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Gain per unit length of boom
My ARRL books go back a decade or more
and the graph showing gain per boom length has several curves based on different measurements e.t.c. Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height? Art |
Hi Art,
While this was the common theory many years ago, there other ways to get gain from an antenna other than boom length and number of elements. ie On 2m we are able to get 11.2 dBd on a 45inch boom with 3 elements stacked 2 wide. Yes, this is range tested see results at http://www.csvhfs.org/ant/CSANT04.HTML 73, Guenther VE3CVS www.degendesigns.com " wrote in message news:xOzcd.263953$D%.243703@attbi_s51... My ARRL books go back a decade or more and the graph showing gain per boom length has several curves based on different measurements e.t.c. Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height? Art |
" wrote in message news:xOzcd.263953$D%.243703@attbi_s51... My ARRL books go back a decade or more and the graph showing gain per boom length has several curves based on different measurements e.t.c. Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height? Art They probably have been done but there will not be much difference between them and the ARRL graphs. Its been long known how to calculate antenna gain, computers just take the teadous labor out of it. |
wrote:
My ARRL books go back a decade or more and the graph showing gain per boom length has several curves based on different measurements e.t.c. Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height? There is a table of data calculated by VE7BQH for a large number of different yagis, at: http://www.ifwtech.co.uk/g3sek/diy-yagi/ve7bqh.htm (These are not calculated by NEC, but by another very adequate program.) You can draw your own curve from the data in the L(WL) and Gain columns. Since all the data have been calculated by the same person, starting from the antenna's mechanical dimensions, and using the same program, this removes a lot of variables. You will see a broad trend of increasing gain with boom length, but there is still a lot of scatter due to variations between different designs. Also bear in mind that gain isn't everything, and a long yagi that has been maximized for gain may be a poor antenna in other ways, such as sidelobe levels, ease of pointing, sensitivity to water on the elements, ease of matching etc. Drawing gain curves is a fun activity... but don't try to read too much into them. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
On Mon, 18 Oct 2004 18:26:35 +0100, "Ian White, G3SEK"
wrote: Drawing gain curves is a fun activity... but don't try to read too much into them. Hi Ian, While at a lecture, the lecturer got a question from the audience that was premised "don't believe everything you think." 73's Richard Clark, KB7QHC |
In any case the curve was normalized across several factors and was to be used
as a guideline to substantiate that the longer the boom the higher the gain. Other factors like F/B, F/S, bandwidth, losses, etc. were not addressed. |
What brought this to my attention was Moxon who advocated 2 element beams
(lightnes translates to greater heights) so I modeled a 20 meter beam on a 7 foot boom and obtained 12dbi max for the band (ala 2:1) but one can get 13dbi if you drop the impedance from 50 to 12 ohms. This then raised the question would a transformer cancel the increased gain. On the F/B question it was of real interest to me to compare the first frontal lobe gain to the second lobe at the rear on the basis that propagation rules the second rear lobe as the most important . But all of this comes to a grinding halt if there is not a datum curve to which one can compare ones modeling when using more than two elements on such a short boom.. I agree that one has to model to one's specific needs and as can be seen from the ARRL curves using short booms max gain varies tremendously.depending on curves chosen none of which are the cat's whiskers such as NEC based curve. Art "Ian White, G3SEK" wrote in message ... wrote: My ARRL books go back a decade or more and the graph showing gain per boom length has several curves based on different measurements e.t.c. Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height? There is a table of data calculated by VE7BQH for a large number of different yagis, at: http://www.ifwtech.co.uk/g3sek/diy-yagi/ve7bqh.htm (These are not calculated by NEC, but by another very adequate program.) You can draw your own curve from the data in the L(WL) and Gain columns. Since all the data have been calculated by the same person, starting from the antenna's mechanical dimensions, and using the same program, this removes a lot of variables. You will see a broad trend of increasing gain with boom length, but there is still a lot of scatter due to variations between different designs. Also bear in mind that gain isn't everything, and a long yagi that has been maximized for gain may be a poor antenna in other ways, such as sidelobe levels, ease of pointing, sensitivity to water on the elements, ease of matching etc. Drawing gain curves is a fun activity... but don't try to read too much into them. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Jimmy,
I did not want to choose a curve that matches my modelling which you can when presented with three different curves all of which are formulated at different times by different people. I would have thought that the advent of NEC would render these curves redundant ! Art "Jimmie" wrote in message . com... " wrote in message news:xOzcd.263953$D%.243703@attbi_s51... My ARRL books go back a decade or more and the graph showing gain per boom length has several curves based on different measurements e.t.c. Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height? Art They probably have been done but there will not be much difference between them and the ARRL graphs. Its been long known how to calculate antenna gain, computers just take the teadous labor out of it. |
Art Unwin wrote:
"Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height?" I don`t know, but I`ve seen Yagi-Uda gain versus boomlength charts. Before relying on such charts, it may be worthwhile to read "The Yagi-Uda Story" on page 246 of the 3rd edition of Kraus` "Antennas". Also, the solution to a Deutsche Welle Short Wave Antenna problem on page 703 is given on page 705: "the gain of a single 1/2-wave dipole is 2.15 dBi and of 2 collinear in=phase 1/2-wave dipoles is 3.8 dBi. The array of 8 such collinear dipoles adds 3+3+3=9 dB. The reflector screen adds 3 more and the ground bounce another 6 dB for a total gain of 3.8+9+3+6=21.8 dBi or a directivity of 151 approx." The solved problem is worth the price of the book as a reality check. Best regards, Richard Harrison, KB5WZI |
"Richard Harrison" wrote in message ... Art Unwin wrote: "Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height?" I don`t know, Neither do I thus the question but I`ve seen Yagi-Uda gain versus boomlength charts. So have I but not based on NEC Before relying on such charts, it may be worthwhile to read "The Yagi-Uda Story" on page 246 of the 3rd edition of Kraus` "Antennas". Also, the solution to a Deutsche Welle Short Wave Antenna problem on page 703 is given on page 705: "the gain of a single 1/2-wave dipole is 2.15 dBi and of 2 collinear in=phase 1/2-wave dipoles is 3.8 dBi. The array of 8 such collinear dipoles adds 3+3+3=9 dB. The reflector screen adds 3 more and the ground bounce another 6 dB for a total gain of 3.8+9+3+6=21.8 dBi or a directivity of 151 approx." The above extract is lost on me as I was looking for maximum gain per unit boom length based on NEC without regard to number of elements required to attain that gain. Thus increases or decreases from critical coupling can be ascertained.. Art The solved problem is worth the price of the book as a reality check. Best regards, Richard Harrison, KB5WZI |
wrote:
The above extract is lost on me as I was looking for maximum gain per unit boom length based on NEC without regard to number of elements required to attain that gain. Thus increases or decreases from critical coupling can be ascertained.. You misunderstand what this curve is telling you. There is a general law that gain is proportional to "aperture area". For something like a dish, "aperture area" is the frontal area of the dish itself (multiplied by an efficiency factor 1). For long yagis, "aperture area" is roughly proportional to boom length. This concept has nothing whatever to do with NEC! But it is the absolute bedrock of all antenna engineering. What you really need right now is to read the first few chapters of Kraus... and understand these most basic principles. NEC calculations will not tell you anything about this. NEC is simply a tool to calculate what the gain of a particular antenna will be (or can be, if you build it as modeled). -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
On Sun, 17 Oct 2004 17:01:22 -0400, "G&R" makes a claim and opens
himself up to skewering: |Hi Art, | |While this was the common theory many years ago, there other ways to get |gain from an antenna other than boom length and number of elements. | |ie On 2m we are able to get 11.2 dBd on a 45inch boom with 3 elements |stacked 2 wide. Yes, this is range tested see results at |http://www.csvhfs.org/ant/CSANT04.HTML Uh Oh! The measured data show 11.2 dBd, the advertising shows 13.97 dBd. I thought maybe I went to the Raibeam site by mistake but no, I went he http://www.degendesigns.com/StackedVwave.htm I love that precision BTW. I've done a fair amount of antenna range testing using HP 8510s for measurement receivers and I've never been able to establish gain within 1/100 dB. But you can do it with a ham receiver and "subjective analysis". Congratulations. Since you're using two 45" booms spaced 58" apart, I would argue that you should compare your design to a 148" boom Yagi and see what happens. How about posting your dimensions so we can see what modeling says about them. One further note: The Dataq DI-194 mentioned at: http://www.degendesigns.com/Downloads.htm WILL NOT work with all computers. This device is powered by the serial port and my Toshiba laptops will not drive it. |
Ian, All the points you made are very good especialy when you
stated that gain is ROUGHLY proportional to boom length and then go on to mention "aperture' The question I asked was very specific but not personal like the presidential debates this newsgroup uses the question as the basis for what they want to say. The reason I asked the specific question was to obtain a datum line for antennas relative to gain and a well used term of boom length. NEC programs can provide this basic if the latest revision is used and the program is all encombassing.( Many are not) Mention coupling and some experts go nuts but NEC is all encompassing provides definitive answers that remove measurement errors presently shown and cuts through a lot of garbage. All encompassing is all important in that sufficient segments are available together with the use of variuable dimensions as this gets away from use of methods to get around inadequacy of a particular program. You mention "aperture" but I don.t believe it changes any results given by NEC. Others ridicule the use of the term critical coupling yet NEC shows that element currents can be changed via coupling and it is current placement that we are interested in, so why so much redicule/ The same goes for element diameters NEC provides the correct construction for elements which is another important variable for gain So in other words, a NEC curve would deflect most arguments and personal agenders from the beginning and if one supplies actual measurement that are contrary to those of NEC then we have a basis for truly specific debate. As somebody pointed out, one slanging match has been going on for more than eight years regarding the use of critical coupling, another is the subject of coils, actual measurement versus a manipulated program calculation. I pretty much have had it with excuses regarding inadequecies of some programs, If NEC is a really viable tool; then let us use it as a datum by using a NEC program that is all encompassing to judge measured claims against so hat true specific can be judged. It is possible after all that even NEC may obtain several more revisions over time because of actual measurement which can only aid all in the understanding of antennas and the removal of old wifes tales and private agendas that evolved prior to NEC. Is it auguments that we yearn for on this newsgroup or true resolution of ideas? Art "Ian White, G3SEK" wrote in message ... wrote: I did not want to choose a curve that matches my modelling which you can when presented with three different curves all of which are formulated at different times by different people. I would have thought that the advent of NEC would render these curves redundant ! The plot of many individual yagis does confirm the general idea of gain being roughly proportional to boom length, and that is a very important thing to understand. clip |
Wes,
You make the point quite well that I was trying to make before I read your post (written simultainiously) and at the present time NEC is seen as judge absolute. Yes there are many ways to increase gain but you cannot use a shackled NEC program to authenticate the results and we often use such as a crutch. On the subject of boom length I was basing things on a single boom length where number, position and physical atributes of additionion elements are brought into play to overcome program idequacies and provide correction of assigned dimensions to achieve maximum gain.(Is this to much to ask now that we have the NEC tool/) To often the accusation comes up that computor input was incorrect or not enough segments provided e.t.c. and a datum curve would prove a valuable tool, not only to those that use computor modelling but also to experimentors who seek real world answers and possibly challenge the authenticicity of either methods Thanks for the links,will read them later, have to get a floooooo shot now Art "Wes Stewart" wrote in message ... On Sun, 17 Oct 2004 17:01:22 -0400, "G&R" makes a claim and opens himself up to skewering: |Hi Art, | |While this was the common theory many years ago, there other ways to get |gain from an antenna other than boom length and number of elements. | |ie On 2m we are able to get 11.2 dBd on a 45inch boom with 3 elements |stacked 2 wide. Yes, this is range tested see results at |http://www.csvhfs.org/ant/CSANT04.HTML Uh Oh! The measured data show 11.2 dBd, the advertising shows 13.97 dBd. I thought maybe I went to the Raibeam site by mistake but no, I went he http://www.degendesigns.com/StackedVwave.htm I love that precision BTW. I've done a fair amount of antenna range testing using HP 8510s for measurement receivers and I've never been able to establish gain within 1/100 dB. But you can do it with a ham receiver and "subjective analysis". Congratulations. Since you're using two 45" booms spaced 58" apart, I would argue that you should compare your design to a 148" boom Yagi and see what happens. How about posting your dimensions so we can see what modeling says about them. One further note: The Dataq DI-194 mentioned at: http://www.degendesigns.com/Downloads.htm WILL NOT work with all computers. This device is powered by the serial port and my Toshiba laptops will not drive it. |
Hi Wes,
Yes I am aware of the difference between the advertising on the site and the range results. As you are aware antennas do not have even gain across the entire band. We have designed the antenna to cover the entire 2m band and as a result do see a variation in the perfromance across the band, hence max gain. And before you cut down my comments, the precision on the results are from the softare and we are in the process of redesigning the format to more accurately reflect our actual results both modelled and actual. Unfortunately our business is antennas and web design. The results posted on the CSVHF society are valid as the antenna was tested with a gain of 11.2dBd at 144.18MHz Horiz Polarization. Design Freq is 146.0MHz. We are in the business of designing and selling antennas not developing antennas and giving them away for free. However, if your serious about the data for the antenna contact me directly so that we can discuss the details (email listed below). As to the DATAQ, well I have no answer for that one, as we don't build it or sell it. Our software is designed to with run it. Strange though, my Toshiba does and so does my SONY through a USB to SERIAL converter. One final point, the purpose of the posting was that identify that an antenna does not always need boom length and elements for gain and that there are other ways to achieve this. Respectfully, Guenther VE3CVS www.degendesigns.com "Wes Stewart" wrote in message ... On Sun, 17 Oct 2004 17:01:22 -0400, "G&R" makes a claim and opens himself up to skewering: |Hi Art, | |While this was the common theory many years ago, there other ways to get |gain from an antenna other than boom length and number of elements. | |ie On 2m we are able to get 11.2 dBd on a 45inch boom with 3 elements |stacked 2 wide. Yes, this is range tested see results at |http://www.csvhfs.org/ant/CSANT04.HTML Uh Oh! The measured data show 11.2 dBd, the advertising shows 13.97 dBd. I thought maybe I went to the Raibeam site by mistake but no, I went he http://www.degendesigns.com/StackedVwave.htm I love that precision BTW. I've done a fair amount of antenna range testing using HP 8510s for measurement receivers and I've never been able to establish gain within 1/100 dB. But you can do it with a ham receiver and "subjective analysis". Congratulations. Since you're using two 45" booms spaced 58" apart, I would argue that you should compare your design to a 148" boom Yagi and see what happens. How about posting your dimensions so we can see what modeling says about them. One further note: The Dataq DI-194 mentioned at: http://www.degendesigns.com/Downloads.htm WILL NOT work with all computers. This device is powered by the serial port and my Toshiba laptops will not drive it. |
A graph from NEC data is going to be pretty much like a graph from the ARRL
books. By putting the data in a graphic form your are placing the same limits on the data as they had to in the ARRL books. The ARRL graphs give you a pretty good idea of what goes on when you change element spacing, number of elements and so on. What they dont do is alllow you to perform optimization like the NEC programs . Graphing a NEC program output would be the same as going back to the time all you had was the graphs to go by unless you are willing to do all the calculations on your slide rule or calculator. What I am saying is that you already have this data. No point in reinventing the wheel.Unless you think yiou can get a patent on it. " wrote in message news:65Zcd.150611$He1.116446@attbi_s01... Jimmy, I did not want to choose a curve that matches my modelling which you can when presented with three different curves all of which are formulated at different times by different people. I would have thought that the advent of NEC would render these curves redundant ! Art "Jimmie" wrote in message . com... " wrote in message news:xOzcd.263953$D%.243703@attbi_s51... My ARRL books go back a decade or more and the graph showing gain per boom length has several curves based on different measurements e.t.c. Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height? Art They probably have been done but there will not be much difference between them and the ARRL graphs. Its been long known how to calculate antenna gain, computers just take the teadous labor out of it. |
" wrote in message news:t4bdd.277152$D%.236528@attbi_s51... Ian, All the points you made are very good especialy when you stated that gain is ROUGHLY proportional to boom length and then go on to mention "aperture' The question I asked was very specific but not personal like the presidential debates this newsgroup uses the question as the basis for what they want to say. The reason I asked the specific question was to obtain a datum line for antennas relative to gain and a well used term of boom length. NEC programs can provide this basic if the latest revision is used and the program is all encombassing.( Many are not) Mention coupling and some experts go nuts but NEC is all encompassing provides definitive answers that remove measurement errors presently shown and cuts through a lot of garbage. All encompassing is all important in that sufficient segments are available together with the use of variuable dimensions as this gets away from use of methods to get around inadequacy of a particular program. You mention "aperture" but I don.t believe it changes any results given by NEC. Others ridicule the use of the term critical coupling yet NEC shows that element currents can be changed via coupling and it is current placement that we are interested in, so why so much redicule/ The same goes for element diameters NEC provides the correct construction for elements which is another important variable for gain So in other words, a NEC curve would deflect most arguments and personal agenders from the beginning and if one supplies actual measurement that are contrary to those of NEC then we have a basis for truly specific debate. As somebody pointed out, one slanging match has been going on for more than eight years regarding the use of critical coupling, another is the subject of coils, actual measurement versus a manipulated program calculation. I pretty much have had it with excuses regarding inadequecies of some programs, If NEC is a really viable tool; then let us use it as a datum by using a NEC program that is all encompassing to judge measured claims against so hat true specific can be judged. It is possible after all that even NEC may obtain several more revisions over time because of actual measurement which can only aid all in the understanding of antennas and the removal of old wifes tales and private agendas that evolved prior to NEC. Is it auguments that we yearn for on this newsgroup or true resolution of ideas? Art "Ian White, G3SEK" wrote in message ... wrote: I did not want to choose a curve that matches my modelling which you can when presented with three different curves all of which are formulated at different times by different people. I would have thought that the advent of NEC would render these curves redundant ! The plot of many individual yagis does confirm the general idea of gain being roughly proportional to boom length, and that is a very important thing to understand. clip There is no direct connection between boom length and gain. This is because lengthing the boom also implies one has added elements and possibly made adjustments to element spacing. A good source of the data you seek may be an antenna catalog(or manufacturers web site). compare the published gains of the different length antennas. |
"Jimmie" wrote in message . com... A graph from NEC data is going to be pretty much like a graph from the ARRL books. Come on Jimmy,' pretty much like' doesn't cut it on this newsgroup or in any of the professions The same as pretty close is not accepted when doing math at college. The curves in the ARRL book were done on 'standard' yagis measured in the field, at least two of the curves therefore have measuring errors, and possibly three of those do not match NEC formulated curves. Since you do not want to reinvent the wheel which curve or formula do YOU want all to follow for short boom antennas i.e. which curve, and there are many, represents the "wheel" . that can be specifically used as the datum curve in response to my specific request? Note, a NEC produced gragh will produce a scattering of points for different yagi's but only ONE point for MAX GAIN PER UNIT LENGTH OF BOOM regardless of how many elements are used which when used on short booms produce coupling effects which change current flow, an effect not generally seen when elements are not critically coupled as in the standard yagi.. Thus the reason I was specific in my request which should have removed comments such as 'Patents" from those who seek arguments . Art By putting the data in a graphic form your are placing the same limits on the data as they had to in the ARRL books. The ARRL graphs give you a pretty good idea of what goes on when you change element spacing, number of elements and so on. What they dont do is alllow you to perform optimization like the NEC programs . Graphing a NEC program output would be the same as going back to the time all you had was the graphs to go by unless you are willing to do all the calculations on your slide rule or calculator. What I am saying is that you already have this data. No point in reinventing the wheel.Unless you think yiou can get a patent on it Geez Jimmy you are just not reading posts of others ! If you have the requested data then point to a link, if I had the data already I wouldn't ask for help seeking it,. Art " wrote in message news:65Zcd.150611$He1.116446@attbi_s01... Jimmy, I did not want to choose a curve that matches my modelling which you can when presented with three different curves all of which are formulated at different times by different people. I would have thought that the advent of NEC would render these curves redundant ! Art "Jimmie" wrote in message . com... " wrote in message news:xOzcd.263953$D%.243703@attbi_s51... My ARRL books go back a decade or more and the graph showing gain per boom length has several curves based on different measurements e.t.c. Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height? Art They probably have been done but there will not be much difference between them and the ARRL graphs. Its been long known how to calculate antenna gain, computers just take the teadous labor out of it. |
Jimmie wrote:
The plot of many individual yagis does confirm the general idea of gain being roughly proportional to boom length, and that is a very important thing to understand. clip There is no direct connection between boom length and gain. This is because lengthing the boom also implies one has added elements and possibly made adjustments to element spacing. Sorry, I should have said that boom length is roughly proportional to the *available* gain, if the whole length of the boom is populated with elements in such a manner as to optimize the gain. That requirement is usually taken as understood. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
|
On Tue, 19 Oct 2004 14:02:18 -0400, "G&R" wrote:
|Hi Wes, | |Yes I am aware of the difference between the advertising on the site and the |range results. So are you going to fix it or not? | |As you are aware antennas do not have even gain across the entire band. We |have designed the antenna to cover the entire 2m band and as a result do see |a variation in the perfromance across the band, hence max gain. Huh? So are you saying that you have nearly 3 dB gain variation in 2 MHz.? | |And before you cut down my comments, the precision on the results are from |the softare and we are in the process of redesigning the format to more |accurately reflect our actual results both modelled and actual. |Unfortunately our business is antennas and web design. In a paper I wrote for the ARRL Antenna Compendium, I said, "Simplified 'antenna analyzers', especially those with digital readouts can lull the user into unjustified confidence in the accuracy of his measurements." Change the words "antenna analyzers" to "computer software" and it describes this situation to a T. | |The results posted on the CSVHF society are valid as the antenna was tested |with a gain of 11.2dBd at 144.18MHz Horiz Polarization. Design Freq is |146.0MHz. | |We are in the business of designing and selling antennas not developing |antennas and giving them away for free. However, if your serious about the |data for the antenna contact me directly so that we can discuss the details |(email listed below). My slightly distorted email is above. If you choose to send me your parameters, I promise to keep it in confidence. I don't not design, or manufacture antennas (or anything else) for a living. | |As to the DATAQ, well I have no answer for that one, as we don't build it or |sell it. Our software is designed to with run it. Strange though, my |Toshiba does and so does my SONY through a USB to SERIAL converter. I know you don't build or sell it, I'm just offering a caution to those who might be tempted to buy one. It works on my desktop but not my laptop, which is a pity because I had a portable use in mind. | |One final point, the purpose of the posting was that identify that an |antenna does not always need boom length and elements for gain and that |there are other ways to achieve this. Absolutely. One driven element at the focus of a 40' parabola is a decent antenna at 2-meters. Regards, Wes N7WS |
"Chuck" wrote in message news:n5gdd.8202$6P5.3752@okepread02... wrote in message news:x_Ycd.281755$3l3.162866@attbi_s03... What brought this to my attention was Moxon who advocated 2 element beams (lightnes translates to greater heights) so I modeled a 20 meter beam on a 7 foot boom and obtained 12dbi max for the band (ala 2:1) Hi Art, Can we assume this gain was calculated at a particular height over ground? But ofcourse a perfect ground and a standard wavelength height Personally, I prefer FS results, in order to eliminate any ambiguity. Field strength (F.S.) introduces ambiguity does it not? but one can get 13dbi if you drop the impedance from 50 to 12 ohms. This paraphrases the spesific example that I gave the question would a transformer cancel the increased gain. Again you paraphased the spoecific sample that I gave which raised the same question I gave regarding transformer losses Optimizing an antenna for a specific Z is not a good idea in my opinion, as the amplitude of an element's current is proportional to the amplitude of its radiation. Ohms law tells us that at a consistant power level, the lower the R (Z), the greater will be the current. Yes there are many laws to remember and I look at critical coupling as something to remember. A zero loss transformer would not reduce the element's current, as the energy being introduced to the element would remain unchanged. Very true but what element would this max energy be applied to? Via critical coupling the driven element may not be the one carrying the maximum current and thus screws up conventional thinking. Energy is one thing but it is current that controls radiation is it not ?. The particular model I was working on used 50 segments per wavelength and used element length and diameters determined by my program input . Thus coupling gains are attained but where it sometimes determined a element diameter is so thin it is incapable of carrying the required current. If I saw a vendor advertise an antenna at 13dbi I would be very suspicious as it not the norm, yet very realiseable when using NEC without being tied down to existing doctrines. Sooooooo ..... I was looking for a datum curve generated by experts from an all encompasing NEC program where the final design reflected the real world design without ambiguities regarding coupling to coils, elements e.t.c. where lumped loads do not reflect the real world appearance. There have been many responses including one suggestion that a suitable datum curve could be formulated from customer claims no less but NONE that responds to my specific request . Thus a conundrum still exists regarding programs based on scientific knoweledge that are held in question as they do not match real world measurements that spawn most of the villifying in this group. Seems like a datum curve could be used as a basis for many discusions where differences do occur instead of just arguing for eight years or more and not resolving the accuracy concerns Seems like I have come full circle and describing the Presidential debates ! Art 73 de Chuck, WA7RAI |
On Wed, 20 Oct 2004 00:21:10 GMT, "
wrote: datum curve Hi Art, No such thing. It takes data (plural) to make a curve. Datum (singular) is a point (i.e. NOT a curve). If you don't see the curve you are looking for, you have an NEC engine, what is preventing you from using it to make one, or two, or several? 73's Richard Clark, KB7QHC |
wrote in message news:Wbidd.156718$He1.38391@attbi_s01... "Chuck" wrote in message news:n5gdd.8202$6P5.3752@okepread02... wrote in message news:x_Ycd.281755$3l3.162866@attbi_s03... What brought this to my attention was Moxon who advocated 2 element beams (lightnes translates to greater heights) so I modeled a 20 meter beam on a 7 foot boom and obtained 12dbi max for the band (ala 2:1) Hi Art, Can we assume this gain was calculated at a particular height over ground? But ofcourse a perfect ground and a standard wavelength height Personally, I prefer FS results, in order to eliminate any ambiguity. Field strength (F.S.) introduces ambiguity does it not? Hi Art, FS = free space :) Modeling in FS, using dBd as a reference eliminates ambiguity. All grounds are not equal. Including ground effects in antenna type models that are not ground dependant, does not reflect the 'real' world, IMO. but one can get 13dbi if you drop the impedance from 50 to 12 ohms. This paraphrases the spesific example that I gave the question would a transformer cancel the increased gain. Again you paraphased the spoecific sample that I gave which raised the same question I gave regarding transformer losses Optimizing an antenna for a specific Z is not a good idea in my opinion, as the amplitude of an element's current is proportional to the amplitude of its radiation. Ohms law tells us that at a consistent power level, the lower the R (Z), the greater will be the current. Yes there are many laws to remember and I look at critical coupling as something to remember. Critical coupling is simply a means to attain element currents of a higher amplitude than what can be expected when one element is excited parasitically. A zero loss transformer would not reduce the element's current, as the energy being introduced to the element would remain unchanged. Very true but what element would this max energy be applied to? Max Energy? I was referring to the element the transformer is attached to. Via critical coupling the driven element may not be the one carrying the maximum current and thus screws up conventional thinking. Ummmm... Critical coupling is a state where currents of equal amplitude flow in two inductors that are in close proximity, as a direct result of the coupling. Critical coupling results in a common field as well. This also applies to wires (elements). Energy is one thing but it is current that controls radiation is it not ?. Yes, and that's what I had said previously. The particular model I was working on used 50 segments per wavelength and used element length and diameters determined by my program input . Thus coupling gains are attained but where it sometimes determined a element diameter is so thin it is incapable of carrying the required current. I'm not sure if I follow this correctly... please elaborate further. If I saw a vendor advertise an antenna at 13dbi I would be very suspicious as it not the norm, yet very realiseable when using NEC without being tied down to existing doctrines. Sooooooo ..... I was looking for a datum curve generated by (data - plural)... :) experts from an all encompasing NEC program where the final design reflected the real world design without ambiguities regarding coupling to coils, elements e.t.c. where lumped loads do not reflect the real world appearance. There have been many responses including one suggestion that a suitable datum curve could be formulated from customer claims no less but NONE that responds to my specific request . Thus a conundrum still exists regarding programs based on scientific knoweledge that are held in question as they do not match real world measurements that spawn most of the villifying in this group. I suspect there can be many examples where this occurs, but not necessarily all are the fault of software. However, we both know from experience, software can be problematic in this regard. Seems like a datum curve could be used as a basis for many discusions where differences do occur instead of just arguing for eight years or more and not resolving the accuracy concerns .... but when one fails to include certain salient functions in their software - software that is the basis for such arguments, there is no way the arguments can be resolved simply because there is no guarantee that the software will be consistent with empirical data in all cases, despite a high order of hubris to the contrary. Seems like I have come full circle and describing the Presidential debates ! Art Indeed... :) 73 de Chuck, WA7RAI |
Chuck
"Chuck" wrote in message news:XrBdd.8254$6P5.7645@okepread02... snip. Yes there are many laws to remember and I look at critical coupling as something to remember. Critical coupling is simply a means to attain element currents of a higher amplitude than what can be expected when one element is excited parasitically. A zero loss transformer would not reduce the element's current, as the energy being introduced to the element would remain unchanged. Very true but what element would this max energy be applied to? Max Energy? Sorry about that.........I.meant current but my fingers ignored me I was referring to the element the transformer is attached to. Via critical coupling the driven element may not be the one carrying the maximum current and thus screws up conventional thinking. Ummmm... Critical coupling is a state where currents of equal amplitude flow in two inductors that are in close proximity, as a direct result of the coupling. Critical coupling results in a common field as well. This also applies to wires (elements). Energy is one thing but it is current that controls radiation is it not ?. Yes, and that's what I had said previously. The particular model I was working on used 50 segments per wavelength and used element length and diameters determined by my program input . Thus coupling gains are attained but where it sometimes determined a element diameter is so thin it is incapable of carrying the required current. I'm not sure if I follow this correctly... please elaborate further. Certainly To attain maximum gain per unit length the model dimensions were all variables as was the number of elements. Not only was the driven element current often less than another element in the array it was sometimes found that the maximum current element required a diameter of a few thousanths that was not sufficient to carry 1Kw.! Obviously the gain attained was over ruled by the inability of the element to meet operational requirements. I might add that I use fibre fishing rods for my antennas where I can apply the correct wire diameters ( or aluminum foil) to an array without being encumbered by mechanical restrictions. This removes me from the normal restrictions applied to antennas where element diameter is pre-controlled for mechanical reasons which often conflict with scientific requirements The above statement does conflicts with your assesment stated above regarding critical coupling but this is what I found and I will leave it at that Regards Art. snip |
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Ian White, G3SEK wrote:
"Drawing gain curves is a fun activity...but don`t try to read too much into them." I searched on "yagi boom". I got many responses. One showed Ian as the custodian of a computer program to design yagis. Another was from the Central States VHF Society and gives results of their 2004 gain comparisons of many different antennas. Gain of these versus boom length looks very ragged. Best regards, Richard Harrison, KB5WZI |
"Chuck" wrote in message news:fVSdd.9064$6P5.7971@okepread02... wrote in message news:bMDdd.293802$3l3.275124@attbi_s03... "Chuck" wrote in message news:XrBdd.8254$6P5.7645@okepread02... snip. I'm not sure if I follow this correctly... please elaborate further. Certainly To attain maximum gain per unit length the model dimensions were all variables as was the number of elements. Not only was the driven element current often less than another element in the array it was sometimes found that the maximum current element required a diameter of a few thousanths that was not sufficient to carry 1Kw.! Obviously the gain attained was over ruled by the inability of the element to meet operational requirements. I might add that I use fibre fishing rods for my antennas where I can apply the correct wire diameters ( or aluminum foil) to an array without being encumbered by mechanical restrictions. This removes me from the normal restrictions applied to antennas where element diameter is pre-controlled for mechanical reasons which often conflict with scientific requirements The above statement does conflicts with your assesment stated above regarding critical coupling but this is what I found and I will leave it at that Regards Art. Hi Art, Ok, I'm always open minded to learn something new... Wow,,,...... there are not many people around who could say that !. Since 99.999% of things presented as new are incorrect most experts have determined that the odds favor them if they label EVERYTHING new as in error. If something comes along that is really new they always have the comment ' I knew about that a long while ago" to fall back on. I'd like to establish a few things, though. First of all, what modeling program are you using? Beasely AOP This is the professional version that has more than enough segments and variable dimensions available to lesson the chances of human input errors plus to handle elements that were in close proximetry to each other, together with 'Sommerfield ground' handling capabilities. Is your empirical data consistent with the models? Not measured, my thought were that NEC would always be closer than field measurements generated by an amateur. How are you ascertaining your empirical data? How are you determining the current amplitudes: By model? Or empirically? By model, The program provides % of max current at every segment, phase and all that good stuff And what are the machinations that demand ultra-thin wires to establish the gain? Go for 80 % gain and the rest (20% ) for swr Added half a dozen elements All dimensions variable except boom length and perfect ground height Remove one element at a time until max gain point is obvious Note all dimensions are kept variable at all times. You can email me if you care to not discuss these things in an open forum. Not necessary, This is the very reason I posted in the first place ! The program shows that the normal 2 element is not the optimum in that a polygon of vectors beats a triangle of vectors. At the same time with added elements you get diminishing returns in std and conventional forms. The program showed that 1 to 1.5 dbi was available over the standard 2 element on the same length boom.if one could overcome mechanical restraints. (I was comparing to a Beasely example of what gain could be attained for two elements on a 7 foot boom) Now that is not the end of the experiment as I cannot verify the accuracy of the program, because I did not write it, and I certainly cannot say that my modelling aproach is without error since that is what many 'experts' point to if they don't like the results. It was for that reason I asked if any similar data had been made available for boom length by reputable programmers and antenna 'experts' for comparison purposes ., If these initial results were quoted as accurrate there would be howls from all the resident antenna ' experts" and I would immediately be placed in the six foot hole that they have been trying to put you in for the last eight years Art 73, de Chuck, WA7RAI wa7rai at cox dot net |
Another was from the
Central States VHF Society and gives results of their 2004 gain comparisons of many different antennas. Gain of these versus boom length looks very ragged. Best regards, Richard Harrison, KB5WZI Gain vs. boom length makes sense only when comparing or tracking the same antenna design i.e. Yagi with multiple elements. One can design lousy antenna on a long boom. Jim Lawson, W2PV was one who after some modeling showed that gain in the properly designed antenna is roughly proportional to the boom length rather than to number of elements. Some manufacturers "beefed up" their antennas by sticking more elements on the same boom claiming better performance. Yuri, K3BU.us |
Yes but I believe that the early computorisationd he used was based first on
mechenical designed elements which were then imputted.He did not mess with the element diameters after that.As an aside if you densly populated a boom with elements many are put off by the low impedance being totaslly unaware that an additional reflector an up the input impedance back again...... another example of what coupling can do for antennas Art "Yuri Blanarovich" wrote in message ... Another was from the Central States VHF Society and gives results of their 2004 gain comparisons of many different antennas. Gain of these versus boom length looks very ragged. Best regards, Richard Harrison, KB5WZI Gain vs. boom length makes sense only when comparing or tracking the same antenna design i.e. Yagi with multiple elements. One can design lousy antenna on a long boom. Jim Lawson, W2PV was one who after some modeling showed that gain in the properly designed antenna is roughly proportional to the boom length rather than to number of elements. Some manufacturers "beefed up" their antennas by sticking more elements on the same boom claiming better performance. Yuri, K3BU.us |
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Tom, where is the link that goes with this info? It doesn't mean anything as
it stands Art wrote in message . .. wrote: My ARRL books go back a decade or more and the graph showing gain per boom length has several curves based on different measurements e.t.c. Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height? Art For VHF/UHF yagis in free space - WA2PHW Gain Figure of Merit G = 10 log (5.4075 B + 4.25) for B GT 1 Where G is gain in dBd and B is boomlength in wavelengths. This is from a database of over 100 VHF/UHF yagis compiled in the early 90's. These are all real buildable yagis, and the antenna range numbers closely agree with the computer models. The numbers were heavily influenced by the 10 to 40 element K1FO series. Thanks again Steve. Note that this predicts a zero length yagi should have about 6 dBd gain. Any ideas on why it intercepts there? tom K0TAR |
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Tom, let me be direct without being disrespectful What I modelled was a boom
length of 7ft for 20 metres and it is an abnormal yagi design which does not fit what you are offering. I do not believe that NEC programs vary too much on standard forms but when using tightly clustered elements on a short boom lots of other things come in to play, and one has to be sure that the program is all encompassing as designed to handle ALL abnormalities. Obviously what you have offerred has serious problems on short yagi's let alone abnormal design yagi's. It is my belief that because an element reradiates a portion of the RF that it received, extra elements that are closely clustered can provide increased gain. Yes. my model confirmed that but I was hoping that experts could point to a mathematical analysis of max gain per unit length that was exacting in gain provided and not "close enough" and not marred by other things that can occur by measuring in the field. It would appear from the responses that efforts in this area has not been undertaken and which I will have to live with that. But I do thank you for your offering Art "Tom Ring" wrote in message . .. wrote: Tom, where is the link that goes with this info? It doesn't mean anything as it stands Art What? Of course it means something. It's an equation along with the constraints. Run any current decent 1 wavelength, or longer, yagi in your favorite modeling program, and it will tell you whether you are near the gain you should get for a well behaved yagi. Or it might tell you the model isn't very accurate. It works well to test known designs against unknown quality programs without having the known good modeling program or test range. If you want the database it was derived from, that might be arranged, but it is in from a database program that Microsoft Office won't read, so you might be out of luck there. tom K0TAR |
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No appreciable difference between them and NEC program results. You can build every bit as good of an antenna using the curves and given formula as you can a NEC program. Optimization of antenna built from either data still requires the same cut and try tweaking to get the last .001 db out. For all practical purposes the ARRL curves are as good as any. Obviously you have some impractical uses in mind. " wrote in message news:gDfdd.278515$D%.137716@attbi_s51... "Jimmie" wrote in message . com... A graph from NEC data is going to be pretty much like a graph from the ARRL books. Come on Jimmy,' pretty much like' doesn't cut it on this newsgroup or in any of the professions The same as pretty close is not accepted when doing math at college. The curves in the ARRL book were done on 'standard' yagis measured in the field, at least two of the curves therefore have measuring errors, and possibly three of those do not match NEC formulated curves. Since you do not want to reinvent the wheel which curve or formula do YOU want all to follow for short boom antennas i.e. which curve, and there are many, represents the "wheel" . that can be specifically used as the datum curve in response to my specific request? Note, a NEC produced gragh will produce a scattering of points for different yagi's but only ONE point for MAX GAIN PER UNIT LENGTH OF BOOM regardless of how many elements are used which when used on short booms produce coupling effects which change current flow, an effect not generally seen when elements are not critically coupled as in the standard yagi.. Thus the reason I was specific in my request which should have removed comments such as 'Patents" from those who seek arguments . Art By putting the data in a graphic form your are placing the same limits on the data as they had to in the ARRL books. The ARRL graphs give you a pretty good idea of what goes on when you change element spacing, number of elements and so on. What they dont do is alllow you to perform optimization like the NEC programs . Graphing a NEC program output would be the same as going back to the time all you had was the graphs to go by unless you are willing to do all the calculations on your slide rule or calculator. What I am saying is that you already have this data. No point in reinventing the wheel.Unless you think yiou can get a patent on it Geez Jimmy you are just not reading posts of others ! If you have the requested data then point to a link, if I had the data already I wouldn't ask for help seeking it,. Art " wrote in message news:65Zcd.150611$He1.116446@attbi_s01... Jimmy, I did not want to choose a curve that matches my modelling which you can when presented with three different curves all of which are formulated at different times by different people. I would have thought that the advent of NEC would render these curves redundant ! Art "Jimmie" wrote in message . com... " wrote in message news:xOzcd.263953$D%.243703@attbi_s51... My ARRL books go back a decade or more and the graph showing gain per boom length has several curves based on different measurements e.t.c. Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height? Art They probably have been done but there will not be much difference between them and the ARRL graphs. Its been long known how to calculate antenna gain, computers just take the teadous labor out of it. |
" wrote in message news:wAYdd.406148$mD.70164@attbi_s02... Tom, where is the link that goes with this info? It doesn't mean anything as it stands Art wrote in message . .. wrote: My ARRL books go back a decade or more and the graph showing gain per boom length has several curves based on different measurements e.t.c. Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height? Art For VHF/UHF yagis in free space - WA2PHW Gain Figure of Merit G = 10 log (5.4075 B + 4.25) for B GT 1 Where G is gain in dBd and B is boomlength in wavelengths. This is from a database of over 100 VHF/UHF yagis compiled in the early 90's. These are all real buildable yagis, and the antenna range numbers closely agree with the computer models. The numbers were heavily influenced by the 10 to 40 element K1FO series. Thanks again Steve. Note that this predicts a zero length yagi should have about 6 dBd gain. Any ideas on why it intercepts there? tom K0TAR |
wrote in message news:tEUdd.167111$He1.55962@attbi_s01... "Chuck" wrote in message news:fVSdd.9064$6P5.7971@okepread02... wrote in message news:bMDdd.293802$3l3.275124@attbi_s03... "Chuck" wrote in message news:XrBdd.8254$6P5.7645@okepread02... snip. ... Hi Art, Ok, I'm always open minded to learn something new... Wow,,,...... there are not many people around who could say that !. Since 99.999% of things presented as new are incorrect most experts have determined that the odds favor them if they label EVERYTHING new as in error. If something comes along that is really new they always have the comment ' I knew about that a long while ago" to fall back on. Hi Art, Anyone who believes they know it all, has much to learn :-) ... The program shows that the normal 2 element is not the optimum in that a polygon of vectors beats a triangle of vectors. At the same time with added elements you get diminishing returns in std and conventional forms. The program showed that 1 to 1.5 dbi was available over the standard 2 element on the same length boom.if one could overcome mechanical restraints. (I was comparing to a Beasely example of what gain could be attained for two elements on a 7 foot boom) Now that is not the end of the experiment as I cannot verify the accuracy of the program, because I did not write it, and I certainly cannot say that my modelling aproach is without error since that is what many 'experts' point to if they don't like the results. It was for that reason I asked if any similar data had been made available for boom length by reputable programmers and antenna 'experts' for comparison purposes ., If these initial results were quoted as accurrate there would be howls from all the resident antenna ' experts" and I would immediately be placed in the six foot hole that they have been trying to put you in for the last eight years Art I get the impression that what you are doing is placing any number of elements on a .1 lambda boomlength, in order to determine if the close proximity EM interactions produce more gain than just the standard 2 elements would on that same boomlength. In the optimization process, some of the resulting element diameters are quite small. You're asking if anyone else has looked into this, and if any results have been published. Is this a correct assessment so far? 73 de Chuck, WA7RAI |
YES
Art "Chuck" wrote in message news:N3ded.9115$6P5.8189@okepread02... wrote in message news:tEUdd.167111$He1.55962@attbi_s01... "Chuck" wrote in message news:fVSdd.9064$6P5.7971@okepread02... wrote in message news:bMDdd.293802$3l3.275124@attbi_s03... "Chuck" wrote in message news:XrBdd.8254$6P5.7645@okepread02... snip. ... Hi Art, Ok, I'm always open minded to learn something new... Wow,,,...... there are not many people around who could say that !. Since 99.999% of things presented as new are incorrect most experts have determined that the odds favor them if they label EVERYTHING new as in error. If something comes along that is really new they always have the comment ' I knew about that a long while ago" to fall back on. Hi Art, Anyone who believes they know it all, has much to learn :-) ... The program shows that the normal 2 element is not the optimum in that a polygon of vectors beats a triangle of vectors. At the same time with added elements you get diminishing returns in std and conventional forms. The program showed that 1 to 1.5 dbi was available over the standard 2 element on the same length boom.if one could overcome mechanical restraints. (I was comparing to a Beasely example of what gain could be attained for two elements on a 7 foot boom) Now that is not the end of the experiment as I cannot verify the accuracy of the program, because I did not write it, and I certainly cannot say that my modelling aproach is without error since that is what many 'experts' point to if they don't like the results. It was for that reason I asked if any similar data had been made available for boom length by reputable programmers and antenna 'experts' for comparison purposes .., If these initial results were quoted as accurrate there would be howls from all the resident antenna ' experts" and I would immediately be placed in the six foot hole that they have been trying to put you in for the last eight years Art I get the impression that what you are doing is placing any number of elements on a .1 lambda boomlength, in order to determine if the close proximity EM interactions produce more gain than just the standard 2 elements would on that same boomlength. In the optimization process, some of the resulting element diameters are quite small. You're asking if anyone else has looked into this, and if any results have been published. Is this a correct assessment so far? 73 de Chuck, WA7RAI |
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