| Home |
| Search |
| Today's Posts |
|
|
|
#2
October 19th 04, 08:37 AM
|
|||
|
|||
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. Note that this is only for long-ish yagis with many elements. For yagis of 2-3-4 elements on a short boom, the first few dB of gain come very easily. Beyond that, the data points settle back towards the long-yagi trend line. To increase the gain by 3dB, you need to either double the boom length (and redesign the yagi, obviously) or else stack two of the same yagis... and either way, in practice you'll achieve slightly less than 3dB. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
|
#3
October 19th 04, 05:15 PM
|
|||
|
|||
|
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 |
|
#4
October 19th 04, 07:46 PM
|
|||
|
|||
|
" 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. |
|
#5
October 19th 04, 07:27 PM
|
|||
|
|||
|
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. |
|
#6
October 19th 04, 10:25 PM
|
|||
|
|||
|
"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$D%.243703@attbi_s51... My ARRL books go back a decade or more and the graph showing gain per boom length has several curves based on different measurements e.t.c. Has a graph been made based solely on NEC program findings over say a perfect ground and at a uniform height? Art They probably have been done but there will not be much difference between them and the ARRL graphs. Its been long known how to calculate antenna gain, computers just take the teadous labor out of it. |
|
#7
October 22nd 04, 06:01 PM
|
|||
|
|||
|
No appreciable difference between them and NEC program results. You can build every bit as good of an antenna using the curves and given formula as you can a NEC program. Optimization of antenna built from either data still requires the same cut and try tweaking to get the last .001 db out. For all practical purposes the ARRL curves are as good as any. Obviously you have some impractical uses in mind. " wrote in message news:gDfdd.278515$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. |
|
#8
October 18th 04, 06:26 PM
|
|||
|
|||
|
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 |
|
#9
October 18th 04, 06:52 PM
|
|||
|
|||
|
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 |
|
#10
October 19th 04, 01:13 AM
|
|||
|
|||
|
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 |
| Reply |
| Thread Tools | Search this Thread |
| Display Modes | |
|
|
Similar Threads
|
||||
| Thread | Forum | |||
| Antenna tuner | Antenna | |||
| Question on antenna symantics | Antenna | |||
| Antenna future | Antenna | |||
Hybrid Mode
