| Page 1 of 2 | 1 | 2 |
|
|
SUPER J-POLE BEATS YAGI BY 1 dB
Hi,
Well, our Super J-pole: http://users.marktwain.net/aschmitz/...jpolecalc.html Is beating our Yagi in ALL directions, even in the forward lobe! Here is the theoretical H-plane plot of our Yagi: http://www.drslick.org/Temp1/yagiplot.jpg And a photo: http://www.drslick.org/Temp1/yagi929.jpg So if you assume the theoretical 2.5 dBi of a regular J-pole, then the Super J-pole has about 3 dB over that, so about 5.5 dBi all around. So we have about 4.52 dB in the forward lobe of our Yagi, so even there, we beat it by about 1 dB with the Super J-pole. That's like 238 watts versus 300 watts. It's even worse in the back lobe, where it's a -12 dB difference. That's like 19 watts versus 300 watts! It's only a theoretical yagi optimization plot, and i don't think it sounded like 19 versus 300 watts in the back, but it's a BIG difference, even in the areas that were already strong....almost full quieting. And yeah, we didn't really optimize the yagi for a strong, narrow lobe...it was designed for a 180 degree pattern, so the gain ain't great, but you still have some control over directivity. It's still not really a fair comparison. At any rate, if you need an omnidirectional, i highly recommend the Super J-pole! Here's another site if you are interested: http://www.geocities.com/n2uhc/jpole.html Questions and comments appreciated! Dr. Slick |
wrote
Well, our Super J-pole: Is beating our Yagi in ALL directions, even in the forward lobe! ____________________ Please explain how this design is directional. It should be essentially omnidirectional in the horizontal plane, unless it is side-mounted on a vertical metallic support, or has some other form of v-pol parasitic radiator near it. And in that case, it's not your j-pole alone that is "beating" a yagi, but the combination of your j-pole and its mounting environment. RF Visit http://rfry.org for FM transmission system papers. |
Dr. Slick,
It's fun to play with numbers, isn't it? you can make them say almost anything you want if you "assume" just one or two small points... 'Doc |
Hi, Well, our Super J-pole: http://users.marktwain.net/aschmitz/...jpolecalc.html Is beating our Yagi in ALL directions, even in the forward lobe! much snippage Must be one horridly poor yagi. Most 3 eleemnt designs are better than 8dBi and with a little effort an be 1 db better than that. Most Stacked Jpoles do not perform as well as predicted on paper with the upper added dipole contributing .5 to 1 db less than guessed at. Allison |
Allison wrote: much snippage Must be one horridly poor yagi. Most 3 eleemnt designs are better than 8dBi and with a little effort an be 1 db better than that. Most Stacked Jpoles do not perform as well as predicted on paper with the upper added dipole contributing .5 to 1 db less than guessed at. Allison Not to mention, also, that that yagi is tuned to 92.9 MHz (in the FM BROADCAST BAND)! --Jim NN7K |
On Sun, 06 Feb 2005 17:56:25 GMT, Jim - NN7K
wrote: Not to mention, also, that that yagi is tuned to 92.9 MHz (in the FM BROADCAST BAND)! --Jim NN7K Yes, that will really help. ;-p I'd add the picture I looked at appeared to have a metal mast mounting a vertical oriented beam and my experience at VHF and up is that hurts performance. All the years of building and testing says, extroadinary claims are simply that. It's interesting to check the CSVHF range tests of antennas on real antennas seperate from their sometimes fanciful claims. Allison KB1GMX |
|
wrote: Hi, Well, our Super J-pole: http://users.marktwain.net/aschmitz/...jpolecalc.html Is beating our Yagi in ALL directions, even in the forward lobe! much snippage Must be one horridly poor yagi. Most 3 eleemnt designs are better than 8dBi and with a little effort an be 1 db better than that. 8 dBi WITH a 180 degree pattern? And WITH A F/B ratio that doesn't exceed 11 dB or so? I don't think so. Do you have a design you can show us? Most Stacked Jpoles do not perform as well as predicted on paper with the upper added dipole contributing .5 to 1 db less than guessed at. Allison How did you come to this conclusion? What sort of field strength equipment did you use? Again, i would be the first to say that reality doesn't fit the math model, sometimes not at all. But is this case, you can really hear the difference. Slick Slick |
On 6 Feb 2005 05:42:42 -0800, wrote:
Here is the theoretical H-plane plot of our Yagi: http://www.drslick.org/Temp1/yagiplot.jpg And a photo: http://www.drslick.org/Temp1/yagi929.jpg After looking at the picture and the plot I fired up yo and the only way I could get that low a gain was to seriously mess up the antenna. The end effect was a 2 element yagi witha spurious useless element. This is further confirmed by the picture. It appears the rightmost element is the fed element (very strange for a three element design) and the proportions suggest a reflector close to the driven and longer. The third element (the leftmost) would be spurious as it's behind the reflector and far away. Please explain that yagi, it's strange. Allison |
wrote: Must be one horridly poor yagi. Most 3 eleemnt designs are better than 8dBi and with a little effort an be 1 db better than that. 8 dBi WITH a 180 degree pattern? And WITH A F/B ratio that doesn't exceed 11 dB or so? I don't think so. On 6 Feb 2005 14:10:37 -0800, wrote: How did you come to this conclusion? What sort of field strength equipment did you use? Simple testing with a stable RF power source and a sensitive field strength meter in a very large yard. It's not hard to determine a 1Db difference and a 3db one is easy. What brand and model field strength meter do you have? what sort of receive antenna did you use? How did you do the conversion from uV/meter to ERP? The other is a colinear design the second element cannot contribute 3db unless the first didn''t radiate any energy. Thats rarely the case. ????? How can the first not radiate any engergy? To get the gain you claim try a 8 or more segment colinear and note that would be about 18-20ft tall for a 2m antenna. According to most of what i have read, every doubling of the sections give approximately 3 dB additional gain. Again, i would be the first to say that reality doesn't fit the math model, sometimes not at all. But is this case, you can really hear the difference. Usually the math model is reality if its a real model. Often it's not. manyy of the simple shorthand models are far for accurate or complete. I used a program called Yagi Optimizer. It should be close, it's not like we are modeling active devices like FETs and such! Also in some locations there are third order factors not considered. For a real model (NEC based) the stacked Jpole is 2.3-2.4dbi better than a plain J and ends up at about 7.4Dbi. [In real terms that's only about 2.4 DB better than a vertical dipole which a basic Jpole is.] Incorrect. A stacked J-pole cannot be 2.4 dBi better than a plain J. It can only be 2.4 dB better. Anyways, You think a plain J-pole is 5 dBi? Incorrect. The Jpole in this case is easier to evaluate because if the SWR is poor it's definately not working well and a lot of things have to be correct or the SWR will be poor. For example, it may work better because its nearly 60inches taller and at a given location that could be the majik. Never ignore height as a significant factor at VHF. Obviously. They are at about the same height, considering the additional height of the Super J. They work well to the designs limit if built carefully. I like them for the ease of assembly of a rugged design that's reproduceable. I would say that at VHF, a Super J is a bit heavy and big, but the additional ERP is worth it. Slick |
wrote: On 6 Feb 2005 05:42:42 -0800, wrote: Here is the theoretical H-plane plot of our Yagi: http://www.drslick.org/Temp1/yagiplot.jpg And a photo: http://www.drslick.org/Temp1/yagi929.jpg After looking at the picture and the plot I fired up yo and the only way I could get that low a gain was to seriously mess up the antenna. The end effect was a 2 element yagi witha spurious useless element. This is further confirmed by the picture. It appears the rightmost element is the fed element (very strange for a three element design) and the proportions suggest a reflector close to the driven and longer. The third element (the leftmost) would be spurious as it's behind the reflector and far away. Please explain that yagi, it's strange. It was an unusual use of the YO program, in that we used two reflectors and NO directors, to get the shape we wanted. We actually couldn't use the optimizer, because it would actually try to narrow the beam too much. Remember that you must keep the pattern about 180 degrees, and the F/B ratio should be no more than about 11 dB. If you could come up with something with a higher overall dBi, i'd like to know, but i doubt it. Slick |
|
You can get just about any "theoretical" result if your theory is
adequately flawed. That's obviously the case here. Roy Lewallen, W7EL |
|
Howard wrote: On 6 Feb 2005 18:10:11 -0800, wrote: snip It was an unusual use of the YO program, in that we used two reflectors and NO directors, to get the shape we wanted. We actually couldn't use the optimizer, because it would actually try to narrow the beam too much. Remember that you must keep the pattern about 180 degrees, and the F/B ratio should be no more than about 11 dB. Slick Slick, Could you explain the use of two reflectors? I've heard that if you are building a two element yagi it's best to use a radiator and reflector but haven't really learned anything about using more than one reflector. Have seen antennas that use 3 reflectors, but they were mounted perpendicular to the plane of the elements and there were several director elements - if memory serves me it was Cushcraft that did that. Haven't seen them added behind the first reflector and am curious as to what characteristic of the antenna's performance it is meant to enhance. For this particular design, it was required in that we needed something with a 180 degree pattern, and not to much F/B ratio. I can't tell you much more other than we had to manually tweak the variables to get a decent result...we couldn't use the program's optimizer, it would have made the forward lobe too small. So what ends up happening in the program, is that you end up using two directors, but in the H-plane the lobe goes to the rear (see link). So in essence, you flip the whole deal around, and your two directors are actually reflectors. Interesting, eh? Slick |
wrote: On 6 Feb 2005 18:10:11 -0800, wrote: Remember that you must keep the pattern about 180 degrees, and the F/B ratio should be no more than about 11 dB. If you could come up with something with a higher overall dBi, i'd like to know, but i doubt it. Want a list... MOXON ( two) Batwing Asymetric array of dipoles Phased array of vertical monopoles Dipole against a plane relector 2 element Jpole yagi Remember that you must keep the pattern about 180 degrees, and the F/B ratio should be no more than about 11 dB. I really doubt if you will supply a link... Slick |
Roy Lewallen wrote: You can get just about any "theoretical" result if your theory is adequately flawed. That's obviously the case here. Yagi optimizer programs with genetic algorithms are well understood and are quite accurate. Come listen for yourself... Slick |
|
You are lucky to see the gain you have, considering the lack
of decoupling...Or at least in that pix....Also, thats a pretty lame yagi, so like you say, not really a fair test... My 3 el vertical yagi would eat that j pole for lunch, being it has about 9.4 dbi gain...Or about 7.3 dbd.... The J poles are ok I suppose, and are good for people with copper and torches...But they would be even better with some additional decoupling...I bet they still have trouble matching the old isopole that was made by AEA...That antenna was well decoupled. Looked like a ballistic missile, but it was hard to beat as far as performance. It was generally the benchmark most other dual 5/8 designs were judged by. :/ MK |
Richard Clark wrote: On 6 Feb 2005 21:22:19 -0800, wrote: Come listen for yourself... Possibly one of the worst methods of absolute measurement. Never said it was an absolute measurement, don't be ridiculous! But, ultimately, that's all we really want, right? Better listenability. I've already said i don't believe the 19 to 300 watt F/B calculations, but bottom line, is: It's a MUCH clearer and cleaner signal ALL around. However, your claim ignores that volume is invariant to signal strength by design at the limiting stage in any FM receiver. ????? Volume has nothing to do with this! You could throw a dead carrier and still have an idea of how close to full quieting you are.... Slick |
|
|
On 6 Feb 2005 21:19:41 -0800, wrote:
Asymetric array of dipoles Phased array of vertical monopoles Remember that you must keep the pattern about 180 degrees, and the F/B ratio should be no more than about 11 dB. I really doubt if you will supply a link... www.andrews.com many of those commercial designs could be duplicated and there are a few repeater builder sites that do exactly that. Allison |
|
Dr. Slick wrote;
"Well, our super J-pole is bearing our yagi in ALL directions, even in the forward lobe." It`s possible. This thread pits a "Super J-Pole" with 6 dBd gain against a "Yagi-Uda" with 2.85 to 17.85 dBd gain (5 to 20 dBi), depending on construction. So, it could be true for some 2-element Yagi or it could untrue for a Yagi with 3 or more elements. A 3-element Yagi may give about 5 or 6 dBd gain. The "ARRL Antenna Book" gives the details. In my 19th edition, the Super J-Pole is asid to give 6 dB gain over a 1/4-wave whip on page 16-27. The whip with a perfect reflection (a ground-plane antenna) is said on page 13-10 to be equivalent to a 1/2-wave dipole in free-space: "---the image of a vertical antenna is in phase with the vertical radiator". The whip with the perfect reflection is thus identical to a 1/2-wave in free-space in performance. Gain of the ground-plane is 0 dBd or +2.15 dBi. Best regards, Richard Harrison, KB5WZI |
|
wrote: wrote: You are lucky to see the gain you have, considering the lack of decoupling...Or at least in that pix....Also, thats a pretty lame yagi, so like you say, not really a fair test... What lack of decoupling? It's got the coax inductive choke on the input, 4 turns of 4" diameter. I don't recall seeing that in the picture. But even still, I wonder if it's as good as a full 1/4 wave decoupling cone, or radials...Much better than nothing though... If you would read my posts more carefully, you would be aware that the reason for the low dBi is that the lobe is 180 degrees, and F/B ratio limited to around 11dB. I only read the first post... My 3 el vertical yagi would eat that j pole for lunch, being it has about 9.4 dbi gain...Or about 7.3 dbd.... So what, the Super J-pole in omnidirectional, so that's not saying much for a Yagi. We could have easily designed it with more gain, but the frontal lobe would have been way narrower. Yea, but if you are going to post a CAPS thread claiming a j pole beats a yagi by 1 db, most are going to assume the yagi isn't crippled up... It's sort of Frackish.....:/ How broad or narrow is the front lobe of your yagi? How many degrees? Much smaller than 180 no doubt. No doubt... I'm not trying to rain on your parade, and surely applaud you for building these, I just don't quite get the purpose of such a comparison...Everyone already knows what the gains of the antennas are.. Well, except for the de-tuned yagi... I mean, is it really a surprise a collinear might beat a yagi with about half the normal gain of the NBS 3 el? I'll bow out...I really have no problem with the antenna, etc...I just wanted to stir it, being you have this frackish thread title...:) MK |
Richard Harrison wrote: Dr. Slick wrote; "Well, our super J-pole is bearing our yagi in ALL directions, even in the forward lobe." It`s possible. it's true. But this doesn't mean that it's going to beat ALL Yagis, which is what some people have thought this thread was all about. Just THIS 180 degree Yagi, with 11 dB F/B ratio. This thread pits a "Super J-Pole" with 6 dBd gain against a "Yagi-Uda" with 2.85 to 17.85 dBd gain (5 to 20 dBi), depending on construction. 6 dBd would be about 8.15 dBi, which is not the case here. The Super J-pole is 5.5 dBi or 3.35 dBd. This particular Yagi is about 4.5 dBi in the front lobe, which was a compromise to get the 180 degree pattern (and 11dB F/B). The "ARRL Antenna Book" gives the details. In my 19th edition, the Super J-Pole is asid to give 6 dB gain over a 1/4-wave whip on page 16-27. Really? If we say the 1/4 wave is 2.15 dBi, then the Super J is 3.35dBd, omni. So i'm not sure where they got these numbers, or if we are talking about the same thing. Slick |
|
Richard Clark wrote: On 7 Feb 2005 01:44:10 -0800, wrote: Come listen for yourself... ????? Volume has nothing to do with this! You could throw a dead carrier and still have an idea of how close to full quieting you are.... Obviously your hearing perception exceeds the characteristics of a larger part of mankind. This makes any claims for someone ELSE to listen to the difference even more problematic. Hearing is the poorest measure second only to "seeing" for one self. Leave this type of testimonial for the Sunday services. A good receiver actually gives you TONS of information. You can hear overmodulation, sideband "splatter" to adjacent channels, spurious oscillations on other channels, dead carrier hum in your signal, the overall intelligibility of your signal and the audio frequency response (roughly). No field strength meter can tell you this information! Bottom line is, human hearing is the ultimate destination. It can be more qualitative that quantity. Slick |
Richard Clark wrote: It takes no great effort to duplicate your rather sloppy presentation to offer many better, smaller designs that eclipse your speculated results. Through selective disclosure, choosing a weak competitor, leaning on abused references, and one thumb on the scale, anyone can inflate performance claims to satisfy a customer (or attract more). I challenge anyone else to use whatever Yagi Optimizers they have to come up with a 3 element design (to keep the size down) with a 180 degree front lobe, and with an 11dB F/B ratio, that has a greater than 4.5 dBi in the front lobe. Plot the H-plane of your simulation too. Slick |
Richard Clark wrote: It takes no great effort to duplicate your rather sloppy presentation to offer many better, smaller designs that eclipse your speculated results. Through selective disclosure, choosing a weak competitor, leaning on abused references, and one thumb on the scale, anyone can inflate performance claims to satisfy a customer (or attract more). I challenge anyone else to use whatever Yagi Optimizers they have to come up with a 3 element design (to keep the size down) with a 180 degree front lobe, and with an 11dB F/B ratio, that has a greater than 4.5 dBi in the front lobe. Plot the H-plane of your simulation too. Slick |
wrote: On 6 Feb 2005 21:19:41 -0800, wrote: Asymetric array of dipoles Phased array of vertical monopoles Remember that you must keep the pattern about 180 degrees, and the F/B ratio should be no more than about 11 dB. I really doubt if you will supply a link... www.andrews.com many of those commercial designs could be duplicated and there are a few repeater builder sites that do exactly that. ???? That's a long distance telephone service site... Slick |
|
On 7 Feb 2005 14:06:03 -0800, wrote:
???? That's a long distance telephone service site... http://www.andrew.com/products/antennas/ I added an "s" by error. Sheesh. I figured you'd know their products as they are well known in broadcast and VHF/UHF ham circles. However that was only one example. There is also CellOne who also do antenna products and other useful items. Of course there are only a few hundred (or more) companies making antennas many of which are suited for a cartiod pattern work. Allison |
|
On Mon, 07 Feb 2005 16:54:15 -0700, Wes Stewart
wrote: I'll admit that I've not followed this thread and don't intend to punch any tar babies. But I must ask; what the hell is a "180 degree" front lobe? What he wants is a cartoid pattern, That is a "D" shaped roughly pattern that's all from and not so much back. The easy way to do that is a good colinear and mount it near the flat face of a tower (usually less than 1/4 wave away) . The net effect is slightly increased gain away from the tower and a mild null on the other side of the tower. Most of the time this is not desired but, there are valid cases where you don't wish to waste power behind you. The most common is coastal commercial broadcat radio and TV. Allison |
Richard Clark wrote: I challenge anyone else to use whatever Yagi Optimizers they have to come up with a 3 element design (to keep the size down) with a 180 degree front lobe, and with an 11dB F/B ratio, that has a greater than 4.5 dBi in the front lobe. Plot the H-plane of your simulation too. This is a hollow challenge in that such designs are already freely available through EZNEC. Again, the thumb on the scale scenario offers easy ways to pencil whip these numbers above, given they are only partial disclosures tricked up for the benefit of marketing to suckers otherwise inflating their egos as "pirates." "Hollow challenge"? I don't think you have the facilities to do this....you're field seems to be more along the lines of a bad used car saleman! If someone can come up with a 3 element yagi (we wanted to keep the size down), with a 180 degree front lobe, and about 11 dB F/B ratio, that has a better than 4.5 dBi in the front lobe, i'd like to see it. Use EZNEC or whatever simulator you have, and make an H-plane plot... i'd like to see that. To that band of would-be broadcasters, it is patently obvious that our salesman here has already admitted that no Yagi Optimizer was fully engaged to optimize the "3 element design." (And there is an absolute I ain't trying to sell anything here, Dip****. I'm just informing other people of my results, take it or leave it. I will leave it to the more industrious customers or would-be customers to simply download the free version of EZNEC and confirm that this clod-hopping 3 element design above would be bettered by a 2 element one. This has already been offered by Allison to no noticeable intelligent response. I will leave it to those who glom onto vacuous marketing with the fatal attraction of a moth for a flame to skip this exercise. The only vacuum is in your head, Richard. Some things never change.... Slick |
wrote: On Mon, 07 Feb 2005 16:54:15 -0700, Wes Stewart wrote: I'll admit that I've not followed this thread and don't intend to punch any tar babies. But I must ask; what the hell is a "180 degree" front lobe? What he wants is a cartoid pattern, That is a "D" shaped roughly pattern that's all from and not so much back. Indeed. Basically like what i showed you: http://www.drslick.org/Temp1/yagiplot.jpg This "D" shape is suitable for when the broadcaster wants some directivity, but will NOT be on the extreme edge of the service area or town. It's obviously not suitable if you are in the center of town, unless you wish to focus more ERP in the direction of some taller buildings, for example. The easy way to do that is a good colinear and mount it near the flat face of a tower (usually less than 1/4 wave away) . The net effect is slightly increased gain away from the tower and a mild null on the other side of the tower. Most of the time this is not desired but, there are valid cases where you don't wish to waste power behind you. The most common is coastal commercial broadcat radio and TV. Do you have a specific design on hand? Slick |
| All times are GMT +1. The time now is 09:14 AM. |
|
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com