|
Current through coils
Cecil Moore wrote: Guess everyone sees the danger in trying to guess what the results of someone else's measurement will be. Tom should have measured something around 15.6 degrees. The fact he didn't sends up a very large red flag. Translation of what Cecil actually is saying: "Whenever multiple measurements by independent sources disagree with me the measurements others made must be wrong." http://www.w8ji.com/agreeing_measurements.htm http://www.w8ji.com/mobile_and_loaded_antenna.htm http://www.w8ji.com/inductor_current_time_delay.htm |
Current through coils
Cecil Moore wrote:
Jerry Martes wrote: I feel like Rip Van Winkle. The engineering community has developed a whole lot of nice things since I left it in 1969. And, its like I've been sleeping for 37 years. Ever heard of a "Triactuated Multicomplicator"? I thought that was three ole farts trying to figger out Ohm's Law :-) |
Current through coils
On Mon, 13 Mar 2006 13:01:15 GMT, Cecil Moore wrote:
from: I cannot figure out how to use the VVM to make a valid measurement it illogically follows that: It is virtually impossible to eliminate reflections from a 75m mobile bugcatcher system so the VVM can't measure what we are trying to measure. aside from the poor grammar - the two statements are consistent to inability. |
Current through coils
Cecil Moore wrote:
(snip) The question is: For a well-designed coil, is the self- resonance method valid for determining the delay through a coil at HF frequencies below the self-resonant frequency? Yes, that is an excellent question. Since that's been an accepted way of doing it for more than a century, This is a conclusion I have not seen you support, except with repeated assertions. Can you offer something more substantial? Surely a few references have accumulated in that century. How did you learn about this as the accepted way? I don't see how anyone could object. Man, what I don't see, could almost fill a universe. But I don't use it to try to win arguments. |
Current through coils
wrote:
Cecil Moore wrote: Guess everyone sees the danger in trying to guess what the results of someone else's measurement will be. Tom should have measured something around 15.6 degrees. The fact he didn't sends up a very large red flag. Translation of what Cecil actually is saying: "Whenever multiple measurements by independent sources disagree with me the measurements others made must be wrong." Other multiple measurements by independent sources agree with me and disagree with you, Tom. Wonder why you neglected to post this reference from your own server? http://lists.contesting.com/archives.../msg00540.html It is a posting to TowerTalk by Jim Lux, W6RMK. I'll just extract some excerpts. "For closewound coils, with length to diameter ratios around 5:1, a series of fairly careful measurements have been made with the coils arranged vertically above a ground plane, fed at the base, with a capacitive load on the other end, and the driving frequency arranged to be at the resonant frequency of the whole assembly." Sure sounds like your 100 uH 10"x2" coil installed in a mobile ham radio antenna environment. "In most cases, the phase shift in the current at top and bottom [of the coil] was on the order of 10-20 degrees." Contrary to the assertions of W8JI. Funny, I predicted 16 degrees for your coil on 4 MHz based on the self-resonant frequency. "For inductance the signficant thing is that the magnetic field of one segment pretty much links to the adjacent segments, and less so for the rest." Contrary to the assertions of W8JI. "At this time, the models are sufficiently well developed that they predict the actual currents and voltages to substantially better than one percent ..." As opposed to W8JI's "accuracy". "The take home message here, regarding loading coils, is that simple lumped approximations of a loading coil may do just fine for an initial design cut, but do not adequately reflect reality." "I think it's best to leave it at: Loading coils are not isolated lumped elements and cannot be modeled as such." To which I add: Since a lumped element model is a subset of the distributed network model, if the lumped element results disagree with the distributed network results, the lumped element results are simply invalid. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil, W5DXP wrote:
"Please explain why a centuries old method of determining phase shift through a coil by measuring its self-resonant frequency is not good enough for you?" A coil is an RLC circuit. At resonance, L offsets C and all that is left is R. In a resistance, the current is in-phase with the applied voltage. But, in a physical length of a tuned circuit or in a straight conductor in its place, in a circuit with reflections, you have energy coming from both directions creating an interference pattern, which is repeated every 1/2-wave (180-degrees) in the line Peaks are 1/2-wave apart, considering the velocity factor of the line. To determine the phase shift, count the maxima. The wavelength of a line is the distance a wave must travel for one complete cycle (360-degrees). If you want the phase shift for a line, take the length of line required for one degree of phase retardation and multiply it by the length of line you have. Best regards, Richard Harrison, KB5WZI |
Current through coils
John Popelish wrote:
Cecil Moore wrote: Since that's been an accepted way of doing it for more than a century, How did you learn about this as the accepted way? I'm a part-time teacher and it is described in a physics history book that is, unfortunately, at work. Interesting book as it gives a biographical treatment of the major famous physicists from Galileo to Einstein. The Maxwell and Heavyside sections are particularly interesting to me. For more information, take a look at: http://lists.contesting.com/archives.../msg00540.html -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Mon, 13 Mar 2006 12:20:15 -0500, John Popelish
wrote: The question is: For a well-designed coil, is the self- resonance method valid for determining the delay through a coil at HF frequencies below the self-resonant frequency? Yes, that is an excellent question. Since that's been an accepted way of doing it for more than a century, This is a conclusion I have not seen you support, except with repeated assertions. Can you offer something more substantial? Surely a few references have accumulated in that century. How did you learn about this as the accepted way? Hi John, Well, I for one note that your call for a reference to that one point (coil self resonance) was met by a "link" to a mailing list on another point (assembly self resonance). Be that as it may. What we do find at that "link" has a rather condemnatory admission: Amateur antennas vary so much in installation and design that a rigorous treatment of one case That case being a Tesla coil SECONDARY which is notably tight wound would not, in general, be applicable to others. which quite defines the coils offered here, and are admitted to in the first words of this sentence. The thread may now diverge towards Tesla secondary coils and away from your "well-designed" coil. SOP 73's Richard Clark, KB7QHC |
Current through coils
Cecil Moore wrote:
(snip) Other multiple measurements by independent sources agree with me and disagree with you, Tom. Wonder why you neglected to post this reference from your own server? http://lists.contesting.com/archives.../msg00540.html It is a posting to TowerTalk by Jim Lux, W6RMK. I'll just extract some excerpts. "For closewound coils, with length to diameter ratios around 5:1, a series of fairly careful measurements have been made with the coils arranged vertically above a ground plane, fed at the base, with a capacitive load on the other end, and the driving frequency arranged to be at the resonant frequency of the whole assembly." Sure sounds like your 100 uH 10"x2" coil installed in a mobile ham radio antenna environment. (snip) The tantalizing part from my perspective is this: "The measurements were made with carefully designed fiberoptic probes that were specifically designed to avoid perturbing the magnetic and electric fields." I would like to read a full description of this instrumentation. |
Current through coils
Cecil Moore wrote:
For more information, take a look at: http://lists.contesting.com/archives.../msg00540.html Very interesting, but not enough information to allow me to repeat their measurements. I also note that the opening statement: "For closewound coils, with length to diameter ratios around 5:1, a series of fairly careful measurements have been made with the coils arranged vertically above a ground plane, fed at the base, with a capacitive load on the other end, and the driving frequency arranged to be at the resonant frequency of the whole assembly." This definitely specifies only a single frequency for the test. While it is not the self resonant frequency of the coil alone, it is definitely a resonant situation, where there will be a considerable standing wave through the coil. So I don't see how this reference supports your claim that measuring the delay at resonance tells you the delay at other frequencies. It also contradicts your claim about how a standing wave makes it difficult to measure the current delay through the coil. What have I missed? |
Current through coils
Richard Harrison wrote:
The wavelength of a line is the distance a wave must travel for one complete cycle (360-degrees). If you want the phase shift for a line, take the length of line required for one degree of phase retardation and multiply it by the length of line you have. If you want to know the velocity factor of a piece of transmission line, the easiest thing to do is find its first self-resonant frequency. A little math will yield the VF which allows prediction of the phase shift through any reasonable length of tranmission line. If you want to know the velocity factor of a coil, the easiest thing to do is find its first self- resonant frequency. A little math will yield the VF of the coil which allows prediction of the phase shift through any reasonable length of coil. Not disagreeing - just expanding. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
If you want to know the velocity factor of a piece of transmission line, the easiest thing to do is find its first self-resonant frequency. A little math will yield the VF which allows prediction of the phase shift through any reasonable length of tranmission line. If you want to know the velocity factor of a coil, the easiest thing to do is find its first self- resonant frequency. A little math will yield the VF of the coil which allows prediction of the phase shift through any reasonable length of coil. If the inductor in question does not take much advantage of mutual induction across its length nor has much capacitance across its length (say, a straight conductor, strung with ferrite toroids), then I can see the similarity with a transmission line. But as the inductor approaches a lumped inductance with significant inter winding capacitance and mutual inductance coupling the current across a significant part of its winding length, I see on reason to assume the transmission line method (delay independent of frequency) strictly applies. It might, but it would take more than you saying so to assure me that it is a fact. In other words, transmission line concepts like uniform inductance per length and uniform capacitance per length get rather muddled in a real inductor. |
Current through coils
Richard Clark wrote:
Well, I for one note that your call for a reference to that one point (coil self resonance) was met by a "link" to a mailing list on another point (assembly self resonance). Give us a break, Richard. Those two subjects were in different paragraphs and completely unrelated. I looked up the reference and it is, "The Great Physicists From Galileo To Einstein, Biography of Physics", by George Gamow, (ISBN: 0486257673) I was going to furnish that information on Thursday when I go back to work. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
John Popelish wrote:
If the inductor in question does not take much advantage of mutual induction across its length nor has much capacitance across its length (say, a straight conductor, strung with ferrite toroids), then I can see the similarity with a transmission line. But as the inductor approaches a lumped inductance with significant inter winding capacitance and mutual inductance coupling the current across a significant part of its winding length, I see on reason to assume the transmission line method (delay independent of frequency) strictly applies. It might, but it would take more than you saying so to assure me that it is a fact. In other words, transmission line concepts like uniform inductance per length and uniform capacitance per length get rather muddled in a real inductor. Tom W8JI posted a good description and summary of inductor operation a little while ago, but it looks like it could bear repeating, perhaps with a slightly different slant. In a transmission line, a field at one end of the line requires time to propagate to the other end of the line. As the EM fields propagate, they induce voltages and currents further down the line, which create their own EM fields, and so forth. These propagating fields and the currents and voltages they produce make the whole concept of traveling voltage and current waves useful and meaningful. But in a tightly wound inductor, a field created by the current in one turn is coupled almost instantly to all the other turns (presuming that the coil is physically very small in terms of wavelength). Consequently, output current appears very quickly following the application of input current. The propagation time is nowhere near the time it would take for the current to work its way along the wire turn by turn. Once again it's necessary to point out that I'm speaking here of an inductor which has very good coupling between turns and minimal field leakage or radiation, for example a toroid. If you make an air wound inductor and slowly stretch it out until it's nothing more than a straight wire, it'll begin by resembling the toroid -- more or less, depending on how well coupled the turns are and how much its field interacts with the outside world -- then slowly change its characteristics to resemble a straight wire. There's no magic transition point. So by choosing the inductor, you can observe behavior anywhere along this continuum. Roy Lewallen, W7EL |
Current through coils
John Popelish wrote:
Cecil Moore wrote: (snip) Other multiple measurements by independent sources agree with me and disagree with you, Tom. Wonder why you neglected to post this reference from your own server? http://lists.contesting.com/archives.../msg00540.html It is a posting to TowerTalk by Jim Lux, W6RMK. I'll just extract some excerpts. "For closewound coils, with length to diameter ratios around 5:1, a series of fairly careful measurements have been made with the coils arranged vertically above a ground plane, fed at the base, with a capacitive load on the other end, and the driving frequency arranged to be at the resonant frequency of the whole assembly." Sure sounds like your 100 uH 10"x2" coil installed in a mobile ham radio antenna environment. (snip) The tantalizing part from my perspective is this: "The measurements were made with carefully designed fiberoptic probes that were specifically designed to avoid perturbing the magnetic and electric fields." I would like to read a full description of this instrumentation. Like many others I don't know everything. In line with reducing my ignorance could you amplify on how the phenomena is measured with a "fiber optic probe". What type of transducer is used to convert energy of an electrical nature to energy of an optical nature with out "perturbing the magnetic and electric fields". Dave WD9BDZ |
Current through coils
John Popelish wrote:
I also note that the opening statement: "For closewound coils, with length to diameter ratios around 5:1, a series of fairly careful measurements have been made with the coils arranged vertically above a ground plane, fed at the base, with a capacitive load on the other end, and the driving frequency arranged to be at the resonant frequency of the whole assembly." This definitely specifies only a single frequency for the test. Yes, a 75m mobile base-loaded antenna is a single frequency antenna. Why are you surprised? Those guys have figured out something that I haven't, probably because they have better tools at their disposal than I do. They seem to have a 1% accurate model at frequencies other than the self-resonant frequency. I, OTOH, am only sure of my accuracy at the self-resonant frequency due to the limited tools at my disposal. So I don't see how this reference supports your claim that measuring the delay at resonance tells you the delay at other frequencies. It also contradicts your claim about how a standing wave makes it difficult to measure the current delay through the coil. What have I missed? You missed the complete point, John. If one cannot eliminate reflections from the measuring process, then use them to your advantage in the measurements. Self-resonance means that the forward wave is in phase with the reflected wave. The first time that happens is when the wave has made a 180 degree round trip to the tip of the antenna and back, i.e. it happens first at self-resonance, when the coil is electrically 90 degrees long. For a well-designed coil, like a well-designed transmission line, it doesn't vary by much over HF frequencies. In short, the self-resonance velocity factor should extend pretty well to all HF frequencies below that self-resonance point. I need to think about the frequencies above the self-resonance point, but that doesn't apply to the present discussion. I guess I should re-phrase my statement. Standing waves make it difficult for *ME* and W8JI to measure the current delay through the coil. I ran essentially the exact experiment that W8JI ran with identical results. I even used the current pickups that W8JI kindly furnished to me. The only difference between W8JI and me is that I recognized the results to be bogus. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
David,
Could it be something as simple as the use of a fiber optic cable as an alternative to a shielded coax cable? I suspect the "without perturbing .. . ." part may be innocent overstatement. Wish I had a set of high-frequency probes with fiber optic cables! Chuck David G. Nagel wrote: John Popelish wrote: Cecil Moore wrote: (snip) Other multiple measurements by independent sources agree with me and disagree with you, Tom. Wonder why you neglected to post this reference from your own server? http://lists.contesting.com/archives.../msg00540.html It is a posting to TowerTalk by Jim Lux, W6RMK. I'll just extract some excerpts. "For closewound coils, with length to diameter ratios around 5:1, a series of fairly careful measurements have been made with the coils arranged vertically above a ground plane, fed at the base, with a capacitive load on the other end, and the driving frequency arranged to be at the resonant frequency of the whole assembly." Sure sounds like your 100 uH 10"x2" coil installed in a mobile ham radio antenna environment. (snip) The tantalizing part from my perspective is this: "The measurements were made with carefully designed fiberoptic probes that were specifically designed to avoid perturbing the magnetic and electric fields." I would like to read a full description of this instrumentation. Like many others I don't know everything. In line with reducing my ignorance could you amplify on how the phenomena is measured with a "fiber optic probe". What type of transducer is used to convert energy of an electrical nature to energy of an optical nature with out "perturbing the magnetic and electric fields". Dave WD9BDZ |
Current through coils
On Mon, 13 Mar 2006 19:26:10 GMT, Cecil Moore wrote:
Those two subjects were in different paragraphs and completely unrelated. 'xactly my point. |
Current through coils
David G. Nagel wrote:
Like many others I don't know everything. In line with reducing my ignorance could you amplify on how the phenomena is measured with a "fiber optic probe". What type of transducer is used to convert energy of an electrical nature to energy of an optical nature with out "perturbing the magnetic and electric fields". Like you (unlike W8JI) I don't know everything. :-) I have hardly any idea how they used a "fiber optic probe" to make their measurements. I suspect they superposed local RF phasors and used a fiber optic system to report the results. That's what I would do. I have invited Jim, W6RMK, to join the discussion. Maybe he can answer your questions. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
But in a tightly wound inductor, a field created by the current in one turn is coupled almost instantly to all the other turns ... "All the other turns"? Here's what Jim Lux, W6RMK, had to say about that: "For inductance the signficant thing is that the magnetic field of one segment pretty much links to the adjacent segments, and less so for the rest." Less to the 3rd, less than that to the 4th, even less than that to the 5th. What do you think it might be by the time it gets to the 80th turn on Tom's coil? Seems that we can assume that the linkage between coil #1 and coil #80 is negligible. Once again it's necessary to point out that I'm speaking here of an inductor which has very good coupling between turns and minimal field leakage or radiation, ... So was W6RMK. There's no magic transition point. Indeed there isn't. I repeat, in case your didn't understand - indeed there isn't. So you can discard your magic lumped- circuit model for a system containing reflections. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Clark wrote:
Cecil Moore wrote: Those two subjects were in different paragraphs and completely unrelated. 'xactly my point. So if your point and my point are exactly the same, what is the point in disagreeing? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Mon, 13 Mar 2006 20:47:53 GMT, Cecil Moore wrote:
So if your point and my point are exactly the same, what is the point in disagreeing? It doesn't respond to John's question. Glad you have no dispute. Now we can proceed to your interpretation of what John apparently (to you) meant by his question, and how you answered THAT. |
Current through coils
Cecil Moore wrote:
I have hardly any idea how they used a "fiber optic probe" to make their measurements. I suspect they superposed local RF phasors and used a fiber optic system to report the results. That's what I would do. Make sure you set those "superposed local RF phasors" on stun before you make the measurement. Otherwise you might hurt someone. 73, Gene W4SZ |
Current through coils
Gene Fuller wrote: Cecil Moore wrote: I have hardly any idea how they used a "fiber optic probe" to make their measurements. I suspect they superposed local RF phasors and used a fiber optic system to report the results. That's what I would do. Make sure you set those "superposed local RF phasors" on stun before you make the measurement. Otherwise you might hurt someone. The current measurements Roy and I independently made using different equipment and antennas on resonant antennas aren't valid, according to Cecil. The measurements I made on multiple inductors on the test bench in a non-resonant system terminated in a load resistor aren't valid either, according to Cecil. What do all these measurements have in common? The phasors were on stun. ;-) |
Current through coils
David G. Nagel wrote:
John Popelish wrote: The tantalizing part from my perspective is this: "The measurements were made with carefully designed fiberoptic probes that were specifically designed to avoid perturbing the magnetic and electric fields." I would like to read a full description of this instrumentation. Like many others I don't know everything. In line with reducing my ignorance could you amplify on how the phenomena is measured with a "fiber optic probe". What type of transducer is used to convert energy of an electrical nature to energy of an optical nature with out "perturbing the magnetic and electric fields". I wish I could, but this is the first I have heard of such instrumentation. That is why I would like to read more about it. |
Current through coils
Cecil Moore wrote:
John Popelish wrote: I also note that the opening statement: "For closewound coils, with length to diameter ratios around 5:1, a series of fairly careful measurements have been made with the coils arranged vertically above a ground plane, fed at the base, with a capacitive load on the other end, and the driving frequency arranged to be at the resonant frequency of the whole assembly." This definitely specifies only a single frequency for the test. Yes, a 75m mobile base-loaded antenna is a single frequency antenna. Why are you surprised? Those guys have figured out something that I haven't, probably because they have better tools at their disposal than I do. They seem to have a 1% accurate model at frequencies other than the self-resonant frequency. I, OTOH, am only sure of my accuracy at the self-resonant frequency due to the limited tools at my disposal. So I don't see how this reference supports your claim that measuring the delay at resonance tells you the delay at other frequencies. It also contradicts your claim about how a standing wave makes it difficult to measure the current delay through the coil. What have I missed? You missed the complete point, John. (snip) I don't think so. Your claim is that one can use a resonant condition to find the current delay at that frequency, and then, assume that that delay holds for all other, lower frequencies. I am skeptical that this is the case for any device that is not inherently a constant delay device. I think you are assuming your conclusion. You may be right, but you can't prove it by assuming it. You have to demonstrate it, (or find a reference where someone else does that) to be persuasive. I am rooting for you, because this would be a handy technique, but I am still skeptical that it is generally applicable. |
Current through coils
It's my policy to keep all email confidential.
However, Cecil persists in sending me unwelcome email. I've requested several times, first politely then bluntly, that he stop sending it, but he ignores my requests and persists. I assume this is driven by the same compulsion that keeps him promoting his alternate theories. Because this email comes after repeated requests that it not be sent, I don't feel bound to give it the same level of privilege as all other email and keep it private. I believe it's relevant to the discussion at hand on this group, so I'll share it here, verbatim and without editing. The subject is "Can't resist". ---- Beginning of quote ---- Sorry, Roy, I forgot to delete your email address from my email address file. When your house of cards based on out and out lying comes tumbling down, exactly how are you going to handle the obvious deliberate attempt at misinformation that you and Tom have been distributing to the unwashed masses for so many years? Did you think you would never get caught in your lies during your lifetime or what? After 20 years of evidence to the contrary, you can hardly plead ignorance. -- no 73 for the "gobbledygook" guy, Cecil, W5DXP ---- End of quote ---- This is from the person who so loudly complains about people making personal attacks in place of reasoned arguments. I've done my best to explain basic theory, and even spent a day carefully constructing and making measurements and honestly reporting the results. I'll continue to do my best to present factual information in spite of these juvenile attacks, and will try my best to remain objective, although it's awfully hard sometimes in an environment that brings responses like this email typifies. Anyone who doesn't want to read what I post should add me to his newsgroup reader filter, as I did Cecil to mine two years ago. Those who do read what I post should know that I have absolutely no reason nor desire to mislead anyone in any way. Roy Lewallen, W7EL |
Current through coils
John Popelish wrote:
I wish I could, but this is the first I have heard of such instrumentation. That is why I would like to read more about it. Hopefully the poster mentioning the optical probe will explain a bit more. But I recall seeing optically coupled instrumentation used in an EMI screen room to couple signals in and out. To my knowledge, though, the probes themselves were conventional, and fiber optics were used only to replace connecting wires. Roy Lewallen, W7EL |
Current through coils
Roy Lewallen wrote:
John Popelish wrote: I wish I could, but this is the first I have heard of such instrumentation. That is why I would like to read more about it. Hopefully the poster mentioning the optical probe will explain a bit more. But I recall seeing optically coupled instrumentation used in an EMI screen room to couple signals in and out. To my knowledge, though, the probes themselves were conventional, and fiber optics were used only to replace connecting wires. Roy Lewallen, W7EL Roy and John; The fiber optic leads are used in the experiment mentioned in the story linked by the URL that was recently mentioned in this thread. I think the whole thing is hilarious and was especially struck by the use of glass fiber to measure an electrical/magnet phenominum with no indication how the measurement is made. Sort of in line with someone's line of thinking in this thread. Dave N |
Current through coils
John Popelish wrote:
I don't think so. Your claim is that one can use a resonant condition to find the current delay at that frequency, and then, assume that that delay holds for all other, lower frequencies. At other *HF* frequencies and within reason, John, within reason. A two to one range wouldn't surprise me. Tom's five to one range from 16 MHz to 4 MHz is surprising. If the frequency kept going to 1 MHz, would the delay go below 3 nS? If Tom measured the delay at the self-resonant frequency of 16 MHz, would he measure 16 nS? If one plots the delay from 1 MHz to 16 MHz would there be any nonlinear points on the curve as implied by Tom's measurements? I am skeptical that this is the case for any device that is not inherently a constant delay device. I didn't mean to imply that it was an absolutely constant delay device. If it is well designed and if the environment is held constant, it should exhibit approximately the same delay over HF below its self-resonant frequency. Tom's measurements implied a 5 to 1 range shift in delay from a 4 to 1 range shift in frequency. Delays changing faster than the frequency certainly don't make sense to me. What would be the cause? From 16 Mhz to 4 Mhz: Does L vary much with frequency? Why? Does C vary much with frequency? Why? Does R vary much with frequency? Why? Does G vary much with frequency? Why? These are the parameters in the "phase constant" equation. Let's take a look at my measured data where I changed the stinger by 2 feet from zero to 12 feet. The 75m bugcatcher coil is mounted on a mobile antenna mount on my GMC pickup. For clearence purposes, it has a one foot bottom section. The stinger goes from 0' to 12': 0, 2, 4, 6, 8, 10, 12 The resonant frequency goes from: 6.7, 5.1, 4.3, 3.8, 3.5, 3.2, 3.0 MHz I just don't see any nonlinear changes such as Tom reported. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Addressed to nobody in particular.
From basic transmission line theory, the velocity of propagation along a coil is estimated by - V = 1 / Sqrt( L * C ) metres per second, where L and C are henrys and farads per metre respectively. The formula for L and C can be found in your Bibles from coil dimensions, numbers of turns, etc. The velocity factor = V / c and Zo = Sqr( L / C ). Attenuation (loss) = R / 2 / Zo nepers, where R is wire resistance plus radiation resistance. From which other interesting facts can be deduced. ---- Reg. |
Current through coils
John Popelish wrote:
... I see no reason to assume the transmission line method (delay independent of frequency) strictly applies. It might, but it would take more than you saying so to assure me that it is a fact. Assume the environment of the coil is fixed like the variable stinger measurement I reported earlier. Besides the frequency term, the phase constant depends upon L, C, R, and G as does the Z0 equation. Why would the L, C, R, and G change appreciably over a relatively narrow frequency range as in my bugcatcher coil measurements going from 6.7 MHz to 3.0 MHz? And I didn't mean to imply that the delay is "independent" of frequency, just that it is not nearly as frequency dependent as Tom's measurements would suggest. If Tom made his measurements from 1 MHz to 16 MHz, what do you think the curve would look like? Freq 1 2 4 8 16 MHz Delay ___ ___ 3 ___ 16 nS That looks non-linear to me. How about you? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
It's my policy to keep all email confidential. Apparently not. That was a private email. Publishing it in public without my permission is unethical but seems you and Tom will seemingly stop at nothing to keep promoting your myths. You have, over and over, rejected the distributed network model even though you know it is a superset of the lumped- circuit model. Would you agree with me that after all this time, you cannot possibly plead ignorance? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
David G. Nagel wrote:
The fiber optic leads are used in the experiment mentioned in the story linked by the URL that was recently mentioned in this thread. I think the whole thing is hilarious and was especially struck by the use of glass fiber to measure an electrical/magnet phenominum with no indication how the measurement is made. Sort of in line with someone's line of thinking in this thread. There exist transducers that will convert RF to light on one end of a fiber optics cable and back to RF at the other end. It's no big deal and keeps the transfer of information from being affected by EM fields. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Oops!
Zo = Sqrt( L / C) |
Current through coils
Reg Edwards wrote:
From basic transmission line theory, the velocity of propagation along a coil is estimated by - V = 1 / Sqrt( L * C ) metres per second, So Reg, for a fixed installation, why would L and C change much with frequency, like from 16 nS at 16 MHz to 3 nS at 4 MHz? If we took it down to 1 MHz, would the delay go below 3 nS? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
I believe it's relevant to the discussion at hand on this group, so I'll share it here, ... So you believe my personal feelings about you are relevant to a technical discussion???? Exactly which technical parameters are affected by my feelings about you? Every time this subject comes up, more and more people realize that the r.r.a.a gurus are not omniscient. Here's a smattering of the email I've received over the past week. Unlike you, I won't mention any names. "I hope ... that [X and Y] will acknowledge the validity of your approach." [X and Y are posters to r.r.a.a] "You are moving pretty fast, but nothing that you are saying sounds like there are any glaring errors." "Distributed constants not lumped constants prevail." "I, too, am skeptical of that 3 ns delay." " ...your Corum reference certainly ends the debate." "I want to let you know your dedication to principle and rational analysis ... are inspiring to many of us." "The unwillingness of the "gurus" to answer specific technical questions is pretty disappointing." Roy, are you listening to that last comment? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
"Cecil Moore" wrote in message . .. Reg Edwards wrote: From basic transmission line theory, the velocity of propagation along a coil is estimated by - V = 1 / Sqrt( L * C ) metres per second, So Reg, for a fixed installation, why would L and C change much with frequency, like from 16 nS at 16 MHz to 3 nS at 4 MHz? If we took it down to 1 MHz, would the delay go below 3 nS? -- 73, Cecil http://www.qsl.net/w5dxp ========================================== Sorry Cec, I havn't the foggiest idea. Having started it, I havn't been taking much notice of this long-winded thread. Its all too clever for poor little me! ;o) ---- Reg. |
Current through coils
Roy Lewallen wrote:
John Popelish wrote: I wish I could, but this is the first I have heard of such instrumentation. That is why I would like to read more about it. Hopefully the poster mentioning the optical probe will explain a bit more. But I recall seeing optically coupled instrumentation used in an EMI screen room to couple signals in and out. To my knowledge, though, the probes themselves were conventional, and fiber optics were used only to replace connecting wires. Such probes are routinely used for RFI, RF hazards and screened-room measurements, where connecting wires would disturb the fields or act as pathways for RF leakage. They do have a disadvantage that might be relevant to this discussion: because the probe head has to be self-powered, and has to include some kind of encoder and optical transmitter as well as the normal current transformer, the battery and extra area of PC board will increase the probe's self-capacitance. A different kind of fibre-optic probe is used in basic research on RF hazards, to measure very localized and very small temperature changes in simulated human heads and bodies. These microprobes are purely optical, and are sensing some temperature-dependent optical property of liquid crystals(?) at the probe tip. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
| All times are GMT +1. The time now is 01:28 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com