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Current through coils
Cecil Moore wrote:
Gene Fuller wrote: Emboldened by this apparent success I tried to substitute the now-famous W8JI coil; 100 turns, 2 inch diameter, 10 inch length. This time the overall 500 segment count was the limiter (I am cheap), so I had to make the coil four-sided. The delay through this coil was about 9 degrees at 5.89 MHz and about 6 degrees at 3.9 MHz. Sooooo, the bottom line for the 17,000 posts in this thread is ... You wish that was the bottom line. Here's some mud in your eye. 1. I have always been talking about my 75m bugcatcher coil which is about 6"x6" and designed for actual mobile use. W8JI's coil is nowhere near what the average ham uses for a 75m bugcatcher coil. It is much too fragile for long-term mobile use. It can't even be considered to be a "bugcatcher" because one Texas- sized bug and it is destroyed. 2. You haven't installed that coil in an 8 foot 75m mobile antenna so you don't know what the delay is in an 8 foot 4 MHz system. Please feel free to try again - no cigar at the present time. You mean your coil has to be attached to an antenna in order to become a transmission line? This is getting better and better. 73, Tom Donaly, KA6RUH |
Current through coils
Tom Donaly wrote:
You mean your coil has to be attached to an antenna in order to become a transmission line? This is getting better and better. My 75m bugcatcher coil has to be attached to a 75m mobile antenna installed on my GMC pickup. That's the boundary conditions and I have been explicit about that. This is getting stranger and stranger. Next you guys will have the coil floating in free space between Sol and Alpha Centauri unconnected from anything in order to remove it from any resemblance to a real-world environment. In virtually all my postings, I have specified that I was talking about a 75m bugcatcher coil installed in a mobile installation. It really doesn't matter what happens outside that specified environment. The gurus are slowly divorcing themselves from reality. The only way they can be right is to take the mobile antenna off the vehicle, throw away the antenna, and keep the coil for testing on a bench. Have you no shame? How far are you willing to retreat from reality to make a feeble attempt to be right? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
I thought we already agreed that there is no phase shift in the real environment, namely, a nearly pure standing wave environment. You were the one who brought up all the special cases in an attempt to prove your point. However, your latest message is refreshing. I was afraid for a while that you were attempting to use a 48 foot tall mobile antenna or drag a 31.5 foot wire terminated in a resistor down the road. 73, Gene W4SZ Cecil Moore wrote: Tom Donaly wrote: You mean your coil has to be attached to an antenna in order to become a transmission line? This is getting better and better. My 75m bugcatcher coil has to be attached to a 75m mobile antenna installed on my GMC pickup. That's the boundary conditions and I have been explicit about that. This is getting stranger and stranger. Next you guys will have the coil floating in free space between Sol and Alpha Centauri unconnected from anything in order to remove it from any resemblance to a real-world environment. In virtually all my postings, I have specified that I was talking about a 75m bugcatcher coil installed in a mobile installation. It really doesn't matter what happens outside that specified environment. The gurus are slowly divorcing themselves from reality. The only way they can be right is to take the mobile antenna off the vehicle, throw away the antenna, and keep the coil for testing on a bench. Have you no shame? How far are you willing to retreat from reality to make a feeble attempt to be right? |
Current through coils
Gene Fuller wrote:
I thought we already agreed that there is no phase shift in the real environment, namely, a nearly pure standing wave environment. You are not arguing in good faith. We agreed that standing wave current with its unchanging phase cannot be used to measure the phase shift through a coil. The fact that there is no phase shift from end to end in a 1/2WL thin-wire dipole proves that using the standing wave phase to measure a phase shift is meaningless. You said the same thing in the following statement. Do you want to retract what you said? Regarding the cos(kz)*cos(wt) term in a standing wave: Gene Fuller, W4SZ wrote: In a standing wave antenna problem, such as the one you describe, there is no remaining phase information. Any specific phase characteristics of the traveling waves died out when the startup transients died out. Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be seen again. You were the one who brought up all the special cases in an attempt to prove your point. No, I'm using your posting to prove that standing wave current phase is meaningless. There's no special case. Standing wave current phase is *always* meaningless. Please install your coils in an 8 foot 75m antenna and get back to us on the results. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
I know how EZNEC calculates propagation from straight wires. It does
it very well. But do you know how it calculates the inductance of coils? How long has it been able to do this? ---- Reg ========================================= "Cecil Moore" wrote in message t... Reg Edwards wrote: How does EZNEC make its calculations? If you don't know you are placing your faith in a mirage. It uses the Moment Method (MM) sometimes called the Method Of Moments (MOM). It's described in Kraus and Balanis and credited to Roger Harrington in the 1960's. Each segment in EZNEC is assumed to have constant current. In the aforementioned 8-sided coil, there are 200 segments, each with an assumed constant current. The standing wave current in each segment depends upon where it is inserted in the standing wave environment as shown at: http://www.qsl.net/w5dxp/1WLDIP.EZ -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
"Roy Lewallen" wrote It's hard to tell from this, but are you still claiming that the end-to-end C of an inductor is the C of an equivalent transmission line? Or even an approximation? Does your program assume this? Roy Lewallen, W7EL =================================== Roy, What do you mean by end-to-end C. But very recently you did say "Reg is right" when I said "All coils behave like transmission lines." You and I agree on most fundamental matters. ---- Reg. |
Current through coils
Reg Edwards wrote:
I know how EZNEC calculates propagation from straight wires. It does it very well. In your last posting, you asked "How does EZNEC make its calculations?" Wow, you're a quick learner. But do you know how it calculates the inductance of coils? Yes. A model of a coil is constructed out of straight wires, making each turn polygonal. A wire containing a source is connected from one end to the other and, providing that the coil is short in terms of wavelength, the reactance seen by the source will be that of the coil at the test frequency. How long has it been able to do this? An automated helix creation feature was introduced in v. 4.0 two years ago this May. It has always been capable of doing the calculation, but until v. 4.0 the user would have had to calculate the wire end coordinates with an external program and import them into EZNEC. The free demo version has this feature. You can create any size helix with it to see how the feature works. You won't, however, be able to calculate its inductance with the demo program due to the segment limitation. As I've pointed out before, EZNEC won't account for proximity effect, so reported loss will be optimistic if the turns are spaced very closely. Roy Lewallen, W7EL |
Current through coils
I've a feeling there is some confusion here between phase delay in
degrees, and delay in time (nano-seconds). The former changes with frequency. The latter does not. You should all make yourselves perfectly clear. ---- Reg. |
Current through coils
Reg Edwards wrote:
"Roy Lewallen" wrote It's hard to tell from this, but are you still claiming that the end-to-end C of an inductor is the C of an equivalent transmission line? Or even an approximation? Does your program assume this? Roy Lewallen, W7EL =================================== Roy, What do you mean by end-to-end C. What most people would call "self capacitance" -- the equivalent capacitance from one terminal to the other. But very recently you did say "Reg is right" when I said "All coils behave like transmission lines." More specifically, you said: EVERYTHING has Inductance, Capacitance and Resistance, and therefore behaves as a transmission line. I agreed with that. This doesn't mean that I agree that you can choose any C you like from any point to any other, plug it into a transmission line formula, and get a meaningful result. Transmission lines are two port, four terminal devices, so a completely isolated inductor or other component, by itself, can't behave as a transmission line, except by assuming some C to the Earth. You and I agree on most fundamental matters. I'll have to take your word for that. It isn't always apparent by what you say in your postings. Roy Lewallen, W7EL |
Current through coils
Reg Edwards wrote:
I know how EZNEC calculates propagation from straight wires. It does it very well. But do you know how it calculates the inductance of coils? I don't think EZNEC cares about the inductance of helical coils. As I have been advocating, the EZNEC helical option treats the coil as just another part of the wire antenna that has been spiraled into a coil. It is ironic, is it not, that EZNEC treats a helix as just coiled up wire? Especially after the gurus have asserted that a coiled up piece of wire is not a piece of wire at all but is instead transformed into something magical that violates the theory of relativity with faster than light propagation? How long has it been able to do this? I don't know exactly. I was creating segmented coils long before EZNEC had the helix option. I even wrote a BASIC program to generate an ASCII file capable of being imported into EZNEC. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Reg Edwards wrote:
I've a feeling there is some confusion here between phase delay in degrees, and delay in time (nano-seconds). The former changes with frequency. The latter does not. You should all make yourselves perfectly clear. EZNEC takes a time-frozen snapshot of the system and reports the phases throughout the system referenced to the source. So, given a 1/2WL thin-wire dipole, what is the difference between the delay in nanoseconds and the phase delay in degrees. Aren't they convertable to each other? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
You and I agree on most fundamental matters.
I'll have to take your word for that. It isn't always apparent by what you say in your postings. Roy Lewallen, W7EL ===================================== Roy, you have a habit of creating arguments where none exist. And communications via the Internet are handicapped by the absence of body language. But we still have smileys ;o) ---- Reg. |
Current through coils
The capacitance of a coil is to the second "wire", that is, to the
"rest of the universe". I forget the name of the current which flows through that capacitance. But undoubtably, it does flow. Apart from end-effects (as with an antenna wire) it is uniformly distributed along a body (as with a transmission line) and is sufficiently accurately calculable. The whole capacitance has an equivalent capacitance which can be connected between the ends of a coil to make a resonant circuit with the coil isolated in space. There is a resonant frequency. But no use can be made of the resonant frequency because as soon anything is connected to either one or both ends of the coil the capcitance to the rest of the world changes and the resonant frequency shifts downwards. I could go on! But Roy, you know all this and I mention it here for the benefit of novices. ---- Reg. |
Current through coils
Gene Fuller wrote:
I thought we already agreed that there is no phase shift in the real environment, namely, a nearly pure standing wave environment. There's no phase shift in the standing wave current in 45 degrees of straight wire. Doesn't that tell you something? You said yourself that the standing wave current phase doesn't contain any phase information. Here's what you guys need to do to convince me that you are right. 1. Develop a coil acceptable to EZNEC that resonates an 8 foot whip on 4 MHz over mininec ground. Send me a copy of the EZNEC file. 2. Put the same coil in the traveling wave environment as I have done at: http://www.qsl.net/w5dxp/test316y.GIF and report the phase shift through the coil. Send me a copy of the EZNEC file. If you are so right and I am so wrong, that shouldn't be too difficult for half a dozen gurus (including the developer of EZNEC). -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
"Cecil Moore" wrote in message . com... Reg Edwards wrote: I've a feeling there is some confusion here between phase delay in degrees, and delay in time (nano-seconds). The former changes with frequency. The latter does not. You should all make yourselves perfectly clear. EZNEC takes a time-frozen snapshot of the system and reports the phases throughout the system referenced to the source. So, given a 1/2WL thin-wire dipole, what is the difference between the delay in nanoseconds and the phase delay in degrees. Aren't they convertable to each other? -- ========================================= Of course they are, you block-head. But one is measured in degrees of phase-shift and the other in nano-seconds of time. So to prevent confusion you must say which one you are waffling about. ---- Reg |
Current through coils
Cec,
Having clarified what *I* am waffling about, are *you* still saying that EZNEC reports propagation delay as being dependent on frequency. Is it phase delay or time delay along the coil which is dependent on frequency? ---- Reg. |
Current through coils
Reg Edwards wrote:
Cec, Having clarified what *I* am waffling about, are *you* still saying that EZNEC reports propagation delay as being dependent on frequency. Is it phase delay or time delay along the coil which is dependent on frequency? ---- Reg. If the question is how is EZNEC reporting it's results the person to ask the question of and the only person who can give a definitive answer is the author of the program. What process did he use in writing the program. A computer program, any program, can only give the answer in terms it is programed to use, using the mathematical formula that is coded into the program. Even R2D2 could only respond according to it's programming. Let's quit attempting to split hairs and look to the original program for the answer. Dave N |
Current through coils
Let's quit attempting to split hairs and look to the original program for the answer. Dave N ====================================== I am not quibbling about what EZNEC reports but what Cecil has *said* it reports. On the other hand, Cecil may be right. But I hope he is wrong! ---- Reg. |
Current through coils
Reg Edwards wrote:
Cec, Having clarified what *I* am waffling about, are *you* still saying that EZNEC reports propagation delay as being dependent on frequency. . . . EZNEC doesn't report time or propagation delay. If it's needed, it must be calculated from the reported phase angles. Roy Lewallen, W7EL |
Current through coils
Reg Edwards wrote:
Is it phase delay or time delay along the coil which is dependent on frequency? Seems to be both. John P. has already done the math in another posting. Here's what he said: John P. said: Here is that list repeated in units of time, instead of degrees: MHz ns delay 5.5 7.1 5.89 7.4 6 7.5 7 8.5 8 10.2 9 14.2 10 24.7 11 35.7 12 37.7 13 36.8 13.7 37.3 -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Reg Edwards wrote:
I am not quibbling about what EZNEC reports but what Cecil has *said* it reports. On the other hand, Cecil may be right. But I hope he is wrong! Well, let me combine my results and John P's. MHz Degrees Delay in Freq Phase Shift nanoseconds 5.5 14.13 7.14 5.89 15.68 7.39 6 16.2 7.5 7 21.36 8.5 8 29.47 10.2 9 45.92 14.2 10 88.95 24.7 11 141.38 35.7 12 163.02 37.7 13 172.28 36.8 13.7 183.82 37.2 -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
EZNEC doesn't report time or propagation delay. If it's needed, it must be calculated from the reported phase angles. In my case, done by installing zero ohm loads at the bottom and top of the coil for the traveling wave antenna. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
I have sent the files to you, as requested. The resonant whip ended up at about 10 feet, not 8, because I tired of the continuing the optimization. The phase shift found from the traveling wave version was about 7 degrees. The coil was similar to the coil you have been using, except squeezed down to 6 inches tall, 4 TPI. You can refine the models or perform the required adjustments as you wish to get the 8 foot version. I would not expect radical changes, but who knows? It is always possible that I made a mistake in the modeling. If so, I am confident the entire world will know in short order. 8-) 73, Gene W4SZ Cecil Moore wrote: Here's what you guys need to do to convince me that you are right. 1. Develop a coil acceptable to EZNEC that resonates an 8 foot whip on 4 MHz over mininec ground. Send me a copy of the EZNEC file. 2. Put the same coil in the traveling wave environment as I have done at: http://www.qsl.net/w5dxp/test316y.GIF and report the phase shift through the coil. Send me a copy of the EZNEC file. If you are so right and I am so wrong, that shouldn't be too difficult for half a dozen gurus (including the developer of EZNEC). |
Current through coils
"Roy Lewallen" wrote EZNEC doesn't report time or propagation delay. If it's needed, it must be calculated from the reported phase angles. Roy Lewallen, W7EL =================================== EXACTLY! Roy, you knew exactly what I was hunting for! The phase angle should indeed increase with frequency. With a true transmission line the increase should be directly proportional to frequency. But the propagation delay, with a true transmission line, should be constant versus frequency as it depends only on coil dimensions and hence on L and C. The velocity factor should also be a constant. When the angle is 90 degrees the coil is 1/4-wave resonant. When the angle is 180 degrees it is 1/2-wave resonant. The 180 degree frequency should be twice the 90 degree freq. The differences between the 'measurements' and expectations, on the basis of a true transmission line, can perhaps be explained by the very small ratio of wire diameter to winding pitch. (Who would use such a coil to load an antenna anyway?) The ratio of coil diameter to coil length is large. Therefore end-effect (as with an antenna wire) becomes quite important. I have no idea what else may have been 'connected' to the coil when inside EZNEC. Could it have affected measurements? Would it be possible to 'measure' input impedance looking into one end of a coil with the other end disconnected? Regarding the calculated values of delay time there seems to be something wrong. There is a simple relationship between phase angle and length of coil and time. What was the formula used to calculate propagation time? If the correct formula was used does this point to somthing peculiar with EZNEC's own calculations? Can't think any more. ---- Reg. |
Current through coils
Reg Edwards wrote:
(snip) What was the formula used to calculate propagation time? Glad you asked. I calculated (1/f)*(angle/360) or period of one cycle times fraction of a period. I assumed that all the phase shifts given were less than one period, total. I was hoping someone else would calculate the delays and correct any mistakes in my method or results. If the correct formula was used does this point to somthing peculiar with EZNEC's own calculations? Can't think any more. Or it points to the coil in question not acting purely like a transmission line over this range of frequencies. How would a short length of transmission line act if you parallel it, end to end with capacitance? This coil certainly has end to end capacitance. At some high frequency, that capacitance will, first resonate with the inductance, forming a trap (with a rapid phase change with respect to frequency), and above that, bypass the antenna current around the inductance. At very low frequencies, with a low impedance on each side, almost pure inductance probably dominates. In between these, (with appropriate impedance connections), there is probably a frequency range where it acts mostly like a short piece of transmission line, with approximately (a lot less approximate than +- 60%) constant delay. In such a large beast, at the intended frequency of operation, unintended parasitic effects may be as big as the intended inductive effect. These are the problems that make designing good (as in, "act as lumps of inductance") coils interesting. |
Current through coils
On Mon, 27 Mar 2006 15:17:35 -0800, Roy Lewallen
wrote: What most people would call "self capacitance" -- the equivalent capacitance from one terminal to the other. Hi Roy, Not strictly speaking. It ("self capacitance") is with respect to a very remote reference, not merely the two plate formulation of the terminal's geometries to each other (that is more part of the distributed capacitance). There are two measures of capacitance. Self capacitance is any body's capacity to store charge. You don't need a second plate to do that in the classical math - merely a reference point from which the voltage is determined (yes, another dimensionless oddity that makes this more easily said than done). Mutual capacitance, two plate construction, is the more usual form we all have come to expect - so much so that the term mutual has fallen into disuse and most express only the second, isolated term - capacitance. Tom, a week or so back, asked about the infinitesimal capacitance of a coil with 15 meters (or so) of wire. He speculated that as the "second" plate of the (mutual) capacitance was withdrawn to infinity, that it forced the value to zero. I, on the other hand showed that in the practical universe: C = 2 · Pi · epsilon0 · L / ( ln(b/a) ) a = 1m (after all, thin is relative at infinite dimensions) L = 15m b= 1,000,000,000,000,000,000,000,...000m (10³³³ meters away) epsilon0 = 0.00000000000885 C = 12 femtofarads This was certainly at the limits of my usual Capacitor Bridge to measure to this resolution 30 years ago, but time has marched on. This sized capacitance is certainly encountered every day in my new field of nanotech, and 1 femtofarad is measured by charge transfer techniques. Consider, Einstein's estimate of the radius of the Universe is roughly 10 Billion Light Years (±3dB) As this result above is vastly further away than Einstein's guess (by more than 300 orders of magnitude), lets look at again from his number: C = 12.5 picofarads Oddly enough, this value is on par with the distributed capacitance of the coil's we've been pounding away on (and even more convergent, is this is roughly the same amount of wire used in them). I extracted this correlation from reports of the coils' self resonant frequency and their inductance. Self Capacitance is nothing more than Mutual Capacitance with a second spherical plate, with a radius of this 10 Billion Light Years. However, this capacitance is the total bulk of the coil rather than that distributed to form a transmission line. Anyway, thinking of a coil in terms of Mutual Capacitance, Distributed Capacitance, Self Capacitance, Self Inductance, and Mutual Inductance is a tantalizing prospect to investigate and elevate the topic to this mythic status of transmission line - but I seem to lack the motivation to go there. The extraordinary farce is more entertaining. 73's Richard Clark, KB7QHC |
Current through coils
John Popelish wrote: In such a large beast, at the intended frequency of operation, unintended parasitic effects may be as big as the intended inductive effect. These are the problems that make designing good (as in, "act as lumps of inductance") coils interesting. Actual time delay of current through 100 turn 10tpi 2 inch diameter ten inch long inductor: http://www.w8ji.com/inductor_current_time_delay.htm 73 Tom |
Current through coils
Gene Fuller wrote:
It is always possible that I made a mistake in the modeling. If so, I am confident the entire world will know in short order. 8-) It is also possible that EZNEC cannot be used for this task. It doesn't make technical sense that the delay through a coil can go from 7 nS at 5.5 MHz to 38 nS at 12 MHz. I think that was what was bothering Reg. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
Actual time delay of current through 100 turn 10tpi 2 inch diameter ten inch long inductor: Here is probably the actual time delay through that coil. W8JI wrote: "By the way, I swept S12 phase with my network analyzer on a 100uH inductor a few hours ago while working on a phasing system. The phase shift through that series inductor was about -60 or -70 degrees on 1 MHz, ... " -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
W8JI wrote: "By the way, I swept S12 phase with my network analyzer on a 100uH inductor a few hours ago while working on a phasing system. The phase shift through that series inductor was about -60 or -70 degrees on 1 MHz, ... " Once again Cecil's famous selective editing allows him to remove things from context and change the results to suit his unusual ideas. Noted is your complete lack of technical response which is obvious by its absence. Were you fibbing when you said you measured "-60 or -70 degrees on 1 MHz"? I didn't change a thing, Tom. That is an exact quote from you. The paragraph above and below were about other topics. This is why I think getting into a long technical discussion with Cecil is a waste of time. You have never engaged me in even a short technical discussion. 99% of the technical content of my postings are ignored by you. One wonders why. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
My oh my! I looked down and saw that there were many hundreds of messages
that I had not read - might have been twice that number, but I do have an automatic purge turned on. For two weeks there has been a theological discussion going on. All of this was thrashed out years ago - perhaps it was at Worms many centuries ago. A lesson from an old man: I ran a rural zoning board for 18 years, McLaughlin's rule for running the meeting was that everyone could have a say and one rebuttal after everyone had had their say. (The perversity that was sometimes exhibited at the zoning board meeting quite exceeded anything you gentle people could put forth.) Perhaps a modern equivalent that is applicable is: do not feed the trolls This is a great group. 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: |
Current through coils
Gene Fuller wrote:
I have sent the files to you, as requested. It is always possible that I made a mistake in the modeling. If so, I am confident the entire world will know in short order. 8-) Ten turns per foot is not what I had in mind for modeling my 4TPI 75m bugcatcher coil and the EZNEC guideline violations are a little discouraging. I have an EZNEC file for a omnidirectional 20 dBi antenna if you would like to have it. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
I take your cryptic message to mean there was something wrong with the files I sent you. If that is your message then I don't understand. I just went back and checked the EZ files. The coil consists of 25 turns over a six-inch length. How does that calculate out to ten turns per foot? 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: I have sent the files to you, as requested. It is always possible that I made a mistake in the modeling. If so, I am confident the entire world will know in short order. 8-) Ten turns per foot is not what I had in mind for modeling my 4TPI 75m bugcatcher coil and the EZNEC guideline violations are a little discouraging. I have an EZNEC file for a omnidirectional 20 dBi antenna if you would like to have it. :-) |
Current through coils
Hohn Popelish wrote:
"I guess this depends on the official definition of "slow wave." My dictionary of electronics defines "slow-wave circuit" as: "-A microwave circuit in which the phase velocity of the waves is considerably below the speed of light. Such waves are used in traveling-wave tubes." William I. Orr wrote on page 6.11 of the 22nd edition of the "Radio Handbook": "Spaced closely around the (TWT) beam is a circuit, in this case a helix of tightly wound wire, capable of propagating a slow wave. The r-f energy travels along the wire at the velocity of light but, because of the helical path, the energy propagates along the length of the tube at a considerably lower velocity than is determined primarily by the pitch of the helix." (I think Mr. Orr probably wrote: that is determined primarily by the pitch of the helix.) I`ve seen several mentions of "slow wave" in the literature and it always meant slower than the speed of light. There is no need to limit the definition to microwaves as the coil slows the velocity across because the wave is guided by the wire wrapped around its form. The wire is longer than the coil form. Best regards, Richard Harrison, KB5WZI |
Current through coils
Gene Fuller wrote:
Cecil, I just went back and checked the EZ files. The coil consists of 25 turns over a six-inch length. How does that calculate out to ten turns per foot? First, thanks for sending me those files. I have never been able to generate a 4 TPI coil in EZNEC because of proximity guidelines. How did you accomplish that? Second, I thought EZNEC stored the design specifications for the latest created coil and I was mistaken about that. EZNEC must default to ten turns per foot. However, the antenna is almost 12 feet tall, not the agreed upon 8 feet. It would take a bigger coil to resonate an 8 foot antenna at 4 MHz. Bigger coil = more delay. And I'm not encouraged by those numerous EZNEC guideline violations. Download http://www.qsl.net/w5dxp/SUPRGAIN.EZ for an omni-directional 20 dBi gain antenna that violates the EZNEC guidelines. Incidentally, there seems to be a bug in EZNEC. When I try to save the segmentation errors to a file, EZNEC barfs and closes. I can't get a look at all the errors so I don't know what they are. I will continue to tweak the files, like adding enough coil to bring an 8 foot antenna to resonance. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Harrison wrote:
Hohn Popelish wrote: "I guess this depends on the official definition of "slow wave." My dictionary of electronics defines "slow-wave circuit" as: "-A microwave circuit in which the phase velocity of the waves is considerably below the speed of light. Such waves are used in traveling-wave tubes." William I. Orr wrote on page 6.11 of the 22nd edition of the "Radio Handbook": "Spaced closely around the (TWT) beam is a circuit, in this case a helix of tightly wound wire, capable of propagating a slow wave. The r-f energy travels along the wire at the velocity of light but, because of the helical path, the energy propagates along the length of the tube at a considerably lower velocity than is determined primarily by the pitch of the helix." (I think Mr. Orr probably wrote: that is determined primarily by the pitch of the helix.) I`ve seen several mentions of "slow wave" in the literature and it always meant slower than the speed of light. There is no need to limit the definition to microwaves as the coil slows the velocity across because the wave is guided by the wire wrapped around its form. The wire is longer than the coil form. It seems that these references are not particularly concerned with the dimensions of the coil with respect to wavelength, or with the mode of propagation within the coil. I suspect that the term has different meanings to different specialties. |
Current through coils
Gene Fuller wrote:
I take your cryptic message to mean there was something wrong with the files I sent you. If that is your message then I don't understand. Your files contain multiple geometry proximity errors. Here is what EZNEC says about your file: http://www.qsl.net/w5dxp/ezerror.GIF I started to print out the error file until I discovered it is 142 pages long. It seems to be impossible to model 4 MHz, 4 TPI coils in EZNEC without multitudes of proximity errors. Proximity errors result in gross errors in EZNEC results. I'm sorry, Gene, but the results of your simulation cannot be trusted. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
As you know, generating the helix coils and using them are two separate things. I have only EZNEC version 3, which does not support automatic helix generation. However, there does not appear to be any reason why helices cannot be used in EZNEC version 3. That is what I did. I copied your wires, edited them, and re-input into EZNEC. As for the height, you asked for an 8 foot whip. I adjusted my model until I got to a 10 foot whip. As I stated, I quit at that point. If you choose to further refine the model, be my guest. I doubt that you will find the magic wormhole into the parallel universe where everything is radically different. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: Cecil, I just went back and checked the EZ files. The coil consists of 25 turns over a six-inch length. How does that calculate out to ten turns per foot? First, thanks for sending me those files. I have never been able to generate a 4 TPI coil in EZNEC because of proximity guidelines. How did you accomplish that? Second, I thought EZNEC stored the design specifications for the latest created coil and I was mistaken about that. EZNEC must default to ten turns per foot. However, the antenna is almost 12 feet tall, not the agreed upon 8 feet. It would take a bigger coil to resonate an 8 foot antenna at 4 MHz. Bigger coil = more delay. And I'm not encouraged by those numerous EZNEC guideline violations. Download http://www.qsl.net/w5dxp/SUPRGAIN.EZ for an omni-directional 20 dBi gain antenna that violates the EZNEC guidelines. Incidentally, there seems to be a bug in EZNEC. When I try to save the segmentation errors to a file, EZNEC barfs and closes. I can't get a look at all the errors so I don't know what they are. I will continue to tweak the files, like adding enough coil to bring an 8 foot antenna to resonance. |
Current through coils
Cecil,
I did what you "challenged", with the exception of the exact whip length. (And the version I sent had a total height of 11 feet 9 inches, which is not absurdly unreasonable.) I have to say I am surprised that it took you more than 24 hours to misinterpret what I sent (10 turns per foot) and then to blame the tools. I don't see any of the errors on my computer. There is little point of carrying this any further. You already stated that the results did not make technical sense to you and that perhaps EZNEC cannot be used for this task. I cannot repair your "technical sense", and I have no control over the capabilities of EZNEC. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: I take your cryptic message to mean there was something wrong with the files I sent you. If that is your message then I don't understand. Your files contain multiple geometry proximity errors. Here is what EZNEC says about your file: http://www.qsl.net/w5dxp/ezerror.GIF I started to print out the error file until I discovered it is 142 pages long. It seems to be impossible to model 4 MHz, 4 TPI coils in EZNEC without multitudes of proximity errors. Proximity errors result in gross errors in EZNEC results. I'm sorry, Gene, but the results of your simulation cannot be trusted. |
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