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Loading Coils; was : Vincent antenna
John Smith wrote:
... Regards, JS Now, let me see, some gurus' are about to explain why EZNEC beats this hands down--my ears are WIDE OPEN! JS |
Loading Coils; was : Vincent antenna
Roy Lewallen wrote in news:13la97elqjdp5e2
@corp.supernews.com: Owen Duffy wrote: . . . The helical problem I posed is not unusual, many if not most low HF helicals wind up with close spaced turns at the top. . . Out of curiosity, why? Why are they made that way, or why my interest? My interest harks back to measurement of field strength of emissions as part of response to the BPL threat. I was interested in whether NEC models might lead to a good estimate of Antenna Factor of typical commercial mobile whips (eg Hamsticks) on a wire frame model of a vehicle. I did create some models of centre loaded whips in on vehicles, but I could do a pretty close estimate of them without resorting to NEC (http://www.vk1od.net/sc/slvaf.htm). I wound up extending that to a piecewise representation of the helical (http://www.vk1od.net/m40/index.htm). Owen |
Loading Coils; was : Vincent antenna
Owen Duffy wrote:
Roy Lewallen wrote in news:13la97elqjdp5e2 @corp.supernews.com: Owen Duffy wrote: . . . The helical problem I posed is not unusual, many if not most low HF helicals wind up with close spaced turns at the top. . . Out of curiosity, why? Why are they made that way, or why my interest? Why are they made that way? Roy Lewallen, W7EL |
Loading Coils; was : Vincent antenna
Richard Harrison wrote:
You can take Kraus to the bank. I don`t know what all the fuss is about. The fuss is about some people using standing-wave current, whose phase is virtually meaningless, to make phase measurements and report those measurements as meaningful "facts" thus creating new old wives' tales that amateur radio doesn't need. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
John Smith wrote:
Cecil, don't take the whole world seriously, where would be the fun? I'm sorry, John, the difference between a duck is serious business. :-) -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Roy Lewallen wrote:
I've always regarded email as being private and confidential, and I'm sorry to see that Cecil doesn't give it the same respect. Roy, some time ago, you posted one of my private emails on this newsgroup without my permission so you have not "always regarded email as being private and confidential". In fact, I was appalled when it happened. Now we are even. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Ian White GM3SEK wrote:
Cecil Moore wrote: A software model that blows up when R=0 is perfectly acceptable in the real world. It is a software bug, not a statement on reality. It's only your model that blows up. If your model sees lumped-component behavior as an impossible singularity, that cannot be correct. It was a statement about a hypothetical model, Ian. The model that I am using does NOT blow up. The model that W8JI used is the one that blew up. Other people's models of antenna loading do not have this problem. A 3 ns delay through a 2", 10 TPI, 100 T coil at 4 MHz is not a problem????? In practical terms, a lumped-inductance model will take you straight to a buildable prototype. Yes, but the person using it will not understand reality as witnessed by the technical impossibilities asserted on this newsgroup and elsewhere. Wouldn't you really rather understand the physics than put blind trust in imaginary components that do not and cannot exist in reality? Isn't it ridiculous to use the lumped inductance in EZNEC to try to prove that there is no delay through a coil? Isn't it ridiculous to assert that reflected waves contain no energy just because you can't figure out where that reflected energy goes? -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Owen Duffy wrote:
So, NEC can model your helical so long as your helical is one that NEC can model! A lot of useful information can be had this way. Here's one such implementation that segment checks OK and illustrates the ~68 degrees of phase shift through the coil on 7.15 MHz. http://www.w5dxp.com/coil512.EZ ... we don't know a measured value for Tom's coil anyway or the true stand alone self resonance. I tried to get him to measure the self-resonant frequency using the coil as a monopole over a ground plane. Corum's equation says the coil has a VF of ~0.033 giving it an effective length of ~25 feet or an electrical 1/4WL around 10 MHz. The measured self-resonant frequency for my 75m Texas Bugcatcher coil was around 6 MHz. It's calculated VF was around 0.02. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
"AI4QJ" wrote in message ... I would assume if I was as far off in what I think the topic is supposed to be, you or others would have jumped in to tell me AND TOLD ME WHAT THE ACTUAL CONTROVERSY IS ALL ABOUT. Some more about it at http://www.k3bu.us/loadingcoils.htm besides Cecil's pages The main argument was the current distribution along the loading coil in a resonant quarter wave radiator. I and bunch stated that there is a drop along the coil, W8JI and bunch argued that not, that EZNEC "proves" it (using lumped inductance model). Nice to see W7EL coming around and recognizing difference between modeling the coil as a solenoid and lumped inductance. The net result is the overall current distribution along the radiator, which reflects efficiency and is significant when elements are employed in the arrays of loaded antenna elements. The rest is just digging deeper into the pesky electron behavior. It would be interesting to get report on W7EL visit to W8JI. Yuri, www.K3BU.us |
Loading Coils; was : Vincent antenna
Yuri Blanarovich wrote:
The main argument was the current distribution along the loading coil in a resonant quarter wave radiator. I and bunch stated that there is a drop along the coil, ... There is not much "drop" through the coil for the forward current and reflected current. The "drop" in standing-wave current is caused primarily by the superposition of the forward current and reflected current with their phasors rotating in opposite directions. Assume there is zero loss in the forward and reflected currents. At the bottom of the coil, the forward current is 1a at 0 deg and the reflected current is 1a at 0 deg. The total current will be 2a at 0 deg. At the top of the coil, the forward current is 1a at -45 deg and the reflected current is 1a at 45 deg. The total current will be 1.414a at 0 deg. Here are the corresponding phasor diagrams: http://www.w5dxp.com/phasor.gif There is no drop in either forward current or reflected current, yet there is a "drop" in total current. Since lossless conditions are assumed, the "drop" is caused 100% by phasing, not by losses or radiation. If we use a loading coil at a particular point in a 1/2WL monopole, we can get a *rise in total current* through the coil. Both examples can be seen at: http://www.w5dxp.com/test316.GIF -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
"Cecil Moore" wrote in message t... Yuri Blanarovich wrote: The main argument was the current distribution along the loading coil in a resonant quarter wave radiator. I and bunch stated that there is a drop along the coil, ... There is not much "drop" through the coil for the forward current and reflected current. The "drop" in standing-wave current is caused primarily by the superposition of the forward current and reflected current with their phasors rotating in opposite directions. Assume there is zero loss in the forward and reflected currents. At the bottom of the coil, the forward current is 1a at 0 deg and the reflected current is 1a at 0 deg. The total current will be 2a at 0 deg. At the top of the coil, the forward current is 1a at -45 deg and the reflected current is 1a at 45 deg. The total current will be 1.414a at 0 deg. Here are the corresponding phasor diagrams: http://www.w5dxp.com/phasor.gif There is no drop in either forward current or reflected current, yet there is a "drop" in total current. Since lossless conditions are assumed, the "drop" is caused 100% by phasing, not by losses or radiation. If we use a loading coil at a particular point in a 1/2WL monopole, we can get a *rise in total current* through the coil. Both examples can be seen at: http://www.w5dxp.com/test316.GIF -- 73, Cecil http://www.w5dxp.com Exactly and thanks for your insight into the subject. The argument was/is about (net, resultant) current along the loading coil in a RESONANT quarter (standing) wave monopole, aka mobile 80 m loaded whip, which was measured by W9UCW and ridiculed by W8JI et al. The rest is QRN. Yuri, K3BU.us |
Loading Coils; was : Vincent antenna
On Dec 3, 8:34 pm, Cecil Moore wrote:
.... It's your tarbaby, Tom, not mine. Hey I'M not the one who's made well over a hundred postings in this thread, man. Can the delusional see that they are? Have a good life; I'll try in the future to not engage you in meaningful discussions about your, um, tarbabies. |
Loading Coils; was : Vincent antenna
On Tue, 04 Dec 2007 02:16:36 GMT, Gene Fuller
wrote: The calculator is at http://hamwaves.com/antennas/inductance.html I believe that Owen first mentioned that website, but I could be wrong. I am looking at the calculation for beta, the axial propagation factor. It appears to be unchanged for any length of coil from very short to much longer than a quarter-wave resonant length. Hi Gene, On visiting the site, I plugged in Tom's numbers, specifically: D = 50mm N = 100 l = 254mm d = 1mm ß varied by frequency in a non-linear fashion, roughly x10 per decade shift up in frequency from 40kHz. What was strange was how "Parallel stray capacitance" wandered the map to become inductive (-1 pF) at 40 MHz (and become a non-number above). 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
On Mon, 03 Dec 2007 20:26:18 -0800, Roy Lewallen
wrote: Both NEC and EZNEC provide simple ways of generating a helical model. Hi Roy, EZNEC refuses to operate with Tom's coil (wire overlaps and geometry issues if I recall from the last failure). 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
On Mon, 3 Dec 2007 18:29:24 -0800 (PST), K7ITM wrote:
I can make the antenna conductor be the outside of a piece of coaxial cable, and use the coaxial inside as a shorted stub which reflects a pretty good (fairly high Q) inductive reactance back to a particular point such as a quarter of the antenna length back from each end, where the stub connects across a gap in the outer conductor. Can I use such an inductive reactance to tune the antenna? Will there then be a difference in current at each end of the gap across which that reactance connects? Hi Tom, Interesting proposition. I like it. 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
Richard Clark wrote:
Hi Roy, EZNEC refuses to operate with Tom's coil (wire overlaps and geometry issues if I recall from the last failure). Please contact me by email if you think there's EZNEC isn't doing something as you think it should. I'll either explain why it's doing what it does or, if there's a bug, will fix it. Roy Lewallen, W7EL |
Loading Coils; was : Vincent antenna
On Tue, 04 Dec 2007 00:31:02 GMT, Cecil Moore
wrote: I apologize, Richard, like W8JI, I am unwilling to cut my 75m Texas bugcatcher coil in half. But then, his coil didn't cost $180 either. :-) The experiment that you are suggesting is exactly the same that I suggested to W8JI but he was unwilling to perform such and I tend to understood why. :-) As a data point, in the previous argument a couple of years ago, W8JI tried to use the lumped inductance feature of EZNEC to "prove" there is never any phase shift through any coil. :-) So, the short of it (the long of it is above) is that neither of you have valid data that demonstrates a Corum solution. I'm not surprised. Seeing that there is no valid conclusion, it must be by the extended logic of your understanding of English that both your and Tom's positions are thus INVALID. Anything left to introduce, barring actual test results, is not superposition, but supposition. |
Loading Coils; was : Vincent antenna
Roy Lewallen wrote in
: Owen Duffy wrote: Roy Lewallen wrote in news:13la97elqjdp5e2 @corp.supernews.com: Owen Duffy wrote: . . . The helical problem I posed is not unusual, many if not most low HF helicals wind up with close spaced turns at the top. . . Out of curiosity, why? Why are they made that way, or why my interest? Why are they made that way? I suspect that it is a technique to try to maximise the current moment to get the highest radiation resistance. They then build out the radation resistance with loss to achieve a specification maximum VSWR for direct feeding at the base with 50 ohm line. Owen |
Loading Coils; was : Vincent antenna
Roy Lewallen wrote:
Richard Clark wrote: EZNEC refuses to operate with Tom's coil (wire overlaps and geometry issues if I recall from the last failure). Please contact me by email if you think there's EZNEC isn't doing something as you think it should. I'll either explain why it's doing what it does or, if there's a bug, will fix it. It's not a bug. Tom's coil dimensions violate the helix segment guidelines at 4 MHz. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Richard Clark wrote:
So, the short of it (the long of it is above) is that neither of you have valid data that demonstrates a Corum solution. I'm not surprised. In addition to my measurements on the 75m Texas Bugcatcher coil, I also measured ~12-13 ns delay through 50 turns of the same coil stock that Tom was using when he measured a 3 ns delay through a 100 turn coil. That 12-13 ns delay is within 15% of the Corum equation predictions. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Owen Duffy wrote:
I suspect that it is a technique to try to maximise the current moment to get the highest radiation resistance. They then build out the radation resistance with loss to achieve a specification maximum VSWR for direct feeding at the base with 50 ohm line. It could also be a technique to move part of the loading up to the top of the antenna. I once won a CA shootout with a top-loaded junk box antenna that, in EZNEC, looks something like this: http://www.w5dxp.com/SHOOTOUT.EZ -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
On Dec 4, 1:26 pm, Cecil Moore wrote:
Owen Duffy wrote: I suspect that it is a technique to try to maximise the current moment to get the highest radiation resistance. They then build out the radation resistance with loss to achieve a specification maximum VSWR for direct feeding at the base with 50 ohm line. It could also be a technique to move part of the loading up to the top of the antenna. I once won a CA shootout with a top-loaded junk box antenna that, in EZNEC, looks something like this: I think the main reason they do that is to improve current distribution. The tighter windings near the top make it act more like a lumped coil which is raised from the base. This should provide a more constant current level up the whip. It's done for the same reason people raise the usual coils used on a bugcatcher , or whatever. To improve current distribution. And most don't add any extra loss on purpose. Most add a extra small winding at the base to act as a matching coil. If you take one of those helical whips, IE: hamstick, etc, and add a longer stinger whip, you will have a pretty decent antenna. I used a 20m hamstick on 40m, by adding a 4-5 ft stinger and it worked very well. Almost as well as the typical bugcatcher. But I later rebuilt that antenna by stripping the helical windings, adding a bigger "lumped" coil, and it was pretty much electrically the same as a bugcatcher. It works all bands 80-10 now. MK |
Loading Coils; was : Vincent antenna
Cecil Moore wrote: Jim Kelley wrote: Honestly, Cecil, it's pretty hard to know what you mean considering the reckless way you throw around the term 'phase'. I'll grant that you might know what you mean, but I don't see how you can expect anyone else to. Jim, if you have trouble understanding the word "phase", look it up in a technical dictionary. I don't have time to waste my time teaching everyone the principles of AC waves in EE201. Thanks. Sorry for the unfinished thought. I meant that because of the reckless way you use the term, I don't know how you expect others to know what you intend by it when you use it. FYI: For a signal proportional to cos(x)*cos(wt), the phase doesn't change with 'x'. That's why standing wave current cannot be used to measure delay. Perfect example. The phase of a cosine wave at it's absolute maximum amplitude is either 0 or 180 degrees. Each point along a sinusoidal plot represents a different phase angle. Phase varies with time at a fixed position, or varies with position at a fixed time. For it to have meaning there must be a reference. You have a habit of switching references without noticing or making note of it. This makes some of your comments a bit confused sounding, if not blatantly inaccurate. With regard to your comment above, if the maximum amplitude and period of a sinusoidal wave are both known, then given any instantaneous amplitude and, knowing whether the slope is positive or negative, the instantaneous phase can be readily determined. FYI: Phase angle (wt) is found on the x axis of a sinusoidal plot. When period or wavelength and length are equated, as is the case with a resonant antenna then phase and position are functionally related. 73, ac6xg |
Loading Coils; was : Vincent antenna
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Loading Coils; was : Vincent antenna
On Dec 4, 3:12 pm, Cecil Moore wrote:
wrote: If you take one of those helical whips, IE: hamstick, etc, and add a longer stinger whip, you will have a pretty decent antenna. Even better is to extend the base section by a few feet. -- 73, Cecil http://www.w5dxp.com I do that too... :) I have a solid hustler mast I use for that. MK |
Loading Coils; was : Vincent antenna
Jim Kelley wrote:
You have a habit of switching references without noticing or making note of it. This makes some of your comments a bit confused sounding, if not blatantly inaccurate. Jim, it's all your fault for not being telepathic. :-) I admit that my thought processes are somewhat chaotic but remember, order often comes out of chaos. I've experienced an epiphany or two in my time. I also have a bad habit of declaring something invalid when it is only irrelevant. It is the conclusions drawn from irrelevant measurements that are invalid, not the measurements themselves. The convention that I try to use is the EZNEC convention. Everything is referenced to the source signal. When I say the phase of a standing wave is unchanging, I mean that it has the same phase as the source signal at the feedpoint and is the same phase as reported by EZNEC. I apologize for not being clear about that. With regard to your comment above, if the maximum amplitude and period of a sinusoidal wave are both known, then given any instantaneous amplitude and, knowing whether the slope is positive or negative, the instantaneous phase can be readily determined. Take I = K1*cos(x)*cos(wt), a standing-wave equation. Let t be any fixed value. cos(x) is an amplitude value and does NOT vary with time. Therefore, the phase of the standing-wave signal is constant at any particular time and does NOT depend upon position along the wire or coil. Now take I = K2*cos(x+wt), a traveling-wave equation. Let t be any fixed value. The length dimension 'x' has an effect on phase, i.e. the phase of of the signal indeed does depend upon BOTH position AND time. Anyone who understands the math would not dare show his ignorance by asserting that the delay through a 100T coil is 3 ns on 4 MHz or that the measured phase shift through a loading coil is somehow proportional to the delay through the coil in a standing-wave antenna. -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
Jim Kelley wrote:
Cecil Moore wrote: Jim Kelley wrote: Honestly, Cecil, it's pretty hard to know what you mean considering the reckless way you throw around the term 'phase'. I'll grant that you might know what you mean, but I don't see how you can expect anyone else to. Jim, if you have trouble understanding the word "phase", look it up in a technical dictionary. I don't have time to waste my time teaching everyone the principles of AC waves in EE201. Thanks. Sorry for the unfinished thought. I meant that because of the reckless way you use the term, I don't know how you expect others to know what you intend by it when you use it. FYI: For a signal proportional to cos(x)*cos(wt), the phase doesn't change with 'x'. That's why standing wave current cannot be used to measure delay. Perfect example. The phase of a cosine wave at it's absolute maximum amplitude is either 0 or 180 degrees. Each point along a sinusoidal plot represents a different phase angle. Phase varies with time at a fixed position, or varies with position at a fixed time. For it to have meaning there must be a reference. You have a habit of switching references without noticing or making note of it. This makes some of your comments a bit confused sounding, if not blatantly inaccurate. With regard to your comment above, if the maximum amplitude and period of a sinusoidal wave are both known, then given any instantaneous amplitude and, knowing whether the slope is positive or negative, the instantaneous phase can be readily determined. FYI: Phase angle (wt) is found on the x axis of a sinusoidal plot. When period or wavelength and length are equated, as is the case with a resonant antenna then phase and position are functionally related. 73, ac6xg It's hardly surprising that Cecil thinks there's no phase information in a standing wave, since he leaves it out on purpose. "Cos(x)*Cos(wt)" is just flat wrong. It's supposed to be "Cos(x + d/2)*e^(i(wt + d/2))." "d" is the phase difference between a wave traveling in the forward direction and an equal amplitude wave traveling in the opposite direction. This is pretty poor shooting for a guy who claims a degree in symbol slinging. 73, Tom Donaly, KA6RUH |
Loading Coils; was : Vincent antenna
Tom Donaly wrote:
It's hardly surprising that Cecil thinks there's no phase information in a standing wave, since he leaves it out on purpose. "Cos(x)*Cos(wt)" is just flat wrong. It's supposed to be "Cos(x + d/2)*e^(i(wt + d/2))." "d" is the phase difference between a wave traveling in the forward direction and an equal amplitude wave traveling in the opposite direction. This is pretty poor shooting for a guy who claims a degree in symbol slinging. I copied the equations from "Optics", by Hecht, page 289 in the 4th edition. Unfortunately, it is apparent that you will sacrifice your technical ethics to try to discredit me. Everything I have written is referenced to a source at zero degrees. Your extra terms do absolutely nothing except obfuscate the concepts. One can only assume that obfuscation is your ulterior motive. Here's what Gene Fuller had to say about this subject: 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. Why don't you two get back to us after you thrash out the details upon which you disagree? -- 73, Cecil http://www.w5dxp.com |
Loading Coils; was : Vincent antenna
On Tue, 04 Dec 2007 10:36:29 -0800, Roy Lewallen
wrote: Richard Clark wrote: Hi Roy, EZNEC refuses to operate with Tom's coil (wire overlaps and geometry issues if I recall from the last failure). Please contact me by email if you think there's EZNEC isn't doing something as you think it should. I'll either explain why it's doing what it does or, if there's a bug, will fix it. Roy Lewallen, W7EL Hi Roy, The complaint is: Wire 3 segment length too short. L = .01914 m; recommended min. = ..07495 m. and so on for 800+ lines. Attempting to find the Src Data results in: Wires 3 and 10 contact improperly or are too close. Wires 3 and 11 parallel and contacting. Wire 3 end 2 contacts improperly or is too close to wire 12. and so on... However, on close examination Pilot Error The wire is too thick (I noticed this in modeling Tom's coil at the Corum calculator and hadn't done the correction yet in EZNEC). The geometry still complains, but it doesn't inhibit processing. Thanx anyway. 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
Ian White GM3SEK wrote: Cecil Moore wrote: I'm not reclassifying anything. The differences between traveling-wave antennas and standing-wave antennas have been known for many decades. Oh good! Exactly where do *you* draw the line between them; and why? Please justify this by giving examples of two antennas that are very close to your chosen line, but on opposite sides. Glad to oblige. The two classical examples are a 1/2WL dipole vs a terminated rhombic. The differences are obvious. The ends of the standing-wave 1/2WL dipole are open-circuited so forward waves undergo a total reflection. Ideally, the traveling-wave rhombic is terminated in its characteristic impedance so reflections are eliminated. The equation for the current in a 1/2WL dipole is roughly proportional to cos(x)*cos(wt). The equation for the current in an ideal rhombic is proportional to cos(x+wt) where w=2*Pi*F. For anyone with a math background, those differences are more than obvious and I pointed that out years ago. Thank you; it's useful to clarify from time to time what you do mean, because many of these disputes are because people are using the same terms with different meanings. Then please justify the difference between your two different classifications of current. I don't have to justify that, Ian. Mathematics automatically justifies it for me. If you would simply take the time to understand the difference between cos(x)*cos(wt) and cos(x+wt), you would understand it also. The current in an ideal rhombic is 100% forward current proportional to cos(x+wt). The current in a 1/2WL dipole is the sum of two currents. The forward current is roughly proportional to cos(x+wt) just as it is in the rhombic. The reflected current is roughly proportional to cos(x-wt) and when those two traveling-wave currents are added the resultant standing-wave current is proportional to cos(x)*cos(wt), a completely different kind of current as is obvious from their different equations. The mathematics is clear enough, but it provides no justification whatever for your conceptual leap to "a completely different KIND of current" (my emphasis). You are only doing that to justify the different kind of behavior that your model demands for a loading inductance - in other words, you are trying to patch one error by adding a second error. I suspect (although it's difficult to separate from the other known errors) that you are also hopping between two different definitions of "phase", one for each case, without noticing that you are doing do. If instead you were to accept that current is simply the net movement of electrons, and inductance always responds to that in a consistent way, you would find the whole topic much simpler than you make it out to be. The Boyer paper that I referenced yesterday shows exactly how the model of an antenna as a reflective unterminated transmission-line handles inductive loading. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
With regard to your comment above, if the maximum amplitude and period of a sinusoidal wave are both known, then given any instantaneous amplitude and, knowing whether the slope is positive or negative, the instantaneous phase can be readily determined. Take I = K1*cos(x)*cos(wt), a standing-wave equation. Let t be any fixed value. cos(x) is an amplitude value and does NOT vary with time. Therefore, the phase of the standing-wave signal is constant at any particular time and does NOT depend upon position along the wire or coil. The item residing inside the parentheses of a sinusoidal function is in fact the 'phase' of that function. In the expression above, at any given time, amplitude is determined by the independent variable, position. Accordingly, for any given position and time there is a unique amplitude and phase. Anyone who understands the math would not dare show his ignorance by asserting that the delay through a 100T coil is 3 ns on 4 MHz or that the measured phase shift through a loading coil is somehow proportional to the delay through the coil in a standing-wave antenna. In the face of such a redoubtable accusation I'm somewhat reluctant to admit my view that a phase shift across a coil of this sort would in fact be directly proportional to any propagation delay through that coil. 73, ac6xg |
Loading Coils; was : Vincent antenna
On Tue, 04 Dec 2007 19:16:01 GMT, Cecil Moore
wrote: I also measured ~12-13 ns delay through 50 turns of the same coil stock that Tom was using when he measured a 3 ns delay through a 100 turn coil. That 12-13 ns delay is within 15% of the Corum equation predictions. Using what equipment? And with what load? |
Loading Coils; was : Vincent antenna
On Dec 4, 3:34 pm, Ian White GM3SEK wrote:
.... The Boyer paper that I referenced yesterday shows exactly how the model of an antenna as a reflective unterminated transmission-line handles inductive loading. For those who may be interested, I have that article in PDF format, along with some relevant pages from one of the references that help with coming up with numerical results. Cheers, Tom |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
Tom Donaly wrote: It's hardly surprising that Cecil thinks there's no phase information in a standing wave, since he leaves it out on purpose. "Cos(x)*Cos(wt)" is just flat wrong. It's supposed to be "Cos(x + d/2)*e^(i(wt + d/2))." "d" is the phase difference between a wave traveling in the forward direction and an equal amplitude wave traveling in the opposite direction. This is pretty poor shooting for a guy who claims a degree in symbol slinging. I copied the equations from "Optics", by Hecht, page 289 in the 4th edition. Unfortunately, it is apparent that you will sacrifice your technical ethics to try to discredit me. Everything I have written is referenced to a source at zero degrees. Your extra terms do absolutely nothing except obfuscate the concepts. One can only assume that obfuscation is your ulterior motive. Here's what Gene Fuller had to say about this subject: 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. Why don't you two get back to us after you thrash out the details upon which you disagree? You're right, I was wrong. It's Cos(kx + d/2). However, there is phase information on a standing wave, and you know it. If you don't have the mathematical facility to see how it works, that's o.k., but don't try to claim you know something about waves if you can't even do the simple math it requires to describe how it works. Parroting an equation from a book without understanding what you are parroting doesn't add a thing to your argument except an admission of ignorance. 73, Tom Donaly, KA6RUH |
Loading Coils; was : Vincent antenna
On Dec 4, 10:23 am, Richard Clark wrote:
On Mon, 3 Dec 2007 18:29:24 -0800 (PST), K7ITM wrote: I can make the antenna conductor be the outside of a piece of coaxial cable, and use the coaxial inside as a shorted stub which reflects a pretty good (fairly high Q) inductive reactance back to a particular point such as a quarter of the antenna length back from each end, where the stub connects across a gap in the outer conductor. Can I use such an inductive reactance to tune the antenna? Will there then be a difference in current at each end of the gap across which that reactance connects? Hi Tom, Interesting proposition. I like it. 73's Richard Clark, KB7QHC Hi Richard, Note that it's also possible to make the stub in the form of a helical resonator operated below resonance--that is, a loading coil that's shielded by the tubular conductor whose outside surface is the antenna. A problem with using plain coax is that the length is prohibitive. For example, if you make an 80-foot long dipole from RG-213-size coax, you find that you need about 550 ohms reactance at points a quarter of the total length in from the ends, to get it to resonate at 3.9MHz. But using a shorted stub of 50 ohm line requires about 85 electrical degrees of line. Even with solid polyethylene dielectric, that's 39 feet of line. Ooops. We only have 20 feet to work with. Lengthen the antenna to, say, 120 feet, and the required reactance drops to a low enough value to be practical to do with a shorted stub co-axial with the antenna wire, but at that point, why bother? You'd only have to add a few feet of wire to get the antenna to resonate without inductive loading. Mostly I find value in thinking about things like this because they make more clear what's really important: it's primarily the inductive reactance that tunes the antenna; the parasitic capacitance from a loading coil to the outside world, which is what causes it to behave like a helical delay line, is of much lower importance in determining the antenna tuning. In a long antenna that's capacitively loaded, the capacitors can have negligible parasitic series inductance and shunt capacitance to the outside world, but they still strongly affect the antenna loading. Of course, the closer to the end of the antenna you put a large loading coil, the more effect its capacitance will have. In the limit, you can dispense with the coil and just add a capacitive hat after all. Even modest size conductive balls on the ends of a thin- wire dipole will have a significant effect on the resonance. Cheers, Tom |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
Take I = K1*cos(x)*cos(wt), a standing-wave equation. Let t be any fixed value. cos(x) is an amplitude value and does NOT vary with time. Therefore, the phase of the standing-wave signal is constant at any particular time and does NOT depend upon position along the wire or coil. Now take I = K2*cos(x+wt), a traveling-wave equation. Let t be any fixed value. The length dimension 'x' has an effect on phase, i.e. the phase of of the signal indeed does depend upon BOTH position AND time. Cecil, I know what you are trying to say, but you got the message screwed up. If 't' is fixed, then the equations are essentially the same with regard to 'x'. That is typical; a snapshot in time does not say much about the wave behavior. 73, Gene W4SZ |
Loading Coils; was : Vincent antenna
Cecil Moore wrote:
Here's what Gene Fuller had to say about this subject: Cecil, There you go again; quoting a questionable source. 73, Gene W4SZ |
Loading Coils; was : Vincent antenna
Richard Clark wrote:
Hi Roy, The complaint is: Wire 3 segment length too short. L = .01914 m; recommended min. = .07495 m. and so on for 800+ lines. Attempting to find the Src Data results in: Wires 3 and 10 contact improperly or are too close. Wires 3 and 11 parallel and contacting. Wire 3 end 2 contacts improperly or is too close to wire 12. and so on... However, on close examination Pilot Error The wire is too thick (I noticed this in modeling Tom's coil at the Corum calculator and hadn't done the correction yet in EZNEC). The geometry still complains, but it doesn't inhibit processing. Thanx anyway. Thanks for the additional info. EZNEC's checks are often not fully understood, so I'll briefly describe what they do. EZNEC provides two types of checks, segmentation (formerly called guideline) and geometry. The first is advisory and tells when segment lengths or segment length/wire diameter ratios are outside NEC recommendations. As I mentioned in an earlier posting, warnings about too-short segments can often be disregarded without significant consequence, and this warning is often seen when a helix is created. The geometry check looks for situations such as touching or overlapping wires which can cause serious calculation errors. It takes finite wire diameter into account, so sometimes the cause of a reported error requires a bit of thought to determine, as it did here. EZNEC won't do calculations if any geometry error is present because of the high probability of the result being erroneous. The geometry check was introduced in EZNEC v. 4.0; the segmentation check has been present for a much longer time. NEC-4 has a check similar to but less complete than EZNEC's geometry check, but no equivalent to the segmentation check. NEC-2 has neither. Roy Lewallen, W7EL |
Loading Coils; was : Vincent antenna
Gene Fuller wrote:
Cecil Moore wrote: Take I = K1*cos(x)*cos(wt), a standing-wave equation. Let t be any fixed value. cos(x) is an amplitude value and does NOT vary with time. Therefore, the phase of the standing-wave signal is constant at any particular time and does NOT depend upon position along the wire or coil. Now take I = K2*cos(x+wt), a traveling-wave equation. Let t be any fixed value. The length dimension 'x' has an effect on phase, i.e. the phase of of the signal indeed does depend upon BOTH position AND time. Cecil, I know what you are trying to say, but you got the message screwed up. If 't' is fixed, then the equations are essentially the same with regard to 'x'. That is typical; a snapshot in time does not say much about the wave behavior. 73, Gene W4SZ It's generally cos(kx), but maybe Cecil is using a wave where k = 1, that is, the wavelength is 2*Pi. 73, Tom Donaly, KA6RUH |
Loading Coils; was : Vincent antenna
Ian White GM3SEK wrote:
The mathematics is clear enough, but it provides no justification whatever for your conceptual leap to "a completely different KIND of current" (my emphasis). You are only doing that to justify the different kind of behavior that your model demands for a loading inductance - in other words, you are trying to patch one error by adding a second error. I suggest you study up on your math because what you said above is just not true. cos(x)*cos(wt) *IS* obviously different from cos(x+wt). Here is a graph of the difference between standing-wave current and traveling-wave current. Please study it until you comprehend the differences. http://www.w5dxp.com/travstnd.gif -- 73, Cecil http://www.w5dxp.com |
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