Roy Lewallen wrote:
I haven't had the time to participate in this, but in a brief look, it looks pretty silly. Of course EZNEC shows no current difference across a load. The EZNEC model of a load has zero length, so the current at both terminals has to be the same. It appears that EZNEC also doesn't account for phase shifts across a zero length coil. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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Cecil Moore wrote in message ...
Mark Keith wrote: As far as the reverse currents Cecil mentions, I'd have to ponder that a while. While you are pondering, here is a quote from _Antenna_Theory_, by Balanis. "Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forward and backward) and represented by traveling wave currents 'If' and 'Ib' in Figure 10.1(a)." Standing wave antennas necessarily have standing waves caused by forward waves and reflected waves. Analyze any coil subjected to forward current and reflected current and you will be forced to agree that the current at one end of the coil is not the same as the current at the other end of the coil. W8JI is thinking lumped circuits when he should be thinking distributed networks. The phase shift through the coil changes the phase relationship between the forward current and reflected current, so of course, their superposed value will be different at each end of the coil. How much though? What would be an average ratio difference you would be likely to see on a 8 ft center loaded whip? Or lets go one better...What would be a likely "worse case" scenario? Will this vary from antenna to antenna? I would think so. I've never said there would not be a difference. I actually expect a small difference. But I still don't think it would be a large amount. Will this change in value be enough to cause large errors in modeling these antennas? It's already obvious to me that any info I may gleen from these tests will have no impact on the position of my loading coils, being I already use them at the optimum heights. Or as close as physically possible anyway. So any info gleaned from these tests would only be useful from a modeling aspect. And I'm not in a position to really comment on that too much. I don't design modeling engines. Is it your opinion that the modeling we now see with these antennas and coils is quite flawed? It's obvious Yuri seems to think so. Myself, I really don't know at this point. I've never worried about it too much. I don't model shorter than 1/4 wave verticals. MK |
I haven't had the time to participate in this, but in a brief look, it looks pretty silly. Of course EZNEC shows no current difference across a load. The EZNEC model of a load has zero length, so the current at both terminals has to be the same. You will see a current change over the length of a model of a conductor, because it does have length. The coil in the web site pictures certainly has length, so why should you be surprised to find a current change over its length? W8JI used it as a "proof" that current in the loading coil is virtually the same at both ends. We were not surprised, but W8JI was insisting that it is, used Eznec to prove it (go see his web site) and ridiculed us. Did the experimenter perhaps do the same test with the meters placed the same distance apart with just a conductor in between? Would there be some great revelation in finding that the current was different at the two points? Not to us, but see W8JI arguments speculating and "knowing" that current must be the same. I was intrigued by the claim that a toroid measured significantly different from one end to the other. I wonder if the tester tried reversing the meters to verify that he got the same reading in both cases. If he did, I'd be interested in learning more details. I believe he did use the same method, and W9UCW can answer that. Looks like you are also not getting the main point of the argument. Appears that the rule is: "loading inductance (whatever form) inserted in the radiating element exhibits current magnitudes at its ends corresponding to the current in the length of radiator in electrical degrees that it replaces." Replacing inductance with piece of wire won't do the simulation, it has to have properties of inductor (replacing radiator's segment in degrees, inductance). Toroid, loading stub, and lumped inductors do the same thing. Unfortunately, the main objective of the web site seems to be to insult Tom, W8JI, rather than to be objective. So in my mind that leaves the possibility open that the experimenter is more interested in finding evidence that would disprove Tom than in presenting carefully measured and objective data. Not so, first I posted on eHam.net fact that current is different at the ends of loading coil. To which W8JI rode in with his "answers" and ridiculed me in public (I don't know the laws, didn't read the books, etc.) to which I responded in kind, provided proof and defended my (and others) position. Because this has happened about fifth time (he did it to others too) I simply will not take the crap and bite back. He is parading as a knowitall guru and pontificating with sometimes erroneous information. If anyone questions or challenges that, he does his routine. If you read the trail from the start you would get the picture. If he discussed the matters in a civil manner, there would be no problem, we can exchange arguments, learn something and mainly give a credit where is due. That's what professionals do. He first argues wrong, then goes away for a while and then emerges with change as a guru or inventor. That does not give hams good name and is poor example for those no-coders coming into ham radio. From the past postings, you could probably see that I can discuss the subjects in a civil manner, but when someone who is wrong starts pulling out smart ass remarks and ridicule, the gloves are off and I will defend the truth to the end. It is not just proving Tom wrong, it is to set the record straight, to bring aspect of antenna engineering to light (after 50 years of perpetuation of wrong in some antenna books), to alert software designers to the problem so they can accommodate the proper procedure or workarounds. I hope you can see how inaccurate results will EZnec produce if you simply inserted 0 size inductors in elements of 3 el. 80m shortened parasitic beam. Magnitudes and current distribution will be off, producing skewed results. Optimizing programs will be chasing wrong tail. Again, I apologize for the tone, but I will not give in to the bully. If he doesn't learn and shape up, I will be at his case, pointing out the wrongs that he is disseminating (he has some more on his web site). We were hoping that you were around, following the discussions, helping to point where we are wrong, suggest workarounds or proper procedure for modeling and we are willing to help with testing and verifications. Cecil brought some insight from the theoretical side, I (and W9UCW?) can do measurements and all this can bring greater understanding of the phenomena, rather than propagating misconceptions and wrong ideas. I found a lot more help and expertise on this NG than on eHam.net no-code flat earth society, for which I am grateful. Can we now look at the modeling problems? Seems that Cecil's way of substituting the lumped inductance with loading stubs allows closer approximation of configuration for the modeling programs. But this can still distort the true picture. I would like to point out, that W6?? replaced loading stubs in 3 el. 80m KLM beam with coils and the performance of the beam, especially pattern improved tremendously. So it looks like loading wires and radiation from them (folded along the element) upset the current distribution and resulting deterioration of performance. (So much for nice, low loss loading.) This was done, tested, measured and verified, no speculations. Is there better way of modeling the case, can we use cosine of degree of electrical length of wire that coil replaces? Roy Lewallen, W7EL Yuri, K3BU |
On Sun, 02 Nov 2003 03:44:03 -0800, Roy Lewallen
wrote: |I haven't had the time to participate in this, but in a brief look, it |looks pretty silly. Of course EZNEC shows no current difference across a |load. The EZNEC model of a load has zero length, so the current at both |terminals has to be the same. You will see a current change over the |length of a model of a conductor, because it does have length. The coil |in the web site pictures certainly has length, so why should you be |surprised to find a current change over its length? Did the experimenter |perhaps do the same test with the meters placed the same distance apart |with just a conductor in between? Would there be some great revelation |in finding that the current was different at the two points? I too have been lurking and while I didn't spend any time reading the eham stuff what was going on here got me looking at a model of this situation. I used MultiNEC to invoke EZNEC for all calculations. I modeled a shorter-than-quarter-wavelength vertical, loaded with an inductor, all of this over perfect ground. Using MultiNEC, I used equations to change the length of the radiator, the position of the inductor, keep the segment length as short as guidelines allow and resonate the result after each change. Nothing I did solved this argument but I did make a couple of slightly related observations. Unless I'm mistaken (always a distinct possibility): 1) When the radiator is electrically very short and near resonant the current does not follow the classic patterns shown in most of the ham literature, i.e. nearly constant below the inductor and close to a straight line taper above. The current actually peaks at the inductor; in other words, the highest current point on the structure is at the inductor. Hanson's paper (Robert C. Hanson, "Optimum Inductive Loading of Short Whip Antennas", IEEE Transactions On Vehicular Technology, Vol VT-24, No. 2, May 1975, pp 21-29) shows this, although his graphs show a steady decrease in current from the feedpoint to where the peaking begins. I did not see that, but instead a steadly increasing current from the feedpoint to the current peak. Not only that, the peaking is almost independent of inductor Q. "Almost" meaning that my model shows that the current is actually slightly higher in a lower Q inductor. 2) The structure Q, defined as the change in reactance with respect to frequency, is independent of inductor Q. 3) For a give length radiator, gain is unaffected by where the inductor is located along the length of the radiator and by inductor Q. If 3 is correct then I can remove the inductor from the radiator without effecting the gain and place it before the feedpoint to resonate the structure. Once out of the radiator, the current through the inductor is constant. Just like it is in the antenna if it has zero length. By now you're all saying, "Huh?" But remember, this is for an antenna over perfect (zero loss) ground. So instead of worrying about perfecting our antennas, we should be trying to perfect ground and/or zero length loading coils. | |I was intrigued by the claim that a toroid measured significantly |different from one end to the other. I wonder if the tester tried |reversing the meters to verify that he got the same reading in both |cases. If he did, I'd be interested in learning more details. Considering that *anything* inserted in the structure upsets the current distribution, as Roy says above, why wouldn't the answer be different. Even the toroid, or the distance between the insertion points, have *some* length. | |Unfortunately, the main objective of the web site seems to be to insult |Tom, W8JI, rather than to be objective. So in my mind that leaves the |possibility open that the experimenter is more interested in finding |evidence that would disprove Tom than in presenting carefully measured |and objective data. Eureka! Wes Stewart N7WS |
Mike,
the differences in current are in order of 40 - 60%, that is significant. The lower the band, the shorter the antenna, the bigger the effect, the more important where the coil is. It will vary from antenna to antenna, depending on the coil "shortening" factor. If the coil is closer to the feedpoint, the current difference is lees, but efficiency suffers most. As you move coil up the radiator, turns increase, current difference increases and effciency goes up. If you replace (part of) coil with top loading, current differences decrease (0 difference at 0 deg. long coil) and your efficiency goes up. Efficiency or radiated power of loaded antenna is roughly proportional to the area under the corresponding current curve of the remaining (straight) radiator. Coil "eats" part of the radiator and its current carrying (radiating) capabilities, this is why the current will be significantly different at the ends of the coil. I hope this illustrates the situation? As Cecil showed, modeling is not accounting for the effect and now that Roy is on, we hope to sort things out and come up with ways to best implement the phenomena in modeling programs. Right now, it appears that the best way to approximate the effect is to use loading stubs of the same inductance as intended coil. Barry and Cecil agreed to cooperate on the article describing in detail (and in civil manner :-) this subject and we hope that Roy will join us adding the modeling aspect to it. Yuri, K3BU/m |
NM5K:
NO , I didn't see the pictures. Like I said, they didn't load on that site. All the pix load except his. Then you are missing a lot. I don't know what the problem with eHam.net site is, I uploaded all the pictures the same way, some showed, some not. This is why I posted link to my page http://www.k3bu.us/loadingcoils.htm which has the pictures, also RIGHT drawings from ON4UN book, latest modeling of W5DXP stub loaded G5RV and some selected comments explaining the phenomena. Check it out. Again, put on the fricken Hustler 80m resonator, feed it 100W and feel it! No meters, no hokus pokus, just "naked" antenna. What would that mean? The hustler coil is known to be flawed, and makes a poor coil to be tested in this manner. The effects of it's metal end caps, and overall design problems are fairly well known. I refuse to use such a lousy coil. You can feed my homebrew coil 100w all day long, and you won't feel anything except the finger on the mike button hand start to go numb from holding the key down. Another "very well known fact" from W8JI's teachings? Metal caps are at both ends, top would feel the same then, it doesn't. Hustler coil is "lousy" because uses aluminum wire to achieve "match" through some loss and that is additional loss. But from the point of view as inductor, it is uniformly wound solenoid, same wire and diameter, so according to I2R law, the heat developed in it is proportional to the square of current. If there is more heat at the bottom, then irrefutably there is more current flowing at the bottom. Here is the shocker: When W9UCW bunch was measuring various coils, they also compared that perfect coil as you and I have (heavy wire, proper form factor, good connections) to "lousy" Webster Banspanner sliding coil (aka cheap screwdriver) they found negligible difference in measured signal strength. They rechecked everything scratched their heads, but that was it. So another myth about the quality of coil (resistance of course applies, but is minuscule) importance. Now when we look at it from the point of view of effect of the coil on the efficiency of antenna, it is explanatory. Coil replaces portion of radiator that is not there anymore, so the significance of its quality is not as important as the position of the coil on the radiator (area under current curve). Of course the ohmic losses are a factor, but that is minuscule (ohms or two) versus reduction in current flowing in remaining radiator. I like and have big fat coils, but looks like they can be optimized better, perhaps heavier wire in first few turns, slimmer construction, less wind load, but placed higher up on the mast. So there is another one you don't have to believe, I sure was surprised. Measure it!!! Yep, it sure is. I sure as hell won't have anything shoved down my throat. I'm sorry, but you all haven't convinced me yet that your measurements are any more accurate than the one I quoted on that same web page. And the one I quoted did give a fairly good description of how he went about it. The guy I quoted said he saw constant current across the coil. How do you explain that? Should I automatically dismiss his findings just because you all have a web page and a bunch of pictures? How do I know who did the more accurate test? I DON'T!!! I am not a salesman, I will not try to convince you of anything. I can elaborate and answer some questions and it is up to you to believe it or not. You can believe engineers with education, their experience and results, or you can believe some "technical impostor" as K7GCO phrased it. You could see almost constant current across the coil if the coil is at the base of quarter wave radiator, has heavy windings and is replacing relatively short electrical length of the radiator. Did he mention what coil, where was the coil placed? We have methods and pictures of W9UCW tests on various bands at different positions, we have yet to get objections or pointed out errors in his setup. We don't know much about the other one. W8JI said that he measured thousands of loading coils, modeled them and found no difference. He is obviously lying. He has yet to tell us about ONE measurement I asked him to do. You believe what you want. As I mentioned we will write concise article on the subject and you can take it from there or stick with Rauchians. I sure enjoyed this exercise, learned from it a thing or two and I am looking forward to implement some of the stuff (measure it too) in the design of new loaded mobile and low band antennas. As they say on FreeRepublic.com, this is series and hugh :-) Yuri, K3BU |
N7WS:
I used MultiNEC to invoke EZNEC for all calculations. I modeled a shorter-than-quarter-wavelength vertical, loaded with an inductor, all of this over perfect ground. How did you model inductor, as physical zero length inductance? Did you try substituting (coil) inductor with equal inductance loading stub? Did you try one of the situations (band, antenna/coil size) that W9UCW describes in his measurements? He used almost "perfect" ground of 60 radials for measurement. Results will be offest by some amount due to varying ground conditions (at very low angles), but in the same way and this is not the subject of the argument. The current actually peaks at the inductor; in other words, the highest current point on the structure is at the inductor. That's what W8JI calculated in EZnec, does it make sense? Like 2+2 is 4.5? Why would inductor "suck" the current up? We should then use "those" inductors to suck the current all the way to the top of the whip - perfect antenna? Cecil, can you 'splain that? 3) For a give length radiator, gain is unaffected by where the inductor is located along the length of the radiator and by inductor Q. (If the inductor is zero length?) This should be huge screaming flag that there is something drastically wrong with your whole approach. Look at any mobile shootout results and you will see 10 - 20 dB differences, ask Cecil, he wittnessed them. Looks like we exhausted reasoning, facts, measurements, found what we wanted, unless there is breakthrough in capturing the effect in modeling software we are at the end of the rope. Yea, Eureka! Thanks! Yuri, K3BU/m |
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Mark Keith wrote:
The guy I quoted said he saw constant current across the coil. How do you explain that? Constant current across the coil is one of the possiblities. Increasing current across the coil is one of the possibilities. Decreasing current across the coil is one of the possibilities. It all depends upon where the coil is inserted in the antenna. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
But this leads me
back to my previous post, which no one has commented on yet. To me, the upper meter is actually measuring a point above the coil. But it hard to tell from the pix exactly where the coupler is mounted. The main question I would like answered is, would the presence of the capacitive whip above the coil effect the current reading you got, being you seem to be measuring slightly above the coil? To me, it seems it would being you are not measuring inside the coil windings themselves, but slightly above the coil. If this capacitance is the cause of the decreased reading, then yes, it would be totally normal to see the same results if you flipped the coil and meters. MK There is no coupler involved. Meter is inserted between the end of the coil and remaining mast or whip. Thermocouple meters have negligible insertion effect, they act as perhaps an inch of wire inserted in the circuit, which is easily compensated for by retuning either the antenna or moving the frequency. Their meter mechanism is virtually immune to any RF field distortion. They are specially designed to measure the RF current with minimum impact on the measured circuit and to be interfered with. If you can grab one at the flea market get it! You could measure current on each turn if you managed to cut it and insert the ammeter. It would show cosine curve decrease across the coil. Measuring it at the first turn, end of the coil or inch or two above or below the coil produces virtually the same results, difference in the current there is really minuscule. Another close way of measuring the current is to fashion the current probe/coupler made of (split) ferrite ring, have few turns of pickup wire, rectifier and small meter. (There is a description on one of G something web pages.) You could slide this contraption up and down the radiator and measure the current. Of course you have to back off and not to touch anything in vicinity, otherwise you will detune the antenna setup and get erroneous results. The most accurate and practical way is the way W9UCW did it, he read the meters with binoculars from the distance. Yet another way is to use thermal effect, use thermal strips, paste it along the coil, put some power to it and watch the colors change. Not terribly accurate, but proof that meters do not disturb the circuit or distort the measurements. You can't use probes, scopes or anything with wires attached to it, it detunes the antenna and gives useless results Yuri, K3BU.us |
Mark Keith wrote:
How much though? What would be an average ratio difference you would be likely to see on a 8 ft center loaded whip? A lot on 75m. Not much on 12m. Or lets go one better...What would be a likely "worse case" scenario? The worse case I can think of is a short center-loaded whip on 160m. :-) The coil is almost all of the necessary 1/4WL. Will this vary from antenna to antenna? I would think so. Of course. It is all capable of being calculated. Is it your opinion that the modeling we now see with these antennas and coils is quite flawed? The antenna current reported by EZNEC is inaccurate because of simplified assumptions. EZNEC assumes that the current doesn't change through the single point inductive load. Therefore, EZNEC cannot be used to prove that the current doesn't change. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Yuri Blanarovich wrote:
in other words, the highest current point on the structure is at the inductor. That's what W8JI calculated in EZnec, does it make sense? Like 2+2 is 4.5? Why would inductor "suck" the current up? We should then use "those" inductors to suck the current all the way to the top of the whip - perfect antenna? Cecil, can you 'splain that? Again, the current can either stay the same, increase, or decrease through an inductor depending upon where it is located. Has that statement sunk in on anyone? If you install a coil 1/8WL up on a 1/2WL vertical, the current through the coil will *INCREASE*. If you install it in the center, the current magnitude will be the same in and out of the coil and opposite in phase. If you install it 1/8WL from the top, the current will decrease through the coil like it does on a 1/4WL mobile antenna. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Again, the current can either stay the same, increase, or decrease through an inductor depending upon where it is located. Has that statement sunk in on anyone? Yes, to be more precise, we are actualy arguing about the case of resonant quarter wave vertical, as a typical mobile antenna. Other losses, such as ground conditions, poor contacts, color of eyes are not considered here. Yuri |
Of course it doesn't account for phase shifts of current, since there
aren't any. It does account for voltage phase shift. It uses the same equations I learned in freshman circuits class. Perhaps they taught those same equations in Texas, too, but I can't be sure. Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: I haven't had the time to participate in this, but in a brief look, it looks pretty silly. Of course EZNEC shows no current difference across a load. The EZNEC model of a load has zero length, so the current at both terminals has to be the same. It appears that EZNEC also doesn't account for phase shifts across a zero length coil. |
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Roy Lewallen wrote:
Of course it doesn't account for phase shifts of current, since there aren't any. It does account for voltage phase shift. It uses the same equations I learned in freshman circuits class. Perhaps they taught those same equations in Texas, too, but I can't be sure. Roy, We are talking about distributed networks. Of course, there is a phase shift in the current as well as the voltage. You and W8JI seem to be using lumped circuit analysis when you should be using distributed network analysis. The center loading coil for a 75m mobile antenna is an appreciable percentage of an electrical wavelength so you cannot use your lumped circuit analysis without introducing errors. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Mark,
This term of reactance "sucking" or "drawing" current up the antenna, I have never heard of reactances described like this before. Has an article been written lately with these terms since I saw another poster use the same terminology? Regards Art (Mark Keith) wrote in message . com... oSaddam (Yuri Blanarovich) wrote in message ... NM5K: NO , I didn't see the pictures. Like I said, they didn't load on that site. All the pix load except his. Then you are missing a lot. I don't know what the problem with eHam.net site is, I uploaded all the pictures the same way, some showed, some not. This is why I posted link to my page http://www.k3bu.us/loadingcoils.htm which has the pictures, also RIGHT drawings from ON4UN book, latest modeling of W5DXP stub loaded G5RV and some selected comments explaining the phenomena. Check it out. I found them earlier... Again, put on the fricken Hustler 80m resonator, feed it 100W and feel it! No meters, no hokus pokus, just "naked" antenna. What would that mean? The hustler coil is known to be flawed, and makes a poor coil to be tested in this manner. The effects of it's metal end caps, and overall design problems are fairly well known. I refuse to use such a lousy coil. You can feed my homebrew coil 100w all day long, and you won't feel anything except the finger on the mike button hand start to go numb from holding the key down. Another "very well known fact" from W8JI's teachings? No, just personal experiences. But I never had a heat issue with a hustler. I never used one long enough to develop any heat...:/ Metal caps are at both ends, top would feel the same then, it doesn't. Hustler coil is "lousy" because uses aluminum wire to achieve "match" through some loss and that is additional loss. Well that also. But I think the windings are also overly tight. But from the point of view as inductor, it is uniformly wound solenoid, same wire and diameter, so according to I2R law, the heat developed in it is proportional to the square of current. If there is more heat at the bottom, then irrefutably there is more current flowing at the bottom. Well, not irrefutably. Obviously the other guy that tested had a case that was excess resistence at the base of the coil. I'm not saying this was a problem in your case, but he seemed to have no more heating issues after he fixed the connection. Here is the shocker: When W9UCW bunch was measuring various coils, they also compared that perfect coil as you and I have (heavy wire, proper form factor, good connections) to "lousy" Webster Banspanner sliding coil (aka cheap screwdriver) they found negligible difference in measured signal strength. They rechecked everything scratched their heads, but that was it. Actually, thats fairly old news. I had heard of that test months ago. Maybe from more than one person. I think others have found the same thing. And it doesn't surprise me one bit when mobiles are involved. Ground losses almost always overshadow coil losses on a mobile. So another myth about the quality of coil (resistance of course applies, but is minuscule) importance. Well, it's not totally a myth. Coil losses can eat your lunch if you want first rate performance. The hustler coils are a case in point. They are pathetic compared to my coils. The difference on the air is like night and day. But! If you have so much ground loss that it overshadows the coil loss, even in that case, a better coil won't help much. In other words, the better the ground system, the more any coil deficiencies will show up. Now when we look at it from the point of view of effect of the coil on the efficiency of antenna, it is explanatory. Coil replaces portion of radiator that is not there anymore, so the significance of its quality is not as important as the position of the coil on the radiator (area under current curve). Of course the ohmic losses are a factor, but that is minuscule (ohms or two) versus reduction in current flowing in remaining radiator. I like and have big fat coils, but looks like they can be optimized better, perhaps heavier wire in first few turns, slimmer construction, less wind load, but placed higher up on the mast. So there is another one you don't have to believe, I sure was surprised. Measure it!!! I have. I've been building different homemade mobile coils for about 13 years. I've come to the conclusion wire size is generally not very important at all, AS LONG as the proper pitch/winding ratio is used. Don't wind them too close together. My current coil uses thinner wire than my old one. I much prefer a lighter coil. But I'm fairly sure it actually works as well if not better than the heavier old one. It is wider than the old one. "3 inch vs 2 inch" I am not a salesman, I will not try to convince you of anything. I can elaborate and answer some questions and it is up to you to believe it or not. You can believe engineers with education, their experience and results, or you can believe some "technical impostor" as K7GCO phrased it. I'm not believing anyone. I'm going by my own experiences, and my own gut hunches. "BS filter" :) W8JI has very little to do with any of my ideas. His was just one viewpoint out of many. You could see almost constant current across the coil if the coil is at the base of quarter wave radiator, has heavy windings and is replacing relatively short electrical length of the radiator. Did he mention what coil, where was the coil placed? We have methods and pictures of W9UCW tests on various bands at different positions, we have yet to get objections or pointed out errors in his setup. I think a lot of that is only a few lurking on there actually know how, or have the equipment to make an accurate measurement. So most wouldn't know if the setup could cause problems or not. I don't say this lightly, as it appears to be quite a "hook" prone undertaking. I sure don't have the setup to do it, or have even tried something like that. I do know from messing around with fluorescent tubes and the mobile antennas, that the electric field around the coil seems to be very steady across, and abruptly decreases once the stinger begins. This while quite possibly an erroneous assumption, led me to believe the current across the coil is also fairly constant in direct relation to that. You believe what you want. As I mentioned we will write concise article on the subject and you can take it from there or stick with Rauchians. Why do you keep involving Tom in this? I have nothing to do with him. Frankly, I find comments like "Raunchians" and "Flat Earthers" etc, kind of tacky. So far I haven't accused you all of any "voodoo" antenna magic, like I do say the EH bunch. I just want to make sure all the bases are covered as far as the accuracy of the measurments, and also the exact locations of the couplers. I still question the accuracy of hooking the top coupler on the lower end of the stinger. No matter how close the coil is.... I sure enjoyed this exercise, learned from it a thing or two and I am looking forward to implement some of the stuff (measure it too) in the design of new loaded mobile and low band antennas. As they say on FreeRepublic.com, this is series and hugh :-) There is no doubt that elevating the coil on a low band antenna improves the current distribution. I've tested it many times, over and over again. BUT! This will not model worth a hoot if you look at gain numbers alone. Note Wes's recent post. If I remember right, most programs will leave the gain pretty much the same, as you vary coil height. They sure don't show the real world increases anyway...But you want to include top loading if you want the best of the best. Omit that, and it'll never happen. BTW, to my thinking, the capacitance is what draws the current through the coil. And I haven't tested it, but I bet the current taper above the coil is much more abrupt with a short stinger, than a longer one. There is no doubt a short stinger does a poor job of drawing current through the coil. Thats what kills the average ham sticks with the short stubby stingers. There is little capacitance to draw current through the coil. A large enough top hat will give you a fairly steady current distribution up the whip, regardless of the coil placement. Raising the coil in addition to the hat helps a bit more. But I think less so than with a non hatted antenna. Coil placement is critical if you run the low bands, and don't use a top hat. But thats nothing really new to people that fart with mobile antennas all the time. I think what you are doing is a good thing, and worthwhile. But I'd chill as far as Tom is concerned. You seem to be taking his criticisms a bit personal, and respond in kind. This all distracts greatly from the original point of the excercise. It's like the parasitic thing with the amps between him and Measures. Even after all the bickering, I'm still not totally sure what to believe as far as parasitic bangs in tube amps. The best answers seemed to get bogged down in the quagmire of constant bickering. :/ If I'm doing something I *think* is right, and someone disagrees, I'll assess it, and if I still think I'm right, I just ignore them. I think that would be your best course. It's his right to disagree with you. Nothing you can really do about it, and no point wasting energy, or stirring discontent over it. MK |
Roy Lewallen wrote:
Of course it doesn't account for phase shifts of current, since there aren't any. You seem to be disagreeing with John Devoldere's "Bible" - "ON4UN's Low Band DXing", 3rd Edition, on page 9-34 at: http://www.k3bu.us/loadingcoils.htm A little thought should prove there is a current phase shift (delay) through the coil. Let's look at an 8 foot long center-loaded mobile antenna for 75m. The 4 feet below the coil gives a phase shift of about 5 degrees. Assume zero phase shift through the coil. The 4 feet above the coil gives a phase shift of another 5 degrees for a total of 10 degrees at the end reflection point. It's an open circuit, so a 180 degree phase shift takes place. That puts the reflected current at 190 degrees. Add the 10 degrees coming back and we see the reflected current arrives mostly out of phase with the forward current at the feedpoint. Since the feedpoint impedance is known to be around 15 ohms, these superposed currents cannot possibly be out of phase and must necessarily be in phase. The phase shift (delay) of the current simply cannot be the same with and without the coil. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
I use lumped circuit analysis when dealing with lumped circuits, and
distributed circuit analysis when dealing with distributed circuits. EZNEC's loads are lumped elements, so when you're talking about EZNEC loads, you're talking about lumped elements. Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: Of course it doesn't account for phase shifts of current, since there aren't any. It does account for voltage phase shift. It uses the same equations I learned in freshman circuits class. Perhaps they taught those same equations in Texas, too, but I can't be sure. Roy, We are talking about distributed networks. Of course, there is a phase shift in the current as well as the voltage. You and W8JI seem to be using lumped circuit analysis when you should be using distributed network analysis. The center loading coil for a 75m mobile antenna is an appreciable percentage of an electrical wavelength so you cannot use your lumped circuit analysis without introducing errors. |
Yes, I disagree with that.
Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: Of course it doesn't account for phase shifts of current, since there aren't any. You seem to be disagreeing with John Devoldere's "Bible" - "ON4UN's Low Band DXing", 3rd Edition, on page 9-34 at: http://www.k3bu.us/loadingcoils.htm A little thought should prove there is a current phase shift (delay) through the coil. Let's look at an 8 foot long center-loaded mobile antenna for 75m. The 4 feet below the coil gives a phase shift of about 5 degrees. Assume zero phase shift through the coil. The 4 feet above the coil gives a phase shift of another 5 degrees for a total of 10 degrees at the end reflection point. It's an open circuit, so a 180 degree phase shift takes place. That puts the reflected current at 190 degrees. Add the 10 degrees coming back and we see the reflected current arrives mostly out of phase with the forward current at the feedpoint. Since the feedpoint impedance is known to be around 15 ohms, these superposed currents cannot possibly be out of phase and must necessarily be in phase. The phase shift (delay) of the current simply cannot be the same with and without the coil. |
The "simplified assumptions" made by EZNEC (and NEC in general) are the
same ones you'll find in any circuit analysis or electromagnetics text. EZNEC includes a model of a lumped inductor (or "load"), which is accurately represented. It also includes an accurate model of a straight conductor which has physical length. If you could build an antenna from straight conductors and lumped inductors, the result would be very close to EZNEC's predictions. EZNEC does not have a model of a coil which has physical length. Neither the straight wire model nor the lumped inductor model can or should be expected to behave exactly like a coil which has physical length. As I've mentioned before, a useful approximation can be made by inserting one or more lumped inductor models into a model wire. I don't have any measurements to assess the accuracy of that approximation, however. Roy Lewallen, W7EL Cecil Moore wrote: The antenna current reported by EZNEC is inaccurate because of simplified assumptions. EZNEC assumes that the current doesn't change through the single point inductive load. Therefore, EZNEC cannot be used to prove that the current doesn't change. |
Tell us, Cecil, at steady state at one frequency, can a lumped inductor
(presumably like the experimenter's toroid) tell whether it's at the base of an antenna or simply in series between a generator and load impedance? Yes_____ No______ If you answered "yes", please explain how and why, and how we'd calculate the current through and voltage across the inductor. If we moved it an inch up the transmission line from the antenna base, can it still tell? If you answered "no", please write us the equations showing just how much the current should be expected to be different from one end of the inductor to the other. And where those coulombs are going, that go into one end and don't come out the other. Going to the fourth dimension as virtual photons, perhaps? Roy Lewallen, W7EL Cecil Moore wrote: Yuri Blanarovich wrote: in other words, the highest current point on the structure is at the inductor. That's what W8JI calculated in EZnec, does it make sense? Like 2+2 is 4.5? Why would inductor "suck" the current up? We should then use "those" inductors to suck the current all the way to the top of the whip - perfect antenna? Cecil, can you 'splain that? Again, the current can either stay the same, increase, or decrease through an inductor depending upon where it is located. Has that statement sunk in on anyone? If you install a coil 1/8WL up on a 1/2WL vertical, the current through the coil will *INCREASE*. If you install it in the center, the current magnitude will be the same in and out of the coil and opposite in phase. If you install it 1/8WL from the top, the current will decrease through the coil like it does on a 1/4WL mobile antenna. |
On Sun, 02 Nov 2003 15:14:28 -0700, I made a booboo:
[snip] |It doesn't "suck it up." Haven't you ever hear of circulating |current? | I meant to type, "heard of circulating current". |
Roy, W7EL addressed several provocative questions to Cecil. Anyone can
comment, so I will. Roy wrote: "And where those coulombs are going that go into one end of the inductor and don`t come out the other." Coulombs travel back and forth in an inductor and may go actually nowhere. Their movement in an unshielded inductance may result in radiation and certainly produces some heat. The purpose of a loading coil in a short loaded vertical antenna is often to add to the existing degrees of antenna length to reach a resonant length of 90-degrees, as shown in Fig 9-22 of ON4UN`s "Low-Band DXing", and included on Yuri`s web pages. Fig 9-22 is illustrative. First, a full-size 90-degree vertical is shown. Current is maximum at the base and zero at the top. This is also true for what Kraus calls a "normal-mode helical antenna". A normal-mode helical antenna has its principal radiation at right-angles to the axis of the helix. The normal-mode helix is fed from a generator with two terminals. One terminal feeds the base end of the helix directly. The other generator terminal feeds the ground end of a capacitance between the ground, various turns, and the tip end of the helix. The impedance is only a few ohms at the ground end of the helix and perhaps several thousand ohms at the tip end of the helix. This means a lot more amps at the ground end of the helix than at the tip end, though the power flow through the generator`s terminals is the same in either terminal. Best regards, Richard Harrison, KB5WZI |
Roy Lewallen wrote:
Yes, I disagree with that. Then you disagree with Balanis. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Roy Lewallen wrote:
If you could build an antenna from straight conductors and lumped inductors, the result would be very close to EZNEC's predictions. Hard to prove since lumped inductors are impossible in reality. Why does EZNEC show so much difference between lumped inductors and stub inductors? The difference in coils Vs stubs in reality is virtually nill. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Can you post a link to this so I know what it is that you think I said, or what I said that I don't remember saying? Wes Stewart N7WS You are right. It wasn't you, it was and credit belongs to Richard Clark, KB7QHC. I apologize for the error, which was caused by my confusion between two of you 7's. Now that you made posting on eHam.net I went back to the archives and found the posting and its rightful author. Sorry if it caused any problems and made you to jump to conclusion that I am making things up. I will be more careful with references. Yuri, K3BU.us |
Roy Lewallen wrote:
Tell us, Cecil, at steady state at one frequency, can a lumped inductor (presumably like the experimenter's toroid) tell whether it's at the base of an antenna or simply in series between a generator and load impedance? This question proves you don't understand the problem. The inductor cannot tell if it is installed in an antenna or transmission line. So I will turn the question around: Does a standing wave antenna have standing waves? Reference _Antenna_Theory- by Balanis, page 17, section 1.4 Current Distrubution on a Thin Wire Antenna. Is Balanis correct when he says: "If the diameter of each wire is very small, the ideal standing wave pattern of the current along the arms of the (1/2WL) dipole is sinusoidal with a null at the end." This is after he takes an unterminated transmission line, discusses standing waves, and then slowly opens up the ends of the transmission line to create a 1/2WL dipole. I took Balanis' antenna course at ASU in 1995. I asked a lot of questions about inductively loaded antennas. The current and standing wave pattern on each side of a loading coil is NOT the same. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Roy Lewallen wrote:
If you answered "yes", please explain how and why, and how we'd calculate the current through and voltage across the inductor. If we moved it an inch up the transmission line from the antenna base, can it still tell? Forget about an inductor becoming conscious. The impedance looking into a six foot whip is the same whether the coil is there or not. The impedance looking into the bottom of the coil is certainly not the same as looking into the six foot whip. I suspect this can be proven by modeling a mobile antenna and then moving the source point from just under the coil to just above the coil. If you answered "no", please write us the equations showing just how much the current should be expected to be different from one end of the inductor to the other. The current will be approximately the same as at the two points of wire it replaces in the antenna without the inductor. I earlier asked you a question that you seem to have missed. Do you agree or disagree with Fig 9-22 of ON4UN`s "Low-Band DXing", included on Yuri`s web pages.? And where those coulombs are going, that go into one end and don't come out the other. You can answer your own question. Where do the coulombs go that enter one end of a 1/4WL stub and don't exit the other end? Please stop using lumped circuit analysis on distributed network problems. You know and I know that it doesn't work. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
|
On Mon, 03 Nov 2003 09:26:05 -0600, Cecil Moore
wrote: |Roy Lewallen wrote: | If you could build an antenna from | straight conductors and lumped inductors, the result would be very close | to EZNEC's predictions. | |Hard to prove since lumped inductors are impossible in reality. Why |does EZNEC show so much difference between lumped inductors and stub |inductors? I see no such difference in my model. |The difference in coils Vs stubs in reality is virtually |nill. |
N7WS:
Why did it take my posting on eHam to get you do do this? The quote above was directed to you in this forum days ago. I thought it was you, didn't make much of it. If it was so important and you accused me of making things up, implying that article was misleading, I investigated Google search options and found the proper posting by KB7QHC and posted the correction. Ju's human me, sorry. Yuri |
Wes Stewart wrote:
On Mon, 03 Nov 2003 09:26:05 -0600, Cecil Moore wrote: |Roy Lewallen wrote: | If you could build an antenna from | straight conductors and lumped inductors, the result would be very close | to EZNEC's predictions. | |Hard to prove since lumped inductors are impossible in reality. Why |does EZNEC show so much difference between lumped inductors and stub |inductors? I see no such difference in my model. There shouldn't be a lot of difference. I have modeled two short dipoles, one loaded with a lumped inductive reactance and one modeled with the same reactance using an inductive stub. EZNEC reports the following: Inductance lumped j335 10'stub current in segment just before the coil .8374 amp .8384 amp current in segment just after the coil .7971 amp .5642 amp The relative difference just before the coil is quite small, 0.12%. The relative difference just after the coil is quite large, 41.28%. There just cannot be that amount of difference between a coil and a stub. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Richard Harrison wrote:
The purpose of a loading coil in a short loaded vertical antenna is often to add to the existing degrees of antenna length to reach a resonant length of 90-degrees, as shown in Fig 9-22 of ON4UN`s "Low-Band DXing", and included on Yuri`s web pages. In order for a current maximum to exist at the feedpoint of a shortened (less than 1/4WL) vertical, the forward current must undergo a phase shift of 90 degrees, followed by the 180 degree phase shift from being reflected by an open circuit, followed by another 90 degree phase shift in the reflected current wave. An 8 foot whip gives about 11 degrees of phase shift end to end on 75m for a total of 22 degrees. If the coil causes no phase shift, where does the other 338 degrees of phase shift come from? -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Roy Lewallen wrote: I use lumped circuit analysis when dealing with lumped circuits, and distributed circuit analysis when dealing with distributed circuits. EZNEC's loads are lumped elements, so when you're talking about EZNEC loads, you're talking about lumped elements. Roy Lewallen, W7EL Hi Roy, Wouldn't it be better not to lump any portions of an antenna that are a part of its electrical length? 73, Jim AC6XG |
|
I don't have Balanis. Can you provide a short quote where he states that
the current at the terminals of a two-terminal lumped component are unequal? Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: Yes, I disagree with that. Then you disagree with Balanis. |
A radiating stub does act differently than a lumped inductor, in both
modeling and reality. EZNEC should reflect this difference accurately. If you're aware of a situation where you think it doesn't, please email me the models illustrating the difficulty. If you model a stub using a transmission line model, it should behave exactly the same as a lossless lumped inductor at a given frequency. However, it's an accurate model of reality only if the real stub has exactly equal and opposite currents on the two conductors. That is, it's an entirely non-radiating stub. Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: If you could build an antenna from straight conductors and lumped inductors, the result would be very close to EZNEC's predictions. Hard to prove since lumped inductors are impossible in reality. Why does EZNEC show so much difference between lumped inductors and stub inductors? The difference in coils Vs stubs in reality is virtually nill. |
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