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#1
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Not so obvious
It's quite obvious the current through a loading coil tapers. As a first
approximation it's because the voltage and current along it varies according to a 'cosine' curve as they do along any other sort of continuous transmission line. V and I on either side of a coil can be opposite in phase as they pass through it. This occurs when the length of the coil passes through a 1/2-wavelength point. 1/2-wave points can occur at any point along a coil depending on where the coil starts and ends along the antenna. This helps to illustrate the action of 'phase-reversing' coils between adjacent antennas lengths. What I find so intriguing is what the 'taper proponents' intend to do with the 'taper' data when at last they have it in the form of numbers? Of what use is it? Into what are the numbers inserted? What is the next stage in the proposed modelling process? ---- Reg, G4FGQ |
#2
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What I find so intriguing is what the 'taper proponents' intend to do with the 'taper' data when at last they have it in the form of numbers? Of what use is it? Into what are the numbers inserted? What is the next stage in the proposed modelling process? ---- Reg, G4FGQ Efiiciency of the loaded radiator is roughly proportional to the area under the current curve along the radiator. 1. Placement of the loading coil can drastically affect that. (Base loaded vs. Top Hat loaded) 2. When using loaded elements in multielement designs, the current distribution and magnitude along the elements needs to be accounted for optimum design and performance. It affects the inter element coupling, current flow in the segments of the elements and how the modeling programs "see" it. Try loaded 3 el. 80m beam or 4 square. Programs that can do optimization (YO, AO, 4NEC2) would give better results if they can deal with real current distribution closely modeled. Now it is up to those program authors that neglected proper modeling of the current in the loading coils to iclude this feature and make their softy wares better and reflect reality mo betta. Yuri, K3BU.us |
#3
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On Sat, 7 Feb 2004 21:28:03 +0000 (UTC), "Reg Edwards"
wrote: What I find so intriguing is what the 'taper proponents' intend to do with the 'taper' data when at last they have it in the form of numbers? That day never seems to arrive. Perhaps eh/cfa testing results are clogging the queue. Of what use is it? Bragging rights of the ****-ant stature. Into what are the numbers inserted? second only to preparation H for that application. What is the next stage in the proposed modelling process? creating a new icon to worship. C'Mon, Reg, you new those answers all along! |
#4
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Reg Edwards wrote:
What I find so intriguing is what the 'taper proponents' intend to do with the 'taper' data when at last they have it in the form of numbers? Of what use is it? As I said on the other newsgroup, Reg, it is useful for discrediting the assertion of one of r.r.a.a's ex-gurus. W8JI wrote: If you look at HOW an inductor works, the current flowing in one terminal ALWAYS equals the current flowing out the other terminal. "ALWAYS" to me, means zero taper. What does it mean to you, Reg? -- 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! =----- |
#5
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Yuri Blanarovich wrote:
1. Placement of the loading coil can drastically affect that. (Base loaded vs. Top Hat loaded) BTW, Yuri, you and others may not be aware that my junk box top-loaded mobile antenna equaled the best-of-the-best in one of the antenna shoot-outs. The loading coil was just some cheap 1.75" dia coil stock from my junk box. It wasn't anything like a bugcatcher and it cost virtually nothing. The bottom section was a 108" conductor curving toward the coil which was ***HORIZONTAL***. Yes, the coil was horizontal as was the top hat to which it was attached. If I had known it was going to do that well, I could have won by making the top hat a little bigger. Here is an ASCII diagram of that antenna: loading coil - ////////////--Capacitive top hat / / / / | Pickup | | | | FP --------GND------------------------------------------------------ So I discovered by accident what is being discussed now. Seems obvious that the coil could be shorted and the top hat disconnected for higher frequencies. -- 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! =----- |
#6
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Reg Edwards wrote: SNIP What I find so intriguing is what the 'taper proponents' intend to do with the 'taper' data when at last they have it in the form of numbers? Of what use is it? Into what are the numbers inserted? What is the next stage in the proposed modelling process? ---- Reg, G4FGQ IMO: The next stage is designing the coil! A long thin coil [like a Hamstick] requires a longer length of wire than a short 'fat' [note the quotes] coil [like a bug catcher or a screwdriver]. The hamstick has a higher current taper than the screwdriver or bugcatcher. The resultant integral of the current and length [in degrees] [ampere*degrees] of the resulting antenna is higher with the short fat coil than with a long thin coil. {This assumes the coils are located approximately at the same location.} Deacon Dave, W1MCE |
#7
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Dave Shrader wrote:
IMO: The next stage is designing the coil! A long thin coil [like a Hamstick] requires a longer length of wire than a short 'fat' [note the quotes] coil [like a bug catcher or a screwdriver]. The hamstick has a higher current taper than the screwdriver or bugcatcher. The resultant integral of the current and length [in degrees] [ampere*degrees] of the resulting antenna is higher with the short fat coil than with a long thin coil. {This assumes the coils are located approximately at the same location.} Deacon Dave, W1MCE Additional note. 75 inches of wire versus 40 inches of wire at 14 MHz is only a 1.1 degree difference. |
#8
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"Yuri Blanarovich" wrote -
Efiiciency of the loaded radiator is roughly proportional to the area under the current curve along the radiator. 1. Placement of the loading coil can drastically affect that. (Base loaded vs. Top Hat loaded) ========================= Typically, shifting the loading coil from the bottom of the antenna to its most efficient location is about 1.5 dB at 7 MHz. Replacing a loading coil at its most efficient location with a large top hat increases efficiency by 14 percent. Hardly drastic! But Yuri's objective is not to find the optimum location of the coil along the antenna. Every twopenny designer knows that THAT point exists. Especially they who use rules of thumb. And there's nothing wrong with that. The objective is to assist the coil designer to design coils by telling him HOW to make use of the EXTRA knowledge of current distribution along the antenna. At present, it seems everybody assumes coil current has a uniform distribution. Nothing wrong with that of course. Especially if everybody makes the SAME assumption. It is unwise to use "roughly" and "drastically" in the same context. After all, it hasn't yet been discovered in which way the taper should go in order to improve efficiency. (Yes, I know, you can't shift the taper.) So that how is it proposed to alter the taper. Or to take advantage of it by altering wire diameter, ie., by putting the lowest wire diameter in the places where the smallest current flows. And vice-versa. IF there is success in improving efficiency by, say, 1 percent, as a result of increasing design and precision engineering costs, plus patenting costs, plus testing and certification costs, plus manufacturing costs, by 5 or 10 times, would customers be prepared to buy it. How accurate are (A-B) tests results expected to be? Within limits of 0.01%, 0.1%, 1% or 10% ? You'll be lucky to obtain an accuracy of antenna power measurements within +/- 20%, or within +/- 0.8 dB. This means you would be unable to GUARANTEE to your customers an improvement in performance better (or worse?) than about +/- 1 dB. But an improvement of such a relatively large amount, by tinkering with coils, I venture to say is impossible. So whatever improvement it is expected to achieve it will be not be possible to honestly demonstrate it. There is the possibility of an antenna actually being worse than measured. But the $64,000 Question is whether customers will be prepared to pay for another 0.5 dB or less gain, which may or may not exist. It would be like searching for non-existent W.M.D. On the other hand, it can be confident expected not to measure an antenna gain worse than about 1 percent of what it actually is. But how do you assess the difference between two antennas on the basis of back-to-front ratio over an angle of 360 degrees in the presence of such small differences. It is suggested the next questions to ask are "What is the expected change in improvement" and "How accurately can the expectation be measured". Economics cannot be avoided. ---- Reg, G4FGQ |
#9
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"ALWAYS" to me, means zero taper. What does it mean to you, Reg?
-- 73, Cecil http://www.qsl.net/w5dxp ============================== There's no such thing as a perfect coil. All coils have stray capacitance and resistance. Consequently, it's exeedingly unlikely the current at one end is equal to the current flowing at the other end. The current flows out of the coil via the stray capacitance to its enironment. So we don't just have I1+I2 - we have I1+I2+I3 to contend with, where I3 is distributed along the length of the coil. Not that anybody in his right mind would ever wish to know the magnitude of the taper of the current or volts. Seems to be an invention of the denizens of this newsgroup, most of whom seem to have lost theirs. Now, Cecil, you understand this as well as I do. Cease pulling my leg. So don't expect me to waste any more of my time discussing it. ;o) ---- Reg, G4FGQ |
#10
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Reg Edwards wrote:
It is suggested the next questions to ask are "What is the expected change in improvement" and "How accurately can the expectation be measured". Obviously, a sour grapes or sweet lemons situation, depending upon which side of the argument you are on. Reg, to settle the original argument, is this statement true? "If you look at HOW an inductor works, the current flowing in one terminal ALWAYS equals the current flowing out the other terminal." A simple "yes" or "no" will settle the original argument and hopefully end the argument. W8JI's own measurements proved his statement to be false. -- 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! =----- |