you make waves in the tank. -- Rick |
No antennae radiate all the power fed to them!
On 01/11/14 21:38, wrote:
As a problem for the student, how big would a wave guide have to be to be able to transfer 7MHz? I'll guess at 34.8488m x 15.7988m by scaling the dimensions for 5.85 to 8.2GHz. (C Band) -- ;-) .. 73 de Frank Turner-Smith G3VKI - mine's a pint. .. http://turner-smith.co.uk .. Ubuntu 12.04 Thunderbirds are go. |
No antennae radiate all the power fed to them!
wrote in message ... gareth wrote: Ignoring, for the moment, travelling wave antenna, and restricting discussion to standing wave antennae ... An antenna is an antenna. A wave is launched, and radiates SOME of the power, and suffers both I2R losses and dielectric and permeability losses associated with creating and collapsing the near field. Nope, voltage is applied to an antenna causing currents to be created which in turn cause an electromagnetic field to be created. As antennas are made of real materials they have a resistance and the current through that resistance leads to losses. However, in the real world most antennas have an impedance in the tens of Ohms while the resistance is in milliohms, so normally the losses are trivial compared to the radiation. At first, there is no standing wave, until the wave reaches the point of reflection in the antenna and heads back the way it has come (because not all has been radiated*****) On the way back, it againn suffers the losses described above, as well as radiating a bit more. Pure nonsense. It then reaches the other end and suffers further reflections ad infinitum. Pure nonsense. An interesting conclusion is, therefore, that the I2R losses are repeated, each tiome with a smaller loss, as the wave decrements. A nonsense conclusion based on a nonsense assumption. ***** Without the remnants of non-radiated power, there could NOT be a standing wave! Sigh. ^^^^^^^^^^^ I was going to point out to Gareth that he is describing behavior in an antenna system, not an antenna. But, I'm done now. No more. |
No antennae radiate all the power fed to them!
rickman wrote:
On 11/1/2014 6:20 PM, wrote: gareth wrote: "Brian Reay" wrote in message ... He is confusing the current and voltage distribution plots for waves. No, there is no confusion on my part. Please explain why you think that, for I fear that there may be confusion on your part. Plus, an RF wave has a magnetic component. Well, i think we all knew that. That can't exist IN the antenna element as it is conductor. Yes, and no, for it is the magnetic componentry in the wire that causes the skin effect. Magnetic fields can exist in a conductor. Electromagnetic fields can not exist in a conductor. Now I'm very confused. How can an EM field not exist in a conductor? Isn't it the E part that creates a gradient which propels the electrons? Actually it is both. As long as the antenna is made of linear material, transmit and receive are reciprocal properties. The only antennas I can think of that use non-linear materials is some microwave antennas that include ferrites. In a perfect conductor, I thought it was the M part that can't exist inside the conductor. That is one of the causes of the loss of superconductivity, penetration by an M field. Or do I have this mixed up? A bit. -- Jim Pennino |
No antennae radiate all the power fed to them!
rickman wrote:
On 11/1/2014 5:31 PM, wrote: rickman wrote: On 11/1/2014 1:03 PM, wrote: gareth wrote: Ignoring, for the moment, travelling wave antenna, and restricting discussion to standing wave antennae ... An antenna is an antenna. Deep thoughts... A wave is launched, and radiates SOME of the power, and suffers both I2R losses and dielectric and permeability losses associated with creating and collapsing the near field. Nope, voltage is applied to an antenna causing currents to be created which in turn cause an electromagnetic field to be created. As antennas are made of real materials they have a resistance and the current through that resistance leads to losses. I thought there were *real* materials with no resistance. Isn't that what a superconductor is? Well, to be pendatic, there are no real materials with zero resistance that can be used to build antennas. Why can't you build an antenna with a superconductor? As all the current existing superconductors require a bunch of supporting equipment to keep them cold, they can't be used for antennas. Really? What is the problem? There are super conductors at liquid nitrogen temperatures and you can have that sitting in a flask on your desk. Why couldn't that cool an antenna? Once you remove the I*R losses, you don't even have to worry about the radiated power heating the N2. If one were realy determined to do it, one could build the antenna in a non-metalic container of some sort and keep the container filled with LN2. I think you are confusing need with practicality. There is nothing to stop you from making a superconducting antenna. There just isn't a need for it unless you live in Gareth's world. Hmmm... wasn't that a movie? Gareth's World? It is not need versus practicality, it is practicality period. If room temperature superconductors are ever invented... However, those are like a cure for the common cold, practical fusion power, and peace in the Middle East, all just around the corner for the past half century or so. I've never heard anyone say either a cure for the common cold or fusion was "around" the corner. I've never heard anyone say at all that peace is expected in the middle east. You must not be very old then... I believe there are rather cold temperatures in space. A superconducting antenna could be used there with *no* supporting "apparatus". You mean other than the shade screen? You do understand two big problems with space stuff is how to get rid of any generated heat and Solar heating? In any case, why? I^2R losses only become significant in very small antennas and there is all the space you could ask for in space to build an antenna. -- Jim Pennino |
No antennae radiate all the power fed to them!
Frank Turner-Smith G3VKI wrote:
On 01/11/14 21:38, wrote: As a problem for the student, how big would a wave guide have to be to be able to transfer 7MHz? I'll guess at 34.8488m x 15.7988m by scaling the dimensions for 5.85 to 8.2GHz. (C Band) Sounds in the ball park to me. For further reading enjoyment and why there is no EM field inside of RG-8: http://en.wikipedia.org/wiki/Cutoff_frequency -- Jim Pennino |
No antennae radiate all the power fed to them!
Wayne wrote:
snip I was going to point out to Gareth that he is describing behavior in an antenna system, not an antenna. I doubt he will EVER understand the difference. But, I'm done now. No more. It does become tiresome correcting the same nonsense over and over again. -- Jim Pennino |
No antennae radiate all the power fed to them!
On Sat, 01 Nov 2014 18:47:32 -0400, rickman wrote:
I think you are confusing need with practicality. There is nothing to stop you from making a superconducting antenna. There just isn't a need for it unless you live in Gareth's world. Hmmm... wasn't that a movie? Gareth's World? (...) I believe there are rather cold temperatures in space. A superconducting antenna could be used there with *no* supporting "apparatus". You don't need to go to outer space to see cryogenic radios in operation. Superconducting radio frequency http://en.wikipedia.org/wiki/Superconducting_radio_frequency In a past project, I worked with cryogenic duplexers and receiver front ends for cellular service. My part had nothing to do with the superconducting components, but I got to watch them perform. Filters with nearly vertical skirts, sky high filter shape factors, zero loss, near zero noise figu http://www.suptech.com/wireless_overview_n.php http://www.suptech.com/pdf_products/cryogenic_receiver_front_end.pdf http://www.suptech.com/pdf_products/SuperLink_850_G3AB.pdf Where cryogenic front ends worked best are in installation without towers, where the coax cable losses were less, and the cryo unit can be located in a nearby rooftop shelter. These tend to be located in urban jungles, where signals are traditionally weak, and handset density rather high. At the same time, TMA (tower mounted amp) technology appeared, which provided many of the benefits of cryogenic receiver front ends, but without the complexity, power consumption, and cost of the cooling components: http://en.wikipedia.org/wiki/Tower_Mounted_Amplifier https://www.google.com/search?q=tower+mounted+amplifier&tbm=isch http://www.commscope.com/catalog/wireless/2147486004/product.aspx?id=162&sortExp=Name&nrp=100 Also, note that spacecraft all have some form of temperature control where the electronics do NOT operate at cryogenic temperatures: http://en.wikipedia.org/wiki/Spacecraft_thermal_control -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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