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Yagi Height Question
Fellows,
I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. It seems to me that raising and lowering the height of a Yagi affects the take-off angle by at least several degrees, meaning that the signal delivery (target area) would be moved by at least many hundreds of miles. It would also affect the average wave incidence angle with the ionosphere, so one could tune (or peak) the signal significantly with a few feet of height adjustment. I am aware of stacked Yagi's being used by some contest stations, where variable phasing feed techniques between the upper and lower Yagi can (and does) affect take-off angle. I'm just suprised at how little literature and practical use of this technique exists. It can't be all that difficult to build a Yagi that can be winched, or slid up and down the side of the tower by several feet. Does anyone have a better theoretical understanding of the possible signal strength change from an ideal one-bounce propagation when a 20m Yagi is varied in height from .9 to 1.0 wavelength in height? How would a 0.1 wavelenght height change compare to a 30 degree rotation angle change? I know that some of the difficulty in quantifying the benefits of such a scheme is that the refractive layers of the atmosphere change in altitude regularly. So take-off/refraction/range calculations become cumbersome. But perhaps some fixed assumptions would allow some general statements about the typical gains vs. antenna heights for a fixed range. Thanks for any input on this apparently unusual technique. 73, CW-AI4MI |
Yagi Height Question
On 14 Oct 2006 06:32:21 -0700, "CW" wrote:
Fellows, I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. [snip] You make the all-too-common assumption that there is one "take off angle" and apparently believe that no usable radiation occurs at any other angle. You wouldn't (I hope) believe that there is one azimuth angle and that if your antenna isn't pointed *exactly* at the target you're SOL, so why the concern about height? |
Yagi Height Question
CW wrote:
I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. Many do, using motor driven towers. In addition to lowering their arrays when a storm hits, some raise and lower their towers during marginal conditions to maximize signal strength. -- 73, Cecil http://www.w5dxp.com |
Yagi Height Question
"Cecil Moore" wrote in message t... CW wrote: I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. Many do, using motor driven towers. In addition to lowering their arrays when a storm hits, some raise and lower their towers during marginal conditions to maximize signal strength. -- its really only practical on crank up type towers, for those with guyed towers its usually not possible. 10' change on 20m would likely not be very useful though. my hf stacks for 10/15/20 are all spaced 30' apart, 40m is spaced about 80'. even with those height changes (which i can select instantly so i can make direct comparisons without worrying about fading) there is often little difference between antennas... though sometims there is a lot of difference. This highlights the fact that often the signals arrive with a wide range of angles, though at some times they must be in a relatively narrow range. so having multiple antennas at different heights that can be selected in various combinations is a handy thing to do. |
Yagi Height Question
Wes,
Of course I didn't assume that there is one "take off angle", but I did realize that there is a theoretical optimum take-off angle, and that the field strength diminishes as one moves away from that angle in a generally smooth and continuous way. This is obvious on any antenna radiation pattern chart. The point I was getting at was that the field strength diminishes in both the horizontal AND vertical planes. The common antenna rotator allows directing the radiated field in the horizontal plane, thereby "peaking" the signal in that plane. There seems to be very little attention paid to peaking the signal in the vertical plane, which can be readily accomplished by raising and lowering the antenna height. I was curious as to the discrepency. The mechanical complexities just don't seem to fully account for the disparity in usage of these thechniques. I would estimate that rotators are at least 2 orders of magnitude more common than variable antenna height mechanisms. Since I'm assuming that both vertical and horizontal components of feild strength are important in HF signal propogation, I was wondering why so relatively little attention is paid to peaking the vertical component. Is it because of mechanical complexity, lack of understanding, or something else? 73, CW-AI4MI Wes Stewart wrote: On 14 Oct 2006 06:32:21 -0700, "CW" wrote: Fellows, I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. [snip] You make the all-too-common assumption that there is one "take off angle" and apparently believe that no usable radiation occurs at any other angle. You wouldn't (I hope) believe that there is one azimuth angle and that if your antenna isn't pointed *exactly* at the target you're SOL, so why the concern about height? |
Yagi Height Question
Dave,
Thanks for the reply. Multiple switched Yagi's at various heights is a practical approach, and I'm delighted to hear that "sometimes there is a lot of difference". What you are describing is a coarse grained approach to the problem, which is also commonly done in the horizontal plane by switching vertical antenna arrays, etc. A fellow ham in the area has a Yagi mounted about half way up his guyed tower, on a swing arm. It can rotate, but is limited to about 300 degrees of rotation. A similar setup could be used on a side mounted tower trolly, where the height could be continuously varied by 30 feet or more, AND rotated through about 300 degrees. 73, CW-AI4MI its really only practical on crank up type towers, for those with guyed towers its usually not possible. 10' change on 20m would likely not be very useful though. my hf stacks for 10/15/20 are all spaced 30' apart, 40m is spaced about 80'. even with those height changes (which i can select instantly so i can make direct comparisons without worrying about fading) there is often little difference between antennas... though sometims there is a lot of difference. This highlights the fact that often the signals arrive with a wide range of angles, though at some times they must be in a relatively narrow range. so having multiple antennas at different heights that can be selected in various combinations is a handy thing to do. |
Yagi Height Question
ORIGINAL MESSAGE:
On 14 Oct 2006 06:32:21 -0700, "CW" wrote: I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. ------------ REPLY FOLLOWS ------------ The answer is because it isn't really necessary in most cases. If you optimize your antenna for low-angle DX signals where you really need the gain, there will still be significant radiation at high angles, which are generally closer to you and will have stronger signals as a result anyway. This might be significant enough for a QRP operator to want to do it, but at the 100 watt or higher level, you wouldn't gain much. Pun intended. :-) Bill, W6WRT |
Yagi Height Question
On 14 Oct 2006 08:20:07 -0700, "CW" wrote:
I was wondering why so relatively little attention is paid to peaking the vertical component. Is it because of mechanical complexity, lack of understanding, or something else? Hi OM, The single biggest factor is cost. You should be able to appreciate the implication there. The second (and related to cost) biggest factor would be wind load. A taller tower is easier to push over. Another factor would be the requirement for a very stout (cost again) mast (more cost to lift more weight too); unless this is a telescoping tower (costs more than a conventional one, doesn't it?). About the cheapest consideration, the last one in this list, is what you call "lack of understanding." The better question is: What is the optimal angle for contact, not for launch? Art recently came aboard here to seek validation for a secret design that aimed "all" his power to England. When I did the modeling, that optimal angle, depending upon Frequency Time of Day Season Sun spot cycle varied from less than 6 degrees to as high as 12 degrees. FYI his secret design is still secret. Anyway, you can fulfill this last requirement (the cheapest) by using two free software packages: EZNEC for the launch characteristic of the NBS yagi vs. height; VOAWIN (VOACAP VOAAREA) for propagation of that same antenna. 73's Richard Clark, KB7QHC |
Yagi Height Question
On 14 Oct 2006 08:20:07 -0700, "CW" wrote:
Of course I didn't assume that there is one "take off angle", but I did realize that there is a theoretical optimum take-off angle, and that the field strength diminishes as one moves away from that angle in a generally smooth and continuous way. This is obvious on any antenna radiation pattern chart. The point I was getting at was that the field strength diminishes in both the horizontal AND vertical planes. Uh huh. But I think there's an apples and oranges thing going on here. If you want to discuss antenna patterns v. height, that is one discussion. If you want to discuss optimum propagation paths that is another. "Theoretical optimum take-off angle" leaves me guessing but I think you're referring to the former above and the latter below. The common antenna rotator allows directing the radiated field in the horizontal plane, thereby "peaking" the signal in that plane. There seems to be very little attention paid to peaking the signal in the vertical plane, which can be readily accomplished by raising and lowering the antenna height. I was curious as to the discrepency. The mechanical complexities just don't seem to fully account for the disparity in usage of these thechniques. I would estimate that rotators are at least 2 orders of magnitude more common than variable antenna height mechanisms. Since I'm assuming that both vertical and horizontal components of feild strength are important in HF signal propogation, I was wondering why so relatively little attention is paid to peaking the vertical component. Is it because of mechanical complexity, lack of understanding, or something else? I personally know at least a couple of dozen serious hf DXers (presumably the more interested in "optimizing" this sort of thing) and know of a lot more and I don't know of one of them that tries to peak a signal by "readily" cranking a tower up and down. But let's say it's easy to have a free-standing, 100' high (the limit in my county), motorized, positive pulldown, crank-up tower that we are absolutely confident we can crank up and down while out of sight, without worry of the coax getting jammed up or the winch cable wearing out, etc. Atop this tower we install a well-designed, 3-element, 20-meter Yagi. The ground is unremarkably average. Suppose that despite all of the propagation vagaries there is a DX station we want to work and the "optimum takeoff angle" to his location is 13 degrees. Let's begin with our antenna at 50' above ground. Using EZNEC, I modeled such an antenna (my design) and find that at 50' above ground, the gain (13 dBi) peaks at an elevation angle of 18 degrees; not "optimum" for this path, so we start cranking. At 75' the gain (13.4 dBi) peaks at 13 degrees but we don't know that so we keep cranking until we reach 100'. At 100' the peak gain (13.6 dBi) occurs at 10 degrees; again not "optimum." At the "optimum" 13 degrees, the penalty for having the antenna at 50' is 0.9 dB and for having it at 100' is 1.2 dB. Now the question has to be, can you tell the difference? (The math is correct BTW. Elevation patterns are not symmetrical) After all of these heroics, for all practical purposes, we can't tell the difference, but if we are wrong, we're better off at the *lower* height. Maybe this is why nobody varies their antenna height to peak the signal. |
Yagi Height Question
On 14 Oct 2006 06:32:21 -0700, "CW" wrote:
I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. It seems to me that raising and lowering the height of a Yagi affects the take-off angle by at least several degrees, meaning that the signal delivery (target area) would be moved by at least many hundreds of miles. Or hows about raising and lowering the angle of the Yagi? Tilting it somewhat? Maybe a winch and cable to the end of the Yagi and some kind of rotatable joint at the tower end. That would also be complex and cost some. Tony |
Yagi Height Question
It is more a question of practicality.
It is being done by those with crankup towers, if they want to optimize, say between DXing at low angles and domestic QSOs at higher angles. If you want to be flexible, get crankup tower and StepIR antenna. What you suggesting is asking for mechanical complexity, guy wires, multiple antennas on the same tower in the way, etc. Propagation is not clear cut X angle. It is more like drunken, wobbly signals varying in angles, polarization and direction. Antennas have quite a wide lobes to accommodate most of that. Serious DXers and contesters use stacks that give them instantaneous selection of major angles. Tilting up antenna about 5 deg. helps somewhat, beyond that it doesn't. Vertical angle of beam is given by the height of the antenna. So it the question of practicality vs. "precision" and complexity. Moving it 10 ft up or down doesn't really buy you anything. 73 Yuri, K3BU "CW" wrote in message oups.com... Dave, Thanks for the reply. Multiple switched Yagi's at various heights is a practical approach, and I'm delighted to hear that "sometimes there is a lot of difference". What you are describing is a coarse grained approach to the problem, which is also commonly done in the horizontal plane by switching vertical antenna arrays, etc. A fellow ham in the area has a Yagi mounted about half way up his guyed tower, on a swing arm. It can rotate, but is limited to about 300 degrees of rotation. A similar setup could be used on a side mounted tower trolly, where the height could be continuously varied by 30 feet or more, AND rotated through about 300 degrees. 73, CW-AI4MI its really only practical on crank up type towers, for those with guyed towers its usually not possible. 10' change on 20m would likely not be very useful though. my hf stacks for 10/15/20 are all spaced 30' apart, 40m is spaced about 80'. even with those height changes (which i can select instantly so i can make direct comparisons without worrying about fading) there is often little difference between antennas... though sometims there is a lot of difference. This highlights the fact that often the signals arrive with a wide range of angles, though at some times they must be in a relatively narrow range. so having multiple antennas at different heights that can be selected in various combinations is a handy thing to do. |
Yagi Height Question
That actually changes it a lot less than raising and lowering
significantly. HF yagis a wavelength or two above ground don't have laser-like beams. The elevation pattern is set up substantially by ground reflection, not only the antenna's free-space elevation pattern. Check out http://n3ox.net/pictures/20m_yagi_el.jpg for an illustration of what happens when you tilt a 5 element 20m yagi up toward the sky. I don't remember how high it is; I think it's about 1 wavelength high. The traces are for 0, 20, 40 and 60 degrees inclination. 73, Dan |
Yagi Height Question
Cecil
That makes a lot of sense after all if one has the antenna primed for low angles then propagation will render it useless as time goes by for those particular angles. If by tipping or feeding another element in an array you can move or thicken the main lobe you can increase the gain of a signal by more than 2 S units then it is certainly worthwhile.To view the subject purely around the maximum gain angle of the main lobe is fallacious as it is the signal that falls just outside the main lobe contour that may be the most desirable and subject to the largest possible gain with the smallest change of TOA. This is because the main lobe thickens out to cover the deep crevice of non coverage of an array tuned for a low TOA.and allows you to emulate the performance of a stacked array with the use of the lower beam alone. 2S unit increase of a signal that can be barely heard is much more advantageous than increasing the gain of a signal that is blowing away all other nearby signals, it certainly allows for more communication data to be transferred where initially very little could be heard. If a good contact is underway it is certainly desirable to maintain that contact even tho propagation is changing and that is what the original poster is seeking Art Cecil Moore wrote: CW wrote: I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. Many do, using motor driven towers. In addition to lowering their arrays when a storm hits, some raise and lower their towers during marginal conditions to maximize signal strength. -- 73, Cecil http://www.w5dxp.com |
Yagi Height Question
ORIGINAL MESSAGE:
On 15 Oct 2006 09:26:05 -0700, "art" wrote: If by tipping or feeding another element in an array you can move or thicken the main lobe you can increase the gain of a signal by more than 2 S units then it is certainly worthwhile. ------------ REPLY FOLLOWS ------------ Not necessarily worthwhile. Remember, if your antenna is optimized for low-angle weak DX signals, the high-angle signals are going to be much closer in and therefore much stronger to begin with. If you lose a few dB on a S-9 signal, it won't matter. If this was really a good idea, everybody would already be doing it. As I mentioned before, it might be desirable for someone running QRP or micropower, but not for most of us at the 100 watt or greater level. Spend your money on other things. Bill, W6WRT |
Yagi Height Question
Bill Turner wrote: ORIGINAL MESSAGE: On 15 Oct 2006 09:26:05 -0700, "art" wrote: If by tipping or feeding another element in an array you can move or thicken the main lobe you can increase the gain of a signal by more than 2 S units then it is certainly worthwhile. ------------ REPLY FOLLOWS ------------ Not necessarily worthwhile. Remember, if your antenna is optimized for low-angle weak DX signals, the high-angle signals are going to be much closer in and therefore much stronger to begin with. If you lose a few dB on a S-9 signal, it won't matter. If a incoming signal aligns with the null between lobes then the receiving station is deaf to your signal. Moving the lobe slightly upwards can add a few db as you call it and allow for communication. If you yell at a closed door you do not increase communication, whisper under the door and you can then be heard, Its all relative. As far as those that follow lemmings do it all the time. Art |
Yagi Height Question
David, are you saying that your three-some stack is made out of tri
banders of the same design such that a lobe null can be filled? I believe that is exactly the coverage the poster is looking for, he wants to be around to hear when the tree falls Art Dave wrote: "Cecil Moore" wrote in message t... CW wrote: I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. Many do, using motor driven towers. In addition to lowering their arrays when a storm hits, some raise and lower their towers during marginal conditions to maximize signal strength. -- its really only practical on crank up type towers, for those with guyed towers its usually not possible. 10' change on 20m would likely not be very useful though. my hf stacks for 10/15/20 are all spaced 30' apart, 40m is spaced about 80'. even with those height changes (which i can select instantly so i can make direct comparisons without worrying about fading) there is often little difference between antennas... though sometims there is a lot of difference. This highlights the fact that often the signals arrive with a wide range of angles, though at some times they must be in a relatively narrow range. so having multiple antennas at different heights that can be selected in various combinations is a handy thing to do. |
Yagi Height Question
my stacks are all monobanders.
on 40m its 4-ele's at 180' & 100' on 20m i have 4-ele's at 150/120/90/60' on 15m and 10m its 4-ele's at 120/90/60/30' on 20m, 15m, and 10m there is another 4 ele fixed south. also on 20m, 15m, and 10m, the middle 2 are fixed at europe and selected together, and the bottom ones are on ring rotors and separately rotatable from the top one. so on 20m, 15m, and 10m, i can select the top along, the middle two at europe together, the bottom one alone, or the south one alone. And then i can also select the top, middle, and bottom all together, and the top, south, and bottom all together to spread the signal out when the bands are open in more than one direction. "art" wrote in message oups.com... David, are you saying that your three-some stack is made out of tri banders of the same design such that a lobe null can be filled? I believe that is exactly the coverage the poster is looking for, he wants to be around to hear when the tree falls Art Dave wrote: "Cecil Moore" wrote in message t... CW wrote: I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. Many do, using motor driven towers. In addition to lowering their arrays when a storm hits, some raise and lower their towers during marginal conditions to maximize signal strength. -- its really only practical on crank up type towers, for those with guyed towers its usually not possible. 10' change on 20m would likely not be very useful though. my hf stacks for 10/15/20 are all spaced 30' apart, 40m is spaced about 80'. even with those height changes (which i can select instantly so i can make direct comparisons without worrying about fading) there is often little difference between antennas... though sometims there is a lot of difference. This highlights the fact that often the signals arrive with a wide range of angles, though at some times they must be in a relatively narrow range. so having multiple antennas at different heights that can be selected in various combinations is a handy thing to do. |
Yagi Height Question
On 14 Oct 2006 22:59:10 -0700, "
wrote: That actually changes it a lot less than raising and lowering significantly. HF yagis a wavelength or two above ground don't have laser-like beams. The elevation pattern is set up substantially by ground reflection, not only the antenna's free-space elevation pattern. Gotcha. That makes sense. Thanks, Tony |
Yagi Height Question
Now now Tony, be carefull in what you say and how you say it
If you placed several dipoles above each other in an array, say nine of them within a height change of half a wave length, in line and each of the dipoles/elements were resonant at the same frequency you are then infering ......,at least I think you are,....... that the lowest dipole/element will have the highest TOA, the next element in height will have a lower TOA and progressively until one energises the top element to get the lowest TOA of them all............ If that is what you are saying........... then you could not be more wrong. I am sure that those who are really knoweledgable in the field will agree with me. Ofcourse somebody lacking true knoweledge will produce a fake series of radiation patterns for each element in the array but that is par for the course on this newsgroup. But then again often interpretations can be varied and thus in error if so I apologise. Best Regards Art Tony VE6MVP wrote: On 14 Oct 2006 22:59:10 -0700, " wrote: That actually changes it a lot less than raising and lowering significantly. HF yagis a wavelength or two above ground don't have laser-like beams. The elevation pattern is set up substantially by ground reflection, not only the antenna's free-space elevation pattern. Gotcha. That makes sense. Thanks, Tony |
Yagi Height Question
"CW" wrote in message ups.com... Fellows, I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. It seems to me that raising and lowering the height of a Yagi affects the take-off angle by at least several degrees, meaning that the signal delivery (target area) would be moved by at least many hundreds of miles. I don't know if this helps, but advice for TV DX says that you get progressively improved performance until the yagi's height-above-average-terrain (HAAT) is equal to about ten wavelengths. (Above that HAAT, the signal strength varies up and down with further increases in the elevation ) I never tested the idea, but if correct and it also holds for HF, there won't ever be anybody _lowering_ a HF yagi. We would want the most height. At the 2006 Field Day, one team had multi-band beam at 85 feet and everybody loved it. Before anybody tells me there is a difference between a yagi and a beam, let me thank you in advance. I cannot formulate a sensible distinction between them and I welcome the knowledge. I presume the terms are related but not interchangeable. 73 |
Yagi Height Question
David that is quite an array of antennas. Two questions come to mind.
Why the separation of a half versus 0.6 of a wave length? and 2 do you ground the top antenna when it is not in use or let it float? I have heard that the top array can remove static noise to advantage and I was wondering how that would compare to an elevated mast that would provide a cone of protection and thus allow use of the top array regardless of conditions. Regards Art art wrote: David, are you saying that your three-some stack is made out of tri banders of the same design such that a lobe null can be filled? I believe that is exactly the coverage the poster is looking for, he wants to be around to hear when the tree falls Art Dave wrote: "Cecil Moore" wrote in message t... CW wrote: I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. Many do, using motor driven towers. In addition to lowering their arrays when a storm hits, some raise and lower their towers during marginal conditions to maximize signal strength. -- its really only practical on crank up type towers, for those with guyed towers its usually not possible. 10' change on 20m would likely not be very useful though. my hf stacks for 10/15/20 are all spaced 30' apart, 40m is spaced about 80'. even with those height changes (which i can select instantly so i can make direct comparisons without worrying about fading) there is often little difference between antennas... though sometims there is a lot of difference. This highlights the fact that often the signals arrive with a wide range of angles, though at some times they must be in a relatively narrow range. so having multiple antennas at different heights that can be selected in various combinations is a handy thing to do. |
Yagi Height Question
Yes there is a difference, A yagi is a planar beam ie on a single plane
so the height of the array is the same for all elements in the array which creates a major lobe or beam. If the array is not planar such as a Quad then the elements are at different heights so the true or effective height of a quad antenna which is also a beam style antenna is approximately the center point of the array or somewhere between the top and bottom of the quad element. The point to stand by is that the height of the feed point is immaterial with respect to the effective height of an array. In another post I pointed out that no matter which element is fed in a array the effective height of the array is always the same and thus the TOA is always the same Regards Art Sal M. Onella wrote: "CW" wrote in message ups.com... Fellows, I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. It seems to me that raising and lowering the height of a Yagi affects the take-off angle by at least several degrees, meaning that the signal delivery (target area) would be moved by at least many hundreds of miles. I don't know if this helps, but advice for TV DX says that you get progressively improved performance until the yagi's height-above-average-terrain (HAAT) is equal to about ten wavelengths. (Above that HAAT, the signal strength varies up and down with further increases in the elevation ) I never tested the idea, but if correct and it also holds for HF, there won't ever be anybody _lowering_ a HF yagi. We would want the most height. At the 2006 Field Day, one team had multi-band beam at 85 feet and everybody loved it. Before anybody tells me there is a difference between a yagi and a beam, let me thank you in advance. I cannot formulate a sensible distinction between them and I welcome the knowledge. I presume the terms are related but not interchangeable. 73 |
Yagi Height Question
On 15 Oct 2006 21:35:43 -0700, "art" wrote:
Yes there is a difference, A yagi is a planar beam ie on a single plane so the height of the array is the same for all elements in the array which creates a major lobe or beam. If the array is not planar such as a Quad then the elements are at different heights so the true or effective height of a quad antenna which is also a beam style antenna is approximately the center point of the array or somewhere between the top and bottom of the quad element. The point to stand by is that the height of the feed point is immaterial with respect to the effective height of an array. In another post I pointed out that no matter which element is fed in a array the effective height of the array is always the same and thus the TOA is always the same Regards Art Hi Art, One of the most demeaning aspects of this newsgroups concerns misunderstandings of definitions and terminology that often leasd to unfortunate and unnecessary arguments. To wit: Yagi vs beam. It's been my understanding that any combination of radiating elements intended to radiate more energy in one direction than omni establishes a major lobe that is called a beam. In other words, any directional system establishes a beam. Therefore, 'beam' is generic to all directional radiators. It then follows that 'Yagi', 'quad', 'W8JK', 'EDZ', are all 'beams' of a particular type or configuration. I believe it's important that correct terminology be used for the benefit of the newcomers--would you not agree? Walt, W2DU |
Yagi Height Question
Walt
I said that both antennas are beams. What I was addressing was the height portion of the question whereas tho they are both beams the effective height measurements were different. i.e Planar beam versus other beams where the quad is not a planar beam. Seems like effective height measurements contribute to most yagi /quad comparison debates. There is also another side of the coin when measuring effective ht and that is when a yagi is positioned vertically where it is still planar when comparing to a quad element moved thru 90 degrees.which is now planar. If you chose to answer the posting what part of my posting would you leave out, or question its veracity especially after reading the total thread? Regards Art Walter Maxwell wrote: On 15 Oct 2006 21:35:43 -0700, "art" wrote: Yes there is a difference, A yagi is a planar beam ie on a single plane so the height of the array is the same for all elements in the array which creates a major lobe or beam. If the array is not planar such as a Quad then the elements are at different heights so the true or effective height of a quad antenna which is also a beam style antenna is approximately the center point of the array or somewhere between the top and bottom of the quad element. The point to stand by is that the height of the feed point is immaterial with respect to the effective height of an array. In another post I pointed out that no matter which element is fed in a array the effective height of the array is always the same and thus the TOA is always the same Regards Art Hi Art, One of the most demeaning aspects of this newsgroups concerns misunderstandings of definitions and terminology that often leasd to unfortunate and unnecessary arguments. To wit: Yagi vs beam. It's been my understanding that any combination of radiating elements intended to radiate more energy in one direction than omni establishes a major lobe that is called a beam. In other words, any directional system establishes a beam. Therefore, 'beam' is generic to all directional radiators. It then follows that 'Yagi', 'quad', 'W8JK', 'EDZ', are all 'beams' of a particular type or configuration. XXXXXXXXXXXXXXXXXXXXXXXXXXX I agree, where did I say different? XXXXXXXXXXXXXXXXXXXXXXXXXXX I believe it's important that correct terminology be used for the benefit of the newcomers--would you not agree? Yes I would agree but if one is unsure of the true terminology should we ban all from ham radio as it has now moved from a hobby to....... IEEE transactions on antennas ? I believe everyone has become too picky as to who is a ham and who is not and thus are becoming adverserial to those not fully versed in the art. Look at the long posting regarding antenna efficiency where everybody jumped on the electrical version of efficiency ie transfer of electrical energy to a time variant field and totaly ignoring the reference to pattern volume.with respect to the main lobe portion. How on earth do electrical engineers chose iapliances for the home when so much device energy is wasted or does not imprint on the required use? The majority of people on this newsgroup including newcomers are now convinced that energy entering an array is nearly equal to the radiation energy contained in the single main lobe and they contest other thoughts by the use of " ratios": which is devoid of units and relavence. Even if they didn't want to read the posting as a whole not one looked at radiation efficiency change when viewing radiation from a complex circuitry direction or in other words driven elements in parallel since elements in parallel alter the resistance DC to resistance radiation ratio ,admittedly small but there none the less. I would admit to a review of antenna efficiency or radiator efficiency if it was normal for radiators to be made of wood As I said earlier to much nittpicking going on such that hams are becoming adverserial to each other and that is to bad if we want newcomers to stay around.NUFF SED Art Walt, W2DU |
Yagi Height Question
On 16 Oct 2006 13:06:58 -0700, "art" wrote:
Walt I said that both antennas are beams. What I was addressing was the height portion of the question whereas tho they are both beams the effective height measurements were different. i.e Planar beam versus other beams where the quad is not a planar beam. Seems like effective height measurements contribute to most yagi /quad comparison debates. There is also another side of the coin when measuring effective ht and that is when a yagi is positioned vertically where it is still planar when comparing to a quad element moved thru 90 degrees.which is now planar. If you chose to answer the posting what part of my posting would you leave out, or question its veracity especially after reading the total thread? Regards Art Walter Maxwell wrote: On 15 Oct 2006 21:35:43 -0700, "art" wrote: Yes there is a difference, A yagi is a planar beam ie on a single plane so the height of the array is the same for all elements in the array which creates a major lobe or beam. If the array is not planar such as a Quad then the elements are at different heights so the true or effective height of a quad antenna which is also a beam style antenna is approximately the center point of the array or somewhere between the top and bottom of the quad element. The point to stand by is that the height of the feed point is immaterial with respect to the effective height of an array. In another post I pointed out that no matter which element is fed in a array the effective height of the array is always the same and thus the TOA is always the same Regards Art Hi Art, One of the most demeaning aspects of this newsgroups concerns misunderstandings of definitions and terminology that often leasd to unfortunate and unnecessary arguments. To wit: Yagi vs beam. It's been my understanding that any combination of radiating elements intended to radiate more energy in one direction than omni establishes a major lobe that is called a beam. In other words, any directional system establishes a beam. Therefore, 'beam' is generic to all directional radiators. It then follows that 'Yagi', 'quad', 'W8JK', 'EDZ', are all 'beams' of a particular type or configuration. XXXXXXXXXXXXXXXXXXXXXXXXXXX I agree, where did I say different? XXXXXXXXXXXXXXXXXXXXXXXXXXX Ok Art, here's the way I saw it: Sal Manela sez: "Before anybody tells me there is a difference between a yagi and a beam, let me thank you in advance." Then you replied, "Yes there is a difference," So Art, my response was only to refute your statement above. I don't dispute your other statements. Walt, W2DU |
Yagi Height Question
Understood
Best regards Art Walter Maxwell wrote: On 16 Oct 2006 13:06:58 -0700, "art" wrote: Walt I said that both antennas are beams. What I was addressing was the height portion of the question whereas tho they are both beams the effective height measurements were different. i.e Planar beam versus other beams where the quad is not a planar beam. Seems like effective height measurements contribute to most yagi /quad comparison debates. There is also another side of the coin when measuring effective ht and that is when a yagi is positioned vertically where it is still planar when comparing to a quad element moved thru 90 degrees.which is now planar. If you chose to answer the posting what part of my posting would you leave out, or question its veracity especially after reading the total thread? Regards Art Walter Maxwell wrote: On 15 Oct 2006 21:35:43 -0700, "art" wrote: Yes there is a difference, A yagi is a planar beam ie on a single plane so the height of the array is the same for all elements in the array which creates a major lobe or beam. If the array is not planar such as a Quad then the elements are at different heights so the true or effective height of a quad antenna which is also a beam style antenna is approximately the center point of the array or somewhere between the top and bottom of the quad element. The point to stand by is that the height of the feed point is immaterial with respect to the effective height of an array. In another post I pointed out that no matter which element is fed in a array the effective height of the array is always the same and thus the TOA is always the same Regards Art Hi Art, One of the most demeaning aspects of this newsgroups concerns misunderstandings of definitions and terminology that often leasd to unfortunate and unnecessary arguments. To wit: Yagi vs beam. It's been my understanding that any combination of radiating elements intended to radiate more energy in one direction than omni establishes a major lobe that is called a beam. In other words, any directional system establishes a beam. Therefore, 'beam' is generic to all directional radiators. It then follows that 'Yagi', 'quad', 'W8JK', 'EDZ', are all 'beams' of a particular type or configuration. XXXXXXXXXXXXXXXXXXXXXXXXXXX I agree, where did I say different? XXXXXXXXXXXXXXXXXXXXXXXXXXX Ok Art, here's the way I saw it: Sal Manela sez: "Before anybody tells me there is a difference between a yagi and a beam, let me thank you in advance." Then you replied, "Yes there is a difference," So Art, my response was only to refute your statement above. I don't dispute your other statements. Walt, W2DU |
Yagi Height Question
that separation comes about from the spacing of guy wires on the rohn towers
they are on. it also happens to work out reasonably well with the elevation pattern software since that many antennas fairly well covers the whole range of take off angles from new england to most of the world. all my yagis are completely grounded designs anyway, so there is no need to further ground them when not in use. when there is rain or snow static the top one often becomes too noisy to use while lower ones are just fine... another good reason to rotate the bottom antennas (except on 40m where it won't turn under the guy wires). "art" wrote in message ps.com... David that is quite an array of antennas. Two questions come to mind. Why the separation of a half versus 0.6 of a wave length? and 2 do you ground the top antenna when it is not in use or let it float? I have heard that the top array can remove static noise to advantage and I was wondering how that would compare to an elevated mast that would provide a cone of protection and thus allow use of the top array regardless of conditions. Regards Art art wrote: David, are you saying that your three-some stack is made out of tri banders of the same design such that a lobe null can be filled? I believe that is exactly the coverage the poster is looking for, he wants to be around to hear when the tree falls Art Dave wrote: "Cecil Moore" wrote in message t... CW wrote: I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. Many do, using motor driven towers. In addition to lowering their arrays when a storm hits, some raise and lower their towers during marginal conditions to maximize signal strength. -- its really only practical on crank up type towers, for those with guyed towers its usually not possible. 10' change on 20m would likely not be very useful though. my hf stacks for 10/15/20 are all spaced 30' apart, 40m is spaced about 80'. even with those height changes (which i can select instantly so i can make direct comparisons without worrying about fading) there is often little difference between antennas... though sometims there is a lot of difference. This highlights the fact that often the signals arrive with a wide range of angles, though at some times they must be in a relatively narrow range. so having multiple antennas at different heights that can be selected in various combinations is a handy thing to do. |
Yagi Height Question
"Sal M. Onella" wrote in message news:w3DYg.5744$gM1.5721@fed1read12... "CW" wrote in message ups.com... Fellows, I've been wondering for some time now why amateur operators don't build their Yagi antenna's so they can be raised and lowered about 10ft in addition to being rotated. It seems to me that raising and lowering the height of a Yagi affects the take-off angle by at least several degrees, meaning that the signal delivery (target area) would be moved by at least many hundreds of miles. I don't know if this helps, but advice for TV DX says that you get progressively improved performance until the yagi's height-above-average-terrain (HAAT) is equal to about ten wavelengths. (Above that HAAT, the signal strength varies up and down with further increases in the elevation ) I never tested the idea, but if correct and it also holds for HF, there won't ever be anybody _lowering_ a HF yagi. We would want the most height. At the 2006 Field Day, one team had multi-band beam at 85 feet and everybody loved it. no, it doesn't hold for hf. tv dx is basically a line of sight vhf/uhf type of propagation where height is everything. the higher you can go the better, i don't know where 10 wavelengths came from since that is actually pretty low on the higher uhf channels! on hf you can't get high enough to get away from the ground reflection effects so you might as well put them to good use. And yes, when bands like 10/15/20m are wide open from new england to europe the best antennas are often the lowest ones here... i.e. my yagi at 30' on 10m will have much stronger signals than the ones at 60, 90, or 120'. and yet at other times, like now, on 10m my yagi at 180' is often the only one to hear any dx. so the answer is: yes, you can be too high, but no, you can't get too high. |
Yagi Height Question
"Dave" wrote in message . .. tv dx is basically a line of sight vhf/uhf type of propagation where height is everything. the higher you can go the better Yes, this has been my experience -- I need to get higher than my neighbor's roof, for example. i don't know where 10 wavelengths came from since that is actually pretty low on the higher uhf channels! Another Yes. At 600 MHz (near mid-band for UHF TV) 10 wavelengths is a mere 5 meters. Not much of a skyhook required to get up there! Doubtful this applies to HF skywaves. Thanks to all.. 73 |
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