wrote:
As gain increases with a yagi design the forward lobe narrows. So to the gurus of this group, what actualy creates the narrowing of the forward lobes ? ______________________ A good analogy that needs no math to understand is that of squeezing an inflated balloon from its normally spherical shape into whatever shape is more appropriate for the application. There is a given volume of air in that balloon. If you want the surface of the balloon to extend further from the origin of its original sphere, the new shape must be narrower in one or more planes than the original shape. The shape changes can come from squeezing the balloon (pattern) horizontally, vertically, or in combination -- which, in antenna hardware is accomplished by an appropriate array of, and feed system for, its radiating elements. RF |
wrote:
So to the gurus of this group, what actualy creates the narrowing of the forward lobes ? The narrowing of the forward lobes is caused by constructive interference during superposition of EM waves. -- 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 =--- |
In message K3B1e.8558$NW5.7100@attbi_s02, "
writes As gain increases with a yagi design the forward lobe narrows . With high gain yagi's the lobe becomes so narrow it is deemed to be a hinderence instead of an advantage. To overcome this perceived problem one has to know what causes it. So to the gurus of this group, what actualy creates the narrowing of the forward lobes ? End effects perhaps! My tuppence worth It is a fundamental energy conservation effect. There is an invariant A * Omega , where A is the capture area of the antenna, proportional to gain and Omega is the solid angle of the lobe. So as A goes up, Omega must come down. One way to reduce the effect is to use a number of vertically stacked low gain yagis. The lobe becomes narrow in the vertical plane , but remains broad in the horizontal plane. This is fairly common technique for VHF/UHF contesters, where a narrow horizontal beam can cause missed contacts Brian -- Brian Howie |
Richard.
No one has come up with a explanation BUT there are real gurus out there, It's just that those who qualify as gurus have just thinned out a bit. The question still pertains to Yagis and the narrowing of lobes You have posted twice now and added nothing that relates to a possible answer. Tho there are many who perceive themselves as experts and then consistently show what they really are. I can think of one or two who can really address this question with a logical answer. Cecil, Roy and a couple of others qualify and have yet to respond You have disqualified yourself based on your responses, so like myself you will have to wait to learn. Yagi's have been studied in depth and for many years by many tho apparently not by you or others that have replied so far. Place your bets on who is the real guru of this group that comes forward to explain with logic and to the point You Richard, can read your old QST's in a hurry and surely find the answer to get back into the ratings as I don't think that new knoweledge is around the bend, just a small manipulation of "old" knoweledge will surely suffice. Think "end effect" and "none- resistive residuals" along coupled radiating elements for starters.If that draws a blank then assuredly you wear no clothes Art "Richard Clark" wrote in message ... On Sun, 27 Mar 2005 18:59:42 GMT, " wrote: the problem: My antenna is somewhat related thus my interest in what creates an elongated lobe the answer: which is formed using Yagi principles. Hi Art, Your question already answers your question. You have a tendency to just blow right on taking no notice of this to create the SAME question again: The question however, is specifically related to Yagi's and its narrowed lobes. Do you know what it is that creats an elongated lobe on a high gain yagi i.e not totally round.? formed using Yagi principles. (to quote you) Nothing more, nothing less. Exactly. Now, are we going to be treated by another round of your complaints about Shakespeare and the quality of gurus; or are you going to stick with technical discussion and respond to the obvious points? 73's Richard Clark, KB7QHC |
"Richard Fry" wrote in message ... wrote: As gain increases with a yagi design the forward lobe narrows. So to the gurus of this group, what actualy creates the narrowing of the forward lobes ? ______________________ A good analogy that needs no math to understand is that of squeezing an inflated balloon from its normally spherical shape into whatever shape is more appropriate for the application. There is a given volume of air in that balloon. If you want the surface of the balloon to extend further from the origin of its original sphere, the new shape must be narrower in one or more planes than the original shape. The shape changes can come from squeezing the balloon (pattern) horizontally, vertically, or in combination -- which, in antenna hardware is accomplished by an appropriate array of, and feed system for, its radiating elements. Right..... so what creats it, this "squeezing" that you talk about and from where does this "squeezing force come from in an "appropiate"array? That's what I was asking not a discussion of what the Yagi array produces. Why does the lobe narrow? Art RF |
Yes Cecil I can go along with that otherwise the resultant volume would be
spherical. What is the scenario that encapsulates this "constructive interference" event? Is it residual reactance where its underpinning reside? Art Art "Cecil Moore" wrote in message ... wrote: So to the gurus of this group, what actualy creates the narrowing of the forward lobes ? The narrowing of the forward lobes is caused by constructive interference during superposition of EM waves. -- 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 =--- |
"Cecil Moore" wrote in message ... wrote: So to the gurus of this group, what actualy creates the narrowing of the forward lobes ? The narrowing of the forward lobes is caused by constructive interference during superposition of EM waves. -- 73, Cecil http://www.qsl.net/w5dxp Darn - I thought it was pure magic. Now we hear all about induced currents and interference patterns cancelling in the rearward and the sides, but constructively interferring in the forward direction. All in an attempt to become the chosen guru of the original poster. If nominated, I will not run - if elected - I will not serve. |
" wrote:
The shape changes can come from squeezing the balloon (pattern) horizontally, vertically, or in combination -- which, in antenna hardware is accomplished by an appropriate array of, and feed system for, its radiating elements. Right..... so what creats it, this "squeezing" that you talk about and from where does this "squeezing force come from in an "appropiate"array? That's what I was asking not a discussion of what the Yagi array produces. Why does the lobe narrow? ______________ Narrowing is the natural result of the vector addition of the separate EM waves radiated from the individual sources comprising the Yagi (or any other kind of directional array). RF |
In article bkE1e.110371$Ze3.24514@attbi_s51,
wrote: Right..... so what creats it, this "squeezing" that you talk about and from where does this "squeezing force come from in an "appropiate"array? There is no "force" in the usual sense of pressure on a physical balloon. That's because the "balloon" is not an object. It's simply a mathematical abstraction - a drawing of lines of equal RF power levels on a graph having a certain set of axes. To think that there's a specific 'force' squeezing the 'balloon', is somewhat like trying to travel from east to west by pulling yourself along the lines of longitude. Hey, the lines are there on the globe, they're there on the map, why can't I just walk along the lines? There's nothing "pushing" on the "boundaries" of the lobe, because there is no lobe in the physical sense. It's not a separate and distinct object. To understand why there's a change in the shape that we visualize (and that's all that the lobe shape is - a selective visualization), we have to step down to the underlying phenomenon and see what's changing. Because the conventional "lobe shape" is simply the result of plotting the strength of the RF energy coming from the antenna, the answer is simple. The lobe's shape is changing, because the amount of RF energy being transmitted in the different directions is changing... .... and *that* happens because the phase-and-location details of the various radiators (and re-radiators) in the antenna system are being altered. Different radiator and re-radiator locations, intensities, and phases... .... cause different "sum of vectors" results ... .... which changes the strength of the RF received ... .... which, when we walk around and try to locate the points having equal RF field strength, means that we walk along different paths ... .... which means that we draw the lines on the map in different places ... .... which means that the "lobes" now have a different shape. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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