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Phase Shift through a 75m Texas Bugcatcher Coil
On May 14, 7:44 pm, Cecil Moore wrote:
In order to get a valid measurement of the delay through a coil, the coil needs to be loaded with its characteristic impedance to minimize the reflected current. What if a 3' long stainless steel whip is loading the coil? ac6xg |
Phase Shift through a 75m Texas Bugcatcher Coil
Jim Kelley wrote:
On May 14, 7:44 pm, Cecil Moore wrote: In order to get a valid measurement of the delay through a coil, the coil needs to be loaded with its characteristic impedance to minimize the reflected current. What if a 3' long stainless steel whip is loading the coil? That makes the antenna a standing wave antenna. Here are the characteristics of standing waves vs traveling waves for 1/4WL of wire. The phase of standing wave current is useless for phase measurements because it it fixed very close to zero degrees over the entire antenna. http://www.w5dxp.com/travstnd.gif Standing wave current has a negligible phase shift in the coil or in the whip and therefore cannot be used to measure the delay through a loading coil. To the best of my knowledge, all attempted phase measurements reported on this newsgroup, on current through a loading coil have been made using standing wave current with its fixed phase. No useful coil delay information can come from such measurements. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
On May 15, 5:42 am, Cecil Moore wrote:
Jim Kelley wrote: On May 14, 7:44 pm, Cecil Moore wrote: In order to get a valid measurement of the delay through a coil, the coil needs to be loaded with its characteristic impedance to minimize the reflected current. What if a 3' long stainless steel whip is loading the coil? That makes the antenna a standing wave antenna. It makes it an antenna. Standing wave current has a negligible phase shift in the coil or in the whip and therefore cannot be used to measure the delay through a loading coil. The delay through the coil depends on inductance and capacitance. To the best of my knowledge, all attempted phase measurements reported on this newsgroup, on current through a loading coil have been made using standing wave current with its fixed phase. No useful coil delay information can come from such measurements. So your claim is that information about Bugcatcher coils with a load resistor attached is more useful? ac6xg |
Phase Shift through a 75m Texas Bugcatcher Coil
Jim Kelley wrote:
Cecil Moore wrote: Jim Kelley wrote: Cecil Moore wrote: That makes the antenna a standing wave antenna. It makes it an antenna. Well, putting a load resistor on a coil is a lot like a T2FD. :-) In fact, the way that a T2FD lowers the 50 ohm SWR is by reducing the reflections from that load resistor. Standing wave current has a negligible phase shift in the coil or in the whip and therefore cannot be used to measure the delay through a loading coil. The delay through the coil depends on inductance and capacitance. Yes, but the delay is not measurable using standing wave current because standing wave current doesn't change phase in a coil or in a wire. So far, all of the phase measurements reported here have been using standing wave current phase. Standing wave current essentially doesn't change phase in a 1/4WL long open-ended antenna. To the best of my knowledge, all attempted phase measurements reported on this newsgroup, on current through a loading coil have been made using standing wave current with its fixed phase. No useful coil delay information can come from such measurements. So your claim is that information about Bugcatcher coils with a load resistor attached is more useful? It is more useful for determining the delay through the coil. If you were trying to measure the phase shift through a 1/4WL stub, would you use the standing wave current with its zero phase shift? Or would you terminate the stub in its characteristic impedance and measure the phase shift in the subsequent traveling wave? Here are some recently generated graphics around which I am going to put some words. Hopefully, they will provide some stand alone information. Given: http://www.w5dxp.com/openstus.GIF How would you determine the phase shift at any point in the open stub? Given: http://www.w5dxp.com/openstus.GIF How would you determine the phase shift at any point in the terminated stub? Note that the two stubs are identical except for one being open and one being terminated so they have identical traveling-wave phase shifts. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
I made a posting with a mistake, canceled it, and
am reposting. If the earlier posting got through, please ignore it. Jim Kelley wrote: Cecil Moore wrote: Jim Kelley wrote: Cecil Moore wrote: That makes the antenna a standing wave antenna. It makes it an antenna. Well, putting a load resistor on a coil is a lot like a T2FD. :-) In fact, the way that a T2FD lowers the 50 ohm SWR is by reducing the reflections from that load resistor. Standing wave current has a negligible phase shift in the coil or in the whip and therefore cannot be used to measure the delay through a loading coil. The delay through the coil depends on inductance and capacitance. Yes, but the delay is not measurable using standing wave current because standing wave current doesn't change phase in a coil or in a wire. So far, all of the phase measurements reported here have been using standing wave current phase. Standing wave current essentially doesn't change phase in a 1/4WL long open-ended antenna. To the best of my knowledge, all attempted phase measurements reported on this newsgroup, on current through a loading coil have been made using standing wave current with its fixed phase. No useful coil delay information can come from such measurements. So your claim is that information about Bugcatcher coils with a load resistor attached is more useful? It is more useful for determining the delay through the coil. If you were trying to measure the phase shift through a 1/4WL stub, would you use the standing wave current with its zero phase shift? Or would you terminate the stub in its characteristic impedance and measure the phase shift in the subsequent traveling wave? Here are some recently generated graphics around which I am going to put some words. Hopefully, they will provide some stand alone information. Given: http://www.w5dxp.com/openstus.GIF How would you determine the phase shift at any point in the open stub? Given: http://www.w5dxp.com/termstus.GIF How would you determine the phase shift at any point in the terminated stub? Note that the two stubs are identical except for one being open and one being terminated so they have identical traveling-wave phase shifts. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil doesnt seem to worry about this error, but just saying it
doesn't actually mean anything without differences. What is different about his claim and Wests'? On May 13, 3:52 pm, Richard Clark wrote: On Sun, 13 May 2007 18:17:29 GMT, Cecil Moore wrote: Tedious Xerography snipped as being obviously unread by Xerographer. Exactly what did I miss? If you have to be taken by the hand to have it pointed out to you, you shouldn't be doing these kind of things without adult supervision. A I have taken Wes's helical coil from: http://www.k6mhe.com/n7ws/Loaded%20antennas.htm B and modeled it with EZNEC. ... That coil512.EZ file can be downloaded from: is distinctly false. A B Does a symbolic reply nail it down? |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil Moore wrote:
The delay through the coil depends on inductance and capacitance. Yes, but the delay is not measurable using standing wave current because standing wave current doesn't change phase in a coil or in a wire. But you aren't measuring it. The point is, it's calculable. So your claim is that information about Bugcatcher coils with a load resistor attached is more useful? It is more useful for determining the delay through the coil. The fact that it doesn't give you an answer that agrees with any other method notwithstanding. If you were trying to measure the phase shift through a 1/4WL stub, would you use the standing wave current with its zero phase shift? If I were trying to measure delay I would use pulses. Or would you terminate the stub in its characteristic impedance and measure the phase shift in the subsequent traveling wave? I would want the system to be configured in exactly the same way as I intended for it to be used. Given: http://www.w5dxp.com/openstus.GIF How would you determine the phase shift at any point in the open stub? Given: http://www.w5dxp.com/termstus.GIF How would you determine the phase shift at any point in the terminated stub? The phase shift of what, with respect to what? ac6xg |
Phase Shift through a 75m Texas Bugcatcher Coil
Jim Kelley wrote:
Cecil Moore wrote: Yes, but the delay is not measurable using standing wave current because standing wave current doesn't change phase in a coil or in a wire. But you aren't measuring it. The point is, it's calculable. But w8ji and w7el *are* measuring it and getting something different from those calculations. They are reporting their flawed measurements as technical fact. That's what the whole argument is about. There is no way in heck to get a 3 nS delay out of a 100 turn, 10", 2" diameter coil. It is more useful for determining the delay through the coil. The fact that it doesn't give you an answer that agrees with any other method notwithstanding. It means that the existing posted methods are invalid. And that doesn't extend just to the side that asserts the delay through the coil is close to zero. It also extends to the other side who accepts the use of standing-wave current as a valid measurement technique. *All* of the measurements made using standing-wave current are bogus. If I were trying to measure delay I would use pulses. How do you know the pulsed delay is the same as the steady-state delay? Has anyone published a delay using pulses? I'm not saying a pulsed delay won't yield valid results - I just don't know. If it is a DC pulse, there would be known problems. I would want the system to be configured in exactly the same way as I intended for it to be used. Then you will find it is impossible to measure the delay through the coil during steady-state. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
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Phase Shift through a 75m Texas Bugcatcher Coil
Cecil Moore wrote:
Jim Kelley wrote: But you aren't measuring it. The point is, it's calculable. But w8ji and w7el *are* measuring it and getting something different from those calculations. They are reporting their flawed measurements as technical fact. That's what the whole argument is about. Only because you keep dragging them into it. I'm perfectly happy just comparing your results with the results I get from Reg's program. There is no way in heck to get a 3 nS delay out of a 100 turn, 10", 2" diameter coil. There is something odd about Tom's printout. It's not clear to me exactly what the instrument is actually displaying. The fact that it doesn't give you an answer that agrees with any other method notwithstanding. It means that the existing posted methods are invalid. :-) There exists no other possibility, naturally. I believe they call these delusions of grandeur. If I were trying to measure delay I would use pulses. How do you know the pulsed delay is the same as the steady-state delay? In the same way, and to the same degree that I know the delay will be the same tomorrow as it is today. Has anyone published a delay using pulses? Delays are typically measured using pulses. If it is a DC pulse, there would be known problems. Oh, I would never use those. :-) I would want the system to be configured in exactly the same way as I intended for it to be used. Then you will find it is impossible to measure the delay through the coil during steady-state. If I thought that was true, I wouldn't have said what I did. ac6xg |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil, W5DXP wrote:
"EZNEC indicates a VF of ~ 0.016." I calculate about 628 inches of wire in the coil compared with about 10 inches of coil length. It is 62.8 times as far to go around the turns on the coil as it is to travel through a 10 inch rod. So, velocity factor is the quotient of 10 divided by 628, or about 0.016. That agrees with EZNEC. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil, W5DXP wrote:
"There is no way in heck to get 3 nanoseconds delay out of a 100 turn, 10-in., 2-in dia. coil." I calculate 628 in. of wire divided by c (@ 1181.1x10 to the sixth power in./sec.) = 0.53x10 to the minus 6 power, delay through the coil. That`s just over 1/2 microsecond delay in the coil. A lot slower than Tom`s coil but my signal sticks to the wire. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
dos'nt make much difference? then none of this has any point then?
On May 15, 10:32 am, Cecil Moore wrote: wrote: Cecil doesnt seem to worry about this error, but just saying it doesn't actually mean anything without differences. Don, I worry about any error but I don't know what the error is and Richard C. won't tell me. But that's just his style. Upon closer reading, Wes's coil is closer to 7 inch diameter but that doesn't make much difference. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
I still dont see differences
just saying it doesmn't make it so. Does it? ok different coil size, but no one seems to be able to say what this abour (sure delay, all coils have delay and none nows how much except that it isnt much different from another coil). coke = pepsi woohoo! On May 15, 11:40 am, Richard Clark wrote: On 15 May 2007 10:27:19 -0700, wrote: Cecil doesnt seem to worry about this error, but just saying it doesn't actually mean anything without differences. What is different about his claim and Wests'? Hi Herbert, Yeah, I've noticed he's sloughed off your tough questions. The differences are in the claim of having modeled Wes' helix, he did not, it is a helix of Cecil's own invention. This is the problem of leverage sources' credibility: use their name and discard their work where it conflicts with your own. The differences (as I understand your desire for actual data content) consist in the wrong pitch and the wrong diameter. Aside from that, they are identical. Now, how far can Cecil take a proof using this identity? All the way within ±CSE (Cecil Standard Error, which as a numeric is 67%). The world of theory is wide open when you cut yourself that much slack. 73's Richard Clark, KB7QHC |
Phase Shift through a 75m Texas Bugcatcher Coil
wrote:
dos'nt make much difference? then none of this has any point then? You've begun to get it. tom K0TAR On May 15, 10:32 am, Cecil Moore wrote: wrote: Cecil doesnt seem to worry about this error, but just saying it doesn't actually mean anything without differences. Don, I worry about any error but I don't know what the error is and Richard C. won't tell me. But that's just his style. Upon closer reading, Wes's coil is closer to 7 inch diameter but that doesn't make much difference. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
herbert.don wrote:
"coke = pepsi woohoo!" A loading coil is important to tune out the capacitive reactance of a too-short whip so that maximum current can be put into the antenna to get the most RF radiation out. A loading coil usually has some loss that takes the form of heat converted from some of the energy pumped into it. One of the debates here may have been triggered by reference to John Devoldere, ON4UN`s treatment of "short verticals" in "Low-Band DXing". He discussed several ways to resonate the too-short vertical antenna. His Fig. 9-22 on page 9-15 of his 1994 edition became notorious. ON4UN occasionly characterizes coils as having "degrees" in the space occupied in the antenna. No one argues that a 1/4-wave vertical does not have 90 degrees, or that at a given frequency, you could not properly say a certain linear measure was not equal to a degree. So, if you are trying to resonate the antenna as a 1/4-wavelength, why not assign the missing length of antenna, in degrees, to the coil or coils which replace the missing length of antenna? The number of turns required of the coil or coils depends on where it or they are placed in the antenna. A certain number of turns are not predetermined to represent so many degrees independent of placement. More than just resonating the antenna, placement of the coil or coils affects current distribution which affects radiation and loss. Several problems need simultaneous solution to get the best performance. I have mostly thought of the velocity of light as being a universal speed limit. I read long ago that energy is transferred by passing an impetus along a group of extremely short gap distances through a file of charges. The individual charges are migrating slowly, if at all, and going nowhere fast. Speeds greater than the speed of light seemed inconceivable to me. Researching the loading coil brought me to Kraus and his helical antenna. On page 253 of the 3rd edition of "Antennas" is Figure 8-32. For certain coils it shows velocities exceeding the speed of light. I guess I`m not too old to learn after all. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
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Phase Shift through a 75m Texas Bugcatcher Coil
"Cecil Moore" wrote in message ... If a Texas Bugcatcher Coil could be turned into a traveling wave device instead of a standing wave device, the inherent phase shift through the coil would become obvious. I used the Helix option in EZNEC to generate a reasonably close model of a 75m Texas Bugcatcher coil and loaded it with a resistance equal to the coil's characteristic impedance which essentially eliminated the reflected current, leaving the forward current intact and visible. All of the data points on the following web page came from EZNEC. All of the files are available for downloading. Please take a look at: http://www.w5dxp.com/current2.htm -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Clark, KB7QHC wrote:
"The velocities of what?" Figure 8-32 labels the ordinate values as "relative phase velocity". Phase velocity is defined in my electronic dictionary as: "The velocity at which a point of constant phase is propagated in a progressive sinusoidal wave." In other words, pick a point on a waveform. The rate at which it moves is phase velocity. That`s the velocity of propagation. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
On Wed, 16 May 2007 08:43:03 -0500, (Richard
Harrison) wrote: In other words, pick a point on a waveform. The rate at which it moves is phase velocity. That`s the velocity of propagation. Hi Richard, The velocity of an imaginary point that contains no information nor energy. 73's Richard Clark, KB7QHC |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Clark wrote:
'The velocity of a point that contains no information nor energy." The topic of "phase shift" relates to alternating electrical current, that is volts and amps. These are essential to energy and they are represented by symbols which are manipulated to solve our problems. A sinusoidal wave is the symbol of the periodic variation of electrical properties with time. Volts and amps taken in-phase represent real energy. All points on a sinusoidal traveling wave move with the same velocity past a fixed point. So, to determine the velocity of the motion, choice of a particular point on the wave, be it zero or peak value, no matter where the wave travels, or how attenuated, is always the zero or peak value of the alternation. For velocity, choice of the particular point to use is immaterial. The symbol of the wave contains the information. The wave itself contains the energy. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Clark wrote: On Wed, 16 May 2007 08:43:03 -0500, (Richard Harrison) wrote: In other words, pick a point on a waveform. The rate at which it moves is phase velocity. That`s the velocity of propagation. Hi Richard, The velocity of an imaginary point that contains no information nor energy. Why such criticism of a meager geometrical object with such useful purpose? It seems your expectations may be too high. ac6xg |
Phase Shift through a 75m Texas Bugcatcher Coil
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Phase Shift through a 75m Texas Bugcatcher Coil
On Wed, 16 May 2007 09:37:17 -0700, Jim Kelley
wrote: Why such criticism of a meager geometrical object with such useful purpose? It seems your expectations may be too high. Hi Jim, MY expectations are too high? "With such useful purpose" is overarching by half. What has Phase Velocity got to do with anything, and what are its expectations either high or low? 73's Richard Clark, KB7QHC |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Clark, KB7QHC wrote:
"The velocity of an imaginary point contains no information nor energy." You could imagine a point like that. I regret omitting the word "imaginary". It was unintentional. I gave a dictionary definition of "phase velocity". It seems to be synonymous with propagation velocity. The same dictionary defines group velocity, and says: "Group velocity differs from phase velocity in a medium in which the phase velocity varies with frequency." If phase variation with frequency is severe, and if the signal contains multiple frequencies, I think it would likely alter the waveform. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Clark wrote:
On Wed, 16 May 2007 09:37:17 -0700, Jim Kelley wrote: Why such criticism of a meager geometrical object with such useful purpose? It seems your expectations may be too high. Hi Jim, MY expectations are too high? "With such useful purpose" is overarching by half. Perception only. Utility in geometrical abstracts exists completely independently of ones appreciation of them. What has Phase Velocity got to do with anything, and what are its expectations either high or low? For the problem at hand (antennas) Kraus uses c = w/k, not dw/dk. Naturally, he was interested in the velocity with which field lines move across a point - the speed at which the wave propagates. VF = v sub p over c, not v sub g over c. The second part of your question is unintelligible to me. ac6xg |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Clark, KB7QHC wrote:
"Richard, if you choose to challenge this, cite an explicit reference that says Phase Velocity contains information and energy." I already have in two previous postings in this thread. One quotation was from Terman and the other was from Lenkurt. Both explained how a traveling wave tube (TWT) works. It uses velocity modulation of an electron beam to alter the phase and power of a signal carried by a coil encircling the electron beam. There`s your information and energy. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Harrison wrote:
I calculate about 628 inches of wire in the coil compared with about 10 inches of coil length. It is 62.8 times as far to go around the turns on the coil as it is to travel through a 10 inch rod. So, velocity factor is the quotient of 10 divided by 628, or about 0.016. That agrees with EZNEC. I think we are talking about two different coils. The 6" dia, 6" long, 30 turn Texas Bugcatcher coil is the one with a VF of 0.016 per EZNEC. The only 10" coil that I remember being mentioned is w8ji's and EZNEC cannot model that coil. Dr. Corum's equation yields a VF of 0.0328 for the w8ji coil, again just about double what the "threaded bolt" approach indicates. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Harrison wrote:
Richard Clark, KB7QHC wrote: "The velocities of what?" Figure 8-32 labels the ordinate values as "relative phase velocity". Phase velocity is defined in my electronic dictionary as: "The velocity at which a point of constant phase is propagated in a progressive sinusoidal wave." In other words, pick a point on a waveform. The rate at which it moves is phase velocity. That`s the velocity of propagation. What Kraus may be talking about is the apparent speeding up of the signal compared to the "threaded bolt" calculation. When 600 inches of wire is coiled into a helix, how can EM waves travel through that 600 inches of wire faster than it can travel through 600 inches in free space? Reckon that is what he is talking about? -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Jim Kelley wrote:
Delays are typically measured using pulses. Please describe the pulse you intend to use on a 1/4WL long standing-wave antenna. If I thought that was true, I wouldn't have said what I did. If the delay through the loading coil in a standing- wave antenna could be measured in situ, then there would not be any argument. But maybe I am missing something. How would you propose to measure the delay through a loading coil during steady-state for a standing-wave antenna? -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil Moore wrote: Please describe the pulse you intend to use on a 1/4WL long standing-wave antenna. Kind of a wispy brunette one, about 5'7". What difference would it make, Cecil? One that is short compared to the delay. If the delay through the loading coil in a standing- wave antenna could be measured in situ, then there would not be any argument. But maybe I am missing something. How would you propose to measure the delay through a loading coil during steady-state for a standing-wave antenna? When you post a question in that way I gotta wonder what you must think is going on inside an antenna. What's different about the 'situ' during steady state that causes electromagnetic fields to propagate differently than at other times? 73, ac6xg |
Phase Shift through a 75m Texas Bugcatcher Coil
Jim Kelley wrote:
What difference would it make, Cecil? One that is short compared to the delay. What difference would it make if the frequency of the pulse is far removed from the operating frequency? What difference would it make if the frequency is far above the self-resonant frequency? What difference would it make if the inductance is completely swamped by the capacitance? Shirley, you jest. What's different about the 'situ' during steady state that causes electromagnetic fields to propagate differently than at other times? They don't propagate differently but how does one separate the forward wave from the reflected wave on a standing-wave antenna? If you can do that, you will have solved the measurement problem. -- 73, Cecil http://www.w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil. W5DXP wrote:
"When 600 inches of wire is coiled into a helix, how can EM waves travel through that 600 inches of wire faster than it can travel through 600 inches in free space?" Good question. Maybe it figuratively travels from both ends of the coil toward the niddle. At one part of the cycle the wave is pushing excess electrons to one end of the coil while it supplies electron deficient atoms to the other end. Then the cycle reverses the charge situation at the ends of the coil. Or maybe the photons do blast off to leap across the length of the coil. My vision isn`t good enough to see what is going on inside of the coil`s conductor. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil, K5DXP wrote:
"I think we are talking about two different coils." Yes, that`s now obvious. I only worked with W8JI`s coil, and your numbers were for the bugcatcher coil. I showed my work, so if my method was wrong, my results are probably wrong too. Someone is likely to point out the error in my ways and I`ll learn something. Best regards, Richard Harrison, KB5WZI |
Phase Shift through a 75m Texas Bugcatcher Coil
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Phase Shift through a 75m Texas Bugcatcher Coil
On Wed, 16 May 2007 12:00:41 -0700, Jim Kelley
wrote: Richard Clark wrote: On Wed, 16 May 2007 09:37:17 -0700, Jim Kelley wrote: Why such criticism of a meager geometrical object with such useful purpose? It seems your expectations may be too high. Hi Jim, MY expectations are too high? "With such useful purpose" is overarching by half. Perception only. Utility in geometrical abstracts exists completely independently of ones appreciation of them. Hi Jim, Wouldn't it be clearer (as you are one who complains of the lack of clarity) to simply call this "useful purpose" as Zen? What has Phase Velocity got to do with anything, and what are its expectations either high or low? For the problem at hand (antennas) Kraus uses c = w/k, not dw/dk. Naturally, he was interested in the velocity with which field lines move across a point - the speed at which the wave propagates. VF = v sub p over c, not v sub g over c. The second part of your question is unintelligible to me. As is your response. Throwing equations over the transom doesn't make them explanations. 73's Richard Clark, KB7QHC |
Phase Shift through a 75m Texas Bugcatcher Coil
Cecil Moore wrote:
Jim Kelley wrote: What difference would it make, Cecil? One that is short compared to the delay. What difference would it make if the frequency of the pulse is far removed from the operating frequency? What difference would it make if the frequency is far above the self-resonant frequency? What difference would it make if the inductance is completely swamped by the capacitance? Shirley, you jest. The advantage to using pulses is that they are 'broadband' - they don't have "A" frequency. The inductance and capacitance of the system are unaffected by the small signals one impresses upon it. What's different about the 'situ' during steady state that causes electromagnetic fields to propagate differently than at other times? They don't propagate differently but how does one separate the forward wave from the reflected wave on a standing-wave antenna? If you can do that, you will have solved the measurement problem. The antenna behaves physically in exactly the same way whether or not it happens to be 'occupied' by waves, standing, sitting, or whatever during measurement. If you want to know how long it take an electromagnetic wave to traverse a conductor in any shape or configuration, you pulse it and measure how long it takes, either to get from one end to the other, or to be reflected back from the other end. There are of course dispersion effects, and by studying the change in the waveshape it is possible to deconvolve the frequency dependent components. This is a matter of routine for practicioners. 73, ac6xg |
Phase Shift through a 75m Texas Bugcatcher Coil
Jim Kelley wrote:
The advantage to using pulses is that they are 'broadband' - they don't have "A" frequency. The inductance and capacitance of the system are unaffected by the small signals one impresses upon it. But we are not interested in the phase delay for all those other frequencies. We are only interested in the phase delay at one particular frequency. And since we are talking about distributed networks and not lumped circuits, the inductance and capacitance of the coil does change with frequency. Whatever measurements we make need to be made at the frequency of operation. The antenna behaves physically in exactly the same way whether or not it happens to be 'occupied' by waves, standing, sitting, or whatever during measurement. If you want to know how long it take an electromagnetic wave to traverse a conductor in any shape or configuration, you pulse it and measure how long it takes, either to get from one end to the other, or to be reflected back from the other end. If the pulse is not at the frequency of operation, the results are hardly useful at all since the response of the loading coil is frequency dependent. So we are back to the original question. How can the delay through a mobile loading coil be measured at the frequency of operation in a standing-wave antenna? -- 73, Cecil, w5dxp.com |
Phase Shift through a 75m Texas Bugcatcher Coil
Richard Clark wrote:
Hi Jim, Wouldn't it be clearer (as you are one who complains of the lack of clarity) to simply call this "useful purpose" as Zen? Hi Richard, You don't like it much, do you. I suggest not dishing out so much of it then. I don't know about you, but I learned about the utility of 'points' in my geometry and mathematics classes. Data is, for example, often obtained by accumulating an array of them. For the problem at hand (antennas) Kraus uses c = w/k, not dw/dk. Naturally, he was interested in the velocity with which field lines move across a point - the speed at which the wave propagates. VF = v sub p over c, not v sub g over c. The second part of your question is unintelligible to me. As is your response. You probably intended that as a clever retort. Throwing equations over the transom doesn't make them explanations. Had I not 'thrown', you would likely have desired to know what I was talking about. It was as concise a presentation as I could conjure in 30 seconds. Equations do offer the advantage of illustrating the point without leaving much need for semantic interpretation. 73, ac6xg |
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