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wrote:
You can ,ofcourse, lower the take off angle by using multiple antenna feeds ie stacking but that is another matter of discussion. Art, if you really want perfect control of your TOA, get a satellite tracking system. :-) -- 73, Cecil, 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 =---- |
On Fri, 04 Mar 2005 18:33:41 GMT, "
wrote: I expect many to come up with antennas better than that. Hi Art, Thanx, I just needed you to confirm that you, in fact, did not have such a design. 73's Richard Clark, KB7QHC |
Judging by newsgroup postings, I'd say the most common meaning of
"takeoff angle" is "that elevation angle at which an antenna radiates". For this to have any meaning, it's necessary to assume that the antenna radiates at only one angle and no others. Since this is a false assumption, the term "takeoff angle" as used by most amateurs is meaningless. I've never seen the term in any non-amateur publication -- it seems to be in the same category as "capture area" and "S unit", creations which only amateurs seem to have a need for. As you say, it has a precise definition as used in EZNEC. The first versions of ELNEC, incidentally, didn't report "takeoff angle" because I thought it to be unnecessary to point out what anyone can see from a glance at the pattern, and felt that the term would be misunderstood and misused. Turns out I was right -- it's misunderstood and misused, despite my best effort at explicitly defining it. But you've gotta give the customer what he wants, not what he needs. Roy Lewallen, W7EL Cecil Moore wrote: wrote: TOA is deemed to be the angle at which maximum gain occurs. Seems like you are fishing for something, but you will not get it from me. The problem seems to be that the definition of TOA is not standardized. Literally, TOA can be any angle but has a special meaning when quoting EZNEC. Neither my antenna books nor "The IEEE Dictionary" define TOA. I did a search for "take off angle" and "TOA" on my ARRL Antenna Book CD with zero results. -- 73, Cecil, W5DXP |
Do you really think that I wasn't wise to the games you play ?
You was gearing up for an augument so I gave you nothing you could argue about. Check mate ! Art "Richard Clark" wrote in message ... On Fri, 04 Mar 2005 18:33:41 GMT, " wrote: I expect many to come up with antennas better than that. Hi Art, Thanx, I just needed you to confirm that you, in fact, did not have such a design. 73's Richard Clark, KB7QHC |
Don't professionals use the term? Seems like it shows up in pro computor
programs. Doesn't the Antenna handbook refer to TOA ? I do know they made a graph of incoming RF ray angles which amounts to the same thing. What is wrong with the common perception that it is the angle of maximum gain? If you were designing a 'point to point' antenna would you not look for the angle of maximum gain? If so what would you call that angle ? If you are refering to an antenna lobe pattern could you not invoke the +/- 3 db points as used in many other places in antenna work? Methinks that people are looking for problems to argue about Art "Roy Lewallen" wrote in message ... Judging by newsgroup postings, I'd say the most common meaning of "takeoff angle" is "that elevation angle at which an antenna radiates". For this to have any meaning, it's necessary to assume that the antenna radiates at only one angle and no others. Since this is a false assumption, the term "takeoff angle" as used by most amateurs is meaningless. I've never seen the term in any non-amateur publication -- it seems to be in the same category as "capture area" and "S unit", creations which only amateurs seem to have a need for. As you say, it has a precise definition as used in EZNEC. The first versions of ELNEC, incidentally, didn't report "takeoff angle" because I thought it to be unnecessary to point out what anyone can see from a glance at the pattern, and felt that the term would be misunderstood and misused. Turns out I was right -- it's misunderstood and misused, despite my best effort at explicitly defining it. But you've gotta give the customer what he wants, not what he needs. Roy Lewallen, W7EL Cecil Moore wrote: wrote: TOA is deemed to be the angle at which maximum gain occurs. Seems like you are fishing for something, but you will not get it from me. The problem seems to be that the definition of TOA is not standardized. Literally, TOA can be any angle but has a special meaning when quoting EZNEC. Neither my antenna books nor "The IEEE Dictionary" define TOA. I did a search for "take off angle" and "TOA" on my ARRL Antenna Book CD with zero results. -- 73, Cecil, W5DXP |
On Fri, 04 Mar 2005 20:42:10 GMT, "
wrote: Do you really think that I wasn't wise to the games you play ? You was gearing up for an augument so I gave you nothing you could argue about. Now THAT sounds like playing games, when I ask for a technical specification in a technical newsgroup. Check mate ! as does that. Hi Art, It remains extremely difficult to separate these obscure postings which defy distinction between your work and your fantasies, Art. This recent introduction of TOA appears to have been fantasy. 73's Richard Clark, KB7QHC |
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"Roy Lewallen" wrote in message ... wrote: Don't professionals use the term? I don't believe so. snip The ARRL Antenna Book probably uses TOA. It's a publication intended for amateurs. No, a graph of incoming ray angles is not a graph of TOA as used by EZNEC and other programs. You've just given a good example of the misunderstanding and confusion that the term is subject to. They give an incoming angle not a spread What is wrong with the common perception that it is the angle of maximum gain? Nothing at all. It's just that a lot of people think it means something else. In some of your postings, in fact, I get the sense that you don't always use it with that meaning. For example, you sometimes seem to give a lot of weight to the TOA as a figure of merit, and none at all to the hing field strength or gain at the angle at which communication is taking place. So either you're using TOA in a different sense, or you have no interest in maximizing the ability of an antenna to communicate effectively. snip Roy, by now you must know that I experiment a lot using computor models and actual building. I built a 80 meter boom yagi which was neat because the underside of the first lobe captured a lot of signals as the band is opening. So was the next step to make even a longer boom yagi to drive the underside of the lobe lower, no ....because I am now too old and weaker. So I now pursue the object of a lower take of angle by using more elements with more coupling and one that can rotate in a circle equivalent to a two element beam. I believe this can be accomplished with the same gain and a lower take off angle than a 60 foot boom yagi. Thus TOA becomes the most important thing for me as well as the "thickness" of the lobe. That is the sense that your response questioned regarding my maximisation of antenna performance for which I use TOA. Best regards Art |
"Cecil Moore" wrote The problem seems to be that the definition of TOA is not standardized. ======================= Cecil, it's worse than that. TOA is almost meaningless. Whoever coined the phrase "Take Off Angle" in conjunction with Eznec-type radiation patterns should be made to provide a 5000-word written explanation before he went to bed on his wedding night. Another form of safe sex? In the first place, your suggestion to hire a helicopter to fly around the sky in the vicinity of an antenna to determine the TOA would provide a completely different TOA from that provided by Eznec. Especially at low angles, say less than 30 degrees. That's because the angle at which radiation is strongest in the vicinity of a vertical antenna, of height 5/8-wavelength or shorter, is ALWAYS at an angle of ZERO degrees. ie., it is strongest along the ground surface regardless of soil conditions. Distance from the antenna is too short for the ground wave to be appreciably attenuated. Somehow or other, Eznec manages to calculate relative field strength at some great distance from the antenna. Which is, of course, an ultimate worthwhile but unobtainable objective. Unfortunately, Eznec ignores what that distance may be, whether the receiver is at ground level or at aircraft height, or in the stratosphere. In the extreme state of uncertainty it ignores the height of the ionospheric reflecting layer and the number of hops. In other words, if the location of the receiving antenna in space or time of day are unknown then the Eznec TOA is meaningless. So why is so much importance or significance attached to an Eznec TOA? It is merely one of the infinite number of angles contained in a very broad lobe of a radiation pattern. The path actually taken by a particular radio wave is of far greater importance. And knowing the location on the Earth's surface of both transmitting and receiving antennas, the path taken, including elevation angle, is calculable purely by geometric means. It has nothing to do with the antenna, not even a G5RV. If the ballpark Eznec TOA, by chance, happens to crudely coincide with the actual radio path angle to a distant receiver then that's the best which can be expected. If not, then there's nothing you can do about it except change the antenna, all the soil in your back yard, or your geograhical location. Save yourself the going-rate per hour of the fee for hiring a helicopter. ;o) By the way, this assessment of the situation in no way demeans the value and usefulness of Roy's Eznec - an excellent practical, educational and free-issue program. My only criticism is that it requres a 4-week course of self-instruction, two hours per day, to understand how to use it. But I suppose, starting from scratch, this is inevitable. I imagine that simply to point to Eznec in response to an elementary query on this newsgroup can often lead to a waste of time down-loading it, disappointment and frustration. ---- Reg, G4FGQ |
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