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Phasing of stacked Yagis
All,
I refer to the diagram at http://www.vk1od.net/lost/Fig6.png which is from an article by the then VK2ZAB (now VK3EJ) on stacking Yagis. I have highlighted two of the diagrams with a yellow background, and seek opinions on them. Referring firstly to the left hand one: I suggest that the figure is in error because the scenario is not ALWAYS wrong. My contention is that at a single frequency, the phase inversion as a result of the left to right swap of one driven element (DE) wrt the other can be fully compensated for by ensuring that low loss feedline to one DE is an odd number of electrical half waves longer than to the other. Where the low loss feedline to one DE is an odd number of electrical half waves longer than to the other, the Yagis are driven in phase. The outcome being that the pattern at that frequency is approximately the same as if equal length feedline branches were used. Referring now to the right hand one: I suggest that the figure is in error because the scenario is not ALWAYS wrong. My contention is that at a single frequency, that where the low loss feedline to one DE is an integral number of electrical full waves longer than to the other, the Yagis are driven in phase. The outcome being that the pattern at that frequency is approximately the same as if equal length feedline branches were used. Note that I am not trying to excite a purist discussion about branch vs distributed feed arrangements for phased arrays. Am I on the wrong track? Owen |
Phasing of stacked Yagis
On Sat, 13 Dec 2008 01:56:27 GMT, Owen Duffy wrote:
I refer to the diagram at http://www.vk1od.net/lost/Fig6.png which is from an article by the then VK2ZAB (now VK3EJ) on stacking Yagis. I see nothing in that diagram that describes the physical/electrical spacing _between_ the driven elements. Jonesy -- Marvin L Jones | jonz | W3DHJ | linux 38.24N 104.55W | @ config.com | Jonesy | OS/2 * Killfiling google & XXXXbanter.com: jonz.net/ng.htm |
Phasing of stacked Yagis
Owen Duffy wrote:
Referring firstly to the left hand one: I suggest that the figure is in error because the scenario is not ALWAYS wrong. My contention is that at a single frequency, the phase inversion as a result of the left to right swap of one driven element (DE) wrt the other can be fully compensated for by ensuring that low loss feedline to one DE is an odd number of electrical half waves longer than to the other. Where the low loss feedline to one DE is an odd number of electrical half waves longer than to the other, the Yagis are driven in phase. The outcome being that the pattern at that frequency is approximately the same as if equal length feedline branches were used. Referring now to the right hand one: I suggest that the figure is in error because the scenario is not ALWAYS wrong. My contention is that at a single frequency, that where the low loss feedline to one DE is an integral number of electrical full waves longer than to the other, the Yagis are driven in phase. In fairness, Gordon did say: "Departures from these rules are possible for special applications outside the scope of this discussion." The exceptions identified above would be exactly what he had in mind. Reversed connections and/or unequal feeder lengths certainly can be used, but they are advanced techniques requiring clear intent and careful engineering. In all other cases they will be "WRONG" as Gordon says. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Phasing of stacked Yagis
Hello Ian,
Ian White GM3SEK wrote in : .... In fairness, Gordon did say: "Departures from these rules are possible for special applications outside the scope of this discussion." The exceptions identified above would be exactly what he had in mind. Yes, he does make that statement. I focussed on the diagram. I guess his "WRONG!" means "possibly wrong (see text)". Reversed connections and/or unequal feeder lengths certainly can be used, but they are advanced techniques requiring clear intent and careful engineering. In all other cases they will be "WRONG" as Gordon says. I received comment on my antenna described at http://www.vk1od.net/4over4/ as follows: 'It "doesn't" work because you have inserted a half-wave time delay in the feed to one antenna (in your case it appears to be the upper antenna) which tilts the beam up or down a bit (in your antenna, it will tilt upwards)' and in following discussion it is asserted that although the feed to one antenna is transposed, it does not correct the additional half wave phase shift of the longer branch. Gordon's paper was offered as support for that position. I think my design is sound, the rationale is set out in the article. I am a little flattered if it is considered an advanced technique, but it seems to me fairly elementary. Actually, since posting the original article, I followed up on Gordon's reference to the ARRL Antenna Handbook. It has a diagram that shows pretty much what I did, it is (c) at http://www.vk1od.net/lost/Fig7.png . (The difference in my case is that the stacking distance was chosen for optimal pattern by trial and error with an NEC model, and the coax has a velocity factor around 0.82.) Owen |
Phasing of stacked Yagis
Owen Duffy wrote:
Reversed connections and/or unequal feeder lengths certainly can be used, but they are advanced techniques requiring clear intent and careful engineering. In all other cases they will be "WRONG" as Gordon says. I received comment on my antenna described at http://www.vk1od.net/4over4/ as follows: 'It "doesn't" work because you have inserted a half-wave time delay in the feed to one antenna (in your case it appears to be the upper antenna) which tilts the beam up or down a bit (in your antenna, it will tilt upwards)' and in following discussion it is asserted that although the feed to one antenna is transposed, it does not correct the additional half wave phase shift of the longer branch. Gordon's paper was offered as support for that position. Your version of the 4/4 is phased correctly as shown. The extra electrical half-wave compensates for the gamma match being on the opposite side, as both are equivalent to a 180deg phase shift. Gordon's paper does not deal with situations where the use of different lengths of feedline is deliberate. I think my design is sound, the rationale is set out in the article. I am a little flattered if it is considered an advanced technique, but it seems to me fairly elementary. It cannot be done without *first* knowing how to make two lengths of feedline exactly equal, so that's got to be "more advanced"... er, right? -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Phasing of stacked Yagis
"Owen Duffy" wrote in message ... Hello Ian, Ian White GM3SEK wrote in : ... In fairness, Gordon did say: "Departures from these rules are possible for special applications outside the scope of this discussion." The exceptions identified above would be exactly what he had in mind. Yes, he does make that statement. I focussed on the diagram. I guess his "WRONG!" means "possibly wrong (see text)". Reversed connections and/or unequal feeder lengths certainly can be used, but they are advanced techniques requiring clear intent and careful engineering. In all other cases they will be "WRONG" as Gordon says. I received comment on my antenna described at http://www.vk1od.net/4over4/ as follows: 'It "doesn't" work because you have inserted a half-wave time delay in the feed to one antenna (in your case it appears to be the upper antenna) which tilts the beam up or down a bit (in your antenna, it will tilt upwards)' and in following discussion it is asserted that although the feed to one antenna is transposed, it does not correct the additional half wave phase shift of the longer branch. Gordon's paper was offered as support for that position. I think my design is sound, the rationale is set out in the article. I am a little flattered if it is considered an advanced technique, but it seems to me fairly elementary. Actually, since posting the original article, I followed up on Gordon's reference to the ARRL Antenna Handbook. It has a diagram that shows pretty much what I did, it is (c) at http://www.vk1od.net/lost/Fig7.png . (The difference in my case is that the stacking distance was chosen for optimal pattern by trial and error with an NEC model, and the coax has a velocity factor around 0.82.) Owen Hi Owen Richard Clark once told me how to combine 4 antennas in an array. He got me to feed 4 antennas, 50 ohms each with 50 ohm coax with no dividers. I just fed each antenna with 50 ohm coax. At the point where the 4 coaxes get combined, I connected two coaxes in series and the other two also in series. Then parallel them to get back to 50 ohms. The result is two 50 ohm loads in series to make 100 ohms and with the other 100 ohms in parallel, the combination is a good 50 ohm load. You can see a sketch in the Feb 2008 QST. It works pretty slick when the antennas are 50 or 70 ohms where it is easy to get the right coax impedance. Jerry KD6JDJ |
Phasing of stacked Yagis
"Jerry" wrote in
: .... Hi Owen Richard Clark once told me how to combine 4 antennas in an array. He got me to feed 4 antennas, 50 ohms each with 50 ohm coax with no dividers. I just fed each antenna with 50 ohm coax. At the point where the 4 coaxes get combined, I connected two coaxes in series and the other Can you explain in more detail what you mean by "I connected two coaxes in series"? two also in series. Then parallel them to get back to 50 ohms. The result is two 50 ohm loads in series to make 100 ohms and with the other 100 ohms in parallel, the combination is a good 50 ohm load. You can see a sketch in the Feb 2008 QST. It works pretty slick when the antennas are 50 or 70 ohms where it is easy to get the right coax impedance. Owen |
Phasing of stacked Yagis
"Owen Duffy" wrote in message ... "Jerry" wrote in : ... Hi Owen Richard Clark once told me how to combine 4 antennas in an array. He got me to feed 4 antennas, 50 ohms each with 50 ohm coax with no dividers. I just fed each antenna with 50 ohm coax. At the point where the 4 coaxes get combined, I connected two coaxes in series and the other Can you explain in more detail what you mean by "I connected two coaxes in series"? two also in series. Then parallel them to get back to 50 ohms. The result is two 50 ohm loads in series to make 100 ohms and with the other 100 ohms in parallel, the combination is a good 50 ohm load. You can see a sketch in the Feb 2008 QST. It works pretty slick when the antennas are 50 or 70 ohms where it is easy to get the right coax impedance. Owen Hi Owen I dont know how to include pictures in this text. I would draw two touching circles to represent the outer conductors. The generator is fed between to the inner conductors. Hence, two 50 ohm loads on the coaxes will look like a 100 ohm load to the generator. Jerry |
Phasing of stacked Yagis
"Jerry" wrote in
: "Owen Duffy" wrote in message ... "Jerry" wrote in : ... Hi Owen Richard Clark once told me how to combine 4 antennas in an array. He got me to feed 4 antennas, 50 ohms each with 50 ohm coax with no dividers. I just fed each antenna with 50 ohm coax. At the point where the 4 coaxes get combined, I connected two coaxes in series and the other Can you explain in more detail what you mean by "I connected two coaxes in series"? two also in series. Then parallel them to get back to 50 ohms. The result is two 50 ohm loads in series to make 100 ohms and with the other 100 ohms in parallel, the combination is a good 50 ohm load. You can see a sketch in the Feb 2008 QST. It works pretty slick when the antennas are 50 or 70 ohms where it is easy to get the right coax impedance. Owen Hi Owen I dont know how to include pictures in this text. I would draw two touching circles to represent the outer conductors. The generator is fed between to the inner conductors. Hence, two 50 ohm loads on the coaxes will look like a 100 ohm load to the generator. Jerry Ok, I understand, you the two inner conductors with a 100 ohm load between them. You have another pair like that from the other two arrays. How do you connect them to the main feedline. Owen |
Phasing of stacked Yagis
"Owen Duffy" wrote in message ... "Jerry" wrote in : "Owen Duffy" wrote in message ... "Jerry" wrote in : ... Hi Owen Richard Clark once told me how to combine 4 antennas in an array. He got me to feed 4 antennas, 50 ohms each with 50 ohm coax with no dividers. I just fed each antenna with 50 ohm coax. At the point where the 4 coaxes get combined, I connected two coaxes in series and the other Can you explain in more detail what you mean by "I connected two coaxes in series"? two also in series. Then parallel them to get back to 50 ohms. The result is two 50 ohm loads in series to make 100 ohms and with the other 100 ohms in parallel, the combination is a good 50 ohm load. You can see a sketch in the Feb 2008 QST. It works pretty slick when the antennas are 50 or 70 ohms where it is easy to get the right coax impedance. Owen Hi Owen I dont know how to include pictures in this text. I would draw two touching circles to represent the outer conductors. The generator is fed between to the inner conductors. Hence, two 50 ohm loads on the coaxes will look like a 100 ohm load to the generator. Jerry Ok, I understand, you the two inner conductors with a 100 ohm load between them. You have another pair like that from the other two arrays. How do you connect them to the main feedline. Owen Hi Owen The two 100 ohm loads in parallel give a 50 ohm load to the 50 ohm coax main feed line. I used a ferrite "balun" where the unbalanced 50 ohm *main feed line* connects to the center conductors that are connected to be a 50 ohm load. . Jerry KD6JDJ |
Phasing of stacked Yagis
"Jerry" wrote in
: .... The two 100 ohm loads in parallel give a 50 ohm load to the 50 ohm coax main feed line. I used a ferrite "balun" where the unbalanced 50 ohm *main feed line* connects to the center conductors that are connected to be a 50 ohm load. . You didn't mention the balun in your fist posting. Without an effective balun, the system would be quite poor. In each pair of antenna side coax lines where the shields are tied together and the inners are used for a 100 ohm connection point, you drive one coax in opposite phase to the other. Your description did not note that there is particular phasing requirement for the coax lines to the antennas, and polarity of connection of the DEs. BTW, you have constructed a type of power divider. There are a lot of different ways to do it. Owen |
Phasing of stacked Yagis
"Owen Duffy" wrote in message ... "Jerry" wrote in : ... The two 100 ohm loads in parallel give a 50 ohm load to the 50 ohm coax main feed line. I used a ferrite "balun" where the unbalanced 50 ohm *main feed line* connects to the center conductors that are connected to be a 50 ohm load. . You didn't mention the balun in your fist posting. Without an effective balun, the system would be quite poor. In each pair of antenna side coax lines where the shields are tied together and the inners are used for a 100 ohm connection point, you drive one coax in opposite phase to the other. Your description did not note that there is particular phasing requirement for the coax lines to the antennas, and polarity of connection of the DEs. BTW, you have constructed a type of power divider. There are a lot of different ways to do it. Owen the simpler way is to just parallel all 4 of the 50 ohm loads which gives you a 12 ohm load at the common point, then parallel 2 pieces of 50 ohm coax 1/4 wave long to form a 25 ohm matching section, that will get you back to a 50 ohm common point with no need for a balun. |
Phasing of stacked Yagis
On Sun, 14 Dec 2008 21:54:45 GMT, "Dave" wrote:
BTW, you have constructed a type of power divider. There are a lot of different ways to do it. Owen the simpler way is to just parallel all 4 of the 50 ohm loads which gives you a 12 ohm load at the common point, then parallel 2 pieces of 50 ohm coax 1/4 wave long to form a 25 ohm matching section, that will get you back to a 50 ohm common point with no need for a balun. Unfortunately, this would be a common mode nightmare. 73's Richard Clark, KB7QHC |
Phasing of stacked Yagis
"Richard Clark" wrote in message ... On Sun, 14 Dec 2008 21:54:45 GMT, "Dave" wrote: BTW, you have constructed a type of power divider. There are a lot of different ways to do it. Owen the simpler way is to just parallel all 4 of the 50 ohm loads which gives you a 12 ohm load at the common point, then parallel 2 pieces of 50 ohm coax 1/4 wave long to form a 25 ohm matching section, that will get you back to a 50 ohm common point with no need for a balun. Unfortunately, this would be a common mode nightmare. 73's Richard Clark, KB7QHC .... why? It's a way it's done for broadcasting antennas. There's little reason why the screen of the feeder can run continuously into the screens of the transformer sections and on into the screens of the cables that feed the individual Yagis. If the drive-points of the Yagis are equipped with adequate baluns then there should be no more common-mode current on the outside of the continuous screen than for the case of a single Yagi. Chris |
Phasing of stacked Yagis
"christofire" wrote in message ... "Richard Clark" wrote in message ... On Sun, 14 Dec 2008 21:54:45 GMT, "Dave" wrote: BTW, you have constructed a type of power divider. There are a lot of different ways to do it. Owen the simpler way is to just parallel all 4 of the 50 ohm loads which gives you a 12 ohm load at the common point, then parallel 2 pieces of 50 ohm coax 1/4 wave long to form a 25 ohm matching section, that will get you back to a 50 ohm common point with no need for a balun. Unfortunately, this would be a common mode nightmare. 73's Richard Clark, KB7QHC ... why? It's a way it's done for broadcasting antennas. There's little reason why the screen of the feeder can run continuously into the screens of the transformer sections and on into the screens of the cables that feed the individual Yagis. If the drive-points of the Yagis are equipped with adequate baluns then there should be no more common-mode current on the outside of the continuous screen than for the case of a single Yagi. Chris Of course I meant to type 'why the screen of the feeder can't run continuously into ...' |
Phasing of stacked Yagis
Owen Duffy wrote:
More likely, 2 - 1/4 wave (with velocity factor)50 ohm coax's to a "Tee" fitting-- Each end also to a "Tee" fitting . ( all 50 ohm coax) (power devider) 2x50 ----------------- 2X Quarter wave | "T" fitting source 50 Ohm 2x50 ----------------- IF this is clear enough-- Jim NN7K Jerry Ok, I understand, you the two inner conductors with a 100 ohm load between them. You have another pair like that from the other two arrays. How do you connect them to the main feedline. Owen |
Phasing of stacked Yagis
On Sun, 14 Dec 2008 23:20:10 -0000, "christofire"
wrote: 50 ohm common point with no need for a balun. If the drive-points of the Yagis are equipped with adequate baluns And your question is about....? 73's Richard Clark, KB7QHC |
Phasing of stacked Yagis
Jim-NN7K . wrote in news:9ch1l.9958$yr3.334
@nlpi068.nbdc.sbc.com: Owen Duffy wrote: Firstly, I didn't write the following, Jim did. More likely, 2 - 1/4 wave (with velocity factor)50 ohm coax's to a "Tee" fitting-- Each end also to a "Tee" fitting . ( all 50 ohm coax) (power devider) 2x50 ----------------- 2X Quarter wave | "T" fitting source 50 Ohm 2x50 ----------------- IF this is clear enough-- Jim NN7K Jim, are you introducing another scheme, or were you trying to explain Jerry's scheme. We sorted Jerry's scheme, he just overlooked some vital details in his first description. (I haven't said it to date, but I dislike Jerry's scheme, principally over its use of the balun.) Yours is another scheme. There are a lot of ways to do it. The original question was over an article's diagram that stated that unequal lines are "WRONG!". Yours and Jerry's responses have not dealt with the original posting, but if anything offered alternatives that might be seen to suggest the original configuration is flawed. Owen |
Phasing of stacked Yagis
"Richard Clark" wrote in message ... On Sun, 14 Dec 2008 23:20:10 -0000, "christofire" wrote: 50 ohm common point with no need for a balun. If the drive-points of the Yagis are equipped with adequate baluns And your question is about....? 73's Richard Clark, KB7QHC Is this a quiz? I simply questioned your statement that the very common arrangement of star-point and transformer, implemented in co-axial line, should be 'a common mode nightmare' as you put it. The middle portion of the diagram (http://www.vk1od.net:80/lost/Fig6.png) posted at the beginning of this thread shows baluns on the drive points of the dipoles and nowadays Yagi antennas for amateur as well as professional use appear to be sold more often with integral baluns. Co-axial feeders always interact to some extent on account of their outer conductors being in the vicinity of the antenna(s) but there are simple steps that can be taken to minimise this. However, I concede there may be some reason to want to combine/power-split using balanced line but ultimately it will need to be connected to a co-axial line - if the intention is to achieve this without use of a balun then I wonder if this would be more of a 'nightmare'. Chris |
Phasing of stacked Yagis
On Mon, 15 Dec 2008 14:19:28 -0000, "christofire"
wrote: Is this a quiz? And then you allow: However, I concede there may be some reason to want to combine/power-split using balanced line but ultimately it will need to be connected to a co-axial line - if the intention is to achieve this without use of a balun then I wonder if this would be more of a 'nightmare'. It must be a quiz - when I point out that Dave does not call out for isolation (*ferrite* BalUns as have been identified through Jerry's and Owen's correspondence) and as you do as an aside - then what is it that you find debatable about my commonplace observation? Common Mode doesn't disappear into the VHF/UHF. Common Mode creates a complex impedance product that is generally unaccounted for (ignored), and would certainly disturb phase relationships where phase relationships are of primary importance. The only other alternative is consuming transmission line in coils to the same purpose. That hasn't been offered as a choice until now. 73's Richard Clark, KB7QHC |
Phasing of stacked Yagis
On Sat, 13 Dec 2008 01:56:27 GMT, Owen Duffy wrote:
I refer to the diagram at http://www.vk1od.net/lost/Fig6.png which is from an article by the then VK2ZAB (now VK3EJ) on stacking Yagis. Hi Owen, This illustration seems to serve other commentary as it is filled with odd eccentricities that are not very germane to the issue you raise below. Eccentricities aside for the moment, I have to make a lot of presumptions about an odd arrangement of 12 radiators. Some of them are symmetrical by groups, but not all of them are symmetrical in toto. I presume the groups are significant; but initially, what they are significant of escapes me. The + and - markings in the top tier four group, along with the commentary, is suggestive; and I have to supply experience in the matter to know that not ALL +s are connected together (and neither are all -s connected together). I presume this top tier is a 4-Bay, but there is nothing to support this except the graphical allusion. Also from experience, I would presume that connections are not horizontally placed, nor diagonally. The impression of incompleteness is accruing. I have highlighted two of the diagrams with a yellow background, and seek opinions on them. This implies (by your statement of "two" diagrams) that along this middle tier of radiators, we have broken away from what might be a 4-Bay; and we are examining three pairs as choices put to an unstated problem. Here, the eccentricity of what looks like an appendix hanging from the folded element is further disturbed by what I can only imagine to be an abstraction for a coax feedline. Incompleteness is compounding. If I am to pursue my forced presumptions, I would have to say that this middle tier lacks many more alternatives in connections and length variations. Incompleteness has reached saturation - which is what I think you are responding to. Referring firstly to the left hand one: I suggest that the figure is in error because the scenario is not ALWAYS wrong. My contention is that at a single frequency, the phase inversion as a result of the left to right swap of one driven element (DE) wrt the other can be fully compensated for by ensuring that low loss feedline to one DE is an odd number of electrical half waves longer than to the other. Where the low loss feedline to one DE is an odd number of electrical half waves longer than to the other, the Yagis are driven in phase. The outcome being that the pattern at that frequency is approximately the same as if equal length feedline branches were used. Well, the original author does neglect to specify length, leaving it to the reader's imagination to "presume" (have to say it) equal feed lengths judged by eye. Unfortunately, the third example explicitly offers this option, but only to those connections where phasing dots are matched. Like I said, there are many missing alternatives. Your imposition of an extra half wavelength in one feed may be technically accurate, but it fights with the importance of their length - which is to be found in the lost commentary, no doubt. I can well guess, but that same commentary may illuminate these limited choices and explain the eccentricities. I wouldn't want to slog through that commentary, however. Referring now to the right hand one: I suggest that the figure is in error because the scenario is not ALWAYS wrong. My contention is that at a single frequency, that where the low loss feedline to one DE is an integral number of electrical full waves longer than to the other, the Yagis are driven in phase. This would be a stretch of the imagination where application has fallen into the ditch to serve argument. If the lengths drive frequency to match to cable proportions in wavelength that do not serve their loads, then such solutions are hardly useful. The outcome being that the pattern at that frequency is approximately the same as if equal length feedline branches were used. Note that I am not trying to excite a purist discussion about branch vs distributed feed arrangements for phased arrays. Am I on the wrong track? I am wondering why you are trying to resurrect this train wreck. 73's Richard Clark, KB7QHC |
Phasing of stacked Yagis
Richard Clark wrote in
: I am wondering why you are trying to resurrect this train wreck. I was seeking comment on the issue of asymetric branch feed topology. It was put to me that accounting for the phase shift due to the different branch lengths does not fully account for the time lag. My contention is that in transforming the problem to the frequency domain, conversion of time lag to phase lag fully and properly accounts for the different branch lengths. Gordon's paper was offered as evidence that my feed was "WRONG!". Yesterday, I note that Kraus has a clear diagram of branch vs distributed feed, and the technique of transposition to offset a half wave phase delay. I also note the ARRL agrees with me (http://www.vk1od.net/lost/Fig7.png (c)), but that isn't a bullet proof recommendation! I am now confident my critic was wrong. Owen |
Phasing of stacked Yagis
On Mon, 15 Dec 2008 21:50:04 GMT, Owen Duffy wrote:
Richard Clark wrote in : I am wondering why you are trying to resurrect this train wreck. I was seeking comment on the issue of asymetric branch feed topology. Hi Owen, That seemed to be a strain based on the illustration offered as it wanders the field. It was put to me that accounting for the phase shift due to the different branch lengths does not fully account for the time lag. My contention is that in transforming the problem to the frequency domain, conversion of time lag to phase lag fully and properly accounts for the different branch lengths. Too many conversions going on there in your statement. I don't see any transformation (conversion?) to OR from the frequency domain; and I don't see what that would offer. Distance, "polarity," phase and time are all hands on the same watch. Their conversion is trivial - as you appear to be rebutting to your critic. Gordon's paper was offered as evidence that my feed was "WRONG!". The offeror left it you to sort it out rather than arguing their own case, hmm? Yesterday, I note that Kraus has a clear diagram of branch vs distributed feed, and the technique of transposition to offset a half wave phase delay. I also note the ARRL agrees with me (http://www.vk1od.net/lost/Fig7.png (c)), but that isn't a bullet proof recommendation! True. I am now confident my critic was wrong. If the criticism is, as you offer above about accounting for "time lag," as if that fell into some special category, then your confidence is well grounded. When I examine your other correspondence to piece together the story, then both sides of the argument have valid points. Yours, being more general, is more conclusive. The second take-home here seems to be, if you wish to teach someone how to perform a task, or build a project, you shouldn't do it with negative examples without being encyclopedic to completion (which invites boredom). A proof with the free version of EZNEC was easily achieved with some minor elaborations for the NBS Yagi. That is the beauty of modeling, it encompasses ALL the ways to fail or succeed. 73's Richard Clark, KB7QHC |
Phasing of stacked Yagis
"Richard Clark" wrote in message ... On Mon, 15 Dec 2008 21:50:04 GMT, Owen Duffy wrote: Richard Clark wrote in m: I am wondering why you are trying to resurrect this train wreck. I was seeking comment on the issue of asymetric branch feed topology. Hi Owen, That seemed to be a strain based on the illustration offered as it wanders the field. It was put to me that accounting for the phase shift due to the different branch lengths does not fully account for the time lag. My contention is that in transforming the problem to the frequency domain, conversion of time lag to phase lag fully and properly accounts for the different branch lengths. Too many conversions going on there in your statement. I don't see any transformation (conversion?) to OR from the frequency domain; and I don't see what that would offer. Distance, "polarity," phase and time are all hands on the same watch. Their conversion is trivial - as you appear to be rebutting to your critic. Gordon's paper was offered as evidence that my feed was "WRONG!". The offeror left it you to sort it out rather than arguing their own case, hmm? Yesterday, I note that Kraus has a clear diagram of branch vs distributed feed, and the technique of transposition to offset a half wave phase delay. I also note the ARRL agrees with me (http://www.vk1od.net/lost/Fig7.png (c)), but that isn't a bullet proof recommendation! True. I am now confident my critic was wrong. If the criticism is, as you offer above about accounting for "time lag," as if that fell into some special category, then your confidence is well grounded. When I examine your other correspondence to piece together the story, then both sides of the argument have valid points. Yours, being more general, is more conclusive. The second take-home here seems to be, if you wish to teach someone how to perform a task, or build a project, you shouldn't do it with negative examples without being encyclopedic to completion (which invites boredom). A proof with the free version of EZNEC was easily achieved with some minor elaborations for the NBS Yagi. That is the beauty of modeling, it encompasses ALL the ways to fail or succeed. 73's Richard Clark, KB7QHC Hi Richard What is the reasoning used to indicate 300 ohm line is used in (B) of the referenced http://www.vk1od.net/lost/Fig7.png .? Jerry |
Phasing of stacked Yagis
On Mon, 15 Dec 2008 23:57:39 GMT, "Jerry"
wrote: Hi Richard What is the reasoning used to indicate 300 ohm line is used in (B) of the referenced http://www.vk1od.net/lost/Fig7.png .? Hi Jerry, It should follow the rule of being the square root of the product of the source and load Z. 73's Richard Clark, KB7QHC |
Phasing of stacked Yagis
"Richard Clark" wrote in message ... On Mon, 15 Dec 2008 23:57:39 GMT, "Jerry" wrote: Hi Richard What is the reasoning used to indicate 300 ohm line is used in (B) of the referenced http://www.vk1od.net/lost/Fig7.png .? Hi Jerry, It should follow the rule of being the square root of the product of the source and load Z. 73's Richard Clark, KB7QHC Hi Richard OK, on the geometric mean, but, the author surely realized *that*. I got the feeling that I was missing something of value when it wasnt obvious to me why 300 ohm line was used. Jerry KD6JDJ |
Phasing of stacked Yagis
"Jerry" wrote in
: .... What is the reasoning used to indicate 300 ohm line is used in (B) of the referenced http://www.vk1od.net/lost/Fig7.png .? The figure is is from the ARRL Antenna Handbook. In (b), the numbers are rounded. A nominal 280 ohm dipole via 1/4 wave of 400 ohm line gives 570 ohms at the tee. Two such branches are paralleled for 285 ohms, which on 300 ohm main feed line line results in a VSWR of 1.05... should be acceptable. Does that help? Owen |
Phasing of stacked Yagis
Richard Clark wrote in
: .... The second take-home here seems to be, if you wish to teach someone how to perform a task, or build a project, you shouldn't do it with negative examples without being encyclopedic to completion (which invites boredom). Richard, That same thought occurred to me on first reading it. Teaching what not to do has its place, but it 'dumbs down' the learner. Explaining the concepts, and how to use them imparts empowering knowledge more than rote learning of negative Rules of Thumb. Still, people keep telling me that that is all old world thinking, today you train (instead of educate) people to specific and narrow tasks, and competency for immediate tasks (train to the need) is more important than knowledge of principles and concepts. I have quals to opearate a fork lift. One of the questions I was asked for assessment was "name six places that you should not park a fork lift". Of course, one cannot just nominate any 6 places that would be inappropriate, it MUST be THE six places on the assessor's list. One of them is "on a railway track". So, rather than training people to identify hazards, and not park the fork lift in a hazardous place or way, "competent people" know the rule to not park the fork lift on a railway track. No doubt accident / incident driven training... a negative driver. (I will leave you to think about 5 other stupid places to park a fork lift!) Owen |
Phasing of stacked Yagis
Keeping in mind simplicity, and , using equal length of 50 0hm
to this power splitter- all antennas should be in phase (all Left elements , to properly phase), and that it gives 4-50 ohm loads for one 50 ohm source. Why reinvent the wheel?? Jim NN7K Owen Duffy wrote: Jim-NN7K . wrote in news:9ch1l.9958$yr3.334 @nlpi068.nbdc.sbc.com: Owen Duffy wrote: Firstly, I didn't write the following, Jim did. More likely, 2 - 1/4 wave (with velocity factor)50 ohm coax's to a "Tee" fitting-- Each end also to a "Tee" fitting . ( all 50 ohm coax) (power devider) 2x50 ----------------- 2X Quarter wave | "T" fitting source 50 Ohm 2x50 ----------------- IF this is clear enough-- Jim NN7K Jim, are you introducing another scheme, or were you trying to explain Jerry's scheme. We sorted Jerry's scheme, he just overlooked some vital details in his first description. (I haven't said it to date, but I dislike Jerry's scheme, principally over its use of the balun.) Yours is another scheme. There are a lot of ways to do it. The original question was over an article's diagram that stated that unequal lines are "WRONG!". Yours and Jerry's responses have not dealt with the original posting, but if anything offered alternatives that might be seen to suggest the original configuration is flawed. Owen |
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