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physical 1/4, electrical 1/2 wavelength
My question(s):
For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards |
If you wind, say, 100 inches of wire into a coil, it doesn't act the
same as 100 inches of straight wire. And no two different coils wound from 100 inches of wire will act the same. A coil's radiation characteristics are very nearly the same as for a wire the outside diameter and length of the coil, not the length of the wire it's made from. And the inductance of the coil is dictated by the length, pitch, number of turns, and diameter of the coil, not the length of the wire it's wound from. So your question can't be answered unless you tell us the diameter of the coil and any two of length, pitch, and number of turns; or the length and diameter of the coil and its inductance at the frequency at which it's being used. Roy Lewallen, W7EL John Smith wrote: My question(s): For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards |
OK, if you notice in my post wire length is in quotes, i.e. "wire length."
In the example, it is a given that this length resonates at 1/2 wave along with the combined length of the whip (hence, electrical 1/2 wavelength.) So, your post, while presenting individual points and your opinions, in general--seems to answer very little, if any, of the original questions raised--and certainly cannot be accused of containing any specifics. The diameter IS stated (1"), the wire length is the lenght of the wire minus 28 inches which is necessary to be a resonate 1/2 wave, AND this is divided over (1/4 wave at 10 meters - 28 inches.) to arrive at the coil length--the pitch is calculated from the coil length ((1/4 wave @ 10 meters) - 28 inches) and the wire lenght divided by pi (number of turns) spread out over the coil ENTIRE length. And, of course, coil length plus whip length is a 1/4 wave. If you refer back to my original post, you will see all of this IS there... However, critical analysis is a wise beginning of any quest for answers. Regards "Roy Lewallen" wrote in message ... If you wind, say, 100 inches of wire into a coil, it doesn't act the same as 100 inches of straight wire. And no two different coils wound from 100 inches of wire will act the same. A coil's radiation characteristics are very nearly the same as for a wire the outside diameter and length of the coil, not the length of the wire it's made from. And the inductance of the coil is dictated by the length, pitch, number of turns, and diameter of the coil, not the length of the wire it's wound from. So your question can't be answered unless you tell us the diameter of the coil and any two of length, pitch, and number of turns; or the length and diameter of the coil and its inductance at the frequency at which it's being used. Roy Lewallen, W7EL John Smith wrote: My question(s): For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards |
"John Smith" wrote in message ... OK, if you notice in my post wire length is in quotes, i.e. "wire length." In the example, it is a given that this length resonates at 1/2 wave along with the combined length of the whip (hence, electrical 1/2 wavelength.) So, your post, while presenting individual points and your opinions, in general--seems to answer very little, if any, of the original questions raised--and certainly cannot be accused of containing any specifics. The diameter IS stated (1"), the wire length is the lenght of the wire minus 28 inches which is necessary to be a resonate 1/2 wave, AND this is divided over (1/4 wave at 10 meters - 28 inches.) to arrive at the coil length--the pitch is calculated from the coil length ((1/4 wave @ 10 meters) - 28 inches) and the wire lenght divided by pi (number of turns) spread out over the coil ENTIRE length. And, of course, coil length plus whip length is a 1/4 wave. If you refer back to my original post, you will see all of this IS there... However, critical analysis is a wise beginning of any quest for answers. Regards Roy's answer is right on the mark. The length of the wire is of no help in answering the question. You are confusing mechanical lengths with electrical lengths. Dale W4OP |
It seems to me that the guy was trying to help, so no need to "bite the hand
that feeds", old chap !! Better to cultivate him, than **** him off, however technically correct you might be ...... Nick "Dale Parfitt" wrote in message news:hMz%d.9885$b_6.3645@trnddc01... "John Smith" wrote in message ... OK, if you notice in my post wire length is in quotes, i.e. "wire length." In the example, it is a given that this length resonates at 1/2 wave along with the combined length of the whip (hence, electrical 1/2 wavelength.) So, your post, while presenting individual points and your opinions, in general--seems to answer very little, if any, of the original questions raised--and certainly cannot be accused of containing any specifics. The diameter IS stated (1"), the wire length is the lenght of the wire minus 28 inches which is necessary to be a resonate 1/2 wave, AND this is divided over (1/4 wave at 10 meters - 28 inches.) to arrive at the coil length--the pitch is calculated from the coil length ((1/4 wave @ 10 meters) - 28 inches) and the wire lenght divided by pi (number of turns) spread out over the coil ENTIRE length. And, of course, coil length plus whip length is a 1/4 wave. If you refer back to my original post, you will see all of this IS there... However, critical analysis is a wise beginning of any quest for answers. Regards Roy's answer is right on the mark. The length of the wire is of no help in answering the question. You are confusing mechanical lengths with electrical lengths. Dale W4OP |
On Sun, 20 Mar 2005 18:26:42 -0800, "John Smith"
wrote: what would the radiation pattern of such an antenna be? Hi John, This appears to be a difficult question to answer, if for only all of the extraneous details. Patterns are determined by the physical size in relation to wavelength. It is all about geometry and distances between what are called current nodes - what you describe has no s in the node(s), so the geometry (pattern) is still quite simple. Obtain a free copy of EZNEC to confirm. 73's Richard Clark, KB7QHC |
The original post is a math problem--its "solution" is an antenna. It is
structured as a "word problem", as opposed to a math problem written using digits and numbers--for the most part--only coil diameter, whip length and wavelength (both physical and electrical) are expressed as numbers. Most will be familiar with this from high school or college mathematics. However, since this alone seems to be such a matter of confusion, let's look at the problem and rely on more numeric means of expression-using only the information from my first post. 1) top whip length = 28 inches 2) coil diameter = 1 inch 3) physical coil length = (1/4 wavelength - 28 inches) 4) antenna physical length = 28 inches + coil length 5) "wire length"(whip + coil wire length) = electrical ½ wavelength 6) number of turns = (wire length / (pi(3.14159) * coil diameter(1 inch))) = (wire length / 3.14159 inches) 7) pitch = number of turns spread/spaced over the ENTIRE (helical) coil length 8) antenna is end fed at the base, EFWHA-a vertical monopole 9) The antenna's physical length is ¼ wave on 10 meters but, is a ½ wavelength electrical length on 10 meters. NOTE: Please feel free to critique/correct any errors I have made in the above, no offense will be taken (but, arguments may be posed!)-indeed, this stands in regard to all my posts. My questions, defined in greater detail, were/a 1) What would the radiation pattern of such an antenna be-favor ¼ wave? Favor ½ wave? A hybrid pattern of ¼ and ½? Or, would it be unique pattern onto this antenna alone, and only vaguely reminiscent to one or the other, or both? (And arrived at by math, charts, measurement or other means which provide "proofs." 2) Would this antenna display a reactance which is capacitive or inductive, or purely resistive (and what proof(s) confirms this?) 3) What would the impedance of this antenna be? (Even a ballpark figure-within 5%-10% but, derived though math, chart or direct measurement-NOT a guess?) 4) What method of matching this antenna to 50 ohm coax would be "best?" (Capacitive hats, l-network, pi-network, balun (unun in this case), ¼ wave line, combinations of these schemes, etc.?) 5) Is there software capable of modeling such an antenna constructed under these specifications (I have mmana but am unable to grasp how it could be used for such a design?) Certainly no disrespect was meant in my response to Ray's comments. Indeed, if I "miss-treat" individuals I don't expect I will get ANY interaction from them-this is NOT my purpose or intent! And, if you re-read my second post, I complement him on his critique of the problem and his analytical powers. In my neck of America, if someone attempts to set up conflict over verbal or text exchanges, we generally consider him/her to be a "chit stirrer." If my intent is NOT clear, let me try again: This is simply an excursion into the exploration of an antenna design and its' properties. If you are intent to read other goals into my posts-you are on your own! I totally expect only those with knowledge, skills and investigative minds to bother in this endeavor and, some will not even see reason to ask these questions at all-one can probably be purchased off a shelf-somewhere in the world. Warmest regards "nick smith" wrote in message ... It seems to me that the guy was trying to help, so no need to "bite the hand that feeds", old chap !! Better to cultivate him, than **** him off, however technically correct you might be ...... Nick "Dale Parfitt" wrote in message news:hMz%d.9885$b_6.3645@trnddc01... "John Smith" wrote in message ... OK, if you notice in my post wire length is in quotes, i.e. "wire length." In the example, it is a given that this length resonates at 1/2 wave along with the combined length of the whip (hence, electrical 1/2 wavelength.) So, your post, while presenting individual points and your opinions, in general--seems to answer very little, if any, of the original questions raised--and certainly cannot be accused of containing any specifics. The diameter IS stated (1"), the wire length is the lenght of the wire minus 28 inches which is necessary to be a resonate 1/2 wave, AND this is divided over (1/4 wave at 10 meters - 28 inches.) to arrive at the coil length--the pitch is calculated from the coil length ((1/4 wave @ 10 meters) - 28 inches) and the wire lenght divided by pi (number of turns) spread out over the coil ENTIRE length. And, of course, coil length plus whip length is a 1/4 wave. If you refer back to my original post, you will see all of this IS there... However, critical analysis is a wise beginning of any quest for answers. Regards Roy's answer is right on the mark. The length of the wire is of no help in answering the question. You are confusing mechanical lengths with electrical lengths. Dale W4OP |
The use of "wire length" to describe the antenna impedance made it
diffiicult to understand what you were asking, and certainly deflected my thinking. If you had only said that the coil had the inductance necessary to make the antenna half-wave resonant (or antiresonant), it would have been more clear. On re-reading it, I see that it's what you meant, and it's what you did say in a slightly unconventional manner. So that gives enough information for at least some general answers to your questions: to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? It would have a pattern very similar to a quarter wave vertical, not a half wave. What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? The resistance would be high, on the order of a couple of thousand ohms or more. If the coil resonantes the antenna, the feedpoint reactance, by definition, is zero. However, a slight deviation of the frequency from resonance will result in a fairly large reactance. It will be inductive below resonance and capacitive above. What would be the best way to provide a match to 50 ohm coax from such an antenna? Connect one conductor of the feedline to the antenna base, and tap up the helix with the other until a good match is achieved. This requires that the antenna be resonated with the coil. What software is available to model such an antenna? EZNEC is able to do it. The demo program could be used to make an approximate model with the inductor modeled as a number of lumped loads along the wire. With the standard or plus programs you can model the inductor directly as a wire helix. I develop and sell EZNEC, so I'll leave it to others to recommend other programs -- I believe there are several which can do the job. Roy Lewallen, W7EL John Smith wrote: OK, if you notice in my post wire length is in quotes, i.e. "wire length." In the example, it is a given that this length resonates at 1/2 wave along with the combined length of the whip (hence, electrical 1/2 wavelength.) So, your post, while presenting individual points and your opinions, in general--seems to answer very little, if any, of the original questions raised--and certainly cannot be accused of containing any specifics. The diameter IS stated (1"), the wire length is the lenght of the wire minus 28 inches which is necessary to be a resonate 1/2 wave, AND this is divided over (1/4 wave at 10 meters - 28 inches.) to arrive at the coil length--the pitch is calculated from the coil length ((1/4 wave @ 10 meters) - 28 inches) and the wire lenght divided by pi (number of turns) spread out over the coil ENTIRE length. And, of course, coil length plus whip length is a 1/4 wave. If you refer back to my original post, you will see all of this IS there... However, critical analysis is a wise beginning of any quest for answers. Regards "Roy Lewallen" wrote in message ... If you wind, say, 100 inches of wire into a coil, it doesn't act the same as 100 inches of straight wire. And no two different coils wound from 100 inches of wire will act the same. A coil's radiation characteristics are very nearly the same as for a wire the outside diameter and length of the coil, not the length of the wire it's made from. And the inductance of the coil is dictated by the length, pitch, number of turns, and diameter of the coil, not the length of the wire it's wound from. So your question can't be answered unless you tell us the diameter of the coil and any two of length, pitch, and number of turns; or the length and diameter of the coil and its inductance at the frequency at which it's being used. Roy Lewallen, W7EL John Smith wrote: My question(s): For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards |
Well Roy (sorry I mis-spelled your name as Ray in a post above), you are not
the first to bring it to my attention, the fact that my manner and methods are "unconventional", indeed, some have not been no kind and have referred to me as eccentric! grin As I type this, I am downloading a demo of your EZNEC program. I will spend a little time with it and see if I can get the hang of it and, how to describe the antenna problem to it. Quite possibly it will provide me with answers, or even (and quite hopefully!) provide me with new questions. Thank you for your time in responding and, if I have offended you, as some others have pointed out may be the case, I apologize, I am sincere when I state that was not my purpose... Warmest regards! "Roy Lewallen" wrote in message ... The use of "wire length" to describe the antenna impedance made it diffiicult to understand what you were asking, and certainly deflected my thinking. If you had only said that the coil had the inductance necessary to make the antenna half-wave resonant (or antiresonant), it would have been more clear. On re-reading it, I see that it's what you meant, and it's what you did say in a slightly unconventional manner. So that gives enough information for at least some general answers to your questions: to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? It would have a pattern very similar to a quarter wave vertical, not a half wave. What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? The resistance would be high, on the order of a couple of thousand ohms or more. If the coil resonantes the antenna, the feedpoint reactance, by definition, is zero. However, a slight deviation of the frequency from resonance will result in a fairly large reactance. It will be inductive below resonance and capacitive above. What would be the best way to provide a match to 50 ohm coax from such an antenna? Connect one conductor of the feedline to the antenna base, and tap up the helix with the other until a good match is achieved. This requires that the antenna be resonated with the coil. What software is available to model such an antenna? EZNEC is able to do it. The demo program could be used to make an approximate model with the inductor modeled as a number of lumped loads along the wire. With the standard or plus programs you can model the inductor directly as a wire helix. I develop and sell EZNEC, so I'll leave it to others to recommend other programs -- I believe there are several which can do the job. Roy Lewallen, W7EL John Smith wrote: OK, if you notice in my post wire length is in quotes, i.e. "wire length." In the example, it is a given that this length resonates at 1/2 wave along with the combined length of the whip (hence, electrical 1/2 wavelength.) So, your post, while presenting individual points and your opinions, in general--seems to answer very little, if any, of the original questions raised--and certainly cannot be accused of containing any specifics. The diameter IS stated (1"), the wire length is the lenght of the wire minus 28 inches which is necessary to be a resonate 1/2 wave, AND this is divided over (1/4 wave at 10 meters - 28 inches.) to arrive at the coil length--the pitch is calculated from the coil length ((1/4 wave @ 10 meters) - 28 inches) and the wire lenght divided by pi (number of turns) spread out over the coil ENTIRE length. And, of course, coil length plus whip length is a 1/4 wave. If you refer back to my original post, you will see all of this IS there... However, critical analysis is a wise beginning of any quest for answers. Regards "Roy Lewallen" wrote in message ... If you wind, say, 100 inches of wire into a coil, it doesn't act the same as 100 inches of straight wire. And no two different coils wound from 100 inches of wire will act the same. A coil's radiation characteristics are very nearly the same as for a wire the outside diameter and length of the coil, not the length of the wire it's made from. And the inductance of the coil is dictated by the length, pitch, number of turns, and diameter of the coil, not the length of the wire it's wound from. So your question can't be answered unless you tell us the diameter of the coil and any two of length, pitch, and number of turns; or the length and diameter of the coil and its inductance at the frequency at which it's being used. Roy Lewallen, W7EL John Smith wrote: My question(s): For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards |
Absolutely Richard! It does seem difficult with available tools--at least
without building it and even then putting much labor into expermenting, testing, pruning and adjusting... Yet, it seems like such a design would suggest itself to many minds and be a good solution to many restricted spaces and, one does ponder why the math, methods, formulas, software, etc. has not been created to make such a matter of childs play--and well documented and explained. Many mobile whips seem centered around designs somewhat similiar to the one proposed. And, indeed, I have seen a few expermentally inclined hams goofing around with similiar designs for shack antennas on the long wavelengths, just wish I had paid more attention at the time.... I am a capable C/C++ software engineer (professional hacker) and am constantly searching for ideas to put to code to feed my personal interests... Warmest regards "Richard Clark" wrote in message ... On Sun, 20 Mar 2005 18:26:42 -0800, "John Smith" wrote: what would the radiation pattern of such an antenna be? Hi John, This appears to be a difficult question to answer, if for only all of the extraneous details. Patterns are determined by the physical size in relation to wavelength. It is all about geometry and distances between what are called current nodes - what you describe has no s in the node(s), so the geometry (pattern) is still quite simple. Obtain a free copy of EZNEC to confirm. 73's Richard Clark, KB7QHC |
On Mon, 21 Mar 2005 13:14:25 -0800, "John Smith"
wrote: Yet, it seems like such a design would suggest itself to many minds and be a good solution to many restricted spaces and, one does ponder why the math, methods, formulas, software, etc. has not been created to make such a matter of childs play--and well documented and explained. Hi John, In fact, nearly every "new" idea that hits this board can be found described with utter simplicity - years ago (10, 20, 40, 80 years). Very little math is demanded and the record is full of documentation. The continuous length of coil you describe has been anticipated by one in using a "slinky." The benefit there is that the springy form allows one to collapse or extend the coil to find resonance. Use two of them and you have a dipole. It performs, and has performed for years. You can buy one too. Why doesn't everyone use one? The reason goes back years ago to rather simple terms: size v. wavelength and the number and separation of nodes. It performs, but not as well as a larger antenna it attempts to replace. Hence: size v. wavelength is a restriction, there is only one node, and it has nothing (another separate node) to combine with. Once you can get your arms around these simple concepts, then you throw in loss - the numbers get ugly and the pain is real. We get tons of small antennas touted here. Many mobile whips seem centered around designs somewhat similiar to the one proposed. However, among the population of those many, when they are all compared the longstanding traditional designs win hands down. They win for very simple reasons. The list of rules, so to speak, is very short. Unfortunately there are too many simple reasons floating around as new and improved theory. The test of the newcomer is to separate those improved theories (noted for their baroque language, elaborate math and lack of field work) from ages-old results nailed down in rather ordinary terms. The new-and-improved theories call upon - separating the E and M fields; - unique properties of fractal math; - improved length efficiency; - proofs of polygonal analysis; - super gain; - over/tight/critical coupling; - faster than light transmission.... As you can see, the field of simple reasons abound. Some reasons have their attractive features, but once you try to pull the conversation into the realm of implementation, barriers to discussion bloom like weeds. 73's Richard Clark, KB7QHC |
Well... Yes, that argument is made with most everything...
It has already been done... everything has been tried... all the answers are known... there is nothing new to be found out... (But, just on the outside chance that thinking is wrong: What about LDE (long delay echo)? You got the answer to that?) The fact is, most, if not all, of the formulas we deal with are crafted from things we have first built--THEN we look for a mathmatical explanation to explain the object we built. While this is better than nothing, it is slow--exploration by first developing the theory and math--then the physical object--is much more suited for really finding "something new" and the rapid development of such objects. (i.e., computers design computers, however, since antennas can't design antennas--we need computers to design the antennas.) Unfortuantly, if all we use are past "rules" and "laws" we can only find the past!!! Anything REALLY NEW will break all the laws we are currently slaving under (or, at the least, re-define these laws) with total disregard to the high esteem we had held these faulty laws.... indeed, being too tied to the past and "conventional thinking" may hold us to the past... However, whenever there seems a danger of this happening, then someone comes in from left field with a new idea, such as quantum physics, and all bets are off, and the physists and mathematicians are sent off to develop new, undenighable and final laws to explain it... If it were all done, if there is nothing new to be found out, if all the existing data and formulas are totally all there is... WHY THE HELL ARE WE HERE? Let's go buy one, go home and have a beer... Fact is, we hate to admit when we are wrong, so, when we are wrong we quickly move on and say these NEW ideas are what we have really believed all along! I am not opposed to the possibility that all that can be known, is known... however, some guy that doesn't know any better usually suddenly pops up and you end up embarassed for your beliefs--one more time. The fact is, I have built those "silly antennas", by hand, with real materials--then modeled them on mathmatical models, evaluating what is actual against what was predicted... few ever provide anything but disappointment. But, I am convinced that while what the developers are claiming may be "false reasoning" and improper models, there is something here which has been overlooked and current conventional thinking and models miss... However, the antenna design I presented is simply a helical loaded 1/2 wave which just happens to correspond to 1/4 wave physical length... It really doesn't challenge any current antenna theory or present anything new, other than perhaps an unconventional arrangement of wire... Frankly, I take it as a "leap of faith", but as long as there are discussions such as these... something new is comming our way right now, we just won't be able to see it till it gets closer, then we will realize we really "knew it all along!" But then the harsh "reality" hits us, we realize and with some disappointment--that once again it has happened, all the final answers and laws are known--nothing to do but go home and grab a beer and wait for next time... grin Warmest regards "Richard Clark" wrote in message ... On Mon, 21 Mar 2005 13:14:25 -0800, "John Smith" wrote: Yet, it seems like such a design would suggest itself to many minds and be a good solution to many restricted spaces and, one does ponder why the math, methods, formulas, software, etc. has not been created to make such a matter of childs play--and well documented and explained. Hi John, In fact, nearly every "new" idea that hits this board can be found described with utter simplicity - years ago (10, 20, 40, 80 years). Very little math is demanded and the record is full of documentation. The continuous length of coil you describe has been anticipated by one in using a "slinky." The benefit there is that the springy form allows one to collapse or extend the coil to find resonance. Use two of them and you have a dipole. It performs, and has performed for years. You can buy one too. Why doesn't everyone use one? The reason goes back years ago to rather simple terms: size v. wavelength and the number and separation of nodes. It performs, but not as well as a larger antenna it attempts to replace. Hence: size v. wavelength is a restriction, there is only one node, and it has nothing (another separate node) to combine with. Once you can get your arms around these simple concepts, then you throw in loss - the numbers get ugly and the pain is real. We get tons of small antennas touted here. Many mobile whips seem centered around designs somewhat similiar to the one proposed. However, among the population of those many, when they are all compared the longstanding traditional designs win hands down. They win for very simple reasons. The list of rules, so to speak, is very short. Unfortunately there are too many simple reasons floating around as new and improved theory. The test of the newcomer is to separate those improved theories (noted for their baroque language, elaborate math and lack of field work) from ages-old results nailed down in rather ordinary terms. The new-and-improved theories call upon - separating the E and M fields; - unique properties of fractal math; - improved length efficiency; - proofs of polygonal analysis; - super gain; - over/tight/critical coupling; - faster than light transmission.... As you can see, the field of simple reasons abound. Some reasons have their attractive features, but once you try to pull the conversation into the realm of implementation, barriers to discussion bloom like weeds. 73's Richard Clark, KB7QHC |
On Mon, 21 Mar 2005 14:58:51 -0800, "John Smith"
wrote: Fact is, we hate to admit when we are wrong Hi John, That never fazed me as long as I was challenged by facts instead of superstition. I have failed to many times to worry about it. As the saying goes, if you haven't failed, you aren't trying hard enough. ... there is something here which has been overlooked and current conventional thinking and models miss... I try those angles, and go the extra mile. Evidence some 300+ pages of examining fractal antennas: http://www.qsl.net/kb7qhc/antenna/fractal/index.htm This work eventually boiled down to a simple conclusion (not that the leading proponent would allow his mystical explanation to be nudged into the corner of drab insight). These days I usually put a filter into the process by asking the "inventor" a simple question: Does it bring more than 1dB gain with it? 73's Richard Clark, KB7QHC |
Does it bring more than 1dB gain with it?
73's Richard Clark, KB7QHC =============================== Richard, asking such awkward questions you get more insensitive to people's feelings every day. Are you not aware that a decrease in gain of even less than 1 dB can lose a contest? ---- Reg, G4FGQ |
On Tue, 22 Mar 2005 02:15:41 +0000 (UTC), "Reg Edwards"
wrote: Does it bring more than 1dB gain with it? 73's Richard Clark, KB7QHC =============================== Richard, asking such awkward questions you get more insensitive to people's feelings every day. Are you not aware that a decrease in gain of even less than 1 dB can lose a contest? Reg, Having failed, I have also lost. Frail egos might feel the pain of contest - me, I got a backache sitting in a Bar too long drinking Rum and listening to Rockabilly. 73's Richard Clark, KB7QHC |
Well... yes... and no....
In investigating small antennas, my quest was not to find antennas which preformed within 1 db as well, as well, or God forbid, better than their full sized counter parts. Rather, I was looking for antennas which preformed better than the poor preformance which standard theory would suggest--a simple suggestion that the theory was in error and, hopefully ones which could be utilized with acceptable results in restricted spaces. Both of those condidtions I did find! While a pocket antenna which would preform as well as a half wave antenna on low freqs (or any freq for that matter) would be fantastic, I lack the faith to believe it possible--except at multiple Ghz, where both become the same! However, it is very possible you might use the pocket antenna in places where you could never never use the halfwave. And of course, under such conditions--I would want the best possible pocket antenna which could be constructed! Warmest regards "Richard Clark" wrote in message ... On Mon, 21 Mar 2005 14:58:51 -0800, "John Smith" wrote: Fact is, we hate to admit when we are wrong Hi John, That never fazed me as long as I was challenged by facts instead of superstition. I have failed to many times to worry about it. As the saying goes, if you haven't failed, you aren't trying hard enough. ... there is something here which has been overlooked and current conventional thinking and models miss... I try those angles, and go the extra mile. Evidence some 300+ pages of examining fractal antennas: http://www.qsl.net/kb7qhc/antenna/fractal/index.htm This work eventually boiled down to a simple conclusion (not that the leading proponent would allow his mystical explanation to be nudged into the corner of drab insight). These days I usually put a filter into the process by asking the "inventor" a simple question: Does it bring more than 1dB gain with it? 73's Richard Clark, KB7QHC |
"Standard theory" has been around for over a hundred years now, and is
the basis for the design of some millions of antennas used for everything from your cell phone to communications beyond the solar system. Laboratories world wide measure antennas daily which have been designed with "standard theory", and in those past hundred years plus, no one has found any credible evidence that "standard theory" is in error. Of course, charlatans claim it almost daily, just as they claim the discovery of perpetual motion but inevitably their claims are shown to fail in objective tests. Backyard tinkerers love to fantasize that they'll be the next Galileo and in a few hours, days, or years, make the breakthrough discovery that shows all them eggheads a thing or two. It's pretty easy for such a person to convince himself that he's done just that, because accurate antenna measurements are much more difficult than amateurs generally appreciate, and the sources of error are often subtle and require knowledge of basic theory to understand. Another common basis for a shouted "Eureka!" is a lack of knowledge of "standard theory", and the gee-whiz revelation that what the discoverer mistakenly thought was true turned out, after all, to be false. Clever ways of applying "standard theory" to make an antenna that's more useful in some way for some application are found frequently. Genuine evidence that "standard theory" is wrong has happened virtually never in the past many decades. The odds are heavily against the new Galileo springing up from the suburbs. My money's sure not on them. People truly wanting to make a better antenna would better spend their time learning "standard theory" and less time tinkering in ignorance of it. Roy Lewallen, W7EL John Smith wrote: Well... yes... and no.... In investigating small antennas, my quest was not to find antennas which preformed within 1 db as well, as well, or God forbid, better than their full sized counter parts. Rather, I was looking for antennas which preformed better than the poor preformance which standard theory would suggest--a simple suggestion that the theory was in error and, hopefully ones which could be utilized with acceptable results in restricted spaces. Both of those condidtions I did find! While a pocket antenna which would preform as well as a half wave antenna on low freqs (or any freq for that matter) would be fantastic, I lack the faith to believe it possible--except at multiple Ghz, where both become the same! However, it is very possible you might use the pocket antenna in places where you could never never use the halfwave. And of course, under such conditions--I would want the best possible pocket antenna which could be constructed! Warmest regards |
On Sun, 20 Mar 2005 18:26:42 -0800, "John Smith"
wrote: My question(s): For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards EZNec will model your antenna. As for the antenna, I believe that the shortened 1/2 wave antenna will radiate with less effect than a stretched 1/2 wave, but possibly better than a 1/4 wave. How much? That depends on the coil and the matching network pending losses. Good luck, Buck N4PGW -- 73 for now Buck N4PGW |
I should add that the antenna you described will be less efficient than
a plain wire of the same height. The use of the coil in place of a straight piece of wi 1. Makes no substantial difference to the pattern shape. 2. Decreases the efficiency. 3. Potentially makes matching more difficult. 4. Unnecessarily increases cost and mechanical complexity. But it might look groovy and impress the good buddies. And it might *seem* to work better -- the placebo effect is genuine and quite powerful and it's been the reason for a lot of satisfied customers. Roy Lewallen, W7EL |
Well, I have 3 test antennas on this project:
1) 1/4 wave stainless steel whip w/4 heavy 1/2 inch, aluminum ground plane radials 2) 1/2 wave without any ground plane/counterpoise, lower 1/4 wave section is 3/4 copper pipe, upper 1/4 is a stainless whip, total of the combination is 1/2 wave... ferrite beads are used on the outer shield of the coax at the point where it connects to the antenna, match is though a simple l-network (ferrite beads are actually un-needed but used anyway, no real detectable radiation from coax either way) 3) This is the antenna I described in the first post(s), I tend to refer to as the "quarter/half", it is constructed on 3/4 ID pvc pipe, and has an OD of just over an inch, the coil is constructed of #8 copper wire and the top whip is the 28 inch stainless whip I mentioned. Is a resonate 1/2 wave and physical 1/4 (whip + helical coil length.) Matching network is a l-network, capactior is constructed of acrylic insulator plates (acrylic "window pane") with copper sheet plates, coil is a 1.3 OD torroid. coil is approx. 1+ uh (computed from toroid data)--I have not measured the capacitance of the capacitor (probably somewhere from 20+ pf to 30+ pf), no groundplane/counterpoise, ferrite beads as above. Naturally, as the models predict, the 1/4 is lower in preformance than the half 1/2, and very noticable in the most distant contacts. However, the "quarter/half" out preforms the 1/4 but falls lower in preformance than the 1/2. Contacts out at 30+ miles are where the electrical 1/2 wave antennas differ most from each other (antennas 2 and 3 above.) FSM measurements of the two 1/2 waves are very simuliar--however, these measurements could have been taken at a greater distance to increase accuracy (meters sensitivity I currently am using limited this.) Franky, I was surprised by the preformance. As others have predicted--I expected the preformance of the shortened 1/2 wave to be poorer than the 1/4 (mainly due to the helical coil skewing the radiation pattern and adding a slight resistance to a physical 1/4 antenna.) However, it seems to fall in the middle between the 1/4 and the 1/2 wave (full length) antennas, favoring being closer to the 1/2 full length by 1/2 S-unit+ The biggest difference between the 1/4 and 1/2 wave full length is 2-3 s-units at stations in the 30+ mile distances. The full 1/2 wave and the shortened 1/2 wave seem close to 1 s-unit on all apparent distant stations. I find this hard to believe, and the models I calculated did not reflect what I had actually seen in s-units. All three antennas were placed at the same height, on the same mast while testing (32 ft above real ground.) And all other conditions the same. The l-network match is the only difference between the two 1/2 wave antennas, in the future I will correct this and finalize the tests... the difference in the matches could be responsible for the difference in expected results. Right now, it actually looks to me, from the above--that the "1/4 physical, 1/2 wave electrical (quarter/half)" antenna was and is exhibiting properties of both a 1/4 and a 1/2 wave antenna. This is the main reason I tossed out this "antenna problem" here, to see others reactions and draw from their experience. Warmest regards "Buck" wrote in message ... On Sun, 20 Mar 2005 18:26:42 -0800, "John Smith" wrote: My question(s): For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards EZNec will model your antenna. As for the antenna, I believe that the shortened 1/2 wave antenna will radiate with less effect than a stretched 1/2 wave, but possibly better than a 1/4 wave. How much? That depends on the coil and the matching network pending losses. Good luck, Buck N4PGW -- 73 for now Buck N4PGW |
If there's no ground system loss, a half wave vertical antenna has about
1.3 dB gain over a quarter wave vertical due to the sharper pattern shape. This is the line-of-sight or surface wave gain difference. If reflection from real ground is included in the analysis, the gain difference is about 1 - 1.5 dB at lower angles, and the quarter wave does much better, by 3 or 4 dB or so, at high angles (very roughly above 50 degrees or so). Coil loading to achieve half wave resonance does have one potential advantage, and that's to reduce ground loss when substantial ground resistance is present. Because of the much higher base impedance, ground current is much less with a half wave resonant base fed antenna than with a quarter wave antenna, even when the resonance is achieved with coil loading. Ground loss is typically pretty low on ten meters in mobile applications, but in some other setups (such as ground mounting over a buried radial system, or a hand-held radio), the reduction in ground current could reduce ground loss more than enough to compensate for coil loss. I suspect this is the explanation for at least some of any advantage you see in the coil loaded antenna over a straight wire of the same length. However, there's a good sized handful of other possible factors. (Every last one of them, incidentally, explainable perfectly well by "standard theory".) If the measurement results don't agree with the model, it nearly always means that the actual antenna -- that is, the "antenna", the "ground" system, and everything connected to either one or in the near field of either one -- differs from the model in some significant way. Or the measurement system is faulty. Someone interested in understanding the operation of an antenna will commonly spend a great deal of time tracking down the factors that differ between the model and real antenna, and it's just about always a truly educational experience. When done, the result is usually a model that really represents the antenna system, and that shows results very close to careful and competent measurements. And an experimenter who knows more about antennas, modeling, and the importance of some factors he never before considered. You go through this exercise a few hundred times, like professional engineers routinely do, and you come out with a great respect for "standard theory" and an even greater level of skepticism toward people who have a weak understanding of it and are convinced they've witnessed a miracle. Those of us who have spent a career using "standard theory" to design real, useful items that work as designed haven't become skeptical because our brains have been petrified by education; it's because we've seen "standard theory" work, over and over and over, and every last miracle inevitably fall, one after another, to careful scrutiny and understanding. But we also eventually come to realize that astrology, homeopathy, and feng shui(*) will be with us forever. People will simply believe what suits them, and won't be bothered by evidence. Especially if the evidence takes effort, knowledge, patience, and understanding to acquire. The "S-Unit" is a nice homey amateur unit of measurement, but it has no meaning. (Some people seem to think it's equal to 6 dB, but vast numbers of others think it's the the size of the markings on their receivers' "S Meter". The two can be very different.) dB, on the other hand, is a universally defined and understood unit. Anyone unable to accurately measure relative values in dB is unable to make quantitative gain measurements at all. (*) My spell checker didn't recognize this, so I did a quick google search to see if I got it right. It came up with 2,180,000 hits. There's no lack of believers. Roy Lewallen, W7EL John Smith wrote: Well, I have 3 test antennas on this project: 1) 1/4 wave stainless steel whip w/4 heavy 1/2 inch, aluminum ground plane radials 2) 1/2 wave without any ground plane/counterpoise, lower 1/4 wave section is 3/4 copper pipe, upper 1/4 is a stainless whip, total of the combination is 1/2 wave... ferrite beads are used on the outer shield of the coax at the point where it connects to the antenna, match is though a simple l-network (ferrite beads are actually un-needed but used anyway, no real detectable radiation from coax either way) 3) This is the antenna I described in the first post(s), I tend to refer to as the "quarter/half", it is constructed on 3/4 ID pvc pipe, and has an OD of just over an inch, the coil is constructed of #8 copper wire and the top whip is the 28 inch stainless whip I mentioned. Is a resonate 1/2 wave and physical 1/4 (whip + helical coil length.) Matching network is a l-network, capactior is constructed of acrylic insulator plates (acrylic "window pane") with copper sheet plates, coil is a 1.3 OD torroid. coil is approx. 1+ uh (computed from toroid data)--I have not measured the capacitance of the capacitor (probably somewhere from 20+ pf to 30+ pf), no groundplane/counterpoise, ferrite beads as above. Naturally, as the models predict, the 1/4 is lower in preformance than the half 1/2, and very noticable in the most distant contacts. However, the "quarter/half" out preforms the 1/4 but falls lower in preformance than the 1/2. Contacts out at 30+ miles are where the electrical 1/2 wave antennas differ most from each other (antennas 2 and 3 above.) FSM measurements of the two 1/2 waves are very simuliar--however, these measurements could have been taken at a greater distance to increase accuracy (meters sensitivity I currently am using limited this.) Franky, I was surprised by the preformance. As others have predicted--I expected the preformance of the shortened 1/2 wave to be poorer than the 1/4 (mainly due to the helical coil skewing the radiation pattern and adding a slight resistance to a physical 1/4 antenna.) However, it seems to fall in the middle between the 1/4 and the 1/2 wave (full length) antennas, favoring being closer to the 1/2 full length by 1/2 S-unit+ The biggest difference between the 1/4 and 1/2 wave full length is 2-3 s-units at stations in the 30+ mile distances. The full 1/2 wave and the shortened 1/2 wave seem close to 1 s-unit on all apparent distant stations. I find this hard to believe, and the models I calculated did not reflect what I had actually seen in s-units. All three antennas were placed at the same height, on the same mast while testing (32 ft above real ground.) And all other conditions the same. The l-network match is the only difference between the two 1/2 wave antennas, in the future I will correct this and finalize the tests... the difference in the matches could be responsible for the difference in expected results. Right now, it actually looks to me, from the above--that the "1/4 physical, 1/2 wave electrical (quarter/half)" antenna was and is exhibiting properties of both a 1/4 and a 1/2 wave antenna. This is the main reason I tossed out this "antenna problem" here, to see others reactions and draw from their experience. Warmest regards "Buck" wrote in message ... On Sun, 20 Mar 2005 18:26:42 -0800, "John Smith" wrote: My question(s): For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards EZNec will model your antenna. As for the antenna, I believe that the shortened 1/2 wave antenna will radiate with less effect than a stretched 1/2 wave, but possibly better than a 1/4 wave. How much? That depends on the coil and the matching network pending losses. Good luck, Buck N4PGW -- 73 for now Buck N4PGW |
"Reg Edwards" wrote
Does it bring more than 1dB gain with it? 73's Richard Clark, KB7QHC =============================== Richard, asking such awkward questions you get more insensitive to people's feelings every day. Are you not aware that a decrease in gain of even less than 1 dB can lose a contest? Reg, G4FGQ __________________ This post started with a question about a 28" loaded whip operating on 10 meters, presumably to be used in a mobile application. The concern of the post was how to model the antenna to determine whether it would have the pattern of a 1/4 wave or a 1/2 wave vertical radiator. But for a mobile application the affect of the auto body, the local environment, and even the direction the car is pointing can alter the free-space pattern of the antenna more than the difference in the relative radiation patterns of 1/4-wave and 1/2-wave verticals -- and particularly so for VHF/UHF antennas. If 1dB of antenna gain is so critical to amateurs, suggest that more attention needs to be paid in its system design to the operating environment of the antenna. Some NEC programs make it fairly straightforward to model the net patterns of antennas as mounted on vehicles, and should lead to a better understanding of antenna performance in the real world. RF |
John Smith wrote:
Well... Yes, that argument is made with most everything... It has already been done... everything has been tried... all the answers are known... there is nothing new to be found out... This post got me to thinking (always dangerous) Whatever happened to that wunderantenna from the University of Rhode Island? ttp://tinyurl.com/5qn4d Especially interesting is the comparison against a 5/8th wave antenna @ 150 MHz. Presemably that antenna was matched by a 9 inch DLM. The BW was apparently 1 MHz better than the 5/8th wave, although thte sentence was a bit unclear with that respect. I remain very skeptical. Bogus or Bonanza? - Mike KB3EIA - |
You said you made your antenna with a base loaded coil and added an
L-matching network. I have been reading the ARRL manual which says that the center loaded coil produces a different current curve and a better match. Assuming that the L-network produces some (any) loss, the better match will theoretically overcome that. However, the inductor has to be considerably larger and inductors are somewhat lossy. Has anyone tried, and/or can anyone model this version to see how it compares? -- 73 for now Buck N4PGW |
On Tue, 22 Mar 2005 09:56:56 -0500, Michael Coslo
wrote: Bogus or Bonanza? Hi Mike, It was a fantastic success! Everyone uses them now, don't you have one yet? 73's Richard Clark, KB7QHC |
The "S-Unit" is a nice homey amateur unit of measurement, but it has
no meaning. (Some people seem to think it's equal to 6 dB, but vast numbers of others think it's the the size of the markings on their receivers' "S Meter". ================================ And one million US housewives can't be wrong! |
Richard Clark wrote: On Tue, 22 Mar 2005 09:56:56 -0500, Michael Coslo wrote: Bogus or Bonanza? Hi Mike, It was a fantastic success! Everyone uses them now, don't you have one yet? I did, but it was so efficient that it melted when I tried to run 100 watts through it.... - Mike KB3EIA - |
Absolutely, and, "If it works don't complain!", is my motto.
Still, my mind ponders and responds with questions... One thing I haven't been forth coming with is the 1/4 wave antenna. Really, I don't know what specs a "proper" one should be constructed to (working off very basic ARRL diagram). The one I built has a very heavy stainless whip--most likely is military surplus, but years ago I bought a whole slew of them and still have not used them up, the whip base is about 3/8 and tapers at approx. 12 feet to a 3/16 dia. I just hacked it to a 1/4 wave with the 1/4 ant length formula provided by the ARRL book and removed length with a very course file, until resonate. The radials are 1/2" aluminum rod and heavy. The insulating material for the whip is cut from 1-1/4" thick nylon sheet. The SWR was originally high, but "drooping" (ARRL book suggested this) the ends of the radials, down near a 45 degree angle, provides 1:1.5. The radials are cut 5% wave longer than the whip (again, suggested by ARRL book), they are grounded to the mast and the mast has a good earth ground. Antenna is directly fed with 50 ohm coax. Perhaps my construction of the 1/4 is less than optimum? And, this may make it appear that the antenna from my original post is performing better than it really is.... thoughtful frown The weather here is high wind and rain. I will not be tempted to do any more experimenting until this passes... Regards Hey! If you can't provide and suggestions, how about just spell checking this for me? "Roy Lewallen" wrote in message ... If there's no ground system loss, a half wave vertical antenna has about 1.3 dB gain over a quarter wave vertical due to the sharper pattern shape. This is the line-of-sight or surface wave gain difference. If reflection from real ground is included in the analysis, the gain difference is about 1 - 1.5 dB at lower angles, and the quarter wave does much better, by 3 or 4 dB or so, at high angles (very roughly above 50 degrees or so). Coil loading to achieve half wave resonance does have one potential advantage, and that's to reduce ground loss when substantial ground resistance is present. Because of the much higher base impedance, ground current is much less with a half wave resonant base fed antenna than with a quarter wave antenna, even when the resonance is achieved with coil loading. Ground loss is typically pretty low on ten meters in mobile applications, but in some other setups (such as ground mounting over a buried radial system, or a hand-held radio), the reduction in ground current could reduce ground loss more than enough to compensate for coil loss. I suspect this is the explanation for at least some of any advantage you see in the coil loaded antenna over a straight wire of the same length. However, there's a good sized handful of other possible factors. (Every last one of them, incidentally, explainable perfectly well by "standard theory".) If the measurement results don't agree with the model, it nearly always means that the actual antenna -- that is, the "antenna", the "ground" system, and everything connected to either one or in the near field of either one -- differs from the model in some significant way. Or the measurement system is faulty. Someone interested in understanding the operation of an antenna will commonly spend a great deal of time tracking down the factors that differ between the model and real antenna, and it's just about always a truly educational experience. When done, the result is usually a model that really represents the antenna system, and that shows results very close to careful and competent measurements. And an experimenter who knows more about antennas, modeling, and the importance of some factors he never before considered. You go through this exercise a few hundred times, like professional engineers routinely do, and you come out with a great respect for "standard theory" and an even greater level of skepticism toward people who have a weak understanding of it and are convinced they've witnessed a miracle. Those of us who have spent a career using "standard theory" to design real, useful items that work as designed haven't become skeptical because our brains have been petrified by education; it's because we've seen "standard theory" work, over and over and over, and every last miracle inevitably fall, one after another, to careful scrutiny and understanding. But we also eventually come to realize that astrology, homeopathy, and feng shui(*) will be with us forever. People will simply believe what suits them, and won't be bothered by evidence. Especially if the evidence takes effort, knowledge, patience, and understanding to acquire. The "S-Unit" is a nice homey amateur unit of measurement, but it has no meaning. (Some people seem to think it's equal to 6 dB, but vast numbers of others think it's the the size of the markings on their receivers' "S Meter". The two can be very different.) dB, on the other hand, is a universally defined and understood unit. Anyone unable to accurately measure relative values in dB is unable to make quantitative gain measurements at all. (*) My spell checker didn't recognize this, so I did a quick google search to see if I got it right. It came up with 2,180,000 hits. There's no lack of believers. Roy Lewallen, W7EL John Smith wrote: Well, I have 3 test antennas on this project: 1) 1/4 wave stainless steel whip w/4 heavy 1/2 inch, aluminum ground plane radials 2) 1/2 wave without any ground plane/counterpoise, lower 1/4 wave section is 3/4 copper pipe, upper 1/4 is a stainless whip, total of the combination is 1/2 wave... ferrite beads are used on the outer shield of the coax at the point where it connects to the antenna, match is though a simple l-network (ferrite beads are actually un-needed but used anyway, no real detectable radiation from coax either way) 3) This is the antenna I described in the first post(s), I tend to refer to as the "quarter/half", it is constructed on 3/4 ID pvc pipe, and has an OD of just over an inch, the coil is constructed of #8 copper wire and the top whip is the 28 inch stainless whip I mentioned. Is a resonate 1/2 wave and physical 1/4 (whip + helical coil length.) Matching network is a l-network, capactior is constructed of acrylic insulator plates (acrylic "window pane") with copper sheet plates, coil is a 1.3 OD torroid. coil is approx. 1+ uh (computed from toroid data)--I have not measured the capacitance of the capacitor (probably somewhere from 20+ pf to 30+ pf), no groundplane/counterpoise, ferrite beads as above. Naturally, as the models predict, the 1/4 is lower in preformance than the half 1/2, and very noticable in the most distant contacts. However, the "quarter/half" out preforms the 1/4 but falls lower in preformance than the 1/2. Contacts out at 30+ miles are where the electrical 1/2 wave antennas differ most from each other (antennas 2 and 3 above.) FSM measurements of the two 1/2 waves are very simuliar--however, these measurements could have been taken at a greater distance to increase accuracy (meters sensitivity I currently am using limited this.) Franky, I was surprised by the preformance. As others have predicted--I expected the preformance of the shortened 1/2 wave to be poorer than the 1/4 (mainly due to the helical coil skewing the radiation pattern and adding a slight resistance to a physical 1/4 antenna.) However, it seems to fall in the middle between the 1/4 and the 1/2 wave (full length) antennas, favoring being closer to the 1/2 full length by 1/2 S-unit+ The biggest difference between the 1/4 and 1/2 wave full length is 2-3 s-units at stations in the 30+ mile distances. The full 1/2 wave and the shortened 1/2 wave seem close to 1 s-unit on all apparent distant stations. I find this hard to believe, and the models I calculated did not reflect what I had actually seen in s-units. All three antennas were placed at the same height, on the same mast while testing (32 ft above real ground.) And all other conditions the same. The l-network match is the only difference between the two 1/2 wave antennas, in the future I will correct this and finalize the tests... the difference in the matches could be responsible for the difference in expected results. Right now, it actually looks to me, from the above--that the "1/4 physical, 1/2 wave electrical (quarter/half)" antenna was and is exhibiting properties of both a 1/4 and a 1/2 wave antenna. This is the main reason I tossed out this "antenna problem" here, to see others reactions and draw from their experience. Warmest regards "Buck" wrote in message ... On Sun, 20 Mar 2005 18:26:42 -0800, "John Smith" wrote: My question(s): For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards EZNec will model your antenna. As for the antenna, I believe that the shortened 1/2 wave antenna will radiate with less effect than a stretched 1/2 wave, but possibly better than a 1/4 wave. How much? That depends on the coil and the matching network pending losses. Good luck, Buck N4PGW -- 73 for now Buck N4PGW |
Buck,
I disagree with you on this. If the coil does indeed resonate the antenna in 1/2 wave, antiresonance, current distribution will be different than the straight quarterwave resonance. The current maximum will occur in roughly the center of the loacing coil length with a current minimum at the bottom. Since photon generation is an ampere/length concern, there must be a greater peak coil current to achieve the same power radiated. That would probably incur greater losses than quarter wave resonance. The half wave resonance might have an advantage if there is a problem achieving an adequate counterpoise under the antenna for normal quarter wave resonance. A lot of through-the-glass mobile antennas have been sold using this principle. I wonder if Roy has a simple way to include the coil Q or losses in the EZNEC model. I'm sure there is a logical way to work it out but I haven't had time to think it through yet. Gary - N0GW |
Buck wrote: On Sun, 20 Mar 2005 18:26:42 -0800, "John Smith" wrote: My question(s): For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards EZNec will model your antenna. As for the antenna, I believe that the shortened 1/2 wave antenna will radiate with less effect than a stretched 1/2 wave, but possibly better than a 1/4 wave. How much? That depends on the coil and the matching network pending losses. Good luck, Buck N4PGW -- 73 for now Buck N4PGW |
John Smith wrote:
Well... Yes, that argument is made with most everything... It has already been done... everything has been tried... all the answers are known... there is nothing new to be found out... Absolutely - someone wanted to close the US patent office over 100 years ago because everything possible had already been invented. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Roy Lewallen wrote:
Laboratories world wide measure antennas daily which have been designed with "standard theory", and in those past hundred years plus, no one has found any credible evidence that "standard theory" is in error. Do you really think an antenna using entangled electrons can be predicted by "standard theory"? :-) -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
N0GW wrote:
. . . I wonder if Roy has a simple way to include the coil Q or losses in the EZNEC model. I'm sure there is a logical way to work it out but I haven't had time to think it through yet. Sure. If modeling it as a helix, simply specify wire loss for the type of wire or plating on the wire used for the coil. (The loss in the coil will be much greater than the loss in the straight wire, so it's no big deal if the straight wire is made from some other material.) If modeling it as lumped loads (not as accurate), include the appropriate value of R in the loads. You can quickly and easily see how much loss the coil is causing by comparing gain with the loss present and absent. A few experiments showed a pretty close agreement between EZNEC's helix model with wire loss and Reg's inductor program with regard to L, resonant frequency, and Q. I didn't, however, run tests with a wide range of coil geometries and wire sizes. The EZNEC helix model will underreport loss if wire spacing is less than one or two wire diameters, since it doesn't account for proximity effect (uneven current density around the wire). Although you can manually (and tediously) build a helix model with EZNEC v. 3.0 or EZNEC-ARRL which is v. 3.0, or create one with an external program and import it, EZNEC v. 4.0 has a built-in helix creation feature that generates a helical coil with a few keystrokes. Roy Lewallen, W7EL |
"John Smith" wrote, " Rather, I was looking for antennas which
preformed better than the poor preformance which standard theory would suggest--..." Perhaps you're thinking of different antennas than I have in mind right now. But using simple resonant half-wave dipoles or quarter waves over ground planes, it seems to me the performance is pretty amazing. Consider that under the right HF skip conditions, you can communicate half way around the world with such antennas, fairly simple receivers, and just a few watts of RF. Put the same amount of RF into a transmission line made of copper wires and consider how far it gets before the power is too low to be useful for communications. Even if your transmission line were extremely low loss (say 2.5cm diameter wires forming a 600 ohm line, giving about 0.15dB/mile at 4MHz), in under 2000 miles, you wouldn't have enough power left on the line to give reliable communications. And the antenna-radiated RF would be detectable over a wide area, not just at the output of a transmission line. Even fairly small antennas, half or a quarter the size required for unloaded resonance, can be efficient enough to allow pretty remarkable transmission of RF energy. In fact, the inefficiencies of small antennas generally come about in the matching systems much more than in the radiating structure itself. So I'm left wondering just why you think antennas that perform as "standard theory" suggests are performing poorly. Or perhaps you're considering the difficulty of concentrating the radiation in a certain direction using small antennas...though I would not have thought that from your base posting. Cheers, Tom |
Absolutely...
Even though it is only necessary to deliver mere nano watts to the receiver on the other end, the atmospheric sphere, combined with the magnetosphere, around this planet is/are an amazing means of conducting rf for communications. And the ducting of vhf and uhf can appear to be even "magically" efficient at times. There was some guy from germany, old ex-postal worker as I remember, never did well in school, and never spoke a word till the age of four, quite a while back now--who claimed it all relative... he might have been right... Regards "K7ITM" wrote in message ups.com... "John Smith" wrote, " Rather, I was looking for antennas which preformed better than the poor preformance which standard theory would suggest--..." Perhaps you're thinking of different antennas than I have in mind right now. But using simple resonant half-wave dipoles or quarter waves over ground planes, it seems to me the performance is pretty amazing. Consider that under the right HF skip conditions, you can communicate half way around the world with such antennas, fairly simple receivers, and just a few watts of RF. Put the same amount of RF into a transmission line made of copper wires and consider how far it gets before the power is too low to be useful for communications. Even if your transmission line were extremely low loss (say 2.5cm diameter wires forming a 600 ohm line, giving about 0.15dB/mile at 4MHz), in under 2000 miles, you wouldn't have enough power left on the line to give reliable communications. And the antenna-radiated RF would be detectable over a wide area, not just at the output of a transmission line. Even fairly small antennas, half or a quarter the size required for unloaded resonance, can be efficient enough to allow pretty remarkable transmission of RF energy. In fact, the inefficiencies of small antennas generally come about in the matching systems much more than in the radiating structure itself. So I'm left wondering just why you think antennas that perform as "standard theory" suggests are performing poorly. Or perhaps you're considering the difficulty of concentrating the radiation in a certain direction using small antennas...though I would not have thought that from your base posting. Cheers, Tom |
Well....
I could have stated a less controversial design I guess. Such as an antiresonate antenna cap--folded from aluminum foil, and intended to cancel out the moon bounced mind control rays from the aliens. Since totally shielding the walls of my home with silver foil has failed to block the penetration of these "antenna rays" into my home, the cap might be just the ticket! The burning question here would be what wavelength of foil the cap should it be folded from, and heck, I don't even think the frequency of their mind control rays registers on earth meters! It is a conspiracy, I TELL YA!!! grin Regards "John Smith" wrote in message ... My question(s): For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards |
Actually, and back to reality:
I am in the San Joaquin Valley in California, while this used to be one of the richest agricultural areas in the world, decades of double and triple farming has depleated the soil of many of the plentiful nutrients (salts, trace minerals, metals, etc.) Also, this area was like a tule swap before levies were built to hold back the water, i.e., a peat bog! Those who mentioned a poor and lossy ground condition might have something there... This area may naturally favor the 1/2 properties. But then too, maybe it is only those damn aliens with their mind control which are placing these ideas in my head! grin Yanno, agriculture uses a lot of those darn illegal aliens' labor!!! Regards "John Smith" wrote in message ... Well.... I could have stated a less controversial design I guess. Such as an antiresonate antenna cap--folded from aluminum foil, and intended to cancel out the moon bounced mind control rays from the aliens. Since totally shielding the walls of my home with silver foil has failed to block the penetration of these "antenna rays" into my home, the cap might be just the ticket! The burning question here would be what wavelength of foil the cap should it be folded from, and heck, I don't even think the frequency of their mind control rays registers on earth meters! It is a conspiracy, I TELL YA!!! grin Regards "John Smith" wrote in message ... My question(s): For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards |
Without line amplifiers across the USA, if all the energy output from
the sun was sent into one end of the phone line, only one electron in a thousand years would trickle out of the other end. |
Richard Fry wrote:
"This post started with a question about a 28" loaded whip operating on 10 meters presumably to be used in a mobile application." As Richard Fry noted, the vehicle and its position affect the antenna`s pattern. Also at 10 meters, a 1/4-wave whip would be little more than 8 feet long. A 28" whip is less than 1/3 a resonant length. Capacitive loading to make up the missing length is probably impractical. A loading coil is lossy but practical. Best choice is likely the 8-ft whip. A CB whip can be trimmed to resonance on 10-meters. If one wanted an antenna to fit between poles about 1/4-wave apart, one could use a 1/4-wave folded dipole, which is resonant due to its 1/2-wave circumference. Gain is only 0.5 dB less than a full 1/2-wave dipole. Like a small loop, the small folded dipole can be resonated with a high-Q series capacitor. Arnold B. Bailey in "TV and Other Receiving Antennas" gives the resistance of the 1/4-wave folded dipole as 6000 ohms at center frequency. This would require transformation to a lower impedance. Another resonant antenna that fits a 1/4-wave space is square and 1/4-wave on each side. It`s about 35 feet of wire for 10 meters and has a feedpoint resistance of 100 to 200 ohms depending on its height over the earth. Over good earth, feed one of its vertical sides in the center. Over poor earth, feed a horizontal side in the center. See ON4UN`s "Low-Band DXing" Chapter 10 for details on large loops. Best regards, Richard Harrison, KB5WZI |
Well, the "1/4 physical, 1/2 electrical" (double quarter as my friend refers
to it) will just have remain as it is. Its' advantage of being lighter and easier to handle, while presenting less of a wind load and "leverage" again the mast and mounting hardware allows me to raise it to a greater height than the full 1/2--NOT to mention the advantage of NO ground radials. With this advantage, its performance rivals the full 1/2. Weather I am daft or not--I will be using this antenna for an omnidirectional source. Those seeking a backpacking antenna, an emergency portable antenna, or an antenna for operation in difficult and remote areas, or those seeking stealth (just hide it in a larger diameter PVC pipe and call it a flag pole!) would, most likely, find this design can be used to their advantage. This posting sequence has been an enlightening experience though, and well worth the trouble. I have learned that most will wage a "religious war" if they think anyone is going to challenge the generally accepted ideas and methods. If you insist on going on, you will run the gauntlet of nay sayers and be attacked. Guffaws and slurs against your mental stability will assualt you. If one is looking to try something new--this is NOT the place to discuss it. Perhaps another news group, where those who seek to intimidate and "out shout" true expermenters would be banned and refused posting would be a workable alternative and more conductive to attempts to break the mold. Regards "John Smith" wrote in message ... Actually, and back to reality: I am in the San Joaquin Valley in California, while this used to be one of the richest agricultural areas in the world, decades of double and triple farming has depleated the soil of many of the plentiful nutrients (salts, trace minerals, metals, etc.) Also, this area was like a tule swap before levies were built to hold back the water, i.e., a peat bog! Those who mentioned a poor and lossy ground condition might have something there... This area may naturally favor the 1/2 properties. But then too, maybe it is only those damn aliens with their mind control which are placing these ideas in my head! grin Yanno, agriculture uses a lot of those darn illegal aliens' labor!!! Regards "John Smith" wrote in message ... Well.... I could have stated a less controversial design I guess. Such as an antiresonate antenna cap--folded from aluminum foil, and intended to cancel out the moon bounced mind control rays from the aliens. Since totally shielding the walls of my home with silver foil has failed to block the penetration of these "antenna rays" into my home, the cap might be just the ticket! The burning question here would be what wavelength of foil the cap should it be folded from, and heck, I don't even think the frequency of their mind control rays registers on earth meters! It is a conspiracy, I TELL YA!!! grin Regards "John Smith" wrote in message ... My question(s): For an example, on the 10 meter band: If I take a 28" whip and mount it at the end of helical wound coil (wound on 1" diameter form), where the "wire length" of the coil, PLUS, the length of the whip (28" + coil wire length) is equal to 1/2 wavelength (electrical length)--BUT, the overall physical length of the antenna (top, tip of whip to base of helical wound coil) is 1/4 wavelength, what would the radiation pattern of such an antenna be? Would it favor the pattern of a 1/4 or 1/2 wave antenna--or, would the pattern be a compromise between the two--or, would the pattern be totally unrelated to either? What could I expect the impedance of such an antenna be? Would the reactance be capacitive or inductive? What would be the best way to provide a match to 50 ohm coax from such an antenna? What software is available to model such an antenna? Thanks in advance, warmest regards |
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