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"Wes Stewart" wrote in message news On Sun, 27 Mar 2005 16:20:58 GMT, " wrote: As gain increases with a yagi design the forward lobe narrows . Let's certainly hope so. But if you knew the answer you could then use the knoweledge to extend the narrowing to provide more gain. All is known about antennas isn't it? It doesn't with my antenna where the lobe gets larger as radiation is deflected to the forward direction. Obviously with a yagi cancellation is occuring as well as addition. With high gain yagi's the lobe becomes so narrow it is deemed to be a hinderence instead of an advantage. Huh, I didn't know this...for several decades now I've thought it was an advantage. You are not alone as I thought it meant quieter contacts but it is said (ARRL publication) that it then becomes more difficult to aim, ala the rombic. That's why I see my antenna's flattening of the main lobe without loss in beam width an advantage. For example my EME friends and I have always believed that focusing the available transmit power on the moon on transmit and rejecting stellar background noise on receive was desirable. How did we go so wrong? But back to the question. ------------------------------------- Do you know what creates the narrowing of the main lobe ? It only takes one diffinitive post from a real guru to explain and then the others will follow. Until the real guru comes forward with an explanation all others will procrastinate and avoid the question without giving a hint that they do not know and are awaiting the explanation from a real guru. If you actually know Wes then jump in so others may follow. Regards Art .. |
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"Dave Platt" wrote in message ... In article FUB1e.8710$NW5.8590@attbi_s02, wrote: It doesn't with my antenna where the lobe gets larger as radiation is deflected to the forward direction. There is a harsh limit, imposed by physics, as to how much gain that approach can give you. Agreed... Do you know what those limits are ? If all of the energy from one hemisphere is redirected into the other hemisphere, and if the forward-direction pattern shape does not change (the forward lobe is not narrowed), then you have a forward gain of 3 dB (2:1 power ratio increase). You *cannot* have more, as this would require that the antenna be radiating more power than it receives from its input. Absolutely incorrect. If I place the air of two balloons ,which reflect the figure eight,into one single balloon and where the laws of partial pressures do not intervene then you will have a balloon that is round and not elongated as the antenna books would have you suggest. "Gain" is a term used to to quantify a small portion of the energy contained in the mythical ball of energy. Since the collection of energy comes from different directions and phases the energy collection is layered depending on the influence of the earth. Thus the layers of radiation are distorted where one layer can be squeezed outwards further than other layers, thus the terminology of "gain" If you are going to interelate the terms of "gain" and "power" then you must define the parameters used to allow that. A Moxon antenna is, to a first approximation, a pretty good example of this approach - it has very little energy in the rear hemisphere, and a broad forward lobe. There are various two-driven-element array designs which achieve a similar pattern and result. And the resulting "gain" is ....what? I have difficulty in getting beyond 16 dbi as any additional energy from the rear has very little effect on the diameter of the frontal lobe. Obviously with a yagi cancellation is occuring as well as addition. You are trying to draw a distinction between "deflection" and "cancellation" which I believe is invalid. Both are simply ways of describing the result of the "sum of vectors" effects of having energy from multiple radiators (driven or passive) combining in different phases at different locations. Same math, two different words. Yes I agree because of conservation laws e.t.c . When cancellation occurs then energy creats energy in another direction similar to pulling steel apart in tension (or using compression) the steel becomes narrower before severing occurrs. This thinning or "waisting" is created by the additional forces created at 90 degrees to the tensile forces and where the break actually occurrs at 45 degrees and not at right angles. Do you know what creates the narrowing of the main lobe ? Conservation of energy *requires* that the main lobe be narrowed, if you wish to achieve more gain than you can get by simply redistibuting the rear-ward energy in the forward direction. This is what you alluded to before and it is still incorrect What "requires" what ? And how is this conclusion generating an elongated lobe? A super-high-gain antenna *cannot* have a wide, uniform beam-width in both azimuth and elevation. Don't know how you can say that unless somehow you generated a single lobe. Now that would be interesting As usual for your postings, Art, it's impossible to tell whether your claims for your antenna are plausible, because you refuse to disclose *anything* (either the invention, or the results you claim) in any halfway-tanglible form (e.g. models, specific numbers, etc.). My antenna is somewhat related thus my interest in what creates an elongated lobe which is formed using Yagi principles. The question however, is specifically related to Yagi's and its narrowed lobes. Do you know what it is that creats an elongated lobe on a high gain yagi i.e not totally round.? Nothing more, nothing less. Regards Art Until you do, I really think it would be to everyone's relief if you'd follow through with your recent statement that you were going to stop posting. You're achieving no good result for yourself by contining as you are. I have not posted as you have inferred. The question is about Yagi design AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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On Sun, 27 Mar 2005 18:59:42 GMT, "
wrote: the problem: My antenna is somewhat related thus my interest in what creates an elongated lobe the answer: which is formed using Yagi principles. Hi Art, Your question already answers your question. You have a tendency to just blow right on taking no notice of this to create the SAME question again: The question however, is specifically related to Yagi's and its narrowed lobes. Do you know what it is that creats an elongated lobe on a high gain yagi i.e not totally round.? formed using Yagi principles. (to quote you) Nothing more, nothing less. Exactly. Now, are we going to be treated by another round of your complaints about Shakespeare and the quality of gurus; or are you going to stick with technical discussion and respond to the obvious points? 73's Richard Clark, KB7QHC |
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Richard.
No one has come up with a explanation BUT there are real gurus out there, It's just that those who qualify as gurus have just thinned out a bit. The question still pertains to Yagis and the narrowing of lobes You have posted twice now and added nothing that relates to a possible answer. Tho there are many who perceive themselves as experts and then consistently show what they really are. I can think of one or two who can really address this question with a logical answer. Cecil, Roy and a couple of others qualify and have yet to respond You have disqualified yourself based on your responses, so like myself you will have to wait to learn. Yagi's have been studied in depth and for many years by many tho apparently not by you or others that have replied so far. Place your bets on who is the real guru of this group that comes forward to explain with logic and to the point You Richard, can read your old QST's in a hurry and surely find the answer to get back into the ratings as I don't think that new knoweledge is around the bend, just a small manipulation of "old" knoweledge will surely suffice. Think "end effect" and "none- resistive residuals" along coupled radiating elements for starters.If that draws a blank then assuredly you wear no clothes Art "Richard Clark" wrote in message ... On Sun, 27 Mar 2005 18:59:42 GMT, " wrote: the problem: My antenna is somewhat related thus my interest in what creates an elongated lobe the answer: which is formed using Yagi principles. Hi Art, Your question already answers your question. You have a tendency to just blow right on taking no notice of this to create the SAME question again: The question however, is specifically related to Yagi's and its narrowed lobes. Do you know what it is that creats an elongated lobe on a high gain yagi i.e not totally round.? formed using Yagi principles. (to quote you) Nothing more, nothing less. Exactly. Now, are we going to be treated by another round of your complaints about Shakespeare and the quality of gurus; or are you going to stick with technical discussion and respond to the obvious points? 73's Richard Clark, KB7QHC |
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On Sun, 27 Mar 2005 19:53:44 GMT, "
wrote: No one has come up with a explanation Hi Art, As usual, I see you simply enjoy posting without corresponding. C'mon, it is more than obvious you have no interest in any explanation other than your own. Roy and a couple of others qualify and have yet to respond You've spit on them so much that is hardly surprising - is it? 73's Richard Clark, KB7QHC |
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Not so. If I cannot accept an answer that I figure to be unreasonable then I
do not accept them. In Roy's case I accept the majority of his explanations, but not all. In your case you come up with many knoweledgable explanations on various facets of science ,but in general, you concentrate more in attacking others opinions with out supplying corrections I say this only where your posts are clear and not smattered with relatively unused words where a shorter one would suffice How ever those are in the minority. If I do not concurr with any explanation offerred .in no way does this suggest that I am spitting on the individual and thus treating him with disrespect. In your case you treat me in disrespect which as far as I am concerned requires reciprical treatment. You ask for it and you will get it from me without retreat On the other hand respect demands respect, your choice as I am now americanised for retaliation without regard to common courtesy as per the Britts Art "Richard Clark" wrote in message ... On Sun, 27 Mar 2005 19:53:44 GMT, " wrote: No one has come up with a explanation Hi Art, As usual, I see you simply enjoy posting without corresponding. C'mon, it is more than obvious you have no interest in any explanation other than your own. Roy and a couple of others qualify and have yet to respond You've spit on them so much that is hardly surprising - is it? 73's Richard Clark, KB7QHC |
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In article uoD1e.110018$Ze3.66917@attbi_s51, wrote: There is a harsh limit, imposed by physics, as to how much gain that approach can give you. Agreed... Do you know what those limits are ? Sure. The simplest way to state it is "the total amount of power delivered by the antenna, summed over all of the possible angles of radiation, must equal the total amount of power radiated by the antenna." If all of the energy from one hemisphere is redirected into the other hemisphere, and if the forward-direction pattern shape does not change (the forward lobe is not narrowed), then you have a forward gain of 3 dB (2:1 power ratio increase). You *cannot* have more, as this would require that the antenna be radiating more power than it receives from its input. Absolutely incorrect. If I place the air of two balloons ,which reflect the figure eight,into one single balloon and where the laws of partial pressures do not intervene then you will have a balloon that is round and not elongated as the antenna books would have you suggest. "Gain" is a term used to to quantify a small portion of the energy contained in the mythical ball of energy. Since the collection of energy comes from different directions and phases the energy collection is layered depending on the influence of the earth. Thus the layers of radiation are distorted where one layer can be squeezed outwards further than other layers, thus the terminology of "gain" Jeez, Art, do you have any idea of just how thoroughly your response qualifies as "Authentic frontier gibberish" (as a Mel Brooks character once said)? I'm sorry, guy, but I believe that you are trying to stretch analogies far beyond the point where they actually apply to the physical phenomena we're discussing. Your concept of "layers of radiation" (as applied to the gain pattern of an antenna) simply doesn't add up. If you are going to interelate the terms of "gain" and "power" then you must define the parameters used to allow that. OK, let's do just that. "Power" is very well defined - it's the rate at which energy is delivered. Pick your units for energy and time as you choose. It's conventional to use watts for power, joules for energy and seconds for time. One watt, equals a rate of energy delivery of one joule per second. "Gain" is a ratio. In discussions dealing with antennas, the gain describes the ratio between the amount of power delivered by a given antenna in a given direction, to the amount of power delivered in that same direction by a "reference" antenna (a dipole in the case of a dBd gain number, and an "isotropic" antenna in the case of a dBi gain number). The gain figures in dB are logarithmic. Those are the definitions everyone uses, I believe. If you, personally, are using different definitions than these, then our discussion (you vs. everyone else) should probably stop right here. Here's my rationale behind the statement I made about the limitations of your approach: - An isotropic antenna has a gain of 0 dBi, by definition. - If you "cut off" the entire rear side of an isotropic antenna's pattern (so that it radiates no power backwards), and precisely overlay this power (energy flow) onto the forward half, you'll end up with a "half-isospheric" antenna. It's radiating exactly the same amount of power, but over only half as much target area. The power (energy flow) towards each point in that targeted hemisphere will be exactly twice as much as in the isotropic antenna. This antenna has a gain of 3 dBi plus a hair. It cannot have *more* gain in any direction (more power into a sub-portion of the hemisphere) unless it has *less* gain in another portion of that hemisphere... in other words, unless is starts exhibiting some form of lobing/nulling. If it *could*, it would be trivial to demonstrate that the antenna was delivering more power (more energy over time) into its loads, than it was accepting from its transmitter. The same line of logic applies even if you start with a dipole. If you begin with a dipole, and then magically "deflect" all of the power from the rear towards the front and overlay the patterns exactly, you'll exactly double the power in each forward-lying half of the sphere, and create a gain of 3 dB over the dipole. In order to have *more* forward gain in any direction in the forward direction, you must necessarily have *less* in another, and this either narrows the pattern in the forward direction or creates partial or complete nulls. To claim otherwise, is to claim an antenna which can be shown to deliver more power than it accepts as input... in other words, one which violates the conservation of energy. The same basic rule applies for any situation in which you take a bidirectional antenna (one which has a symmetrical forward-and- backward gain pattern) and then "deflect" all of the rearward energy into a forward direction. This will gain you at most 3 dB over the basic gain pattern of the antenna you started with. Any further maximum forward gain, over the antenna you were starting with, can *only* be achieved by decreasing the gain somewhere in the pattern (narrowing or weakening the main lobe or one of the sidelobes). A Moxon antenna is, to a first approximation, a pretty good example of this approach - it has very little energy in the rear hemisphere, and a broad forward lobe. There are various two-driven-element array designs which achieve a similar pattern and result. And the resulting "gain" is ....what? According to Cebik's web site, a 2-meter Moxon shows a maximum forward gain of about 10.7 dBi, or a bit more than 8 dB over a dipole. One could gain at most 3 dB due to the forward "deflection" of rear- hemisphere energy, and hence the remaining 5 dB or so of gain over a dipole must come from a narrowing of the antenna's pattern in either azimuth or elevation or both. Yes I agree because of conservation laws e.t.c . When cancellation occurs then energy creats energy in another direction similar to pulling steel apart in tension (or using compression) the steel becomes narrower before severing occurrs. This thinning or "waisting" is created by the additional forces created at 90 degrees to the tensile forces and where the break actually occurrs at 45 degrees and not at right angles. Art, I think your analogies between radiation patterns, balloons, stretching metal, etc. are leading you astray more than they are helping you. Conservation of energy *requires* that the main lobe be narrowed, if you wish to achieve more gain than you can get by simply redistibuting the rear-ward energy in the forward direction. This is what you alluded to before and it is still incorrect What "requires" what ? And how is this conclusion generating an elongated lobe? A super-high-gain antenna *cannot* have a wide, uniform beam-width in both azimuth and elevation. Don't know how you can say that I say that because the opposite case would contradict the law of conservation of energy. If you have an antenna which puts all of its power, uniformly, into a forward beam which covers only 1/10 of the sphere, then that forward beam will carry 10 times as much power per angle, for a gain of 10 dBi. If you squeeze the beam down in size so that it covers only 1/100 of the sphere, it will carry 100 times as much power per angle, for a gain of 20 dB. You can't have a broad forward lobe (say, one which covers a full 1/10 of the sphere), and achieve a high gain of 20 dB (100 times as much power per angle) without violating the law of conservation of energy. *THAT* is the fundamental limit I'm talking about, Art. As usual for your postings, Art, it's impossible to tell whether your claims for your antenna are plausible, because you refuse to disclose *anything* (either the invention, or the results you claim) in any halfway-tanglible form (e.g. models, specific numbers, etc.). My antenna is somewhat related You DID IT AGAIN, Art. You said "is somewhat related", you didn't say related to *what*, you didn't give any details whatsoever. The question however, is specifically related to Yagi's and its narrowed lobes. Do you know what it is that creats an elongated lobe on a high gain yagi i.e not totally round.? Nothing more, nothing less. You're acting as though the lobe were a physical object, and that something is "putting pressure" on it to squeeze it out of shape like a physical balloon. That is a FALSE ANALOGY, Art. It's meaningless. The "shape" of the lobe is simply a way of plotting numbers on a graph. It depends on the scaling of the graph, and it's a *relative* scale. A dipole's lobes may look perfectly round on one sort of graph, elliptical on another, and lumpy on a third, depending on whether the plot's axes are logarithmic, linear, or somewhere in between the two. Fundamentally, the reason that the shape of the lobe (on a conventional plot) changes from somewhat-circular to more-eliptical is due to the fact that the antenna is sending more of its power in a favored direction (to achieve gain), at the expense of sending less in other directions. Period. The *mechanism* by which this is done, in a Yagi (or an actively- driven set of phased radiators), is simply one of dividing up the power being radiated so that it's radiated (or re-radiated) from multiple points, in different spatial and phase relationships, so that the resulting waves cancel out in certain directions and reinforce in others. If you really want to know the details, I suggest that you dig up and read the original papers by Uda and Yagi. Until you do, I really think it would be to everyone's relief if you'd follow through with your recent statement that you were going to stop posting. You're achieving no good result for yourself by contining as you are. I have not posted as you have inferred. The question is about Yagi design It all seems to come down to the same thing with you, Art. I suppose I should just killfile you and completely ignore your postings. I'm sorry, I've tried my best to steer you in directions that I think will actually help your efforts, but it seems quite futile. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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"Dave Platt" wrote in message ... In article uoD1e.110018$Ze3.66917@attbi_s51, wrote: There is a harsh limit, imposed by physics, as to how much gain that approach can give you. Agreed... Do you know what those limits are ? Sure. The simplest way to state it is "the total amount of power delivered by the antenna, summed over all of the possible angles of radiation, must equal the total amount of power radiated by the antenna." If all of the energy from one hemisphere is redirected into the other hemisphere, and if the forward-direction pattern shape does not change (the forward lobe is not narrowed), then you have a forward gain of 3 dB But the forward pattern DOES change with a YAGI design. In fact it inferes unequal pressures within the pattern. I would have no problem with a lot of what you say BUT the YAGI does not follow the theoretical aproach that you supplied thus what you say regarding a yagi is based on a straw man augument. My question was for the Yagi pattern which does not follow your aproach You cannot relate gain and power since with a yagi tho power is an all encompasing term (three dimensional) gain is not. What you stated earlier regarding gain as a ratio is correct but for a Yagi its parameters must be defined which is not by the term power. as you have used it. (2:1 power ratio increase). You *cannot* have more, as this would require that the antenna be radiating more power than it receives from its input. Absolutely incorrect. If I place the air of two balloons ,which reflect the figure eight,into one single balloon and where the laws of partial pressures do not intervene then you will have a balloon that is round and not elongated as the antenna books would have you suggest. "Gain" is a term used to to quantify a small portion of the energy contained in the mythical ball of energy. Since the collection of energy comes from different directions and phases the energy collection is layered depending on the influence of the earth. Thus the layers of radiation are distorted where one layer can be squeezed outwards further than other layers, thus the terminology of "gain" Jeez, Art, do you have any idea of just how thoroughly your response qualifies as "Authentic frontier gibberish" (as a Mel Brooks character once said)? I'm sorry, guy, but I believe that you are trying to stretch analogies far beyond the point where they actually apply to the physical phenomena we're discussing. Your concept of "layers of radiation" (as applied to the gain pattern of an antenna) simply doesn't add up. If you are going to interelate the terms of "gain" and "power" then you must define the parameters used to allow that. OK, let's do just that. "Power" is very well defined - it's the rate at which energy is delivered. Pick your units for energy and time as you choose. It's conventional to use watts for power, joules for energy and seconds for time. One watt, equals a rate of energy delivery of one joule per second. "Gain" is a ratio. In discussions dealing with antennas, the gain describes the ratio between the amount of power delivered by a given antenna in a given direction, to the amount of power delivered in that same direction by a "reference" antenna (a dipole in the case of a dBd gain number, and an "isotropic" antenna in the case of a dBi gain number). The gain figures in dB are logarithmic. Those are the definitions everyone uses, I believe. I can go along with that If you, personally, are using different definitions than these, then our discussion (you vs. everyone else) should probably stop right here. Here's my rationale behind the statement I made about the limitations of your approach: - An isotropic antenna has a gain of 0 dBi, by definition. - If you "cut off" the entire rear side of an isotropic antenna's pattern (so that it radiates no power backwards), and precisely overlay this power (energy flow) onto the forward half, you'll end up with a "half-isospheric" antenna. It's radiating exactly the same amount of power, but over only half as much target area. The power (energy flow) towards each point in that targeted hemisphere will be exactly twice as much as in the isotropic antenna. This antenna has a gain of 3 dBi plus a hair. As you say, when you are refering to isentropic It cannot have *more* gain in any direction (more power into a sub-portion of the hemisphere) unless it has *less* gain in another portion of that hemisphere... For the isotropic aproach which has little relationship to the real world of yagis that some how narrows not only the main lobe but also the other lobes all of which have seperate gains created by the movement of energy from the rear and not constrained by your theoretical 3 db aproach in other words, unless is starts exhibiting some form of lobing/nulling. If it *could*, it would be trivial to demonstrate that the antenna was delivering more power (more energy over time) into its loads, than it was accepting from its transmitter. The same line of logic applies even if you start with a dipole. If you begin with a dipole, and then magically "deflect" all of the power from the rear towards the front and overlay the patterns exactly, you'll exactly double the power in each forward-lying half of the sphere, and create a gain of 3 dB over the dipole. In order to have *more* forward gain in any direction in the forward direction, you must necessarily have *less* in another, and this either narrows the pattern in the forward direction or creates partial or complete nulls. To claim otherwise, is to claim an antenna which can be shown to deliver more power than it accepts as input... in other words, one which violates the conservation of energy. The same basic rule applies for any situation in which you take a bidirectional antenna (one which has a symmetrical forward-and- backward gain pattern) and then "deflect" all of the rearward energy into a forward direction. This will gain you at most 3 dB over the basic gain pattern of the antenna you started with. Any further maximum forward gain, over the antenna you were starting with, can *only* be achieved by decreasing the gain somewhere in the pattern (narrowing or weakening the main lobe or one of the sidelobes). A Moxon antenna is, to a first approximation, a pretty good example of this approach - it has very little energy in the rear hemisphere, and a broad forward lobe. There are various two-driven-element array designs which achieve a similar pattern and result. And the resulting "gain" is ....what? According to Cebik's web site, a 2-meter Moxon shows a maximum forward gain of about 10.7 dBi, or a bit more than 8 dB over a dipole. One could gain at most 3 dB due to the forward "deflection" of rear- hemisphere energy, and hence the remaining 5 dB or so of gain over a dipole must come from a narrowing of the antenna's pattern in either azimuth or elevation or both. Yes I agree because of conservation laws e.t.c . When cancellation occurs then energy creats energy in another direction similar to pulling steel apart in tension (or using compression) the steel becomes narrower before severing occurrs. This thinning or "waisting" is created by the additional forces created at 90 degrees to the tensile forces and where the break actually occurrs at 45 degrees and not at right angles. Art, I think your analogies between radiation patterns, balloons, stretching metal, etc. are leading you astray more than they are helping you. Conservation of energy *requires* that the main lobe be narrowed, if you wish to achieve more gain than you can get by simply redistibuting the rear-ward energy in the forward direction. This is what you alluded to before and it is still incorrect What "requires" what ? And how is this conclusion generating an elongated lobe? A super-high-gain antenna *cannot* have a wide, uniform beam-width in both azimuth and elevation. Don't know how you can say that I say that because the opposite case would contradict the law of conservation of energy. If you have an antenna which puts all of its power, uniformly, into a forward beam which covers only 1/10 of the sphere, then that forward beam will carry 10 times as much power per angle, for a gain of 10 dBi. If you squeeze the beam down in size so that it covers only 1/100 of the sphere, it will carry 100 times as much power per angle, for a gain of 20 dB. You can't have a broad forward lobe (say, one which covers a full 1/10 of the sphere), and achieve a high gain of 20 dB (100 times as much power per angle) without violating the law of conservation of energy. *THAT* is the fundamental limit I'm talking about, Art. As usual for your postings, Art, it's impossible to tell whether your claims for your antenna are plausible, because you refuse to disclose *anything* (either the invention, or the results you claim) in any halfway-tanglible form (e.g. models, specific numbers, etc.). My antenna is somewhat related You DID IT AGAIN, Art. You said "is somewhat related", you didn't say related to *what*, you didn't give any details whatsoever. Oh come on Dave, don't twist things around. I have stated that my antenna, which is not a yagi, when transposing pattern volume from the rear to the front does it in an orderly fashion by expansion of the receiving vessel in a circular form. .. Thus the gain increased as the rear volume decreased with a diminishing increase in gain. The yagi does something different as other vectorial interferences is creating "outward pressures" on the so called balloon to NARROW the beam width. Disregarding any effects that can be attributed to other antennas my question is related to the YAGI design which actually creates a narrowing beam as progress is made in transposing energy from the front to the rear. This is a fact , thus the question "why" a question that is pertinent to the YAGI design and not any other design or multiple arrangements of such.. You have supplied plenty of dots regarding antennas but none that remotely relates to the question The question however, is specifically related to Yagi's and its narrowed lobes. Do you know what it is that creats an elongated lobe on a high gain yagi i.e not totally round.? Nothing more, nothing less. You're acting as though the lobe were a physical object, and that something is "putting pressure" on it to squeeze it out of shape like a physical balloon. That is a FALSE ANALOGY, Art. It's meaningless. The "shape" of the lobe is simply a way of plotting numbers on a graph. It depends on the scaling of the graph, and it's a *relative* scale. A dipole's lobes may look perfectly round on one sort of graph, elliptical on another, and lumpy on a third, depending on whether the plot's axes are logarithmic, linear, or somewhere in between the two. Fundamentally, the reason that the shape of the lobe (on a conventional plot) changes from somewhat-circular to more-eliptical is due to the fact that the antenna is sending more of its power in a favored direction (to achieve gain), at the expense of sending less in other directions. Period. The *mechanism* by which this is done, in a Yagi (or an actively- driven set of phased radiators), is simply one of dividing up the power being radiated so that it's radiated (or re-radiated) from multiple points, in different spatial and phase relationships, so that the resulting waves cancel out in certain directions and reinforce in others. If you really want to know the details, I suggest that you dig up and read the original papers by Uda and Yagi. Until you do, I really think it would be to everyone's relief if you'd follow through with your recent statement that you were going to stop posting. You're achieving no good result for yourself by contining as you are. I have not posted as you have inferred. The question is about Yagi design It all seems to come down to the same thing with you, Art. I suppose I should just killfile you and completely ignore your postings. I'm sorry, I've tried my best to steer you in directions that I think will actually help your efforts, but it seems quite futile. By all means put me on your kill file. I asked a simple question and you want to reply to a different question of your liking and place your question as one preferable to mine. No one has been able to supply the answer to my question, Using your words ,what steers the pattern away from a circular form from a natural circular form. I am not asking for the extraneious information that all feel they are compelled to supply to make their posting look informative. Regards Art -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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In article P2G1e.110904$Ze3.11791@attbi_s51,
wrote: By all means put me on your kill file. I asked a simple question and you want to reply to a different question of your liking and place your question as one preferable to mine. Art, in cases like this, you keep asking "simple questions" which imply, by their very wording, a whole bunch of assumptions about how things work which just ain't so. The fact that you keep getting answer after answer, from a lot of knowledgeable people, which you either don't understand or "blow past" or that you feel evade the point of your question, ought to be saying something to you: that there's something wrong with the questions you ask. No one has been able to supply the answer to my question, Using your words ,what steers the pattern away from a circular form from a natural circular form. That depends on what you mean by "a natural circular form." If you're referring to the fact that the main lobe of a dipole tends to look circular on many of the commonly-used plots, then the pattern isn't "circular" in any cosmic sense of the word. It's just as correct to say that it's elliptical, or bumpy, or squashed, because that's exactly how it will look on plots which use different circular axes (linear, logarithmic, etc). To try it again, though: you're asking why the pattern appears to be compressed, as the gain increases. Fundamentally, it's due to the fact that the antenna is sending more power out in the desired directions (more gain), at the expense of sending less in other directions. This is done by creating multiple radiators, which are offset in power and location and phase so that their individual radiation wavefronts reinforce in the desired directions, and cancel in the undesired directions. When we plot the resulting RF strengths, the RF in the desired direction is stronger (we got the gain that we want). Let's assume that (as is common practice) we continue to plot the signal in the strongest direction on the outer circle of the graph. Now, one of two things will have to be true: [1] Every other direction in the main lobe had its power "scaled up" by the same amount... the increase in gain worked the same for all directions within the main lobe. In this case, the shape of the main lobe will not change at all. In this case, the additional power required to achieve the increase in gain in the main lobe will have had to come for somewhere. Since it didn't come from the main lobe, it will have had to come either from the sidelobes, or from the rear half of the antenna's pattern. There's a limit to how far you can take approach [1]. It stops working when your sidelobes and rear half of the pattern drop to zero... and it becomes rather ineffective some time before that, when the largest of the side/rear lobes is maybe 10-15 dB down. Beyond that point, there just isn't enough power left in those backlobes to be useful. [2] The other possibility is that you didn't manage to boost the gain, uniformly, in the entire main lobe. In this case, if you're still plotting the strongest signal on the outermost circle of the graph, you'll notice that the shape of the main lobe has changed. Any direction in which the gain increase was less than the maximum you achieved, will be closer to the center of the circle than before. [Another way of looking at this is that by increasing your maximum directional gain, you've "enlarged the circle" on which you're plotting it, but that some points didn't move outwards by the same ratio.] In the common case of a Yagi, when you boost the gain (say, from 10 dB to 15 dB) there just isn't enough power available in the side and rear lobes to make up this gain... you can't 'rob' enough directivity from the sidelobes and rear lobe. Instead, you 'rob' the power from the outer edges of the main lobe, and shift it in towards the center. You do this, most commonly, by adding additional parasitic elements, whose location and phasing are such that their radiation reinforces that moving in the "forward" direction, and interacts destructively with (cancels) radiation moving outwards at an angle. When you plot the resulting pattern, and scale it so that the strongest signal is on the outer circle of the plot, you find that the main lobe looks narrower. Part of this is due to the actual redirection of power, and part of it is due to the fact that you've re-scaled the graph.a .. I am not asking for the extraneious information that all feel they are compelled to supply to make their posting look informative. [invokes several wrathful deities...] Art, if you continue to ask "simple questions", and you continue to get back complicated and detailed answers, it really ought to convey to you the possibility that your "simple" question is oversimplified. Or, perhaps, that you've been given the actual (simple) answer three or four or five times already, have rejected it, and people are trying to explain to you why it's actually correct. Goodbye, Art. This is/was my last attempt, I think. I doubt I'll try again. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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