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Chuck, WA7RAI wrote:
"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 boom length." Close element spacing was once used to make a class called supergain antennas. Kraus notes in his 1950 "Antennas" that: "Until the antenna power was considered by G.H. Brown (Proc. I.R.E. January, 1937) the advantages of closely spaced elements were not appreciated." The W8JK array by Kraus is closely spaced. Kraus notes a downside: "Hence, a considerable reduction in radiating efficiency may result from the presence of any loss resistance, (The radiatiation resistance drops as spacing shrinks.)" See "Antennas" edition 3 for close spaced antennas. Best regards, Richard Harrison, KB5WZI |
Richard Harrison wrote in message ... "Hence, a considerable reduction in radiating efficiency may result from the presence of any loss resistance, (The radiatiation resistance drops as spacing shrinks.)" See "Antennas" edition 3 for close spaced antennas. Best regards, Richard Harrison, KB5WZI Hi Richard, Indeed. And Kraus' speculation in this regard has been the basis for some debate, if I recall. It is my opinion that .1 lambda spacing has been somewhat established as optimum spacing for a 2 el yagi with a director - and I get the impression that this is the basic structure that Art is using as a benchmark. Perhaps the next step is to determine whether the modeled gain Art is getting is a result of artifacts or not. 73 de Chuck, WA7RAI |
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"Chuck" wrote in message news:DCyed.11049$6P5.8562@okepread02... wrote in message news:oYeed.289823$MQ5.38322@attbi_s52... YES Hi Art, snip. If you haven't already done do, I would be trying frequency sweeps over a limited bandwidth, and scaling them to higher frequencies to see if the results remain consistent. If not, this could be an indication of artifacts. I'l think about that I get the impression you are making physical models to test as well. Perhaps scaling to a much higher freq, say 50 or 145 mHz or so, would make FS tests more manageable. The goal, is to simply determine if the gain of the experimental structure is greater than that of the benchmark (the 2 el yagi) - measuring the exact amount, should be of no real concern at this point. 73 de Chuck, WA7RAI Chuck, I am an experimentor, I am not advocating changing the aproach to antennas by amateurs When light weight fishing poles on E Bay became less than a dollar a foot I was able to get rid of most of my aluminum stock.When I got Beasely's NEC Pro program all prior constraints regarding antenna experimenting were removed (ala aluminum or copper foil). Last year I made a 160M dipole that was rotatable and frequency controlable with moveable bandwidth, I succeeded, but it still was a large structure and winter provided many unwanted occasions to repair the unexpected. This winter I am being less ambitious and am confining myself to a 8 foot boom. First I was to check if more elements can improve the gain. From prior experiments I knew that feed impedance can be change upwards by placing an element close the rear of the feed dipole which is contrary to the ARRL handbook. I also was aware from previous experiments that element diameter was very important if one is not controlled by mechanical requirements. I also knew from reading that in stacking when only the bottom array was being used one obtained protection from static noise so this would also be a good opportunity to have one element say 30 inches higher than the rest on the mast which would be part of the original array to give room for experimentation. My present model has a gain of 13 dbi at a ht of 820 inches over perfect ground and is less than 2:1 across the audio portion of 20 M. The number of elements is six which suggest things are heavy but with fishing poles it is extremely light. ( note, fishing poles when ice laden bend as if it had caught a fish and the ice then slides off) I have not used the f/b to rest upon as I believe that the lower lobe at the rear is not important where the second lobe is when considering direction of propagation. So thats it Chuck, I enjoy myself with playing with antennas to find out things for myself as I have more options at hand that the ARRL have not considered as yet and thus are not held hostage to the knoweledge of the many psuedo experts who thou knoweledgable about the past which is very usefull have decided that there is no future since all is known. By the way with the advent of cheap cameras $30 it is easy to place a SWR meter or power meter right at the feed point and eliminate questions regarding transmission lines. Regards Art |
"Chuck" wrote in message
A reduced-noise (E-field loaded) vertical for 40m with a VSWR bandwidth of 1.3:1 from 7.0 to 7.3 mHz, (it's not a dummy load as one would generally deduce from the above description), and has proven to be as good a performer on DX and local as my conventional top loaded vertical. What is E-field loaded? Not sure what you mean with that... The conventional vertical sees a noise level here of around S-7 or greater, and the E-field loaded vertical, around S-3 to S-5 (on IC-756, normal BW, no NB, no DSP). I'd be very leary...Also would depend on the polarization of the noise, and any possible changes in the pattern...But in general, if a certain vertical picks up more far field noise than another, it's the superior vertical. Noise is rf like any other signal. So unless I'm missing something here, the conventional antenna should also receive the *desired* signal better than the low noise version. And being things are generally reciprical, it should probably transmit a better signal also...How careful have your on the air tests been? Are you quickly A/B'ing using a switch? Needless to say, I'm kind of dubious of the claims of equal performance. Unless the noise was common mode or polarity related, I've never seen an antenna that received lower noise, outdo one that picked up more noise. If the change is not efficiency related, that would leave me to think that your vertical pattern is being skewed somewhat, and is more horizontally polarized than the other, and thus , picks up less vertically polarized noise. If thats not the case, I would think the low noise version is less efficient. Just my opinion tho... Neither of these were developed using computer modeling, though. Neither were my comments...:/ MK |
"Chuck" wrote in message news:B3Ted.11167$6P5.7719@okepread02... wrote in message news:MzAed.448084$Fg5.138935@attbi_s53... "Chuck" wrote in message news:DCyed.11049$6P5.8562@okepread02... wrote in message news:oYeed.289823$MQ5.38322@attbi_s52... YES Hi Art, snip. If you haven't already done do, I would be trying frequency sweeps over a limited bandwidth, and scaling them to higher frequencies to see if the results remain consistent. If not, this could be an indication of artifacts. I'l think about that I get the impression you are making physical models to test as well. Perhaps scaling to a much higher freq, say 50 or 145 mHz or so, would make FS tests more manageable. The goal, is to simply determine if the gain of the experimental structure is greater than that of the benchmark (the 2 el yagi) - measuring the exact amount, should be of no real concern at this point. 73 de Chuck, WA7RAI Chuck, I am an experimentor, I am not advocating changing the aproach to antennas by amateurs Hi Art, I apologize if I gave that impression. When light weight fishing poles on E Bay became less than a dollar a foot snip A 2:1 VSWR bandwidth over the 20m phone portion implies a good Q, but aren't you even a bit curious if the gain is indeed as high as 13 dBi? Funnily today I changed the model slightly and the gain exceeded 14 dbi with an increase in Q So this is the model that I am going to make but with the anticipation that by curving the elements I will narrow the beam width. It shows 66 degrees at the moment and a take off angle of 12 degrees. It should be up in a few weeks. When I test I will look for feed impedance and lobe width using a laptop program with a distant signal. I seem to recall from years ago, a yagi that had several close spaced directors on a relatively short boom - I just can't recall if it was commercial, in an article, or any other significant details about it. It may have been the 13 element I made for 20 M on I think a 80 foot boom and that was the first time I used two reflectors to get a 50 ohm feed. I seem to remember that Roy modelled that also on EZNEC or is it ELNEC and he confirmed the 50 ohm feed as did my modelling and the actual antenna.This was about 10 years ago. So thats it Chuck, I enjoy myself with playing with antennas to find out things for myself as I have more options at hand that the ARRL have not considered as yet and thus are not held hostage to the knoweledge of the many psuedo experts who thou knoweledgable about the past which is very usefull have decided that there is no future since all is known. By the way with the advent of cheap cameras $30 it is easy to place a SWR meter or power meter right at the feed point and eliminate questions regarding transmission lines. Regards Art The camera idea is a good one :) Yes I first used a micro video camera for direction of my prop pitch rotor and then to observe stepping motor angles on capacitors There are always new things to learn... My latest experiments have produced some unusual antennas: A unique dipole that does not inductively couple with surrounding conductors (the perfect attic dipole), that can be 'tuned' at ground level, which, at first glance, appears to have a somewhat omni- directional pattern. A reduced-noise (E-field loaded) vertical for 40m with a VSWR bandwidth of 1.3:1 from 7.0 to 7.3 mHz, (it's not a dummy load as one would generally deduce from the above description), and has proven to be as good a performer on DX and local as my conventional top loaded vertical. The conventional vertical sees a noise level here of around S-7 or greater, and the E-field loaded vertical, around S-3 to S-5 (on IC-756, normal BW, no NB, no DSP). Neither of these were developed using computer modeling, though. Keep up the fun... Well that seems all very interesting but you are very much out of my league which is just as well because mention of E and H waves agitates the experts more than my talk of coupling does Art 73 de Chuck, WA7RAI |
Chuck, WA7RAI wrote:
"Indeed. And Kraus` speculation in this regard has been the basis for some debate if I recall." Kraus gets support from Terman`s 1955 edition on page 906: "A characteristic of all close-spaced arrays is that as size to antenna gain is reduced, the radiation resistance also goes down; this is illustrated by Fig. 23-36." Best regards, Richard Harrisopn, KB5WZI |
Richard Harrison wrote in message ... Chuck, WA7RAI wrote: "Indeed. And Kraus` speculation in this regard has been the basis for some debate if I recall." Kraus gets support from Terman`s 1955 edition on page 906: "A characteristic of all close-spaced arrays is that as size to antenna gain is reduced, the radiation resistance also goes down; this is illustrated by Fig. 23-36." Best regards, Richard Harrisopn, KB5WZI Hi Richard, No one can argue with Kraus and Terman or anyone else on this. What is "debatable" is: at what point does radiation resistance become too low - where high current losses cancels any gain achieved by the tight coupling. This is JMO, of course. 73 de Chuck, WA7RAI |
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Mark Keith wrote in message om... "Chuck" wrote in message A reduced-noise (E-field loaded) vertical for 40m with a VSWR bandwidth of 1.3:1 from 7.0 to 7.3 mHz, (it's not a dummy load as one would generally deduce from the above description), and has proven to be as good a performer on DX and local as my conventional top loaded vertical. What is E-field loaded? Not sure what you mean with that... The conventional vertical sees a noise level here of around S-7 or greater, and the E-field loaded vertical, around S-3 to S-5 (on IC-756, normal BW, no NB, no DSP). I'd be very leary...Also would depend on the polarization of the noise, and any possible changes in the pattern...But in general, if a certain vertical picks up more far field noise than another, it's the superior vertical. Noise is rf like any other signal. So unless I'm missing something here, the conventional antenna should also receive the *desired* signal better than the low noise version. And being things are generally reciprical, it should probably transmit a better signal also...How careful have your on the air tests been? Are you quickly A/B'ing using a switch? Needless to say, I'm kind of dubious of the claims of equal performance. Unless the noise was common mode or polarity related, I've never seen an antenna that received lower noise, outdo one that picked up more noise. If the change is not efficiency related, that would leave me to think that your vertical pattern is being skewed somewhat, and is more horizontally polarized than the other, and thus , picks up less vertically polarized noise. If thats not the case, I would think the low noise version is less efficient. Just my opinion tho... Neither of these were developed using computer modeling, though. Neither were my comments...:/ MK Hi MK, When I stated: (it's not a dummy load as one would generally deduce from the above description) I wasn't joking. The fact that you've never known a vertical antenna to behave in this manner, is not surprising. The purpose of my experiment was to investigate the possibility of loading (shortening) an element while still maintaining a relatively normal BW. Avoiding parallel wires and coils, the resulting loading system is what I call E-field loading (perhaps a poor choice of terms) - a method of conductive loading that resulted in reducing the off-resonance reactance in the FP. I suspect it is effecting the susceptance of the voltage loop in some way. The unexpected bonus, of course, was a reduced susceptibility to electrical noise. 73 de Chuck, WA7RAI |
You place another element closely (behind usually) to the driven element
such that with a 'critical coupling' the feed impedance increases to the desired level. It is beyond me why antenna manufactures still ask people to match to a low impedance which provides losses, when the antenna can be provided with a feed impedance of 50 Ohm ! I must be in error ofcourse with the above statement as everything is already known and utilised May I also point out that if you allow elements to vary in diameter and height and still keeping to a .1 boom length, gain increases until ultimately the elements form a combined parabolic shape and progressively place rearward radiation energy into the forward direction until the ultimate is reached, where there is no radiation to the rear and F/B is absent. I would remind you that the top element is going to be designed to be disconnected and connected to ground to determine impact on static noise. It is also my intent to string nylon from one end of the elements to the other, progresively tightening it until a suitable bend or bow is put in place such that the beam width narrows to somewhere in the range of 30 degrees. (ala point to point to get highes gain together with a lower take off angle) I do have a fold over tower by the way over 1/2 acre of clear ground with embedded wire screen and I am surrouded by sloping farmland with Drummond soil..The 1 inch hardline is routed undeground. The above experimentation is why I have so much fun with antenna experimenting where in other ways the experts would say it is useless to try before I even put my shoes on. Regards Art "Chuck" wrote in message news:w6bfd.12458$6P5.534@okepread02... wrote in message news:08_ed.243129$wV.18192@attbi_s54... "Chuck" wrote in message news:B3Ted.11167$6P5.7719@okepread02... ... A 2:1 VSWR bandwidth over the 20m phone portion implies a good Q, but aren't you even a bit curious if the gain is indeed as high as 13 dBi? Funnily today I changed the model slightly snipped I am curious: how are you handling the driven element's low input impedance? ... Keep up the fun... snipped Hardly :) 73 de Chuck, WA7RAI |
You place another element closely (behind usually) to the driven element
such that with a 'critical coupling' the feed impedance increases to the desired level. It is beyond me why antenna manufactures still ask people to match to a low impedance which provides losses, when the antenna can be provided with a feed impedance of 50 Ohm ! I must be in error ofcourse with the above statement as everything is already known and utilised May I also point out that if you allow elements to vary in diameter and height and still keeping to a .1 boom length, gain increases until ultimately the elements form a combined parabolic shape and progressively place rearward radiation energy into the forward direction until the ultimate is reached, where there is no radiation to the rear and F/B is absent. I would remind you that the top element is going to be designed to be disconnected and connected to ground to determine impact on static noise. It is also my intent to string nylon from one end of the elements to the other, progresively tightening it until a suitable bend or bow is put in place such that the beam width narrows to somewhere in the range of 30 degrees. (ala point to point to get highes gain together with a lower take off angle) I do have a fold over tower by the way over 1/2 acre of clear ground with embedded wire screen and I am surrouded by sloping farmland with Drummond soil..The 1 inch hardline is routed undeground. The above experimentation is why I have so much fun with antenna experimenting where in other ways the experts would say it is useless to try before I even put my shoes on. Regards Art "Chuck" wrote in message news:w6bfd.12458$6P5.534@okepread02... wrote in message news:08_ed.243129$wV.18192@attbi_s54... "Chuck" wrote in message news:B3Ted.11167$6P5.7719@okepread02... ... A 2:1 VSWR bandwidth over the 20m phone portion implies a good Q, but aren't you even a bit curious if the gain is indeed as high as 13 dBi? Funnily today I changed the model slightly snipped I am curious: how are you handling the driven element's low input impedance? ... Keep up the fun... snipped Hardly :) 73 de Chuck, WA7RAI |
"Chuck" wrote in message
Hi MK, When I stated: (it's not a dummy load as one would generally deduce from the above description) I wasn't joking. The fact that you've never known a vertical antenna to behave in this manner, is not surprising. Oh, I have, but the lower noise was always due to increased losses somewhere in the system... The purpose of my experiment was to investigate the possibility of loading (shortening) an element while still maintaining a relatively normal BW. Adding loss would do that... Avoiding parallel wires and coils, the resulting loading system is what I call E-field loading (perhaps a poor choice of terms) - a method of conductive loading that resulted in reducing the off-resonance reactance in the FP. Still doesn't say too much... I suspect it is effecting the susceptance of the voltage loop in some way. Ditto...But I don't know how long the vertical is. Being you need loading, I'll assume it's shorter than a quarter wave...Dunno...This just doesn't really add up to me...I've fed verticals in many points, at the max current, or max voltage points, or in between, and have never seen this to effect noise pickup. Again, the only thing I've ever seen to reduce noise, *and* keep the same pattern, was to increase loss. The unexpected bonus, of course, was a reduced susceptibility to electrical noise. Due to extra losses? If you reduce susceptibility to far field electrical noise, you are also reducing the desired signals at those same angles. Rf is rf...What am I missing here? Myself, I consider the so called "low noise" antennas to be old wives tails... Even the shielded electrostatic versions, for the most part. IE: shielded loops, etc...They are no more quiet than any other well balanced loop made of normal wire windings. The shielded design is not to magically reduce noise, it's to ensure balance. I'm not trying to be ornery, but so far, what I read is not flushing to *me*...But I don't believe in "low noise" antennas. To me, low far field noise compared to another vertical antenna at the same angles and same polarization, means increased loss somewhere if the pattern hasn't changed. :( MK |
Art Unwin wrote:
"You place another element closely (behind usually) to the driven element such that with a "critical coupling" the feed impedance increases to the desired level." That`s not the way it works. More coupling lowers the feed impedance. Check under "Close-spaced Arrays -- Super-=gain Antennas" on page 906 of Terman`s 1955 edition: "A characteristic of all close-spaced arrays is that as the ratio of size to antenna gain is reduced, the radiation resistance also goes down;---." The Yagi antenna of Fig.23-39, and the corner reflector, represent almost the best that can be achieved in a compact array." Notice that Terman said "almost". There`s always hope, but looking for more gain by element spacing changes has been thoroughly investigated. This is akin to to drilling in a field which is already overdrilled in the search for oil. Moving elements closer together brings the radiation resustance down. The elements don`t know if a coupled element is ahead of the driven element or behind it. It brings the drivepoint impedance down for the driven element. Impedance adjustment is done through transformation. Best regards, Richard Harrison, KB5WZI |
Mark Keith wrote in message om... "Chuck" wrote in message ... I suspect it is effecting the susceptance of the voltage loop in some way. Ditto...But I don't know how long the vertical is. Being you need loading, I'll assume it's shorter than a quarter wave... Hi Mark, Yes, its vertical height is 23 ft. It is elevated 6' above ground with elevated horizontal radials. The input Z at the junction of the radials and DE is 50 ohm j0 with no matching system. There is a current un-un at the feedpoint, thus no common-mode, and the Tx line is 1wl electrical. The experiments with this type of loading was begun around '95 - '96, and this vertical antenna was erected in '98. It has been through near I/2 solar cycle, and all seasons. Time has a way of dispelling illusions, and don't think for a moment that I ignored the "loss" question. To me, low far field noise Do not assume all noise is the same or that all originates in the 'far field' as EM particle-waves. 73 de Chuck, WA7RAI |
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Then the book is incorrect assuming you are using statements corectly
Art "Richard Harrison" wrote in message ... Art Unwin wrote: "You place another element closely (behind usually) to the driven element such that with a "critical coupling" the feed impedance increases to the desired level." That`s not the way it works. More coupling lowers the feed impedance. Check under "Close-spaced Arrays -- Super-=gain Antennas" on page 906 of Terman`s 1955 edition: "A characteristic of all close-spaced arrays is that as the ratio of size to antenna gain is reduced, the radiation resistance also goes down;---." The Yagi antenna of Fig.23-39, and the corner reflector, represent almost the best that can be achieved in a compact array." Notice that Terman said "almost". There`s always hope, but looking for more gain by element spacing changes has been thoroughly investigated. This is akin to to drilling in a field which is already overdrilled in the search for oil. Moving elements closer together brings the radiation resustance down. The elements don`t know if a coupled element is ahead of the driven element or behind it. It brings the drivepoint impedance down for the driven element. Impedance adjustment is done through transformation. Best regards, Richard Harrison, KB5WZI |
No Chuck, that is not going to happen.When you are an experimentor you don't
have to be hindered by diminishing returns as it is the chase that is the most rewarding part. There has been many oilfields and silver mines that have been abandoned ONLY because of diminishing returns which is usually because of greed and not for the joy of doing what one likes to do. For those who quote from books without a real understanding of what is being said are doomed to only quoting books without the self determination needed to explore new frontiers. A book is to be used to explore the past but to explore the future one has to avoid generating bed sores and procrastination and explore what the future holds for those who are willing to move without fear of failure. On diminishing rear radiation, that can only go so far as the efficiency relates heavily to the ratio of the element diameters relative to spacing of elements on the reflective medium, so one can easily be disapointed when stacking two 2 element beams using only 4 elements instead of the many required for a "dish", but the low take off angle can still be reproduced as well as a narrow beam with extra gain if the corrective reflective contour can be obtained. Sure beats argueing about current decline versus current drop versus current flow or what pack of wolves to join. By the way, do you know if dish antennas suffer from static like dipole arrays? I would think they would be immune but I really don't know. Regards Art KB9MZ XG "Chuck" wrote in message news:hSwfd.12591$6P5.1429@okepread02... wrote in message news:vYcfd.314858$3l3.210855@attbi_s03... ... May I also point out that if you allow elements to vary in diameter and height and still keeping to a .1 boom length, gain increases until ultimately the elements form a combined parabolic shape and progressively place rearward radiation energy into the forward direction until the ultimate is reached, where there is no radiation to the rear and F/B is absent. I would remind you that the top element is going to be designed to be disconnected and connected to ground to determine impact on static noise. It is also my intent to string nylon from one end of the elements to the other, progresively tightening it until a suitable bend or bow is put in place such that the beam width narrows to somewhere in the range of 30 degrees. (ala point to point to get highes gain together with a lower take off angle) I do have a fold over tower by the way over 1/2 acre of clear ground with embedded wire screen and I am surrouded by sloping farmland with Drummond soil..The 1 inch hardline is routed undeground. The above experimentation is why I have so much fun with antenna experimenting where in other ways the experts would say it is useless to try before I even put my shoes on. Regards Art Many years ago - before computer modeling - I was talking with a fellow down under (VK or ZL, I can't recall) who was experimenting with parabolic elements. Like you, he was using fishing line to achieve the shape. Don't let banal criticism get under your skin... not everyone feels secure when venturing to the outer edge of the envelope g 73 de Chuck, WA7RAI |
Art Unwin wroyte:
"Then the book is incorrect assuming you are using statements correctly." I included page numbers to make it easy to check the accuracy of my translation. Art said elements are "critically coupled". Critical coupling is defined as maximum energy transfer at the resonant frequency. Coupling additions (more loads) to a feedpoint lowers the impedance unless additional measures (transformations) are taken. Coupling more loads to a feedpoint is tantamount to paralleling resistors. Terman is right. Best regards, Richard Harrison, kB5WZI |
"Critical" coupling is a coupling that achieves that which is desired in the
application involved. Thus "critical" coupling varies dependent on the situation or application involved which in your 'specific ' application may well be defined as you stated but is not all inclusive.. That's how I see it and what I spoke of is confirmed by NEC and by personal experimentation If you choose to disagree that is your choice but goes directly to my statement regarding quoting of text without full understanding. I have no interest in argueing the fact, try somebody else. Art "Richard Harrison" wrote in message ... Art Unwin wroyte: "Then the book is incorrect assuming you are using statements correctly." I included page numbers to make it easy to check the accuracy of my translation. Art said elements are "critically coupled". Critical coupling is defined as maximum energy transfer at the resonant frequency. Coupling additions (more loads) to a feedpoint lowers the impedance unless additional measures (transformations) are taken. Coupling more loads to a feedpoint is tantamount to paralleling resistors. Terman is right. Best regards, Richard Harrison, kB5WZI |
I wrote:
"Critical coupling is defined as maximum energy transfer at the resonant frequency." Also: "Coupling additions (more loads) to a feedpoint lowers the impedance unless additional measures (transformations) are taken." I`ve since consulted Terman, and critical coupling is defined as I said above. Terman adds coupled elements differently than I did above. On page 64 of his 1955 edition, Terman defines critical coupling as: "These trends continue as the coefficient of coupling is increased until the coupling is such that the resistance which the secondary circuit couples into the primary at resonance is equal to the primary resistance. This is called the CRITICAL COUPLING and causes the secondary current to have the maximum value it can attain." On page 65, Terman`s statement supports Art: "When the coupled impedance is added to the self-impedance of the primary circuit, the effect at resonance is to increase the effective primary resistance above the value that would exist in the absence of the secondary. This causes the primary current at resonance to be reduced in all cases by the presence of the secondary." I wrongly assumed a coupled load would add to the primary current. I apologize to Art and to others who I misled. Best regards, Richard Harrison, KB5WZI |
Richard,
It was ten years ago that this subject came up and which I used as a basis for parallel circuit antennas versus series type antennas. It also led to the use of circuitry analysis (complex circuitry) to provide for lossless feed systems and cluster coupled antennas. All of the above was ridiculed by the experts over the years because of my use of element coupling terminology, such that what it pertained to was never taken seriously and sometimes mocked. What is more frausterating to me is that many commercial antennas still pursue gain to the extent that low impedance occurs and where the purchaser is forced to purchase loss generating matching systems which robs him of some of the purchased gain. Force1 even notes in their literature that manufactures are supplying poor matching impedances in the search of financial competitive gain YOU are the first expert on this newsgroup to take a step back and pursued a rethink of this subject and supplied your findings in a posting. Possibly some will now subject you to ridicule or, if your enunciation of Terman is convincing enough, will say they knew it all the time but preferred to pursue harassement. I thank you from the bottom of my heart for your courage shown in your last posting and hopefully, others will build on, or pursue the implications/contents of your posting. Best regards Art KB9MZ Xg "Richard Harrison" wrote in message ... I wrote: "Critical coupling is defined as maximum energy transfer at the resonant frequency." Also: "Coupling additions (more loads) to a feedpoint lowers the impedance unless additional measures (transformations) are taken." I`ve since consulted Terman, and critical coupling is defined as I said above. Terman adds coupled elements differently than I did above. On page 64 of his 1955 edition, Terman defines critical coupling as: "These trends continue as the coefficient of coupling is increased until the coupling is such that the resistance which the secondary circuit couples into the primary at resonance is equal to the primary resistance. This is called the CRITICAL COUPLING and causes the secondary current to have the maximum value it can attain." On page 65, Terman`s statement supports Art: "When the coupled impedance is added to the self-impedance of the primary circuit, the effect at resonance is to increase the effective primary resistance above the value that would exist in the absence of the secondary. This causes the primary current at resonance to be reduced in all cases by the presence of the secondary." I wrongly assumed a coupled load would add to the primary current. I apologize to Art and to others who I misled. Best regards, Richard Harrison, KB5WZI |
Art Unwin wrote:
"My ARRL books go back a decade or more and the graphs showing the gain per boom length has several curves based on different measurements e.t.c." I haven`t encountered similar curves based on NEC, but I`ve found thye old ARRL curves on page 163 of my 1970 edition of the "A.R.R.L. Antenna Book" (cover price=$2.50). Variation between curves from 3 different groups of observers are within "1 S-unit" (6 dB). Gain ranges from a minimum of about 7 dB for a Yagi with a 1/2-wave boom length (pessimistic) to a 19 dB gain for a 6.5-wavelength boom length (optimistic). The optimistic curve is labeled "Greenblum", and seems too good to be true. The other two curves have flattened out as the number of wavelengths increases. The Greenblum curve is almost a straight line. As Kraus showed in his solution to the Deutsche Welle antenna gain problem, you often need to double the total number of elements to get a 3 dB antenna gain. Best regards, Richard Harrison, KB5WZI |
Richard, the more I study the boom length question the more I feel that the
ARRL should drop the three curve gain/boom length graph. First there has to be a condition that all elements are on the same plane. The other condition must be that all the elements are straight and parallel. The more I study the two element antenna I find that changing the added element height relative to one another , even if a small distance , can change the gain. I understand that there are "Landorfer ?"curved elements that can also increase the gain. I also proved that by NEC. If one allows elements numbers to be added to increase ad hoc then NEC shows that a quasi dish shape will occur where the focus can stay equal to .1 wavelength and where gain increases to over 14 dbi. If one takes a further step by "shaping "the elements whether it be the feed element or the reflective elements then not only does the beam width narrow with increased gain but the TAO decreases about one degree which is a huge advantage when using small garden type antennas. Based on the above findings it would be impossible to generate a NEC curve that would make sense unless the above two conditions are set in place for the average amateur. The latter would give some protection against fraudulent vendors and supply a datum curve that is meaningful to all. I do believe that this posting should put an end to this thread and I thank you again for your input. Regards Art "Richard Harrison" wrote in message ... Art Unwin wrote: "My ARRL books go back a decade or more and the graphs showing the gain per boom length has several curves based on different measurements e.t.c." I haven`t encountered similar curves based on NEC, but I`ve found thye old ARRL curves on page 163 of my 1970 edition of the "A.R.R.L. Antenna Book" (cover price=$2.50). Variation between curves from 3 different groups of observers are within "1 S-unit" (6 dB). Gain ranges from a minimum of about 7 dB for a Yagi with a 1/2-wave boom length (pessimistic) to a 19 dB gain for a 6.5-wavelength boom length (optimistic). The optimistic curve is labeled "Greenblum", and seems too good to be true. The other two curves have flattened out as the number of wavelengths increases. The Greenblum curve is almost a straight line. As Kraus showed in his solution to the Deutsche Welle antenna gain problem, you often need to double the total number of elements to get a 3 dB antenna gain. Best regards, Richard Harrison, KB5WZI |
Art Unwin wrote:
"I do believe that this posting should put an end to this thread and I thank you again for your input." All the questions answered? Any topic is eventually tiresome, but not everyone tires of it at the same time. Gain per unit length is likely not a straight line at any particular frequency. There is probably much more to be said about best coupling for maximum gain. There was an article by Joe Reisert, W1JR in the December 1986 issue of "Ham Radio" about a 28-element, 21-foot boom, 432 MHz (about 70 cm WL) Yagi Joe built. The gain was about 19 dBi, or about 0.9 dB per foot at 432 MHz. The pattern shown and gain are said to come from MININEC. Best regards, Richard Harrison, KB5WZI |
Richard Harrison wrote:
There was an article by Joe Reisert, W1JR in the December 1986 issue of "Ham Radio" about a 28-element, 21-foot boom, 432 MHz (about 70 cm WL) Yagi Joe built. The gain was about 19 dBi, or about 0.9 dB per foot at 432 MHz. The pattern shown and gain are said to come from MININEC. Best regards, Richard Harrison, KB5WZI That was a 24 foot (7.3 wavelength) antenna, with 19.15 dBi claimed, which was actually higher than newer modeling programs give it. tom K0TAR |
Richard Harrison wrote:
There was an article by Joe Reisert, W1JR in the December 1986 issue of "Ham Radio" about a 28-element, 21-foot boom, 432 MHz (about 70 cm WL) Yagi Joe built. The gain was about 19 dBi, or about 0.9 dB per foot at 432 MHz. The pattern shown and gain are said to come from MININEC. Best regards, Richard Harrison, KB5WZI Oops, my mistake, 10.5 wavelengths, and about .9 dB under what it could be, assuming the model is correct for mininec. tom K0TAR |
There is probably much
more to be said about best coupling for maximum gain. Maximum Gain, that seems to be all people think about. Max. Gain is not always a good thing. Example which is better for 2 meter mobile a 1/4 wave 0 dB whip a 3 dB 5/8 wave or a 6 dB collinear ? A true 6 dB collinear makes a very poor mobile antenna. Unless your parked on level ground, then it works fine. The 3 dB 5/8 wave works good if you are on fairly flat terrain. But get into the mountains or use repeaters that are on 10,000 ft. + mountains like we have here in WY and Colorado. A 0 dB 1/4 wave whip can some times work better. People put a 3 dB gain mag mount on the back corner of the finder, setting at a 30 degree angle and wonder why it don't work as well as my 0 dB 1/4 wave mounted in the center of the roof of a van. (Mounted in a hole in the roof, not a mag mount.) All I am saying is there is more to an antenna than Max gain. What about bandwidth, pattern etc. There, I feel better. 73 Al Lowe N0IMW Arrow Antenna |
"N0IMW" wrote in message ... There is probably much more to be said about best coupling for maximum gain. Maximum Gain, that seems to be all people think about. Max. Gain is not always a good thing. Example which is better for 2 meter mobile a 1/4 wave 0 dB whip a 3 dB 5/8 wave or a 6 dB collinear ? A true 6 dB collinear makes a very poor mobile antenna. Unless your parked on level ground, then it works fine. The 3 dB 5/8 wave works good if you are on fairly flat terrain. But get into the mountains or use repeaters that are on 10,000 ft. + mountains like we have here in WY and Colorado. A 0 dB 1/4 wave whip can some times work better. People put a 3 dB gain mag mount on the back corner of the finder, setting at a 30 degree angle and wonder why it don't work as well as my 0 dB 1/4 wave mounted in the center of the roof of a van. (Mounted in a hole in the roof, not a mag mount.) All I am saying is there is more to an antenna than Max gain. What about bandwidth, pattern etc. There, I feel better. 73 Al Lowe N0IMW Arrow Antenna Son, you forgot "loss". When I drilled that hole in the middle of the roof of the brand new Durango, I married that truck. Then there are the two BIG holes, one in each rear quarterpanel. At 90,000 miles I'm about to do the FIRST brake job; It's an OK truck. Anyone remember how Chrysler's still in business? Anyway, here's my rig: Comet 144/222/440 on an NMO mount topside center, small Hi-Q screwdriver 5' above ground on the left rear quarterpanel. Tarheel 4' screwdriver 4' above ground with a 4' whip on the right rear quarter panel, toroidal transformer matched for 20 ohms. For 160/80 I also have a BIG Hi-Q for the right side. Rigs are Kenwood: 742 and 480HX. No tuners. 73 H., NQ5H |
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Hi Richard Unfortunatly shortly after making his last post Art was rushed to hospital and underwent emergency surgery to remove a miss-behaving gall bladder. At the time of writing I have been informed he is recovering and hopes to be home in about a week or so. Regards Derek unwin Hope all goes well and he is back to antenna stuff soon, wishing speedy recovery. While speaking of gall bladder, my XYL had bad attack of gall stones, instead of going for operation we dissolved the stones with apple juice/lemon jucie/oil tretment and avoided the knife. Worth looking into it and do it as preventive measure from time to time. Info is on Internet pages under alternative medicine. GL Yuri, K3BU.us |
Richard Clark wrote in message . ..
On 30 Oct 2004 03:29:59 -0700, (Derek Unwin) wrote: At the time of writing I have been informed he is recovering and hopes to be home in about a week or so. Regards Derek unwin Hi Derek, I hope all goes well without complications for your father. 73's Richard Clark, KB7QHC Hi Richard Thank you for your kind regards, I am sure Art will appreciate them. I must point out I am his brother. Regards Derek. |
Derek Unwin wrote:
Richard Clark wrote in message . .. On 30 Oct 2004 03:29:59 -0700, (Derek Unwin) wrote: At the time of writing I have been informed he is recovering and hopes to be home in about a week or so. Regards Derek unwin Hi Derek, I hope all goes well without complications for your father. 73's Richard Clark, KB7QHC Hi Richard Thank you for your kind regards, I am sure Art will appreciate them. I must point out I am his brother. Regards Derek. Hi Derek, here's hoping Art will be back on here shortly, hearty and hale and ready to tell us more about his ideas. 73, Tom Donaly, KA6RUH |
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