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#41
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On Sun, 06 Mar 2005 14:11:30 GMT, "
wrote: Now I understand where you are coming from !. I've given a lot of info out about the antenna and its attributes, many of which are unique. Hi Art, To that, all that info rarely comes in one post or even within the scope of one thread. Also why I am following this path I do not consider these posts mention of the attributes such as feed point height or details regarding F/B as meaningless and certainly not points about which to argue. No, no argument, simply put, it is needed information to base any discussion upon. When it is lacking (and when only you can supply it), then there is no point for discussion. You might want to consider this in light of your next quoted line: I did ask on another posting if there was anything written on a particular subject regarding a particular feature but there was no response so there is not a lot of interest in some aspects but at this point I am not ready to publish all details which I am sure that you understand I don't, but that is not the point. If you don't have all the details, that is fine as long as you say so. This allows correspondents to add their own insights to help you. If you do have all the details, and say nothing, there is not much to talk about and we have to wonder why you are posting at all. 73's Richard Clark, KB7QHC |
#42
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Needing a break from the exceedingly excruciating task of preparing income
taxes, I took a break to investigate what EZNEC/4 has to say. To facilitate checking and to use an antenna with more vertical pattern than that of a dipole, I used as an antenna the 14.2 MHz five-element Yagi provided with EZNEC. I looked at the first and second peak and the first null (above the horizon) for three types of ground. I also used three heights. ---We all know the uncertainties with estimates of the characteristics of ground, so let us not replay the issue.--- The conductivity in SI units and the relative dielectric constant immediately follow the height in meters. Angles are in degrees above horizon. H = 22 meters 0.005 13 peak 12.5; null 28.3; second peak 41.6 0.01 14 peak 12.6; null 28.3; second peak 41.6 0.002 10 peak 12.5; null 28.4; second peak 41.6 Use of equation: N = 1: 13.9; N = 2: 28.7; N= 3: 46.0 H = 33 meters 0.005 13 peak 8.7; null 18.5; second peak 27.8 0.01 14 peak 8.6; null 18.5; second peak 27.6 0.002 10 peak 8.6; null 18.6; second peak 27.7 Use of equation: N=1: 9.2; N = 2: 18.7; N = 3: 28.7 H = 44 meters 0.005 13 peak 6.6; null 13.8; second peak 20.7 0.01 14 peak 6.7; null 13.8; second peak 20.7 0.002 10 peak 6.6; null 13.8; second peak 20.7 Use of equation: N = 1: 6.9; N = 2: 13.9; N= 3: 21.1 ------- One could conclude that the farther above ground one is and the smaller the relevant angles are, the better the fit with the equation. Think about why the first peak above real ground occurs at a smaller angle than what would be the case with a perfect ground. As several have commented, what counts is to have gain at the angles to be used for propagation. The equation provides some useful information but it needs to be understood. No substitute exists for having a horizontally polarized antenna at heights that are appropriate for the task. One extensive project that I worked on involved distances less than one hop. A significant issue was the desire to minimize gain at low angles where interference resided. Among other things, it was important to suppress vertical radiation as much as possible by choking the transmission lines and by having the wires be close to horizontal. A point in engineering is to know/learn what the desired end results are and then to use tools that are to-hand to approximate the desired end results. In the case of HF systems, as many have observed, a statistical knowledge of propagation plays a large role. Back to taxes. Any man-made system of such complexity is inherently inequitable. 73 Mac N8TT P.S. For receiving purposes, combining a high antenna with an identical antenna about 0.5 WL lower can almost cancel the second lobe and thus attenuate much of the first hop (strong) QRM. Such a scheme does little for transmitting effectiveness. Compare the placement of the null using H= 33 with the second peak using H = 44. -- J. Mc Laughlin; Michigan U.S.A. Home: |
#43
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This is not my thread which is about TOA. I did add a posting remarking
about TOA and you took on yourself to say it was meaningless. In your normal fashion you took on laying a foundation for augument rather than correcting the term to make it meaningfull.If you contribute to the thread by giving the correct term for the angle of take off, then many would be interested. On the other hand I did initiate a post regarding max gain and F/b being on the same frequency and the basis or logic that I drew upon to make that statement. You often take the aproach that all is known ( or you know it all) and if there is no written evidence pertaining to it then it is false and an augument then follows. Now that is you chance for you to wax and wane as to why that logic is faulty which by being the author I would be duty bound to respond and defend my statement . All I do ask for is you keep your responses to the subject at hand and not to invoke Shakespeare or the Doyle Carte company renderance of the Pirates of Penzance as proof knoiweledge of your critique. "Richard Clark" wrote in message ... On Sun, 06 Mar 2005 14:11:30 GMT, " wrote: Now I understand where you are coming from !. I've given a lot of info out about the antenna and its attributes, many of which are unique. Hi Art, To that, all that info rarely comes in one post or even within the scope of one thread. Also why I am following this path I do not consider these posts mention of the attributes such as feed point height or details regarding F/B as meaningless and certainly not points about which to argue. No, no argument, simply put, it is needed information to base any discussion upon. When it is lacking (and when only you can supply it), then there is no point for discussion. You might want to consider this in light of your next quoted line: I did ask on another posting if there was anything written on a particular subject regarding a particular feature but there was no response so there is not a lot of interest in some aspects but at this point I am not ready to publish all details which I am sure that you understand I don't, but that is not the point. If you don't have all the details, that is fine as long as you say so. This allows correspondents to add their own insights to help you. If you do have all the details, and say nothing, there is not much to talk about and we have to wonder why you are posting at all. 73's Richard Clark, KB7QHC |
#44
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If one writes the equation, for elevation angles of nulls and maximums, in
terms of free-space wavelength instead of frequency, an even more simple equation is obtained : Beta = ArcSin( N * Lambda / 4 / Height ) degrees. Where Lambda is free-space wavelength and Height is height above ground. When N is odd, Beta corresponds to a maximum in the pattern. When N is even, Beta correspnds to a null in the pattern. ---- Reg, G4FGQ |
#45
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Dear Reg:
Quite. I have found it more useful to use frequency. 73 Mac N8TT P.S. The peaks and nulls suggested by the equation agree quite well when compared to those resulting from using a "perfect" ground with EZNEC/4 as long as the angles are less than about 30 degrees. In FS, the Yagi is down 1 db at 21.5 degrees and down 2 db at just under 30 degrees. -- J. Mc Laughlin; Michigan U.S.A. Home: "Reg Edwards" wrote in message ... If one writes the equation, for elevation angles of nulls and maximums, in terms of free-space wavelength instead of frequency, an even more simple equation is obtained : Beta = ArcSin( N * Lambda / 4 / Height ) degrees. Where Lambda is free-space wavelength and Height is height above ground. When N is odd, Beta corresponds to a maximum in the pattern. When N is even, Beta correspnds to a null in the pattern. ---- Reg, G4FGQ |
#46
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Art Unwin wrote:
Gon`t professionals use the term (take off angle)?" The FCC publishes vertical radiation patterns for grounded vertical radiators of several heights between 0.25 and 0.625 wavelengths. These and selected other curves are made a part of the rules. These curves must be used to compute the probable skywave intensity in another station`s service area whenever it appears a questionable interference may occur. Skywave computations are approximate but give results which are reliable over a fairly predictable percentage of the time. The term used by the FCC is "elevation angle" or departure angle. The FCC governs radiation. Determining radiation from broadcast stations is a job for professionals who use the term "elevation angle". Best regards, Richard Harrison, KB5WZI |
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