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#251
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Yuri, K3BU wrote:
"Point by point please." to a list of 7 facts supporting his contention that a non-uniform current exists in a 1/4-wave antenna with a loading coil inserted at a spot from 50 to 70% of the radiator length, on Wed. Nov. 5, 2003, 3:15 am (CST + 6). 1. Coil is warmer at bottom than top. As power dissipation is proportional to the square of the current, it shows that in a uniform structure heat is where the current is high. 2. Current indicators at the top and bottom of a loading coil show 40 to 60% difference in ends of the loading coil. High accuracy may not be available, but the argument is between same current or dissimilar currents at the ends of the coil. High accuracy is not needed. 3. Let`s look at the RF choke. It`s not what the coil is called. It`s position and size with respect to wavelength. 4. W9UCW used a toroid and got the same results. The results were based on phase delay, not coil radiation. Antenna current in a coil results from overcoming an opposition. This impedance is a vector sum of reactance and resistance. The reactance of the coil is the same in both directions of energy travel. The impedance the antenna presents at the ends of the coil is not the same in both directions. Any coil reactance produces a delay. Inductors used in telephone circuits to block audio and pass d-c and low-frequency ringing current are called "retardation coils". A delay time of the signal is called "phase lag". These are appropriate names. Toroid coils cause phase lag too. 5. Cecil explained the reflected wave situation and delay in the coil---. Cecil did it accurately and well. 6. ON4UN in his Low Band DXing book for years has shown and explained the distribution of current in various configurations of loading coils----etc. ON4UN did it right and it has stood the test of time. Don`t hold your breath waiting for revisions. 7. How could it be if the voltage (neon bulb test) is increasing along the coil towards the top, current has to be decreasing. Yes, unless the power is increasing in the same direction, and it`s not. The neon shows high potential gradient points. In the driven quarter-wave radiating element, loaded or unloaded, the maximum voltage always seems to be at the tip end. We know that as in a transmission line, in a standing-wave antenna, reflection produces current maxima at voltage minima, and vice versa. Yuri shouldn`t bemoan lack of response to his Antenna Group 7. It only shows there is not much to contradict. Best regards, Richard Harrison, KB5WZI |
#252
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Yuri shouldn`t bemoan lack of response to his Antenna Group 7. It only shows there is not much to contradict. Best regards, Richard Harrison, KB5WZI Hi Richard, thanks very much for the positive reinforcement. Seems that those who get their hands dirty from antenna grease know a thing or two, those who model their world on the computer know their paper stuff. So far not a one "overthrow" of my 7 points, so I take it that we are on the right track and hope that others get it too and help us to use it properly. BTW I just found good source for liquid crystal strip thermometers, they have them in the pet shops, they are used for aquarium temperature measurements cost around $2. Cheap and easy way to verify the heat from current. I will get some and run som visual tests on Hustlers. 73 Yuri |
#253
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K7JEB wrote:
I will be happy to send out the .EZ file for this to any interested parties. Splice together the e-mail address below to contact me. Good stuff, as usual, Jim. It comes as no surprise to me that a three dimensional component with distributed resistance, distributed inductance, and distributed capacitance changes the voltages and currents at each end of the component. The changes are accentuated in a standing-wave environment. And to improve on your model a tad, make the capacitive wires equal on each side of the installation point, i.e. instead of a 2 foot wire sticking out horizontally, make it one foot of wire sticking out in two opposite directions. That will minimize radiation from those wires. -- 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! =----- |
#254
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Cecil, W5DXP, wrote:
And to improve on your model a tad, make the capacitive wires equal on each side of the installation point, i.e. instead of a 2 foot wire sticking out horizontally, make it one foot of wire sticking out in two opposite directions. That will minimize radiation from those wires. Good suggestion, Cecil. I had planned to make the capacitive wires into little square-shaped contraptions having about the same size as a turn of wire on the loading coil and then duplicate them up and down in the Z direction. I may still do this, but I wanted to publish the preliminary results as soon as I saw an effect, however imperfectly perceived. Jim, K7JEB |
#256
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However Yuri your experimenting supplies an advantage over the experts
in that it is in the real world that true invention has its value. Art I guess it is a sign of where "modern" technology and modeling is leading us - to the imaginary paper world. It just disturbs me that some of the "learned" people would not "lower" themselves to the reality, question the facts and adjust their "knowledge" out of the modeling world. As Cecil said, modeling supposed to model reality or close to it, not the other way around. In view of this exercise I am going to revise and investigate some of the topics I asked about here before. Looks like the "advice" I got might not be based on reality. I am sorry to see some of the "gurus" ridiculing and making snotty remarks, rather than pausing and stepping back to have a closer look or question or discuss it in a civil manner. Oh well, good thing it is only a hobby :-) 73 Yuri, K3BU |
#257
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Somehow I'm getting the image here of engineers sitting at their
computers, proposing lofty but unsupportable theories and modeling idealized but impossible circuits, while the tinkerers -- REAL MEN -- with grease under their fingernails, wrenches in hand, are designing and producing the practical items that REALLY WORK. Lemme tell 'ya. Those generators that make your power, those turbine blades that spin them. Those jet engines and airframes that get you across the country with nearly unbelievable reliability and safety. The little HTs you yak on. The signal generators, spectrum analyzers, oscilloscopes you use to make measurements. The marvelous ICs that do everything from running your microwave oven to being the guts of your PC. Those weren't designed by technicians or back room tinkerers. Those were designed by engineers who know and understand basic principles and how to apply them. Nearly anything designed in the last couple of decades has been extensively modeled before the first metal is cut, the first wire soldered, the first circuit board or IC produced. And when the extensively modeled airplane is built, it flies. The IC and circuit board work. They work by the thousands or hundred of thousands, despite tolerances, component variations, and temperature changes. Because they were modeled and they were understood. Not because somebody made one sorta work once on a workbench by experimenting. People who reject modeling as "paper stuff" and decry established theory have simply crippled themselves. It's their choice, but there's no reason to be proud of it. Part of the everyday work of an engineer involves making measurements of one sort or another. And it's when the results are surprising that you'll see the difference between someone who has a solid background in fundamentals and the person who doesn't. The former will work to resolve the surprising measurement results with known and trusted theory. The latter will question the theory, not having a solid background to build on. I've seen technicians quickly reject Ohm's law on the basis of a single careless measurement. From then on, that person has lost the ability to rely on a powerful principle, and can never be quite sure what kind of relationship to expect among voltage, current, and resistance. A person who does understand the principles will search for what errors or shortcomings have been made in the measurement process, or what simplifications have been made that aren't valid, will resolve them, and will learn from them. Let me give just one example from my own experience -- there've been scores like it over the years. Years ago, I was measuring the input impedance of a simple antenna (folded dipole, as I recall) through a one wavelength piece of coax. Assuming that the measured impedance was the same as at the antenna, the results were very different than modeling had shown. Some people, it seems, would have immediately posted the results on the web, challenging the modeling and transmission line theory, loudly and forcefully demanding that everyone who doesn't believe the results should immediately go out and make measurements. After all, that's proof, is it not, that the modeling is bunk and transmission line theory is bunk. Well, the reason for the strange results turned out to be coax loss. A bit of analysis (based on known principles) shows that even a small amount of transmission line loss will skew the measured Z toward the line's Z0. The effect is surprisingly strong when the impedance to be measured is quite different from the line's Z0, as it was in this case. Another thing I learned was that the coax I was using, a small diameter 75 ohm cable, was extraordinarily lossy at the low frequency of 7 MHz where I was making the measurements. I determined this to be due to the small center conductor, made of strands of tiny Copperweld wire. The copper coating was thick in terms of percentage, but thin in terms of skin depths at the low frequency because of the very small strand diameter. So current was flowing in the steel cores. I ended up learning two important things from the episode, which I've applied ever since to similar problems, and other ones too. If I were someone who was quick to throw out conventional theory or modeling results, I never would have learned from it, and I wouldn't be able to depend on either modeling or transmission line theory. Now, getting to the issue at hand. Those of us who studied and understood basic circuit analysis know that a vanishingly small inductor or any other two-terminal component must have equal currents in and out. When measurements show results that differ from this, it means -- to we who understand and believe the principles -- that either there's something we don't know about the measurement method that's skewing the results, or the approximation of a vanishingly small component isn't valid. Of course a lengthy inductor in an antenna isn't vanishingly small, and it also couples strongly to the antenna above and below it. So no one who understands basic principles would be the least bit surprised to find different currents at the inductor ends. However, the statement that significant current differences were found at the ends of an apparently small toroid aroused my curiosity. Either there's a peculiarity in the measurement, or there's a sneak current path, such as stray capacitance, accounting for the current imbalance. Being curious, I made some measurements of my own of a loading inductor at the base of an antenna. The details of the test are a bit lengthy, and this posting is already long, so I'll post it separately. I feel kind of sorry for people who are quick to abandon established principles each time a casual measurement -- or even a careful one -- seems to contradict them. They're pretty much doomed to randomly trying this or that, without ever having the hope of understanding what they're doing. It's just the sort of thing that gives rise to astrology and phrenology, as ways to try to understand the mysteries around us. I greatly prefer science, but each to his own. It is true that a person with marginal math skills might not be able to discover, let alone quantitatively prove, that coax loss was the culprit in the example I gave above. Without some background in math, as well as basic principles, it's not really possible to understand things on a very fundamental level. So a person without math skills is pretty much limited to general, rather than specific, understanding. As a footnote, I was a technician for quite a few years, first self taught, and later going through the Air Force radar technician school. I worked as a broadcast engineer, and repaired various equipment from radios, TVs, and telephone answering machines to heavy ground military radar. (I was, incidentally, regarded as being a very good technician. One reason was that I did firmly believe in the basic principles as I was able to understand them, and applied them whenever possible.) But I was often frustrated because I kept encountering things I didn't understand as fully as I wanted, which is why I ended up working my way (with a little help from Uncle) through engineering school. It gave me the theoretical and mathematical tools to understand a whole lot more about how things work, and on a much deeper level. I use modeling extensively, as do nearly all my fellow engineers, and I've been able to consistently design quality electronic equipment in a wide variety of categories -- by understanding and applying basic principles. Far from converting me to the effete theoretician I'm seeing caricatured here, the education and engineering experience has added immeasurably to my ability to understand this fascinating field. Roy Lewallen, W7EL Art Unwin KB9MZ wrote: oSaddam (Yuri Blanarovich) wrote in message ... Yuri shouldn`t bemoan lack of response to his Antenna Group 7. It only shows there is not much to contradict. Best regards, Richard Harrison, KB5WZI Hi Richard, thanks very much for the positive reinforcement. Seems that those who get their hands dirty from antenna grease know a thing or two, those who model their world on the computer know their paper stuff. Yuri you make a very good point there. Those skilled in the arts have often used gimmicks or quasi ruses in their studies especialy in the use of mathematics where one can show on paper that one plus one equals three but cannot prove it factually. Engineers also use imaginary things in the search of knoweledge where those that use their hands have to deal with the real world. For many inductance is pure but imaginary as is capacitance, each of these in the real world is a network but engineers with the help of Laplace have learned to deal with the real world with altered equations yet use the same name such as inductance which in the real world there is no such thing. The fact that you used an imaginary term such as inductance instead of a network unfortunately placed you in their camp in the world of imagination. An example with respect to your subject is for you to ask them to provide you with an inductance of unlimited Q which in the imaginary world that they frequent is no big deal, where in the real world you are finding that Q beyond a 1000 is nigh impossible. Since speach itself cannot resolve factual things to the satisfaction of all then their will be no resolution. All this reminds me of a problem I had years ago when I reffered to capacitive coupling where its inherrent inductive component can be used for matching purposes. Now you tell me how you can convince experts that a capacitor is a network and thus has a usefull inductance component when they see for mathematical reasons that the word capacitance refers to an imaginary term to describe what cannot be in the real world? However Yuri your experimenting supplies an advantage over the experts in that it is in the real world that true invention has its value. Art |
#258
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Here are some preliminary details about the inductor current measurement
I made. My antenna isn't nearly as ideal as the one Yuri described. (But if my results are different from the ones reported at the web site Yuri referenced, I'll be eager to hear why.) It's about 33 feet high, and has only 7 buried radials. The feedpoint impedance indicates a loss of about 25 ohms at 7 MHz, so I'd expect it to be a bit more at 3.8. It's bolted to a galvanized fence line post which protrudes nearly four feet from the ground, with spacing between the antenna and the post of about 1/4". This mounting has only a minor effect on the feedpoint impedance at 7 MHz, which is the antenna's intended frequency of use. It's quite profound at 3.8 MHz, though. The expected 370 or so ohms of capacitive reactance is transformed to 185, while the feedpoint R is 35 ohms, not far from the expected value. So the overall feedpoint Z is 35 - j185 ohms at 3.8 MHz, measured with a GR 1606A impedance meter. (I found that my MFJ 269 was about right with the X, but measured R as zero -- apparently the combination of low frequency and large X is a problem for it in resolving the R.) So I built an inductor with measured impedance of 0.6 + j193 ohms. It's 26 turns on a T-106-6 toroid core. Q is a bit over 300. This was placed in series at the antenna feedpoint. For current measurements, I made two identical current probes. Each one consists of 10 turns wound on an FT-37-73B ferrite core. The two leads from the winding are twisted and wound in bifilar fashion on another FT-37-73B core, 10 turns. This is then connected to an oscilloscope input via a two-foot (approx.) piece of RG-58. A 50 ohm termination is also at the scope input. This gives the probe a theoretical insertion impedance of 0.5 ohm. While making the measurements, I moved, grabbed, and re-oriented the coax cables, with no noticeable effect. This gave me confidence that the outsides of the coax weren't carrying any significant current. One probe went to each channel of the scope. I left the two scope inputs in the cal position, put both probes on the wire at the input end of the inductor, and recorded the p-p values with the scope's digital measurement feature. Then I reversed the order of the probes and remeasured. I found a slight prejudice toward the probe closest to the source -- 1.2% in one ordering, and 2.1% in the other. Averaging the two channels, though, showed them to be the same within less than 1%. (Each probe was always connected to the same scope channel, so this is a test of the probe-scope channel combinations.) Then I moved one probe to the output side of the inductor, and measured input and output current. And I reversed the probe positions on inductor input and output. The ratio of output to input current in the two tests differed by only 1.4%. When I encounter an astrologist, they invariably ask what "sign" I "am", then proceed to tell me how my personality meets their expectations. So what I do instead is to have them tell *me* what "sign" I "am" *first* -- which they should easily be able to do, based on my personality. Well, they don't find that to be fair, for some reason (although I certainly find it amusing). And so, I doubt if the following challenge will be regarded to be fair, for much the same reason. Those with alternative rules for solving circuit problems are challenged to predict what the ratio of output current to input current will be. I'm particularly targeting Cecil, and others who have bandied about a lot of pseudo-analysis about electrical length, reflections, and the like. And, Richard (Harrison), who said something like "an inductor without phase shift is like". . . I don't recall. . .hot dog without ketchup or something. Pull out your theories, and calculate it, like any competent engineer should be able to do. For cryin' out loud, it's a simple series circuit (except for Cecil, where it's some kind of distributed thing). First post your answers, then I'll post the result of my measurements. Roy Lewallen, W7EL |
#259
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Roy Lewallen wrote:
Pull out your theories, and calculate it, like any competent engineer should be able to do. For cryin' out loud, it's a simple series circuit (except for Cecil, where it's some kind of distributed thing). First post your answers, then I'll post the result of my measurements. What is the value of the distributed capacitance between each two turns on the toroid? That distributed capacitance is what makes a 75m mobile loading coil act like a transmission line. Question: Why didn't you use a 75m bugcatcher coil for the experiment? -- 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! =----- |
#260
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Roy Lewallen wrote:
I'm particularly targeting Cecil, and others who have bandied about a lot of pseudo-analysis about electrical length, reflections, and the like. Balanis would be surprised to know that you consider the material that he teaches in his classes at ASU to be pseudo-analysis. Some of the stuff I have posted is in Balanis' book, _Antenna_Theory_ which you haven't read. In particular, he says: "Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forwards and backwards) as represented by traveling wave currents If and Ib in Figure 10.1(a)." I'm just wondering how you can be so sure that what I have offered is pseudo- analysis and which of the following statements you disagree with. Please be specific. 1. The feedpoint impedance of a typical traveling wave antenna is in the hundreds of ohms since there are no reflected waves. 2. The feedpoint impedance of a standing wave antenna is the result of superposition of forward and reflected waves (which cause the observable standing waves). 3. At the feedpoint of a 1/2WL resonant dipole, the forward current, reflected current, and forward voltage are all in phase. The reflected voltage is 180 degrees out of phase. This results in a purely resistive low-voltage/high-current ratio for the feedpoint impedance. 4. The above relationship is true for any dipole, 1/2WL or physically shorter, that has a purely resistive feedpoint impedance. (No resistive loading) 5. The phases of the signals at the feedpoint are known. The phases of the signals at the open tips of the dipole are known. Any loading used in order to increase the electrical length to 1/2WL must maintain those known phase conditions in order to achieve a purely resistive feedpoint impedance. On page 18, in Figure 1.15, Balanis shows how a 1/2WL dipole is achieved by flaring out the last ~1/4WL of an unterminated transmission line. He says: "As the section of the transmission line begins to flare, it can be assumed that the current distribution is essentially unaltered in form in each of the wires." -- 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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