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Loading Coils; was : Vincent antenna
John Smith wrote:
John Smith wrote: Cecil Moore wrote: John Smith wrote: There is SOMETHING we are ALL missing ... but, I do listen to your arguments, I admit--I have a hard time following you ... Well, let's take a simple example. Given a lossless 90 degree stub. What is the phase shift in the total current from one end of the stub to the other? Hmmm, 360? No, 180? Hmmm, 90? Well, 89.999999999999999999? Ok, I give up, tell me ... :-) Regards, JS Anyway, why current, wouldn't voltage make the same shift, although inversely proportional? Regards, JS Which, even more, bakes ones' noodle, as the same power level exists at every single point along the length of the element, right? Seemingly, suggesting, all points are as efficient in radiation characteristics, right? However, I ask this while placing myself at risk of looking like an idiot because I really am NOT sure ... oh well. But then, you already knew, I don't know it all ... :-( Regards, JS |
Loading Coils; was : Vincent antenna
On Thu, 29 Nov 2007 17:44:39 -0600, Cecil Moore
wrote: Jim's point is that it can be done! In that particular coil at 4 MHz - no, it cannot be done. On Thu, 29 Nov 2007 17:50:36 -0600, Cecil Moore wrote: The measured delay through my 75m bugcatcher coil is 25 nS. In one case, the measurement "cannot be done," and in another case 6 minutes later it can be done; and the difference all because of one "particular" coil? That is 1. the first coil is one mighty particular coil; or 2. no measurement was done for the second, not so particular coil. Of course, for those who readily admit that English is not their best language of communication (and their writing tends to support that excuse); then we could be encountering: 1. another meaning, generally unknown or archaic, for particular; or 2. another meaning, generally unknown or archaic, for measurement; or 3. both. My bet is the answer will not hinge on blaming poor spelling, failing eyesight, a slip in thought, or the wrong meter setting (rubber crutches of the past), but ultimately a novel definition of the word "measurement" which will reveal a visit to the bench is superfluous to the conceptual clarity of it all = intellectual mooching. Of course, a novel definition of particular would amuse us all.... |
Loading Coils; was : Vincent antenna
On Thu, 29 Nov 2007 22:08:45 -0500, "AI4QJ" wrote:
"Richard Clark" wrote in message .. . On Thu, 29 Nov 2007 20:50:29 -0500, "AI4QJ" wrote: So, in other words you agree Hi Dan, I use my own words, not other words, and certainly not laden with artificial constraints and presumptions. If you want to ask a question without all these drapes, go ahead; it is far simpler, and consumes less bandwidth. 73's Richard Clark, KB7QHC OK, I will ask it like this: On an article at http://www.w8ji.com:80/inductor_current_time_delay.htm the author discusses time delay through an inductor. Do you agree with the following 2 paragraphs in that article: "How does the current travel through the inductor so fast? At first this seems impossible, but the answer is actually quite obvious. Time-varying current gives rise to time-varying magnetic flux. This magnetic flux, since conductor spacing is close and the distance very small, links the starting turn very tightly to the next turn. The rapidly changing magnetic flux causes charges to move in the next conductor, and the changing magnetic field couples through all the close spaced turns with very little time delay. It is this magnetic flux coupling that provides the primary mechanism for energy transfer through the inductor, and the path is much shorter than the circuitous and much longer path along the conductor." The close spacing of the coils reduces the time delays because the current is "pushed along" faster. Agree? Not particularly. You got any more questions? 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
On Fri, 30 Nov 2007 01:11:44 -0500, "AI4QJ" wrote:
We will have to wait for Richard's answer to be sure, however. Now there's a conceit, if ever one was written here. 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
"Cecil Moore" wrote
Adding or subtracting loading-coil degrees is what happens while one is tuning a screwdriver antenna. At resonance, the screwdriver is electrically very close to 90 degrees in length. _______________ It may have the reactance of an unloaded ~90-degree, self-resonant radiator. But in normal applications that doesn't make a screwdriver the radiational equivalent of that full-sized radiator, because the radiation resistance of the physically/electrically short screwdriver whip is less than a full-sized antenna -- and much less on the lower bands. A dummy load can have the reactance of a resonant screwdriver, too, but a dummy load is not a very good antenna. I doubt you would claim that it is electrically 90 degrees in length, just because it has the same reactance as an unloaded ~90 degree, self-resonant monopole. That conclusion applies to a screwdriver antenna system, as well. RF |
Loading Coils; was : Vincent antenna
John Smith wrote:
Cecil Moore wrote: John Smith wrote: There is SOMETHING we are ALL missing ... but, I do listen to your arguments, I admit--I have a hard time following you ... Well, let's take a simple example. Given a lossless 90 degree stub. What is the phase shift in the total current from one end of the stub to the other? Hmmm, 360? No, 180? Hmmm, 90? Well, 89.999999999999999999? Ok, I give up, tell me ... :-) In a lossless stub, the *total current* is 100% standing-wave current. There is zero phase shift in the current from one end of the stub to the other. That's why total current cannot be used to measure a delay through a coil in a standing-wave antenna. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
John Smith wrote:
Anyway, why current, wouldn't voltage make the same shift, ... In the case of a stub, voltage could be measured. In the case of an antenna, voltage is difficult to measure (against ground). -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
John Smith wrote:
Which, even more, bakes ones' noodle, as the same power level exists at every single point along the length of the element, right? Seemingly, suggesting, all points are as efficient in radiation characteristics, right? A lossless stub doesn't radiate. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Richard Clark wrote:
In one case, the measurement "cannot be done," and in another case 6 minutes later it can be done; and the difference all because of one "particular" coil? Good Grief! I cannot do the measurement on the W8JI coil because I don't have the coil. Upon the coil that I do have, a 75m bugcatcher coil, the measurement was easy. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
On Fri, 30 Nov 2007 17:09:42 GMT, Cecil Moore
wrote: Richard Clark wrote: In one case, the measurement "cannot be done," and in another case 6 minutes later it can be done; and the difference all because of one "particular" coil? Good Grief! I cannot do the measurement on the W8JI coil because I don't have the coil. Upon the coil that I do have, a 75m bugcatcher coil, the measurement was easy. My goodness, it has been a long time since I've heard "Hearts and Flowers" attempted through posting on this newsgroup. How sad! It must be a titanic struggle to find the W8JI coil's description and build one. All the more strange for this shortfall given: On Wed, 28 Nov 2007 13:25:34 -0600, Cecil Moore wrote: http://www.w8ji.com/inductor_current_time_delay.htm No doubt your eyes are failing, or memory has lapsed momentarily, or perhaps a recent personal crisis diverted your attention - or more likely (and here we can all agree) the topic is utterly boring except for these charming flirtations you offer (otherwise considered to be intellectual pan-handling). Anyway, the "suggestion" of measurement of a time delay in the quote above is nothing more than that - a suggestion. If we were to press for more details (always absent in these proclamations passing as technical content), then we would find that, no, the measurement was one of resonance (and likely not even that) which then through a weak chain of rusty links of logic once again summons up the corrupted reading of Corum(s) to INFER not measure. I think the group was short-changed on the lack of a definition for the amusing application of "particular." At least we would have gotten some value added to drape the coffin of this thread. |
Loading Coils; was : Vincent antenna
Richard Fry wrote:
"Cecil Moore" wrote Adding or subtracting loading-coil degrees is what happens while one is tuning a screwdriver antenna. At resonance, the screwdriver is electrically very close to 90 degrees in length. Note that the electrical length and the physical length are nowhere near the same value. The electrical length can be 90 degrees at resonance while the physical length is only 13 degrees for a 75m mobile antenna. It may have the reactance of an unloaded ~90-degree, self-resonant radiator. But in normal applications that doesn't make a screwdriver the radiational equivalent of that full-sized radiator, because the radiation resistance of the physically/electrically short screwdriver whip is less than a full-sized antenna -- and much less on the lower bands. I agree 100% and have never disagreed. I have already stated that the radiation characteristics of an antenna depend upon its *physical* length while the feedpoint impedance depends upon its *electrical* length. A screwdriver antenna may be only 13 degrees long *physically* on 75m. Of course, it is NOT going to radiate like a physical 90 degree antenna. It is going to radiate more like a 13 degree (short) antenna. You have apparently misunderstood what I am trying to say. I have made *zero assertions about radiation patterns* except to answer your earlier posting on that subject. A dummy load can have the reactance of a resonant screwdriver, too, but a dummy load is not a very good antenna. I doubt you would claim that it is electrically 90 degrees in length, just because it has the same reactance as an unloaded ~90 degree, self-resonant monopole. A dummy load's feedpoint impedance is not (Vfor+Vref)/(Ifor+Iref), i.e. not a virtual impedance, so your comment is irrelevant in this context. The IEEE Dictionary distinguishes between those two definitions of impedance, (B) for an antenna, (C) for a dummy load. That conclusion applies to a screwdriver antenna system, as well. Since it is possible to tune a screwdriver antenna to the 270 degree mode, the following will assume the screwdriver antenna system is used only in the 90 degree mode: A screwdriver antenna system has radiation characteristics appropriate for its *physical* length of, e.g. 13 degrees. A screwdriver antenna system with a low resistive feedpoint impedance is electrically 90 degrees long because (Vfor+Vref)/(Ifor+Iref) is resistive. The only way for Vfor and Vref to be 180 degrees out of phase is for the antenna to be electrically 90 degrees long. The only way for Ifor and Iref to be in phase is for the antenna to be electrically 90 degrees long. That's simple wave reflection model physics. In abandoning the wave reflection model, many people have abandoned any possibility of understanding what happens in a standing-wave antenna. Sooner or later, their short cut methods bite them in the posterior. The W8JI and W7EL current measurements are an example. Anyone who never looks for the "missing" phase shifts in a mobile antenna will never find them. Side 1 of the argument assumes they are not there. Side 2 of the argument assumes they are there in the loading coil. Both sides are wrong. I have gone looking for the "missing" phase shifts and have found them. Here is a lossless transmission line example which is *physically 45 degrees long*: ---Z0=600, 22.5 degrees---+---Z0=100, 22.5 degrees---open What is the impedance looking into the stub? Where are the "missing" 45 degrees? -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
K7ITM wrote:
On Nov 29, 9:11 am, Jim Kelley wrote: ... Over the range of a few octaves, propagation delay on the other hand does not vary to any significant extent as a function of frequency. Ostensibly, it should be equal to sqrt(LC) series L, shunt C. Actually, Jim, I do expect it to have considerable frequency dependence. I think you can find info about this in books that address the design of travelling-wave tubes. But...one must be very careful about describing exactly the experiment or the conditions around a particular scenario. That's why I don't have much interest in getting involved in this "discussion": it could well be that much of the difference among all the claims and counter- claims could be trivially resolved through better communication. Cheers, Tom I don't think they're writing about real transmission lines, Tom. If they were doing that, there would be no discussion because then it would be too hard to understand. 73, Tom Donaly, KA6RUH |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
... In a lossless stub, the *total current* is 100% standing-wave current. There is zero phase shift in the current from one end of the stub to the other. That's why total current cannot be used to measure a delay through a coil in a standing-wave antenna. Cecil: Of course you are correct--it was meant to be a joke man, albeit a silly one ... Regards, JS |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
Jim Lux wrote: I should think that many hams have things that can measure 3 ns (1000mm light time), particularly in a repetitive system. That's one cycle at 300 MHz, or 36 degrees at 30 MHz. The referenced W8JI 3 nS "measurement" was the delay in a 2' dia, 100 T, 10" long loading coil on 4 MHz, i.e. 4.5 degrees. 4.5 degrees is easy to measure at 4 MHz with a variety of systems. Basic measurement theory says that the phase measurement uncertainty is uncertainty in radians = 1/sqrt(T * Psig/No) where T is the integration time, Psig is the signal power, and No is the noise spectral density (W/Hz) Let's throw in some numbers.. Psig = 1 mW (1E-3W) No = -160 dBm/Hz (kTB noise + 14 dB) T = 10 millisecond uncertainty = 1/sqrt(1E-2 * 1E16) = 1 / 1E7 = 1E-7 radian 1 degree is about 0.017 radian, so I think you wouldn't have much problem measuring the phase shift, from a physics standpoint.. all a matter of experimental technique.. Anyway, there are LOTS of ways to do the measurement, most of which would require only things that hams have sitting around, with a few hours of cobbling together. |
Loading Coils; was : Vincent antenna
K7ITM wrote:
On Nov 29, 9:11 am, Jim Kelley wrote: ... Over the range of a few octaves, propagation delay on the other hand does not vary to any significant extent as a function of frequency. Ostensibly, it should be equal to sqrt(LC) series L, shunt C. Actually, Jim, I do expect it to have considerable frequency dependence. I think you can find info about this in books that address the design of travelling-wave tubes. I can't think of an example of an active (or reactive) device which doesn't have frequency dependent characteristics. To the extent that indices of refraction are frequency dependent, propagation velocity does in fact vary with frequency. If it didn't, we wouldn't see rainbows. Dielectric constants do indeed have a frequency dependence. But to first order, at radio frequencies, in amateur applications, for the purposes of this discussion, and in my opinion, the effect is less than considerable - particularly if we assume the L and C in sqrt(LC) are correct at the frequency of interest. ;-) 73, Jim AC6XG |
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Tom, May I point out that a Tesla coil is an "antenna" that does not conform to Maxwells laws with respect to the adherance to the LC ratio. The LC ratio is out of balance such that the capacitor is not of the correct size to store and then return the imposed energy from the inductive heavy coil which is visually seen as resulting in a spark. Regards Art Huh... tesla coils follow all of Maxwells equations quite nicely. Paul Nicholson did some very nice analysis on this a few years back, published at a link previously posted. They're two coupled LC resonant circuits, with the coupling adjusted to around k=0.2. There are higher order systems with 3 or more resonators, as well (called Magnifiers in the TC world) The challenge in spark making is choosing appropriate operating parameters (coupling, radius of curvature, topload capacitance, etc.) to optimally promote spark growth. |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
I measured a ~25 nS delay in a 75m bugcatcher coil. What did you use to make that measurement? (I hope you don't say you used a Bird Wattmeter.) 73, ac6xg |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
Richard Clark wrote: Cecil Moore wrote: The referenced W8JI 3 nS "measurement" was the delay in a 2' dia, 100 T, 10" long loading coil on 4 MHz, i.e. 4.5 degrees. Jim's point is that it can be done! In that particular coil at 4 MHz - no, it cannot be done. measuring the phase shift between two sinusoidal currents at 4MHz to a precision of hundredths of a degree is easy. HP sold a box (the 8405 vector voltmeter) that did this decades ago. Actually, they've sold two different boxes (the 8508A ), both of which I've used. My point was that you don't even need to go that far, and that most experimentally oriented hams probably have stuff that can be used to make an improvised measurement of that accuracy. I note that the TAPR or N2PK VNAs could easily do the measurement. The practical challenge is figuring out how to get a current probe that doesn't perturb the measurement. Optical pickups are one approach. high impedance probes with resistive leads are another. Both are commonly used in antenna measurements where you want to measure the fields directly. One could, of course, also do a near field range type measurement, but the inversion from measurements at one set of locations to values at another presumes that you believe Maxwell's equations, which I seem to think might be at issue among the contenders here. now, if you said you wanted to measure tenths of a degree at 50 GHz, I'd say you have a real challenge in front of you |
Loading Coils; was : Vincent antenna
Cecil Moore wrote: That's why total current cannot be used to measure a delay through a coil in a standing-wave antenna. Not even if the frequency is known and there's a standing wave current loop at one end of the coil and a standing wave current node at the other end? 73, ac6xg |
Loading Coils; was : Vincent antenna
On Fri, 30 Nov 2007 14:29:12 -0500, "Jimmie D"
wrote: "Tom Donaly" wrote in message et... Cecil Moore wrote: Tom Donaly wrote: And, if the total electrical length isn't 90 degrees, you add a few degrees to the loading coil to make it come out right. Very ingenious. Adding or subtracting loading-coil degrees is what happens while one is tuning a screwdriver antenna. At resonance, the screwdriver is electrically very close to 90 degrees in length. Suuurrrre it is. You've got 90 degrees on the brain, Cecil. Next, you'll be talking about 90 degree equilibrium. 73, Tom Donaly, KA6RUH I must be wrong too which doesnt surprise me. Are you saying that if I put a center loaded antenna on my trucks tool box, tune it to reonance at some freqency then the antenna is not electrically 90 degrees or some integer mutilple of 90 degrees in length at that frequency. Some integer multiple meaning "odd integer multiple" if we are to continue abusing this implication. The concept that a resonant antenna could be some other electrical length is something new to me as I thought this was the defintion of resonance being equivalent to saying the feedpoint impedance is non reactive. Hi Jimmie, Basically the land-mine issue here is the hijacking of the usage of 90 degrees (or any other application of this unit) to describe a resonant condition. That is because more frequently, and certainly more appropriately, the usage of degrees is restricted to the physical dimension as its significance is especially marked in relation to a simple antenna's directivity. As you anticipate above, the simple electrical 90 degree observation repeats through an infinite multitude with a turn of the wheel. There are posters who visit intermittently, and those who post frequently that confuse the expressed electrical degrees as also inheriting the directivity qualities associated ONLY with the physical dimension expressed in degrees. This might be observed through the example of a quarterwave antenna. Its directivity is well known. If some "inventor" were to add a lumped (or distributed) Z to the same structure, that "inventor" could easily claim they added (for the sake of argument) 135 degrees to make the structure exhibit the gain of a 5/8ths wave antenna. Frequently this charade is carried out with smaller antennas being "elevated" to full size performance (hence the appeal of the current topic in its original subject line and the "invention" of adding coils). With this in mind, you might enjoy how gaming the group is played out by the more frequent poster(s) insisting on polluting the topic of directivity with the "electrical" length. The entertainment factor has been zested up recently by adding the term "equilibrium." 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
John Smith wrote:
Of course you are correct--it was meant to be a joke man, albeit a silly one ... Sorry, I didn't know you were joking. Some pretty intelligent, educated people on this newsgroup do not know the answer else they would never try to use standing-wave current to measure the phase shift through a loading coil. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
On Nov 30, 10:59 am, Jim Kelley wrote:
K7ITM wrote: On Nov 29, 9:11 am, Jim Kelley wrote: ... Over the range of a few octaves, propagation delay on the other hand does not vary to any significant extent as a function of frequency. Ostensibly, it should be equal to sqrt(LC) series L, shunt C. Actually, Jim, I do expect it to have considerable frequency dependence. I think you can find info about this in books that address the design of travelling-wave tubes. I can't think of an example of an active (or reactive) device which doesn't have frequency dependent characteristics. To the extent that indices of refraction are frequency dependent, propagation velocity does in fact vary with frequency. If it didn't, we wouldn't see rainbows. Dielectric constants do indeed have a frequency dependence. But to first order, at radio frequencies, in amateur applications, for the purposes of this discussion, and in my opinion, the effect is less than considerable - particularly if we assume the L and C in sqrt(LC) are correct at the frequency of interest. ;-) 73, Jim AC6XG OK, that leaves us with a difference of opinion, or a difference in what we are describing. There was an article in "RF Design" maybe 15 years ago now by John Mezak, K2RDX, describing a helical transmission line model for coils. At the time, he offered free software to execute the calculations (which also, to me, offered a very practical way to calculate coil parameters like inductance, effective shunt capacitance, and first parallel and series self resonances). He later charged a nominal fee for an improved version of the software, which I have. For the "100 turn, 10 inch long, 2 inch diameter" coil wound with 15AWG copper wire, using John's program, I see a variation of about 2:1 in propagation velocity between 1MHz and 20MHz. Since the first parallel self-resonant frequency is predicted to be around 8MHz, it's perhaps not fair to look as high as 20MHz, but even between 1MHz and 4MHz, I see about 25% change in predicted propagation velocity. You may say that perhaps John messed all that up terribly, but I don't think so...and there are other places you can find similar results. There's an excellent inductance calculator on-line at http://hamwaves.com/antennas/inductance.html, and though the absolute value of its prediction of propagation velocity is about 5% different than Mezak's, they both show very nearly the same percentage change with frequency. It might be worth having a bit closer look at, Jim. Perhaps it's just that you're thinking of a different effect than what these two programs (and the theory behind them) are modelling. Cheers, Tom |
Loading Coils; was : Vincent antenna
Jim Lux wrote:
4.5 degrees is easy to measure at 4 MHz with a variety of systems. If at 4 MHz, you measured 4.5 degrees change in the phase of *standing-wave current* on each side of a loading coil in a standing-wave antenna system, would you report that value as the delay through the loading coil? One glance at the standing-wave current equation should convince one that is an invalid measurement technique. For instance, the change in the phase of the standing- wave current is ~5 degrees from feedpoint to tip in a 90 degree long 1/4WL monopole. How can that standing- wave current possibly be used to measure the delay through a loading coil in the middle of that antenna? -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Jim Kelley wrote:
Cecil Moore wrote: I measured a ~25 nS delay in a 75m bugcatcher coil. What did you use to make that measurement? (I hope you don't say you used a Bird Wattmeter.) I've described it before. I used a dual-trace 100 MHz O-scope and estimated the phase angle between the two traces at about 7% of a cycle. That phase angle was certainly NOT ANYWHERE NEAR the 4.5 degrees reported by W8JI. W8JI measured a 4.5 degree phase shift in the standing-wave current being used for the measurement although virtually no phase information exists in the standing-wave current phase. W7EL made exactly the same mistake in his measurements. No wonder the two agree. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
On Nov 30, 10:30 am, "Tom Donaly" wrote:
K7ITM wrote: On Nov 29, 9:11 am, Jim Kelley wrote: ... Over the range of a few octaves, propagation delay on the other hand does not vary to any significant extent as a function of frequency. Ostensibly, it should be equal to sqrt(LC) series L, shunt C. Actually, Jim, I do expect it to have considerable frequency dependence. I think you can find info about this in books that address the design of travelling-wave tubes. But...one must be very careful about describing exactly the experiment or the conditions around a particular scenario. That's why I don't have much interest in getting involved in this "discussion": it could well be that much of the difference among all the claims and counter- claims could be trivially resolved through better communication. Cheers, Tom I don't think they're writing about real transmission lines, Tom. If they were doing that, there would be no discussion because then it would be too hard to understand. 73, Tom Donaly, KA6RUH ;-) Yeah, I know what (they think) they are writing about; I'm writing about coils more-or-less in open air, which should match pretty well with the current discussion. But again, as with so many of the discussions here, it's not worth getting tangled up in. I just thought it bears mentioning that there are some coil models available out there that go beyond simple inductance. Inductors are among the least ideal components I deal with, and having models that address the discrepancies has been helpful to me in practical designs. If people want to argue, rant, get red in the face, ... about how something works, more power to them, but I've got some designs to work out and I'd rather be spending time on them. (How small can I make a 1MHz bandpass filter that has less than a couple dB passband attenuation, more than 120dB attenuation on 2MHz and 3MHz, and shows distortion below -140dBc for inputs up to half a watt or so...??) Cheers, Tom |
Loading Coils; was : Vincent antenna
Jim Lux wrote:
Cecil Moore wrote: In that particular coil at 4 MHz - no, it cannot be done. measuring the phase shift between two sinusoidal currents at 4MHz to a precision of hundredths of a degree is easy. Jim, you misunderstood what I was trying to say and that is: It is impossible to measure a 3 ns delay through a 2"dia, 100T, 10" long coil at 4 MHz because the delay is much longer than 3 ns. It is closer to 30 ns. I DID NOT say it is impossible to measure a 3 ns delay at 4 MHz! I said it is impossible for that coil to exhibit a 3 ns delay at 4 MHz, therefore 3 ns is not a possible measurement value. -- 73, Cecil http://www.w5dxp.com |
tesla coils antennas maxwell Loading Coils; was : Vincentantenna
On 30 Nov, 11:01, Jim Lux wrote:
Tom, May I point out that a Tesla coil is an "antenna" that does not conform to Maxwells laws with respect to the adherance to the LC ratio. The LC ratio is out of balance such that the capacitor is not of the correct size to store and then return the imposed energy from the inductive heavy coil which is visually seen as resulting in a spark. Regards Art Huh... tesla coils follow all of Maxwells equations quite nicely. Paul Nicholson did some very nice analysis on this a few years back, published at a link previously posted. They're two coupled LC resonant circuits, with the coupling adjusted to around k=0.2. There are higher order systems with 3 or more resonators, as well (called Magnifiers in the TC world) The challenge in spark making is choosing appropriate operating parameters (coupling, radius of curvature, topload capacitance, etc.) to optimally promote spark growth. Let me make it quite clear. I was referring to a single coil and not the feeding arrangement. I used that as a refernce only in conjunction with the subject of antenna coils. This single coil, tho resonant, does not meet the requirements that Maxwell demands ie equilibrium. Further study of that coil will show the effect of ground beyond the coil which thus involves the system as well as the associated coil for feed coupling. Regards Art Unwin..KB9MZ....xg |
Loading Coils; was : Vincent antenna
Jim Kelley wrote:
Cecil Moore wrote: That's why total current cannot be used to measure a delay through a coil in a standing-wave antenna. Not even if the frequency is known and there's a standing wave current loop at one end of the coil and a standing wave current node at the other end? Total current phase is the context of my posting above. We were talking about total current phase, not total current amplitude. To be precise, the statement should read: "That's why total current phase cannot be used to measure a delay through a coil in a standing-wave antenna". It is difficult to post context-free English. W8JI and W7EL both used standing-wave current *phase* to try to determine the delay through a coil. That is an invalid measurement concept. If they had used the standing- wave current amplitude instead to calculate the phase shift, they would have gotten much closer to a valid result. But they are arguing about current amplitude drops which are simply relative phase shifts between the forward and reflected current. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
On 30 Nov, 12:25, K7ITM wrote:
On Nov 30, 10:59 am, Jim Kelley wrote: K7ITM wrote: On Nov 29, 9:11 am, Jim Kelley wrote: ... Over the range of a few octaves, propagation delay on the other hand does not vary to any significant extent as a function of frequency. Ostensibly, it should be equal to sqrt(LC) series L, shunt C. Actually, Jim, I do expect it to have considerable frequency dependence. I think you can find info about this in books that address the design of travelling-wave tubes. I can't think of an example of an active (or reactive) device which doesn't have frequency dependent characteristics. To the extent that indices of refraction are frequency dependent, propagation velocity does in fact vary with frequency. If it didn't, we wouldn't see rainbows. Dielectric constants do indeed have a frequency dependence. But to first order, at radio frequencies, in amateur applications, for the purposes of this discussion, and in my opinion, the effect is less than considerable - particularly if we assume the L and C in sqrt(LC) are correct at the frequency of interest. ;-) 73, Jim AC6XG OK, that leaves us with a difference of opinion, or a difference in what we are describing. There was an article in "RF Design" maybe 15 years ago now by John Mezak, K2RDX, describing a helical transmission line model for coils. At the time, he offered free software to execute the calculations (which also, to me, offered a very practical way to calculate coil parameters like inductance, effective shunt capacitance, and first parallel and series self resonances). He later charged a nominal fee for an improved version of the software, which I have. For the "100 turn, 10 inch long, 2 inch diameter" coil wound with 15AWG copper wire, using John's program, I see a variation of about 2:1 in propagation velocity between 1MHz and 20MHz. Since the first parallel self-resonant frequency is predicted to be around 8MHz, it's perhaps not fair to look as high as 20MHz, but even between 1MHz and 4MHz, I see about 25% change in predicted propagation velocity. You may say that perhaps John messed all that up terribly, but I don't think so...and there are other places you can find similar results. There's an excellent inductance calculator on-line athttp://hamwaves.com/antennas/inductance.html, and though the absolute value of its prediction of propagation velocity is about 5% different than Mezak's, they both show very nearly the same percentage change with frequency. It might be worth having a bit closer look at, Jim. Perhaps it's just that you're thinking of a different effect than what these two programs (and the theory behind them) are modelling. Cheers, Tom- Hide quoted text - - Show quoted text - Where can I obtain a copy of Johns program? TIA Art |
Loading Coils; was : Vincent antenna
Jimmie D wrote:
The concept that a resonant antenna could be some other electrical length is something new to me as I thought this was the definition of resonance being equivalent to saying the feedpoint impedance is non reactive. Stand by your guns, Jimmie, you are correct. It's just that some otherwise intelligent people on this newsgroup have forgotten everything they ever learned in Fields&Waves 101. In an antenna physically shorter than 1/4WL, there is no way that I know of to get the reflected wave back in phase with the forward wave at the feedpoint without the reflected wave making an electrical 180 degree round trip, i.e. 90 electrical degrees in each direction. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
K7ITM wrote: OK, that leaves us with a difference of opinion, or a difference in what we are describing. There was an article in "RF Design" maybe 15 years ago now by John Mezak, K2RDX, describing a helical transmission line model for coils. At the time, he offered free software to execute the calculations (which also, to me, offered a very practical way to calculate coil parameters like inductance, effective shunt capacitance, and first parallel and series self resonances). He later charged a nominal fee for an improved version of the software, which I have. For the "100 turn, 10 inch long, 2 inch diameter" coil wound with 15AWG copper wire, using John's program, I see a variation of about 2:1 in propagation velocity between 1MHz and 20MHz. Since the first parallel self-resonant frequency is predicted to be around 8MHz, it's perhaps not fair to look as high as 20MHz, but even between 1MHz and 4MHz, I see about 25% change in predicted propagation velocity. You may say that perhaps John messed all that up terribly, but I don't think so...and there are other places you can find similar results. There's an excellent inductance calculator on-line at http://hamwaves.com/antennas/inductance.html, and though the absolute value of its prediction of propagation velocity is about 5% different than Mezak's, they both show very nearly the same percentage change with frequency. It might be worth having a bit closer look at, Jim. Perhaps it's just that you're thinking of a different effect than what these two programs (and the theory behind them) are modelling. Cheers, Tom Hi Tom - I suspect that for a given coil, depending on construction, L and/or C may vary enough over several ocataves to resolve any apparent 'dispute' between my comments and the results provided by Mr. Mezak's modelling program. I do not believe these effects are large enough to be responsible for the differences being reported in phenomenon under discussion. I would be interested in knowing the results your program produces for the 100 turn, 2" diameter, 10" long coil that Cecil is concerned about, if you wouldn't mind sharing them. Thanks and 73, Jim, AC6XG |
Loading Coils; was : Vincent antenna
Richard Clark wrote:
With this in mind, you might enjoy how gaming the group is played out by the more frequent poster(s) insisting on polluting the topic of directivity with the "electrical" length. The entertainment factor has been zested up recently by adding the term "equilibrium." Richard, check out my posting on a stub that is 45 degrees in physical length but performs like a 1/4WL stub. The "electrical" length has to do with its performance, not its physical length. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
K7ITM wrote:
For the "100 turn, 10 inch long, 2 inch diameter" coil wound with 15AWG copper wire, using John's program, I see a variation of about 2:1 in propagation velocity between 1MHz and 20MHz. Now the question becomes, what was that propagation velocity at 4 MHz? An EXCEL program that I have gives a VF of around 0.03 for that coil making a 3 ns delay through it impossible at 4 MHz. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
On Nov 30, 12:48 pm, art wrote:
On 30 Nov, 12:25, K7ITM wrote: On Nov 30, 10:59 am, Jim Kelley wrote: K7ITM wrote: On Nov 29, 9:11 am, Jim Kelley wrote: ... Over the range of a few octaves, propagation delay on the other hand does not vary to any significant extent as a function of frequency. Ostensibly, it should be equal to sqrt(LC) series L, shunt C. Actually, Jim, I do expect it to have considerable frequency dependence. I think you can find info about this in books that address the design of travelling-wave tubes. I can't think of an example of an active (or reactive) device which doesn't have frequency dependent characteristics. To the extent that indices of refraction are frequency dependent, propagation velocity does in fact vary with frequency. If it didn't, we wouldn't see rainbows. Dielectric constants do indeed have a frequency dependence. But to first order, at radio frequencies, in amateur applications, for the purposes of this discussion, and in my opinion, the effect is less than considerable - particularly if we assume the L and C in sqrt(LC) are correct at the frequency of interest. ;-) 73, Jim AC6XG OK, that leaves us with a difference of opinion, or a difference in what we are describing. There was an article in "RF Design" maybe 15 years ago now by John Mezak, K2RDX, describing a helical transmission line model for coils. At the time, he offered free software to execute the calculations (which also, to me, offered a very practical way to calculate coil parameters like inductance, effective shunt capacitance, and first parallel and series self resonances). He later charged a nominal fee for an improved version of the software, which I have. For the "100 turn, 10 inch long, 2 inch diameter" coil wound with 15AWG copper wire, using John's program, I see a variation of about 2:1 in propagation velocity between 1MHz and 20MHz. Since the first parallel self-resonant frequency is predicted to be around 8MHz, it's perhaps not fair to look as high as 20MHz, but even between 1MHz and 4MHz, I see about 25% change in predicted propagation velocity. You may say that perhaps John messed all that up terribly, but I don't think so...and there are other places you can find similar results. There's an excellent inductance calculator on-line athttp://hamwaves.com/antennas/inductance.html, and though the absolute value of its prediction of propagation velocity is about 5% different than Mezak's, they both show very nearly the same percentage change with frequency. It might be worth having a bit closer look at, Jim. Perhaps it's just that you're thinking of a different effect than what these two programs (and the theory behind them) are modelling. Cheers, Tom- Hide quoted text - - Show quoted text - Where can I obtain a copy of Johns program? TIA Art You might start by asking John. I'm sure he's in the QRZ database. Cheers, Tom |
Loading Coils; was : Vincent antenna
Jimmie D wrote:
"Tom Donaly" wrote in message t... Cecil Moore wrote: Tom Donaly wrote: And, if the total electrical length isn't 90 degrees, you add a few degrees to the loading coil to make it come out right. Very ingenious. Adding or subtracting loading-coil degrees is what happens while one is tuning a screwdriver antenna. At resonance, the screwdriver is electrically very close to 90 degrees in length. Suuurrrre it is. You've got 90 degrees on the brain, Cecil. Next, you'll be talking about 90 degree equilibrium. 73, Tom Donaly, KA6RUH I must be wrong too which doesnt surprise me. Are you saying that if I put a center loaded antenna on my trucks tool box, tune it to reonance at some freqency then the antenna is not electrically 90 degrees or some integer mutilple of 90 degrees in length at that frequency. The concept that a resonant antenna could be some other electrical length is something new to me as I thought this was the defintion of resonance being equivalent to saying the feedpoint impedance is non reactive. Jimmie Slap it on your truck, and tell us at what frequencies it resonates. Can you get it to resonate at odd multiples of its fundamental frequency? 73, Tom Donaly, KA6RUH |
Loading Coils; was : Vincent antenna
On Nov 30, 1:03 pm, Jim Kelley wrote:
K7ITM wrote: OK, that leaves us with a difference of opinion, or a difference in what we are describing. There was an article in "RF Design" maybe 15 years ago now by John Mezak, K2RDX, describing a helical transmission line model for coils. At the time, he offered free software to execute the calculations (which also, to me, offered a very practical way to calculate coil parameters like inductance, effective shunt capacitance, and first parallel and series self resonances). He later charged a nominal fee for an improved version of the software, which I have. For the "100 turn, 10 inch long, 2 inch diameter" coil wound with 15AWG copper wire, using John's program, I see a variation of about 2:1 in propagation velocity between 1MHz and 20MHz. Since the first parallel self-resonant frequency is predicted to be around 8MHz, it's perhaps not fair to look as high as 20MHz, but even between 1MHz and 4MHz, I see about 25% change in predicted propagation velocity. You may say that perhaps John messed all that up terribly, but I don't think so...and there are other places you can find similar results. There's an excellent inductance calculator on-line at http://hamwaves.com/antennas/inductance.html, and though the absolute value of its prediction of propagation velocity is about 5% different than Mezak's, they both show very nearly the same percentage change with frequency. It might be worth having a bit closer look at, Jim. Perhaps it's just that you're thinking of a different effect than what these two programs (and the theory behind them) are modelling. Cheers, Tom Hi Tom - I suspect that for a given coil, depending on construction, L and/or C may vary enough over several ocataves to resolve any apparent 'dispute' between my comments and the results provided by Mr. Mezak's modelling program. I do not believe these effects are large enough to be responsible for the differences being reported in phenomenon under discussion. I would be interested in knowing the results your program produces for the 100 turn, 2" diameter, 10" long coil that Cecil is concerned about, if you wouldn't mind sharing them. Thanks and 73, Jim, AC6XG Hi Jim, Just go to the website I provided a link for. The results of the calcs it performs are certainly within typical experimental tolerance of the results from Mezak's program. But it's just one model, and you MUST understand the model and what it's trying to accomplish if you're going to be successful in applying it. As for the effects being "large enough to be responsible for...," I think you will find that the explanation there is adequately covered by people thinking they understand what someone else has described, and thinking it's at odds with what they have observed, or with their own theory (which may or may not be flawed in itself). Like I wrote before, I'm really not much interested in getting mired down in that same old stuff (once again). I'm having way too much fun actually building things with coils (and other parts) and getting them to perform useful functions. I've learned FAR more about coils and the circuits they're used in over the past year from designing and building circuits than I have from looking at the same old stuff here on r.r.a.a. that's never going to get resolved because someone has too much invested in wanting to be "right." Cheers, Tom |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
... Note that the electrical length and the physical length are nowhere near the same value. The electrical length can be 90 degrees at resonance while the physical length is only 13 degrees for a 75m mobile antenna. ... I have been thinking on this. From past posts, I think some think that a 1/4 wave monopole and a 1/2 wave electrical length monopole shortened to 1/4 physical length have very similar launch/radiation characteristics... if they do, then it is obvious that their modeling program is "BLOWING SMOKE!" A 90 degree shift in 1/4 wave physical space will never duplicate a 180 shift in the same physical dimensions! Regards, JS |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
W8JI measured a 4.5 degree phase shift in the standing-wave current being used for the measurement although virtually no phase information exists in the standing-wave current phase. W7EL made exactly the same mistake in his measurements. No wonder the two agree. Cecil, I have stared at the W8JI web page http://www.w8ji.com/inductor_current_time_delay.htm for a long time, and I just cannot find anyplace where he mentions 4.5 degrees. Is that your calculation rather than Tom's? The graphic appears to be a screen shot from a network analyzer. W8JI does not describe it any further on that page, but it may be an HP 8753D, based on information elsewhere on his site. In any case the plot appears to be S21 "delay" vs. frequency. I do not know anything about that instrument, but this appears to be an appropriate choice for the question at hand. There are two markers active. Marker 1 shows 3.0361 ns at 3.825 MHz. Marker 2 shows 486.43 ns at 16.11525 MHz. Marker 1 presumably represents a typical 80 m frequency. Marker 2 is at a peak in the graph, and it appears to mark a resonance. Sooooo, the questions a * Who made the mistake? * Does the HP network analyzer system not work correctly? * Do you think the HP engineers were not aware of standing waves? * Did Tom make the hook-up incorrectly? * Is there some other calibration factor needed? (Perhaps the Corum factor or the Cecil factor was omitted.) * Did the analyzer place the decimal point in the wrong spot? * Is "new math" needed? Does 3.0361 ns really equal 30 ns in some other coordinate system? Inquiring minds want to know. 8-) 73, Gene W4SZ |
tesla coils antennas maxwell Loading Coils; was : Vincent antenna
"AI4QJ" wrote in message ... "art" wrote in message ... On 30 Nov, 11:01, Jim Lux wrote: Tom, May I point out that a Tesla coil is an "antenna" that does not conform to Maxwells laws with respect to the adherance to the LC ratio. The LC ratio is out of balance such that the capacitor is not of the correct size to store and then return the imposed energy from the inductive heavy coil which is visually seen as resulting in a spark. Regards Art Huh... tesla coils follow all of Maxwells equations quite nicely. Paul Nicholson did some very nice analysis on this a few years back, published at a link previously posted. They're two coupled LC resonant circuits, with the coupling adjusted to around k=0.2. There are higher order systems with 3 or more resonators, as well (called Magnifiers in the TC world) The challenge in spark making is choosing appropriate operating parameters (coupling, radius of curvature, topload capacitance, etc.) to optimally promote spark growth. Let me make it quite clear. I was referring to a single coil and not the feeding arrangement. I used that as a refernce only in conjunction with the subject of antenna coils. This single coil, tho resonant, does not meet the requirements that Maxwell demands ie equilibrium. Further study of that coil will show the effect of ground beyond the coil which thus involves the system as well as the associated coil for feed coupling. Regards Art Unwin..KB9MZ....xg But you made the straightforward statement: "Tesla coils do not conform to Maxwell's laws", thus opening the door to a new field of study in Electromagnetics. In fact, if you could look into this a little deeper, you may in fact be the first person to unify field theory (something Albert Einstein himself failed to do). This may be related to the success of the Philadelphia Experiment. I think you are on to something here :-) That would appear to be a partial quote from the sentence and implies a completely different meaning from what was stated. I interpreted the statement to mean that Tesla coils exhibit extreme LC ratios which are outside the ranges that have been found to be most efficient in resonant circuits for radio communication. (As established by Maxwell and others from experimentation.) A resonant circuit for any given frequency can be made up using a capacitor and inductance of any suitable values. Using very a very large capacitor and a small inductor, or a large inductor and small capacitance may well work very well in a given situation, but experience has shown that selecting components with median values results in more stable and efficient circuit operation. Tesla coils form very sharply tuned circuits with some quite extreme component values and voltage levels. Their operating parameters do tend to lie outside what is considered 'normal' for amateur radio. The Philadelphia Experiment was a success? Why didn't anybody tell me? What time did the ship get back? Mike G0ULI |
Loading Coils; was : Vincent antenna
"AI4QJ" wrote in
: .... Calculates DC resistance of wi Now, 18 AWG wire is .00751 Ohms/foot. At 53 feet, R(L) = 0.398 Ohms And proceeds to use DC resistance of wire to analyse performance at RF: Phase angle: tan(theta) = 3600/0.398 = 9045 |
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