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Current through coils
Gene Fuller wrote:
Again, what extra information would be gained if somehow the traveling wave components could be measured? Here's a pretty good animation of forward, reflected, and standing waves. http://users.pandora.be/educypedia/e...stwaverefl.htm -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
That's probably what he has in mind: using longer coils to
get the correct phase shift. He'll have to use the formulas in the reference to make coils that will test his ideas. I don't understand why he uses a coil at all, in that case, since he could just as easily use a length of coiled up transmission line to accomplish the same thing. I think he's been trying to prove that coils, as people currently use them, are really transmission lines that automatically shift the current phase the correct amount to cancel antenna reactance. If he applies his reference formulae to one of Tom's coils and it doesn't show the correct phase shift, though, his theory is in trouble. 73, Tom Donaly KA6RUH chuck wrote: Hello Tom, I understand that on page 6, the reference qualifies the statement in the abstract by saying that for heights " . . . less than 15 degrees . . . one passes to the lumped element regime . . ." I thought Cecil was drawing examples for heights greater than 15 degrees. Have I misunderstood? 73, Chuck, NT3G Tom Donaly wrote: Cecil Moore wrote: Tom Donaly wrote: What's the formula, Cecil? http://www.ttr.com/TELSIKS2001-MASTER-1.pdf equation (32) The velocity factor can also be measured from the self- resonant frequency at 1/4WL. VF = 0.25(1/f) I suppose you also have something that will tell us how to find your coil's characteristic impedance; o.k., out with it. http://www.ttr.com/TELSIKS2001-MASTER-1.pdf equation (43) The characteristic impedance can also be measured at 1/2 the self-resonant frequency at 1/8WL. For a lossless case, the impedance is j1.0, normalized to the characteristic impedance so |Z0| = |XL|. For a Q = 300 coil, that should have some ballpark accuracy. We don't need extreme accuracy here. We just need enough to indicate a trend that the velocity factor of a well-designed coil doesn't increase by a factor of 5 when going from 16 MHz to 4 MHz. In "Antennas for All Applications", Kraus gives us the phase of the standing wave current on standing wave antennas like a 1/2WL dipole and mobile antennas. 3rd edition, Figure 14-2. It clearly shows that the phase of the standing wave is virtually constant tip-to-tip for a 1/2WL dipole. It is constant whether a coil is present or not. There is no reason to keep measuring that phase shift over and over, ad infinitum. There is virtually no phase shift unless the dipole is longer than 1/2WL and then it abruptly shifts phase by 180 degrees. I agree with Kraus and concede that the current phase shift in the midst of standing waves is at or near zero. There is no need to keep providing measurement results and references. You load your antennas with a Tesla coil? Did you read the part about a Tesla coil going to a lumped inductor when it was shortened? 73, Tom Donaly, KA6RUH |
Current through coils
Cecil Moore wrote:
Tom Donaly wrote: You load your antennas with a Tesla coil? Did you read the part about a Tesla coil going to a lumped inductor when it was shortened? A minimum Tesla coil is 1/4WL. My 75m bugcatcher coil mounted on my pickup as a base-loaded coil with no whip is 1/4WL on 6.6 MHz. Going from 6.6 Mhz to 4 MHz is only 40% shortening. I think the lumped inductor crossover point is probably pretty far below 4 MHz. Why don't you crunch the numbers using your reference and find out for sure? (If your reference is correct, that is. Some of the papers by academics on the web don't always give information that corresponds to reality.) You should be able to analyze your bugcatcher easily and report what you find. It sure beats sitting around drinking Ripple and feeling persecuted. 73, Tom Donaly, KA6RUH |
Current through coils
Tom Donaly wrote:
If he applies his reference formulae to one of Tom's coils and it doesn't show the correct phase shift, though, his theory is in trouble. His reference formulae are for traveling waves, not standing waves. We already know that the phase of the standing wave current on a 1/2WL thin-wire dipole varies not one degree over that entire 180 degrees. Yet we know the forward wave undergoes a 90 degree phase shift from feedpoint to tip and the reflected wave undergoes a 90 degree phase on the trip back to the feedpoint. Standing wave phase is virtually unchanging and is therefore useless for trying to determine the electrical length of a wire or a coil. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
John P. wrote, "A network analyzer is way beyond my budget."
Though I'd love for you to buy a nice new Agilent Vector Network Analyzer, I have to say that for things up through low VHF at least, the very economical project at http://users.adelphia.net/~n2pk/index.html is well worth looking at. The performance, when properly calibrated, needs no apologies, for sure. Paul is one of the Good Guys in ham radio, and not just for making this project available. One of Tom's links probably won't work for you, but I'd highly recommend some of the ap notes you can find after a somewhat diligent search. I'm sorry to say that the search engine on the Agilent web site is a poor relative of Google, but you should be able to find these two ap notes the Agilent AN 1287-1: Understanding the Fundamental Principles of Vector Network Analysis Agilent 1291-1B: 10 Hints for Making Better Network Analysis Measurements. They are in PDF files, and I just saved a copy of each...just in case you can't find them. A Google search on phrases like "network analysis application note" and "VNA application note" should yield some interesting things. Here's one thing I found, which has links to others: http://na.tm.agilent.com/vnahelp/appnotes.html Finally, there is an old HP ap note on S-parameters that you should try to find. It _may_ be on the Agilent web site, but if not, a Google search will probably turn it up. Though a Vector Network Analyzer does not necessarily have to do S-parameter measurements, the 8753 is set up to do them as its fundamental measurement, and they are generally useful in making higher frequency measurements, since the standard methodology in the industry is to use S parameters to characterize both passive and active devices. If you look at network analyzers on eBay, you may see ones offered without the S-parameter test set, and you can find the S-parameter test sets offered separately; that's all fine so long as you understand what you are looking at. Cheers, Tom |
Current through coils
K7ITM wrote:
John P. wrote, "A network analyzer is way beyond my budget." Though I'd love for you to buy a nice new Agilent Vector Network Analyzer, I have to say that for things up through low VHF at least, the very economical project at http://users.adelphia.net/~n2pk/index.html is well worth looking at. The performance, when properly calibrated, needs no apologies, for sure. Paul is one of the Good Guys in ham radio, and not just for making this project available. One of Tom's links probably won't work for you, but I'd highly recommend some of the ap notes you can find after a somewhat diligent search. I'm sorry to say that the search engine on the Agilent web site is a poor relative of Google, but you should be able to find these two ap notes the Agilent AN 1287-1: Understanding the Fundamental Principles of Vector Network Analysis Agilent 1291-1B: 10 Hints for Making Better Network Analysis Measurements. They are in PDF files, and I just saved a copy of each...just in case you can't find them. A Google search on phrases like "network analysis application note" and "VNA application note" should yield some interesting things. Here's one thing I found, which has links to others: http://na.tm.agilent.com/vnahelp/appnotes.html Finally, there is an old HP ap note on S-parameters that you should try to find. It _may_ be on the Agilent web site, but if not, a Google search will probably turn it up. Though a Vector Network Analyzer does not necessarily have to do S-parameter measurements, the 8753 is set up to do them as its fundamental measurement, and they are generally useful in making higher frequency measurements, since the standard methodology in the industry is to use S parameters to characterize both passive and active devices. If you look at network analyzers on eBay, you may see ones offered without the S-parameter test set, and you can find the S-parameter test sets offered separately; that's all fine so long as you understand what you are looking at. Thank you for all this useful information. |
Current through coils
FWIW, the "single loop terminated in a diode" that provides both
magnetic and electric coupling at the same time is not the only way to make a directional coupler. It can be done with a ferrite toroid to measure the current and a capacitive voltage divider to measure the voltage; it can be done with a pair of identical RF transformers, one to monitor the voltage (connected step-down across the line) and one to monitor the current (connected step-up in series with the line). In fact, RFSim99 has a window you can access from the Tools--Component--Coupler pulldown menu, that will help design a directional coupler in several different ways. (Beware that the coupling they tell you for coupled lines is only for coupling sections 1/4 wave [or 3/4 or 5/4 or...] long.) Of the ones shown there, only the transformer one is broadband. Cheers, Tom |
Current through coils
On Wed, 15 Mar 2006 01:39:54 GMT, Cecil Moore wrote:
Tom Donaly wrote: You load your antennas with a Tesla coil? Did you read the part about a Tesla coil going to a lumped inductor when it was shortened? A minimum Tesla coil is 1/4WL. My 75m bugcatcher coil mounted on my pickup as a base-loaded coil with no whip is 1/4WL on 6.6 MHz. An 11.4 meter tall bugcatcher coil - sure.... Such are the rewards of a Xerox based education. |
Current through coils
Tom, K7ITM wrote:
"FWIW, the "aingle loop terminated in a diode" that provides both magnetic and electric coupling at the same time" is not the only way to make a directional coupler." Agteed, but the Bird Electronic Corporation has been successful making the plug-ins for their "Thruline Wattmeter" that way for about 50 years. Best regards, Richard Harroison, KB5WZI |
Current through coils
Richard Clark wrote:
Cecil Moore wrote: A minimum Tesla coil is 1/4WL. My 75m bugcatcher coil mounted on my pickup as a base-loaded coil with no whip is 1/4WL on 6.6 MHz. An 11.4 meter tall bugcatcher coil - sure.... Such are the rewards of a Xerox based education. The physical height of my 75m bugcatcher coil is about 0.167 meters. Dividing 0.167m by 11.4m gives the velocity factor equal to 0.015. Your 11.4 meter value assumes a VF of zero. Multiply the 11.4 meters by the VF of the environment and you will obtain the physical length for something with an electrical length of 90 degrees. To obtain an electrical 90 degrees using RG-213: 11.4m * 0.66 = 7.5m To obtain an electrical 90 degrees using my 75m bugcatcher coil: 11.4m * 0.015 = 0.167m -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Objection, your Honor! Answer is unresponsive to the question.
Sustained. 8-) Gee Cecil, how does one learn of such a "hidden mathematical concept", when it does not seem to be embodied in the formalism? Let's try again. Suppose the standing wave is examined to perfection. Everything that can be determined is measured without error. Now we take the superposition in reverse; specifically we divide the standing wave into forward and reverse traveling components. It would seem that we have a complete and accurate definition for the two traveling wave components. The interrelations, as you call them, between the variables and parameters are fully defined by the basic math and the carefully measured standing wave. What else is needed to describe the traveling waves? Additional variables? Additional coefficients or parameters? Additional hidden mathematical concepts? There seems to be a lack of understanding and appreciation for what the concepts of "linear" and "superposition" really mean. These are not just mathematical concepts. When they apply it means that the system under study is fully and completely described by ** either ** the individual functional subcomponents ** or ** the full superimposed functional component. It is not necessary to use both formats, and there is no added information by doing so. Take a look at any of your favorite antenna references with an eye toward the treatment of standing wave antennas. I believe you will find only passing discussion of traveling waves. There will be some mention of the equivalence between the two types of waves, but little else. It is unlikely that you will find anything that says you will get more information if you take the time and trouble to analyze traveling waves. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: As you have stated, including references from Hecht, it is customary to mathematically show traveling waves in the form: cos (kz +/- wt) Through straightforward addition and simple trigonometry is is seen that the standing wave corresponding to the sum of equal magnitude forward and reverse traveling waves has the form: cos (kz) * cos (wt) I see I made a typo and typed a '+' sign in my previous equation. Of course, it should have been a '*' sign for multiply. Are there some hidden variables that have not been considered? Not a hidden variable, but there seems to be a hidden mathematical concept, at least hidden from some individuals. In case some might not know, 'z' is the position up and down the wire, omega (w) is our old friend 2*pi*f, and 't' is, of course, time. In the traveling wave equation, cos(kz +/- wt), the position on the wire and omega*time are added or subtracted *before* the cosine function is taken. That means that the position on the wire and the phase velocity are inter-related. One cannot have one without the other. And that is indeed a characteristic of a traveling wave. Physical position, frequency, and time all go into making a traveling wave. It is modeled as a rotating phasor. However, in the equation, cos(kz) * cos(wt), the physical position, 'z' is disconnected from the phase velocity, 'wt'. The standing wave is no longer moving in the 'z' dimension. If you pick a 'z' and hold it constant, i.e. choose a single point on the wire, the standing wave becomes simply some constant times cos(wt). Thus at any fixed point on the line, the standing wave is not moving - it is just oscillating at the 'wt' rate and a current probe will certainly pick up the H-field signal. The phase of the standing wave current is everywhere, up and down the 1/2WL thin-wire, equal to zero. The sum of the forward phasor and reflected phasor doesn't rotate. Its phase doesn't change with position. Only its magnitude changes with position and if the forward wave magnitude equals the reflected wave magnitude, it is not flowing in the real sense that current flows. It is a standing wave and it is just standing there. The main thing to realize is that the standing wave equation divorces the position of the standing wave from its phase velocity such that the phase velocity is not active in the 'z' dimension, i.e. up and down the wire. The standing wave current "pseudo phasor" is not rotating. The standing wave is not going anywhere. It is not flowing along a wire or through a coil. Measuring its phase is meaningless because the phase is already known to be constant and unchanging from tip to tip in a 1/2WL dipole or across a loading coil in a mobile antenna. Thinking that standing wave current flows from the middle of a dipole to the ends is just a misconception. The equation for a standing wave indicates that it doesn't flow. What is flowing are the forward and reflected waves. |
Current through coils
Richard Harrison wrote:
Tom, K7ITM wrote: "FWIW, the "aingle loop terminated in a diode" that provides both magnetic and electric coupling at the same time" is not the only way to make a directional coupler." Agreed, but the Bird Electronic Corporation has been successful making the plug-ins for their "Thruline Wattmeter" that way for about 50 years. My old Heathkit HM-15 SWR meter has a short slotted through-line with two parallel pick up wires located about halfway between the center conductor and the shield. A 50 ohm resistor to ground at one end kills the voltage in that direction. A diode at the other end rectifies the voltage in the opposite direction. With two resistors and two diodes on opposite ends of the two pickup wires, they separate the forward wave from the reflected wave. The operation of the slotted line + pickup wires seems to be a lot like the Thruline element in a Bird but with no slug to rotate. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
WOW! Thanks! I took all of those endless physics and math classes before the Internet arrived, so I had no idea how a standing wave was formed. 8-) 8-) 8-) OK, the same question. It is a pretty picture, but what extra information would be gained if somehow the traveling wave components could be measured? 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: Again, what extra information would be gained if somehow the traveling wave components could be measured? Here's a pretty good animation of forward, reflected, and standing waves. http://users.pandora.be/educypedia/e...stwaverefl.htm |
Current through coils
On Wed, 15 Mar 2006 15:02:23 GMT, Cecil Moore wrote:
Your 11.4 meter value assumes a VF of zero. :-) The crippling symptoms of Xerographic research strike again. A quarter wave tall, two inch diameter coil is not resonant - at least not at a fundamental in the 80M band. |
Current through coils
Gene Fuller wrote:
... how does one learn of such a "hidden mathematical concept", when it does not seem to be embodied in the formalism? The standing wave function equation, cos(kz)*cos*wt), is different in kind and function from the traveling wave function equation, cos (kz ± wt). When two traveling waves are moving along the same path in opposite directions, their two phasors are rotating in opposite directions. It is the sum of their phase angles that is a constant number of degrees. It is that constant phase angle that has been measured and reported here. Kraus shows a plot of the standing wave angle for a 1/2WL thin- wire dipole. It is zero from tip to tip. Kraus has already told us that its value is zero degrees. For a non-thin-wire, it deviates from zero degrees, but not by much. There's no good reason to keep measuring it over and over. A quantity whose phase is fixed at zero degrees cannot tell us anything about the phase shift (delay) through a coil or even through a wire. Given: The phase shift in the standing wave current through 1/8WL of wire in a 1/2WL thin-wire dipole is zero degrees. What valid technical conclusions can be drawn from that statement? That there is no phase shift in 45 degrees of wire in a 1/2WL dipole? Suppose the standing wave is examined to perfection. Everything that can be determined is measured without error. Now we take the superposition in reverse; specifically we divide the standing wave into forward and reverse traveling components. It would seem that we have a complete and accurate definition for the two traveling wave components. The interrelations, as you call them, between the variables and parameters are fully defined by the basic math and the carefully measured standing wave. No argument. What some individuals seem to have missed are key concepts involved in that process. In fact, that very process is what I am presenting here. What else is needed to describe the traveling waves? Additional variables? Additional coefficients or parameters? Additional hidden mathematical concepts? What else is needed is already there but unrecognized by a number of individuals. The equations for the forward and reflected waves are different in kind and function from the equations for the standing wave. Assuming equal magnitudes and phases for the forward and reflected waves, the superposition of those two phasors yields a result that is really not a bona fide phasor because it doesn't rotate. One cannot use a quantity whose phasor doesn't rotate to measure phase shifts (delays) through coils or through wires. Pardon me for having to state the obvious. Picture one end of the 1/2WL thin-wire dipole and set the reference phase of the forward current at 90 degrees. This is for reference only to make the math easy. When the forward current hits the end of the dipole, it undergoes a 180 degree phase shift and starts traveling in the opposite direction as the reflected current. For ease of math, let's assume the magnitude of the forward current and reflected current at the end of the dipole is one amp. Here's what the standing wave current will be at points along the dipole wire looking back toward the center. The first column is the number of degrees back toward the center from the end of the dipole, i.e. the end of the dipole is the zero degree reference for 'z'. The center of the dipole is obviously 90 degrees away from the end. Back forward current reflected current standing wave current 0 deg 1 at 90 deg 1 at -90 deg zero 15 deg 1 at 75 deg 1 at -75 deg 0.52 at 0 deg 30 deg 1 at 60 deg 1 at -60 deg 1.00 at 0 deg 45 deg 1 at 45 deg 1 at -45 deg 1.41 at 0 deg 60 deg 1 at 30 deg 1 at -30 deg 1.73 at 0 deg 75 deg 1 at 15 deg 1 at -15 deg 1.93 at 0 deg 90 deg 1 at 0 deg 1 at 0 deg 2.00 at 0 deg Seven points on the standing wave current curve have been produced by superposing the forward current and reflected current. One can observe the phase rotation of the forward and reflected waves. Please note the phase of the standing wave current is fixed at zero degrees. Measuring it in the real world will produce a measurement close to zero degrees. Its phase is already known. Measuring it multiple times over multiple years continues to yield the same close-to-zero value. Except for proving something already known, those measurements were a waste of time. The above magnitudes and phases of the standing wave current are reproduced in a graph by Kraus, "Antennas for All Applications", 3rd edition, Figure 14-2, page 464. There seems to be a lack of understanding and appreciation for what the concepts of "linear" and "superposition" really mean. These are not just mathematical concepts. When they apply it means that the system under study is fully and completely described by ** either ** the individual functional subcomponents ** or ** the full superimposed functional component. It is not necessary to use both formats, and there is no added information by doing so. No argument there. But the individual doing the superposition needs to understand exactly what he is doing or else he may make some conceptual mental blunders. Trying to measure the phase shift of a quantity that doesn't shift phases is one of those mental blunders. Take a look at any of your favorite antenna references with an eye toward the treatment of standing wave antennas. I believe you will find only passing discussion of traveling waves. There will be some mention of the equivalence between the two types of waves, but little else. It is unlikely that you will find anything that says you will get more information if you take the time and trouble to analyze traveling waves. My only bona fide antenna references are Kraus and Balanis. Quoting: Kraus: "A sinusoidal current distribution may be regarded as the standing wave produced by two uniform (unattenuated) traveling waves of equal amplitude moving in opposite directions along the antenna." Balanis: "The sinusoidal current distribution of long open-ended linear antennas is a standing wave constructed by two waves of equal amplitude and 180 degree phase difference at the open-end traveling in opposite directions along its length." Balanis: "The current and voltage distributions on open-ended wire antennas are similar to the standing wave patterns on open-ended transmission lines." Balanis: "Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forward and backward) and represented by traveling wave currents ..." -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote:
OK, the same question. It is a pretty picture, but what extra information would be gained if somehow the traveling wave components could be measured? Hopefully, some individuals would gain enough information that they would cease trying to use a quantity that doesn't change phase for the measurement of phase shifts. Maybe iteration would help. The phase shift of standing wave current through 30 degrees of coil or wire is close to zero degrees. The phase shift of standing wave current through 45 degrees of coil or wire is close to zero degrees. The phase shift of standing wave current through 75 degrees of coil or wire is close to zero degrees. Measuring the phase shift of standing wave current through a wire or a coil is pointless. One cannot use a quantity that doesn't change phase for the measurement of phase shifts. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
Tom Donaly wrote: If he applies his reference formulae to one of Tom's coils and it doesn't show the correct phase shift, though, his theory is in trouble. His reference formulae are for traveling waves, not standing waves. We already know that the phase of the standing wave current on a 1/2WL thin-wire dipole varies not one degree over that entire 180 degrees. Yet we know the forward wave undergoes a 90 degree phase shift from feedpoint to tip and the reflected wave undergoes a 90 degree phase on the trip back to the feedpoint. Standing wave phase is virtually unchanging and is therefore useless for trying to determine the electrical length of a wire or a coil. Tell me a couple of things, Cecil: 1. the diameter of your bugcatcher coil, and 2. the turn to turn wire spacing. I'd like to use the information, using the formulae in your reference, to see just how long your bugcatcher coil is electrically. Thanks, Tom Donaly, KA6RUH |
Current through coils
Richard Clark wrote:
Cecil Moore wrote: Your 11.4 meter value assumes a VF of zero. A quarter wave tall, two inch diameter coil is not resonant - at least not at a fundamental in the 80M band. Nobody said it was resonant. The electrical length at 4 MHz can be *estimated* from the self-resonant frequency of 16 MHz. 90 degrees at 16 MHz estimates to be approximately 90(4/16) = ~23 degrees at 4 MHz. Dr. Corum's strongly suggested minimum electrical length for valid application of the lumped- circuit analysis is 15 degrees. Let's do a simple calculation to see how much error would be had by using the lumped-circuit model in the following: X---15 degrees of 450 ohm ladder-line---50 ohm load The lumped-circuit model says the impedance at X is 50 ohms. The impedance at X is really 53.5+j119 According to Dr. Corum, that's the maximum acceptable error when using the lumped-circuit model. His standards apppear to be lower than mine. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Wed, 15 Mar 2006 17:30:10 GMT, Cecil Moore wrote:
Richard Clark wrote: Cecil Moore wrote: Your 11.4 meter value assumes a VF of zero. A quarter wave tall, two inch diameter coil is not resonant - at least not at a fundamental in the 80M band. Nobody said it was resonant. You seem to be shy of many details from your reference. VF of zero indeed.... You can't even plug-n-chug your own referred equations. Such are the hazards of a Xerox research method. Hi Tom, As you, I didn't expect to see any concrete numbers from that last flurry of equations. I don't see how with his free mix of quarterwave substituted as resonant to backfill an argument of a short coil justified as a long one. Tom's simple example, a 2 inch diameter coil of 10 inches with 100 turns seems to have buffaloed his finding the Velocity Factor or Characteristic Impedance. And how would it compare in contrast to Reggie's formulas? That would seem to invite discussion of results instead, which would have collapsed this opus to a thread of three postings. As such, it serves only to entertain on a rainy morning (your weather may vary - but in Seattle, never). 73's Richard Clark, KB7QHC |
Current through coils
Tom Donaly wrote:
Tell me a couple of things, Cecil: 1. the diameter of your bugcatcher coil, and 2. the turn to turn wire spacing. I'd like to use the information, using the formulae in your reference, to see just how long your bugcatcher coil is electrically. Please note that when my 75m bugcatcher coil is mounted just above my GMC pickup ground plane, it is electrically almost four times longer than it is laying on a stack of books in my hamshack. The coil capacitance to ground is obviously a lot higher when mounted over a ground plane. The ground plane reduces the VF to approximately 1/4 the value obtained in isolation. 1. The measured self-resonant frequency of the coil mounted on my pickup is ~6.6 MHz. 2. The measured self-resonant frequency of the coil on a mag mount on my all-metal desk is ~6.6 MHz. 3. The measured self-resonant frequency of the coil isolated from any ground is ~24.5 MHz. The self-resonant frequency needs to be measured in the environment in which it is installed. That means one needs to model the coil 3 inches above a perfect ground plane before calculating the self-resonant frequency, Z0, or VF. I doubt that Dr. Corum's equations take that into account since it would seem self defeating to operate a Tesla coil over a physically close ground plane. But I could be wrong on that point. The coil data is: ~6" dia, ~6.7" long, 26.5 T, seems very close to 4 TPI. Looks to be #14 solid wire. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Food for thought.
At this moment in time it seems Cecil is claiming an inductor acts like so many electrical degrees, but of course at any moment another waffle might pops out of the Texas toaster and change everything. Let's assume we have a mobile antenna that is 25 electrical degrees tall. Now following the logic a loading coil acts like a transmission line, we have a 65-degree loading coil. Following the same twisted logic, since the loading inductor is 65-degrees long, we should be able the move it anywhere in the antenna without changing antenna tuning. Our 75 meter antenna should also work on 25 meters as a 3/4 wave antenna, and on 37.5 meters as a half-wave. Of course we all know it doesn't behave anything close to this way. Wouldn't it be nice if Cecil could show us all how to predict the resoances of an antenna based on his idea that loading inductor acts like a transmission line? Where are the design equations we can all use? 73 Tom |
Current through coils
Gene Fuller wrote:
Indeed, it is clear from the quotes that the two treatments are equivalent. And indeed, the two treatments are equivalent for anyone who understands both of them. The two treatments are obviously not equivalent for someone who understands one and not the other. It is an individual ignorance problem, not a problem with the models. If the standing wave analysis results are reported by an individual to be different from the traveling wave analysis results, what can we assume? If they are equivalent, why would the results ever be different except for the ignorance of the reporter? Here is a 'yes' or 'no' technical question for everyone. Is it possible to measure a phase shift through a wire or coil using a signal (standing wave current) that doesn't ever change phase? The answer to that question is the entire crux of the argument. If anyone answers 'yes' to that question, please explain in detail how to accomplish that measurement feat. Of course these authors were disadvantaged by a lack of understanding of your "hidden mathematical concepts." 8-) I thought we had agreed to stop using inuendo to try to influence a technical argument. The mathematical concepts are certainly NOT hidden. They are there for all to understand and accept but are being ignored by certain individuals. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Here is a 'yes' or 'no' technical question for everyone.
Is it possible to measure a phase shift through a wire or coil using a signal (standing wave current) that doesn't ever change phase? There is no "standing wave current". There is only current. Current can't stand. Phase difference can be measured in a system that has standing waves, just as it can in one without standing waves. The answer to that question is the entire crux of the argument. If anyone answers 'yes' to that question, please explain in detail how to accomplish that measurement feat. Any number of ways, if we disallow the impossible situiation where you seem to think we can have current "standing still". Direct measurement methods abound. First Cecil says: I thought we had agreed to stop using inuendo to try to influence a technical argument. The mathematical concepts are certainly NOT hidden. Then Cecil does the opposite of what he asks Gene to do: They are there for all to understand and accept but are being ignored by certain individuals. Cecil first asks Gene to stop using inuendo. One sentence later, Cecil uses inuendo. :-) 73 Tom |
Current through coils
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Current through coils
On Wed, 15 Mar 2006 18:03:28 GMT, Cecil Moore wrote:
The coil data is: ~6" dia, ~6.7" long, 26.5 T, seems very close to 4 TPI. Looks to be #14 solid wire. Hmmm, dare I plunge into the next, obvious question? Provide the Velocity Factor and Characteristic Impedance per the formulas you offered: Tom Donaly wrote: What's the formula, Cecil? http://www.ttr.com/TELSIKS2001-MASTER-1.pdf equation (32) The velocity factor can also be measured from the self- resonant frequency at 1/4WL. VF = 0.25(1/f) I suppose you also have something that will tell us how to find your coil's characteristic impedance; o.k., out with it. http://www.ttr.com/TELSIKS2001-MASTER-1.pdf equation (43) and we can then achieve closure by comparing the same results with Reggie's formulas. |
Current through coils
wrote:
Food for thought. At this moment in time it seems Cecil is claiming an inductor acts like so many electrical degrees, but of course at any moment another waffle might pops out of the Texas toaster and change everything. That's not food for thought. That's emotional gut feelings. I thought we agreed to cease and desist from ad hominem attacks? Let's assume we have a mobile antenna that is 25 electrical degrees tall. Now following the logic a loading coil acts like a transmission line, we have a 65-degree loading coil. *False assumption!* The phase delay through the coil is what it is and we don't know exactly what it is. We do know it is not what has been measured and reported using a signal source (standing wave current) that doesn't ever change phase. Our present choice is between a reported measurement that is 100% flawed, in the absolute sense of the word, and an estimate with unknown accuracy based on the laws of physics. Given those two, and only two, present choices, which choice should one make? Please see the end of this posting for a description of the logical diversion that is taking place here. The phase delay through the coil is what it is and we don't know exactly what it is. We do know it is not zero as the standing wave current phase shift measurement would predict. Let me focus the subject of the argument back upon the actual subject of the argument and try to avoid diversions into the unknown, like the above. How does one measure the phase delay through a coil or wire using a signal with forever unchanging phase? All of the phase delay experiments so far have used the above flawed method. So far, we only have experimental measurements that are flawed except for the self-resonant experiments. Which is preferred? The results from experiments known to be 100% flawed or estimates with unknown accuracy based on the laws of physics? Those are presently our only two choices. Following the same twisted logic, since the loading inductor is 65-degrees long, we should be able the move it anywhere in the antenna without changing antenna tuning. *False assumption!* The superposition of all four of the forward and reflected waves is much more complicated than that. Our 75 meter antenna should also work on 25 meters as a 3/4 wave antenna, and on 37.5 meters as a half-wave. It's not as simple as that but I have the EZNEC current distribution patterns that indicate something akin to that indeed does develop. Give me a few hours and I will post those results. Where are the design equations we can all use? Asked and answered but not sure of the accuracy applied to 75m bugcatcher loading coils. Someone is working on that. Please stand by. The logical diversion that is happening here goes like this: Person A says: "The moon is 10,000 miles from the earth. Person B says: "That can't be true." Person A says: "How far do you say the moon is from the earth?" Person B says: "I don't know, but I do know it is not 10,000 miles." Person A says: "Well, if you don't know and can't give me the correct answer, I am right and you are wrong. The moon is 10,000 miles from the earth." Does an absolutely false answer beat ignorance? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
Tom Donaly wrote: Tell me a couple of things, Cecil: 1. the diameter of your bugcatcher coil, and 2. the turn to turn wire spacing. I'd like to use the information, using the formulae in your reference, to see just how long your bugcatcher coil is electrically. Please note that when my 75m bugcatcher coil is mounted just above my GMC pickup ground plane, it is electrically almost four times longer than it is laying on a stack of books in my hamshack. The coil capacitance to ground is obviously a lot higher when mounted over a ground plane. The ground plane reduces the VF to approximately 1/4 the value obtained in isolation. 1. The measured self-resonant frequency of the coil mounted on my pickup is ~6.6 MHz. 2. The measured self-resonant frequency of the coil on a mag mount on my all-metal desk is ~6.6 MHz. 3. The measured self-resonant frequency of the coil isolated from any ground is ~24.5 MHz. The self-resonant frequency needs to be measured in the environment in which it is installed. That means one needs to model the coil 3 inches above a perfect ground plane before calculating the self-resonant frequency, Z0, or VF. I doubt that Dr. Corum's equations take that into account since it would seem self defeating to operate a Tesla coil over a physically close ground plane. But I could be wrong on that point. The coil data is: ~6" dia, ~6.7" long, 26.5 T, seems very close to 4 TPI. Looks to be #14 solid wire. Thanks, Cecil. 73, Tom Donaly, KA6RUH |
Current through coils
wrote:
There is no "standing wave current". There is only current. Current can't stand. Addressed and proven to be a false statement. cos(kz)*cos(wt) proves it is standing and not flowing. Phase difference can be measured in a system that has standing waves, just as it can in one without standing waves. Addressed and proven to be a false statement. A signal with unchanging phase cannot be used to measure the phase delay through a wire or coil. Any number of ways, if we disallow the impossible situiation where you seem to think we can have current "standing still". Please take a look at the equation for standing wave current. It proves that the standing wave current is standing still, just oscillating in place at any point on the wire. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Clark wrote:
Provide the Velocity Factor and Characteristic Impedance per the formulas you offered: Tom Donaly has graciously volunteered to provide those values. Please stand by. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Wed, 15 Mar 2006 20:08:18 GMT, Cecil Moore wrote:
Richard Clark wrote: Provide the Velocity Factor and Characteristic Impedance per the formulas you offered: Tom Donaly has graciously volunteered to provide those values. Please stand by. You have nothing to show of your own work employing your own references? I can do this myself, as certainly Tom can too; but it says nothing about your well coming up dry when we ask you to carry your own water in supporting your claims. |
Current through coils
Richard Clark wrote:
.. I can do this myself, as certainly Tom can too; but it says nothing about your well coming up dry when we ask you to carry your own water in supporting your claims. Pure humor with zero technical content follows: So sue me for being lazy. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Wed, 15 Mar 2006 20:57:21 GMT, Cecil Moore wrote:
So sue me for being lazy. :-) The legacy of Xerox research. |
Current through coils
Richard Clark wrote:
Cecil Moore wrote: So sue me for being lazy. :-) The legacy of Xerox research. Please remind us of the technical content of your posting. Do you think experimental technical results depend upon whom is doing the experiment? If I dropped dead, could Tom's results change from valid to invalid? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Wed, 15 Mar 2006 21:29:14 GMT, Cecil Moore wrote:
Do you think experimental technical results depend upon whom is doing the experiment? Clearly you have nothing to offer that conflicts in that respect. If I dropped dead, could Tom's results change from valid to invalid? are you asking would you be technically dead, or clinically dead, or dead lazy? This appears to be a reverse progression question. None of your work appears by your admitted laxity. None of your testing appears by lack of its accomplishment. No pulse can be discerned through the evidence of correspondence (classic result of The Chinese Room Argument). Diagnosis: Xerox induced narcosis. |
Current through coils
Cecil Moore wrote: Richard Clark wrote: Cecil Moore wrote: So sue me for being lazy. :-) The legacy of Xerox research. Please remind us of the technical content of your posting. Do you think experimental technical results depend upon whom is doing the experiment? If I dropped dead, could Tom's results change from valid to invalid? 73, Cecil http://www.qsl.net/w5dxp Probably, since it appears you are the only one finding fault with them. It appears you have painted yourself into a corner by trying o apply a paper about Tesla coils that specifically states it applies only to inductors at self-resonance to inductors operating away from self-resonance. For example, if you look at this time-delay plot: http://www.w8ji.com/inductor_current_time_delay.htm you'll see time delay is essentially flat except near the 16MHz self-resonant frequency and a higher-frequency resonance at 26 MHz. If I coupled that inductor to a oscillator like a Telsa coil has, it would indeed oscillate near the frequency where the inductor has considerable time delay. That time delay is largely because the inductor looks like a combination of shunt C and series L, and is indeed in mode similar to what we find in a transmission line. It is a narrow bandwidth effect because the resonance is high-Q. It does not surprise me at all. 73 Tom |
Current through coils
Richard Clark wrote:
None of your work appears by your admitted laxity. None of your testing appears by lack of its accomplishment. My testing results have been reported. Here are the results of the VF calculation for my 75m bugcatcher coil. The test for physical structure is met. The paper asserts that the expression gives acceptable results with errors less than 10%. The VF of my 75m bugcatcher coil calculates out to be VF = 0.0175 at 6.6 MHz where it measured to be self- resonant. That self-resonant measurement included a length of coax and a one foot bottom section so the actual self-resonant frequency will be somewhat higher than I measured. I could probably make a calculation to adjust for the coax and bottom section. The VF calculated directly from the too-low self- resonant frequency was 0.015 which is 14% different from Dr. Corum's equation. Given the uncertainly in the exact self-resonant frequency in my measurements, that's pretty reasonable. Ballpark is all we need to understand the concepts. Working backward, Dr. Corum's VF would make the coil self-resonant at 7.7 MHz. There's probably enough slop in my measurement configuration to account for the 1.1 MHz difference. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil, W5DXP wrote:
"How is it possible to use a signal (standing wave current) that is known not to change phase, to measure the phase delay through a wire or coil?" Ignore it. Lissajous figures result from applying signals to the vertical and horizontal deflection circuits of an oscilloscope simultaneously. Phase difference between signals of the same frequency make a distinctive pattern. One can use coax lines with identical delays to couple the inputs with phase sampling loops. Take samples of the currents at the two points where the phase difference would be known. Amplitudes can be adjusted for a suitable pattern. It will be destinctive. Then take samples from the same source. Add a known delay to one channel until you have reproduced the distinctive pattern you had observed when testing the felay between the points that have the unknown phase difference. With a few elaborations, that`s how a phase monitor works. Best regards, Richard Harrison, KB5WZI |
Current through coils
wrote:
Probably, since it appears you are the only one finding fault with them. Tom Donaly hasn't even posted any results yet. How could I possibly be finding fault with them? It appears you have painted yourself into a corner by trying o apply a paper about Tesla coils that specifically states it applies only to inductors at self-resonance to inductors operating away from self-resonance. Quoting from the previously referenced paper: ".. is an approximation ... appropriate for quarterwave resonance and is valid for helices with (5*N*D^2)/lamda 1. N is the turns/inch, D is the diameter of the coil, and lamda is the self-resonant frequency. That calculation for my 75m bugcatcher coil is ~0.4 so it meets the criteria. The VF calculation of 0.175 is therefore valid. There is no valid reason to suspect that the VF wouldn't hold approximately down to 4 MHz and below. There is no warning of such abrupt shifts in the VF anywhere in the article. And Dr. Corum's VF equation is close enough to my rough earlier estimate of 0.15 to be acceptable. you'll see time delay is essentially flat except near the 16MHz self-resonant frequency and a higher-frequency resonance at 26 MHz. But cos(kz)*cos(wt) is what is being measured. That signal has zero phase shift from tip to tip in a 1/2WL thin-wire dipole. It cannot be used to measure phase shift because it is incapable of a phase shift through 180 degrees of wire or 180 degrees of coil. It only changes phase every 180 degrees of a wire or coil. What is happening in the above measurement is that when the coil is more than 1/2WL, the phase of the standing wave current suddenly reverses from close to zero to close to 180 degrees. This is all explained in Kraus', "Antennas for All Applications", 3rd edition, Figure 14-4 and is perfectly understandable. The phase of the standing wave current changes from zero to 180 degrees every 1/2WL. I've seen exactly the same thing in my experiments just as Kraus predicts and it supports my side of the argument. The standing wave current, which has unchanging phase, cannot be used to determine the phase shift in a wire or coil. A signal with a cos(kz)*cos(wt) equation doesn't change phase with variations in 'z'. How can it possibly be used to detect phase changes in the 'z' dimension? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Harrison wrote:
Cecil, W5DXP wrote: "How is it possible to use a signal (standing wave current) that is known not to change phase, to measure the phase delay through a wire or coil?" Ignore it. Lissajous figures result from applying signals to the vertical and horizontal deflection circuits of an oscilloscope simultaneously. Phase difference between signals of the same frequency make a distinctive pattern. One can use coax lines with identical delays to couple the inputs with phase sampling loops. Take samples of the currents at the two points where the phase difference would be known. Amplitudes can be adjusted for a suitable pattern. It will be destinctive. Then take samples from the same source. Add a known delay to one channel until you have reproduced the distinctive pattern you had observed when testing the felay between the points that have the unknown phase difference. With a few elaborations, that`s how a phase monitor works. Many analog scopes aren't capable of producing a meaningful Lissajous figure at HF because of the limited bandwidth of the horizontal channel. Significant phase delays occur at frequencies well below the nominal cutoff frequency, which is often much lower than the vertical channel. Before believing in the validity of any figure, you should look at the figure you get when you apply the signal to both axes at the same time. If it deviates significantly from a single diagonal line, you won't be able to trust other patterns. It would be a simple matter for a digital scope to present a good Lissajous figure, since the bandwidth is determined solely by the input samplers rather than a series of amplifiers and the CRT deflection structure as in an analog scope. I haven't looked closely at digital scopes lately, but I'd be surprised if most don't have the capability of making a good Lissajous figure at HF. It would be simply a matter of internal firmware programming. Of course, a dedicated phase monitor would be designed for good phase and amplitude match between channels at the frequencies it's specified to be used at. Roy Lewallen, W7EL |
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