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Current through coils
Ian White GM3SEK wrote: 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. There are two advantages to a fiberoptic coupled probe. One advantage of fiber optic coupling from probes to indicator is the coupling leads from sensor to indicating instument do not have a good direct path to earth or equipment like conventional probes. I actually built a form of this for one of the measurements Ceci rejected. http://www.w8ji.com/building_a_current_meter.htm In this case the information, current, is conveyed by light through air directly to my eye. For the purposes of this discussion, however, the real advantage is different. Since it is unlikely anyone disagreeing has a fiber-optic coupled probe (the fiber optical cable simply replaces the wire between the sensor and the indicator or sensor information processing system) it is unlikely anyone can prove Cecil wrong. This all seems logical to me, because Cecil has asked for measurements. The pattern has been after he gets measurement results and finds they disagree with his theory, he has to blame the difference on something. The most logical thing any person can do when they repeatidly accept results of measurements made by multiple people using multiple methods is to come up with a measurement no one can make. For example? Most people understand a current transformer measures current. The original debate was K3BU and W9UCW made a statement current is high only in the first few turns of a loading inductor, and thus loading inductor Q did not matter for efficiency of an antenna. I proposed antenna losses were swamped out by ground losses in a vehicle, and because of very high ground losses the effects of coil resistance were diluted. I measured the inductor and found as quite logically anyone would expect that current ratio depended on the ratio of stray C from the coil to load C at the open end of the coil. Yuri K3BU argued the coil replaced a certain number of degrees electrical height, and I disagreed. I said a 20-degree long antenna with a loading coil did NOT have 70 degrees of antenna wound up in the coil. Most people experienced in systems like this from an engineering standpoint agreed with me. Somewhere about that time Cecil brought reflected waves into the discussion. After a series of "what happens if" Cecil wanted measurements. When they were made, he and Yuri announced the measurements proved their points. When the person making the measurements corrected those misstatements and pointed out the measurements didn't support their claims, the only logical course was to discredit the measurements and ask for new ones. When new measurements again disagreed with the concept of huge current or phase delay of current that was tied to degrees the coil replaces, the only course was to reject those measurements. So here we are today, two or three years later, still trying to find a measurement that will agree with what Cecil and Yuri proposed or for another person of reasonable engineering experience to agree with the notion the coil behaves as a coiled up antenna or transmission line rather than behaving more like a lumped component in a small heavily loaded mobile antenna. Since dozens of hours of measurements acceptable to most people were rejected, the only solution would be to require a measurement with instrumentation no one has. This way Cecil can say no one can prove him wrong, and that allows him to continue to demand others agree with him. In my opinion, the real advantage of optically coupled probes in this thread is no one is likely to have them. 73 Tom |
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 ========================================== Sorry Cec, I havn't the foggiest idea. ---- Reg. =========================================== On second thoughts, since L and C are functions of a coil's physical dimensions it must be something else which is changing with frequency. ---- Reg. |
Current through coils
wrote:
Before I comment on your posting below, I think you can prove to yourself that your measurements are flawed. You measured 3 nS delay through your coil at 4 MHz. Now perform the same measurement at the self-resonant frequency. The delay through the coil is known to be 15.6 nS at the self-resonant frequency. If your delay measurement isn't 15.6 nS, then there is something wrong with your methods. Better yet, measure the delay at 1, 2, 4, 8, &16 MHz and report the results. ... it is unlikely anyone can prove Cecil wrong. That's because in order to prove me wrong, you have to prove yourself right. You simply haven't done that because you refuse to engage me at a technical level. You have ignored my technical questions and refused to discuss the technical details. Many readers have noticed that, wonder why, and have commented on it in emails to me. This all seems logical to me, because Cecil has asked for measurements. The pattern has been after he gets measurement results and finds they disagree with his theory, he has to blame the difference on something. Tom, your measurements agree perfectly with my theory. You are measuring standing wave currrent. That standing wave current magnitude is pictured in every good book on antennas. Kraus also shows the phase which, for a thin wire dipole, is fixed at zero from tip to tip on the antenna. It is understandable why you measured zero standing wave current phase shift through the coil. THE STANDING WAVE CURRENT PHASE SHIFT IS ZERO WHETHER THE COIL IS IN THE CIRCUIT OR NOT! Since the phase of the standing wave current is fixed and unchanging whether the coil is in the circuit or not, why do you think measuring that unchanging phase around a coil proves anything? I proposed antenna losses were swamped out by ground losses in a vehicle, and because of very high ground losses the effects of coil resistance were diluted. I agree with that and have never argued otherwise. I measured the inductor and found as quite logically anyone would expect that current ratio depended on the ratio of stray C from the coil to load C at the open end of the coil. Yuri K3BU argued the coil replaced a certain number of degrees electrical height, and I disagreed. The following reports a 10-20 degree phase shift through most coils. http://lists.contesting.com/archives.../msg00540.html Most people experienced in systems like this from an engineering standpoint agreed with me. Somewhere about that time Cecil brought reflected waves into the discussion. Those "most people" don't understand forward and reflected waves on a standing-wave antenna. You have proven by your postings here that you do not understand forward and reflected waves on a standing- wave antenna like a 75m bugcatcher mobile antenna. Worse yet, you refuse to discuss the antenna at a technical level and have simply sandbagged your misconceptions. I remember when you were using the lumped inductance feature of EZNEC to try to prove your point, certainly an invalid proof. When we started this thread, it was obvious that you didn't know the standing wave current phase is fixed near zero degrees so measuring it is futile. After a series of "what happens if" Cecil wanted measurements. When they were made, he and Yuri announced the measurements proved their points. Yes, they did prove that the current at the ends of the coil were NOT equal. You said they were. I said they were not. Out of all of your and Roy's measured results, the current was equal in only the case of the small toroidal coil and that's because it was located at a standing wave current maximum (loop). When the person making the measurements corrected those misstatements and pointed out the measurements didn't support their claims, the only logical course was to discredit the measurements and ask for new ones. You sure have selective memory, Tom. I fully accepted your standing- wave current measurements. But standing-wave current measurements cannot be used to measure the traveling-wave delay through a coil. That should be obvious to everyone by now. The delay through the coil causes a phase shift in the forward wave and the reflected wave, not in the standing wave. THE PHASE OF THE STANDING WAVE CURRENT IS KNOWN NOT TO CHANGE AND THAT'S EXACTLY WHAT YOU MEASURED, VIRTUALLY NO SHIFT. Kraus agrees. Figure 14-2 of "Antennas For All Applications", 3rd edition shows a graph of the phase of the standing wave current. That phase is zero tip-to-tip for a thin-wire 1/2WL dipole. When new measurements again disagreed with the concept of huge current or phase delay of current that was tied to degrees the coil replaces, the only course was to reject those measurements. THOSE MEASUREMENTS WERE NOT REJECTED! They were accepted as perfectly valid measurements of standing wave current. Those characteristics are pictured in Kraus and your measurements agree perfectly with them. Your argument is a strawman. The fact is that a standing wave measurement CANNOT yield the current delay through the coil any more than it can yield the current delay through a wire. YOU CANNOT MEASURE THE DELAY THROUGH THE COIL USING CURRENT KNOWN NOT TO CHANGE PHASE! So here we are today, two or three years later, still trying to find a measurement that will agree with what Cecil and Yuri proposed or for another person of reasonable engineering experience to agree with the notion the coil behaves as a coiled up antenna or transmission line rather than behaving more like a lumped component in a small heavily loaded mobile antenna. This is not about you or me or Yuri. It is about getting down to the truth. Yet you rave on and on about personalities. Why don't you discuss technical issues instead of personalities? There is a phase shift in the forward current through the loading coil. There is a phase shift in the reflected current through the loading coil. Those phasors are rotating in opposite directions so the net phase is fixed. You can measure standing wave current phase in thousands of experiments from now to kingdom come and you will not be measuring the phase shift of the forward and reflected current through the coil. Your measurements, so far, are meaningless. You have NEVER measured the delay through the coil. I guess I'm going to have to draw you some pictures and post them on my web page. Since dozens of hours of measurements acceptable to most people were rejected, the only solution would be to require a measurement with instrumentation no one has. I fully accept your standing wave current measurements, Tom, but standing wave current measurements will not yield the information that we are after. We need to know the phase shift in the forward and reflected currents through the coil. Standing wave measurements simply will not yield that information. Self-resonance measurements will yield that information. The delay through a coil that is self-resonant on 16 MHz is 15.6 nS. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Reg Edwards wrote:
Having started it, I havn't been taking much notice of this long-winded thread. Its all too clever for poor little me! ;o) Just curious, Reg, are you familiar with phasors used to represent traveling waves where the phasor has a rotation about the origin proportional to the frequency? Are you familiar with the phasor addition of two of those waves traveling in opposite directions forming standing waves? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Reg Edwards wrote:
On second thoughts, since L and C are functions of a coil's physical dimensions it must be something else which is changing with frequency. Or maybe nothing is changing appreciably over relatively small frequency excursions. Maybe the measurements are not measuring what someone thinks they are measuring. The only experiment so far that has actually measured the delay through a coil is the self-resonant frequency measurement. Tom's and Roy's results are perfectly consistent with the measurement of standing wave current whose phase is known to be constant and unchanging. That measurement yields no new information. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil, W5DXP wrote:
"Kraus agrees." Pity the fool that argues with Terman or Kraus! In Kraus` Figure 14-2 of the 3rd edition of "Antennas", the 1/2-wave is resonant and shows no phase shift from end to end. In Figure 14-4, phase is shown to make an abrupt phase transition at a point 1/2-wave back from the open circuit at the tip of the antenna. This is predictable from the behavior of an open-circuited transmission line as shown by Terman in Fig. 4-7 in his 1955 edition. Kraus` Figure 23-21 shows how a self-resonant coil can replace a short-circuited 1/4-wave stub in a phase-reversing trap. If you don`t have the 3rd edition of "Antennas", get it. Cecil wrote: "I am not asking for fiber optic measurements." Very likely they aren`t necessary. I`ve measured currents along antennas draging a sampling loop along them with a rope. A transit determined the position and its telescope made the r-f ammeter in the loop readable. Surely a loop and its ammeter can be small enough not to upset the measurements if you use enough power and have a low enough frequency. As Richard Clark might say: "We don`t need no stinkin` fiber optics." Best regards, Richard Harrison, KB5WZI |
Current through coils
Cecil Moore wrote:
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? We are not talking about L, C, R, or any other inherent property changing with frequency. We are talking about the delay of a current wave in a single direction (anybody have a pair of directional coupler current probes?) through a complex component that has several different mechanisms that contribute to the total current passing through it. It is the vector sum (superposition) of those current components that is in question. Over a narrow frequency range, it is conceivable to me, that the phase (delay) of that sum might shift, dramatically, though any component of that sum might change its magnitude only slightly (no faster than in proportion to the frequency), and the phase of that component might change not at all. 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? Definitely nonlinear, just like impedance is very nonlinear as the frequency passes through any resonance. This is why I am suspicious of a measurement made at resonance, being extrapolated to non resonant conditions. |
Current through coils
John Popelish wrote:
We are not talking about L, C, R, or any other inherent property changing with frequency. The velocity factor of the coil is based on those quantities and can be calculated. The velocity factor of a transmission line is based on those quantities and can be calculated. Freq 1 2 4 8 16 MHz Delay ___ ___ 3 ___ 16 nS That looks non-linear to me. How about you? Definitely nonlinear, just like impedance is very nonlinear as the frequency passes through any resonance. Care to fill in the blanks above? This is why I am suspicious of a measurement made at resonance, being extrapolated to non resonant conditions. Self-resonance is simply where the round trip delay through the coil puts the forward and reflected voltages and the forward and reflected currents either at zero degrees or 180 degrees. That's what happens at an open-ended 1/4WL stub. That's also what happens at the feedpoint of a resonant standing wave antenna like a 75m mobile bugcatcher antenna. Resonant mobile antennas are "self-resonant antenna systems". -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
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Current through coils
Cecil Moore wrote: John Popelish wrote: We are not talking about L, C, R, or any other inherent property changing with frequency. The velocity factor of the coil is based on those quantities and can be calculated. I am not familiar with the velocity factor of coils. The velocity factor of a transmission line is based on those quantities and can be calculated. Not quite. The velocity factor in transmission lines is based on ratios: capacitance per length, and inductance per length. Where do you get the equivalent length numbers when dealing with semi lumped inductors? Freq 1 2 4 8 16 MHz Delay ___ ___ 3 ___ 16 nS That looks non-linear to me. How about you? Definitely nonlinear, just like impedance is very nonlinear as the frequency passes through any resonance. Care to fill in the blanks above? (snip) My guesses at those numbers without a well tested method are as useful as yours. |
Current through coils
Richard Clark wrote: Having built nigh on an hundred, you are right - I don't have one now. I don't plan to build anymore either as it would do nothing to lower the text noise floor. I've enjoyed the speculation tho'. The two most humorous parts of this entire thing: 1.) RF current can stand still, yet cause current in a transformer secondary. 2.) We have to use a "directional current coupler" to sort current flowing one way from current floing the other, because of standing wave current. This entire thing has become almost laughable. It looks like the thread has regressed to the point where people no longer understand directional couplers or current transformers. Anyone who knows how a directional coupler works is rolling around on the floor laughing at the suggestion of sorting "forward current" from "reflected current". It appears this thread has reached the lowest level, where impossible to build instrumentation is now demanded as the only acceptable proof. What a trip! 73 Tom |
Current through coils
wrote:
The velocity factor of a transmission line is based on those quantities and can be calculated. Not quite. The velocity factor in transmission lines is based on ratios: capacitance per length, and inductance per length. There exist formulas for calculating the Z0 and VF of helical transmission lines. I'll bet Reg can do it. A coil has a capacitance per length and inductance per length. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil and Roy, Please stop Ad Hominem.
Keep to the subject where we can disagree or agree. Hopefully, some of us will learn. Cecil Moore wrote: 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? |
Current through coils
wrote:
1.) RF current can stand still, yet cause current in a transformer secondary. Please provide a technical response to the following. Hecht, in "Optics" says of standing waves of light in space: "Its profile *DOES NOT MOVE* through space; it is clearly not of the form f(x+vt). At any point x = x', the amplitude is a constant equal to 2Eot*sin(kx') and E(x',t) [the electric field] varies harmonically as cos(wt)." page 289, 4th edition. The 'z' movement for a standing wave current magnitude along a wire is completely divorced from the frequency of the wave. Its profile *DOES NOT MOVE* through the wire. Same as light standing waves above. It is not of the form f(z+wt). Since standing waves of light in space do not move, why is it surprising that standing waves of RF on a wire do not move for exactly the same reason since they have identical equations? The standing wave energy in the H-field of RF standing waves will certainly cause current in a transformer secondary just as the standing wave light electric field will activate a light detector. 2.) We have to use a "directional current coupler" to sort current flowing one way from current flowing the other, because of standing wave current. There really may be humor in that statement which I never made. I've never heard of a "directional current-only coupler". If anyone knows of one, it sure would solve the measurement problem. Anyone who knows how a directional coupler works is rolling around on the floor laughing at the suggestion of sorting "forward current" from "reflected current". And I'm one of them. I've never said there existed such a device, just that if it did exist, it would solve the measurement problem. As it is, we haven't solved the measurement problem. The only means I've seen of actually measuring the phase shift through a coil is using the self-resonance method. Measuring the phase shift of standing waves won't work because STANDING WAVES HAVE NO PHASE SHIFT WHETHER THERE'S A COIL IN THE CIRCUIT OR NOT! It appears this thread has reached the lowest level, where impossible to build instrumentation is now demanded as the only acceptable proof. It was a wish, not a demand. But we can indeed separate out the forward wave from the reflected wave in a transmission line by using a directional coupler calibrated for the Z0 of the line. We can then carry those concepts over to a standing wave antenna, according to Balanis. So consider this experiment. coil source---50 ohm coax---X-////-Y---50 ohm coax---Load We have directional couplers installed at 'X' and 'Y' and we can in theory look at the phases of the forward and reflected currents on each side of the coil. Will the forward and reflected currents through the coil show a phase shift or not? Seems we should start at a pretty low frequency (low reactance) and work our way up. I think the phase shift pattern would be clear. Note that a cap to ground to the left of 'X' and a cap to ground to the right of 'Y' would result in a pi-net tuner. Wonder if there's any phase shift through the coil in a pi-net tuner? Is a pi-net tuner a "phasing network"? How could the coil cause an arc on the Smith Chart without changing the phase of the wave through the coil? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Dave wrote:
Keep to the subject where we can disagree or agree. Done! See my postings of today. I apologize for my previous emotional outbursts. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
John Popelish wrote: We are not talking about L, C, R, or any other inherent property changing with frequency. The velocity factor of the coil is based on those quantities and can be calculated. What's the formula, Cecil? Also, what is the dominant mode of a single wire, loading-coil transmission line: TE, TM, TEM, or what? If not TEM, how do you calculate the cutoff frequency? If I terminate one of these things in the right impedance will it act like an infinite transmission line? Given your loading coil terminated in a given impedance, what is the expression for the impedance looking into it? I suppose you also have something that will tell us how to find your coil's characteristic impedance; o.k., out with it. All this bluster and threatening rhetoric aren't advancing the acceptance of your crackpot theory one inch, Cecil. I don't see anything wrong with at least attempting to characterize a loading coil as a transmission line as long as the attempt is done dispassionately with real theory and an acceptance of the possibility of failure as part of the effort. Desperately thinking up excuses for an idea you made up in your head, and becoming emotionally distraught when people don't buy those excuses, is a waste of your time and everyone else's. 73, Tom Donaly, KA6RUH |
Current through coils
Anyone who knows how a directional coupler works is rolling around on
the floor laughing at the suggestion of sorting "forward current" from "reflected current". And I'm one of them. I've never said there existed such a device, just that if it did exist, it would solve the measurement problem. As it is, we haven't solved the measurement problem. I've solved the measurement problem. I measured current and voltage levels and phase of each. I've measured time delay of current appearing at the coil output compared to input. We have directional couplers installed at 'X' and 'Y' and we can in theory look at the phases of the forward and reflected currents on each side of the coil. Will the forward and reflected currents through the coil show a phase shift or not? With all the respect I can muster, here we go again Cecil. Current is current. Voltage is voltage. A traditional directional coupler works by comparing voltage across the line at any one point to current in the line at that same point. The current sampling device is summed at the operating frequency with the voltage sampling device, and the resulting voltage is measured. When voltage and current are in phase, the detected voltage levels add. When they are fully out of phase they subtract. Now we could build a transmission line system of measuring SWR that would work the very same way (normally done at VHF). Or we could build a line section that allows us to slide a probe along it and measure voltage or current nodes and finding maximum and minimum calculate SWR. In every single device we would be able to build, we would never be able to sort reflected current from forward because current is current. There really isn't any such thing as current traveling two directions at one past one point in a system. You have taken this argument to an absolute dead end, because you insist current can flow two directions at the same time at one single point in a system. You are demanding a measurement method that uses a device that cannot be built to measure something that does not exist. That is either humorous, sad, or frustrating. It sure isn't science. 73 Tom |
Current through coils
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. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Tom,
Whenever Cecil gets in a total lather I am reminded of John Belushi in Animal House. "Were you there when the Germans bombed Pearl Harbor?" This entire saga has been greatly extended and quite thoroughly confused by imprecise and flat-out-incorrect terminology. It probably won't get better any time soon. Currents, waves, and fields are used interchangeably as the mood strikes. Phase shift can refer to almost anything, it seems. Free-space optics are used as an analog to current in a wire. Descriptions that almost certainly have little transferability from one human to another abound, such as "superposed local RF phasors". Oh well, it's entertaining, at least for a while. 73, Gene W4SZ wrote: With all the respect I can muster, here we go again Cecil. Current is current. Voltage is voltage. [snip] In every single device we would be able to build, we would never be able to sort reflected current from forward because current is current. There really isn't any such thing as current traveling two directions at one past one point in a system. You have taken this argument to an absolute dead end, because you insist current can flow two directions at the same time at one single point in a system. You are demanding a measurement method that uses a device that cannot be built to measure something that does not exist. That is either humorous, sad, or frustrating. It sure isn't science. 73 Tom |
Current through coils
wrote:
I've solved the measurement problem. I measured current and voltage levels and phase of each. There you go again, "I, I, I". This is not about you. This is about valid measurements. I concede that when one measures the current phase shift in a standing wave environment, that the result will be zero or close to zero. But we are not interested in measuring a constant phase whether the coil is in the circuit or not. We are interested in measuring the phase shift through the coil and it is NOT zero. Reference: Kraus' "Antennas for All Applications", 3rd edition, Figure 14-2. Kraus clearly shows if you measure the phase shift between any two points on a 1/2WL dipole, that measured shift will be close to zero degrees whether a coil is present or not. There is no need to keep performing those same measurements. I agree with Kraus. We know a 1/2WL dipole is 180 degrees long. The fact that the standing wave current doesn't change phase from end to end doesn't mean the 1/2WL dipole is zero degrees long. The fact that the standing wave current doesn't change phase on each side of a coil doesn't mean the coil is zero degrees long. I've measured time delay of current appearing at the coil output compared to input. There you go again, "I, I, I". It doesn't matter who does the measurement or whether a coil is in the circuit or not. The standing wave current's phase doesn't change in the antenna's 180 degrees of length. That has nothing to do with anybody's measurements. That's just a fact of physics. One cannot use standing wave current to measure the delay through a coil OR A WIRE in a standing wave environment. If one takes a known 30 degrees of a 1/2WL dipole and uses standing wave current to measure the phase shift through that 30 degrees of wire, the measurement yields zero degrees. Does that mean the phase shift in 30 degrees of wire in a 1/2WL dipole is zero? Of course not. One simply cannot ascertain the phase shift in a piece of wire (or coil) by measuring the phase of the standing wave current. Current is current. On the contrary, one can look at the formula for standing wave current and see that standing wave current is NOT like traveling wave current. Traveling wave current is of the form f(z+wt) or f(z-wt) depending upon the direction of travel. Standing wave current is of the form f(z) + f(wt) so they are quite different and therefore have *different* characteristics. As you can see from the functions, magnitude and phase are interlocked for a traveling wave. Magnitude and phase are unlocked for a standing wave. With a phasor fixed at zero degrees, how does a standing wave phasor manage to flow? As is my custom, I am going to trim the part of your posting with which I agree. In every single device we would be able to build, we would never be able to sort reflected current from forward because current is current. On the contrary, we do it all the time for transmission lines with a known Z0. We separate forward power from reflected power. It is trivial to take forward power in a certain Z0 feedline and convert that value of power into forward current. It is trivial to take the reflected power in that same line and convert that power into a reflected current. Here are the formulas: |Ifor| = SQRT(Pfor/Z0) |Iref| = SQRT(Pref/Z0) In our directional couplers, we throw away the phase when we rectify it, but we don't have to throw away the phase. We can look ahead of the diodes with an o'scope probe and actually compare the phases of the two waves. You have taken this argument to an absolute dead end, because you insist current can flow two directions at the same time at one single point in a system. There you go again, "you, you, you". Everyone has requested that we cease and desist from the personal attacks. "We" means "you and me". But it is well accepted in the distributed network model that two currents can flow in opposite directions at the same time. There's probably no other way to get standing waves and a 75m mobile bugcatcher antenna system *IS* a standing-wave antenna. You are demanding a measurement method that uses a device that cannot be built to measure something that does not exist. That is either humorous, sad, or frustrating. It sure isn't science. There you go again, "you, you, you". This is not about you or me or our feelings. We can certainly measure the two currents flowing in opposite directions in a transmission line. Not having a voltage reference common is why it's hard to do in an antenna but I suspect it could be done with E-field and H-field probes and a little superpositioning. We are sometimes a rational species. We can perform our experiments on a transmission line with known Z0 and if we are careful, project out results on a standing wave antenna with an unknown Z0. Actually, the Z0 for a 1/2WL dipole made from #14 wire at 30 ft. from the ground is pretty well known to be about 1200 ohms. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Tom, W8JI wrote:
"A traditional directional coupler works by comparing voltage across the line at any one point to current in the line at that same point." Almost. It compares a voltage sample to a current sample, both of which have been converted into d-c voltages. These have been carefully crafted to be exactly equal d-c voltages regardless of the power level in the line. I`m giving up on correcting line by line. Important fact is that a reflection reverses the phase between the voltage and current produced by a wave. So when the samples from the forward wave are siummed, their total is exactly 2x the value of either the voltage-derived sample or the current-derived sample. When the samples from the reflected wave are summed, being equal but opposite in polarity, they add to ZERO. Calibration is so the total produces the correct value on the power scale for the wave in the forward direction. To get the power in the reverse direction, the input and output are effectively exchanged so that the forward power indication cancels and the reverse power indication is produced by the sum of its voltage and current d-c sample outputs. Best regards, Richard Harrison, KB5WZI |
Current through coils
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
Richard Harrison wrote: Tom, W8JI wrote: "A traditional directional coupler works by comparing voltage across the line at any one point to current in the line at that same point." Almost. It compares a voltage sample to a current sample, both of which have been converted into d-c voltages. These have been carefully crafted to be exactly equal d-c voltages regardless of the power level in the line. That's absolutely incorrect Richard. If you get out the schematic of ANY directional coupler, you will see the current sampling device is in series with a voltage sampling device. The radio frequency voltage ratios of sampling system are combined BEFORE detection. The dc voltage level does vary with both voltage and current (power), and that is why the meter on the front of your watt meter goes up and down with power levels. Only a phase detector levels voltages. 73 Tom |
Current through coils
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Current through coils
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Current through coils
Richard Harrison wrote:
Tom, W8JI wrote: "A traditional directional coupler works by comparing voltage across the line at any one point to current in the line at that same point." Almost. It compares a voltage sample to a current sample, both of which have been converted into d-c voltages. These have been carefully crafted to be exactly equal d-c voltages regardless of the power level in the line. I`m giving up on correcting line by line. Important fact is that a reflection reverses the phase between the voltage and current produced by a wave. So when the samples from the forward wave are siummed, their total is exactly 2x the value of either the voltage-derived sample or the current-derived sample. When the samples from the reflected wave are summed, being equal but opposite in polarity, they add to ZERO. Calibration is so the total produces the correct value on the power scale for the wave in the forward direction. To get the power in the reverse direction, the input and output are effectively exchanged so that the forward power indication cancels and the reverse power indication is produced by the sum of its voltage and current d-c sample outputs. Thank you for this concise summary. |
Current through coils
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
John Popelish wrote: To get the power in the reverse direction, the input and output are effectively exchanged so that the forward power indication cancels and the reverse power indication is produced by the sum of its voltage and current d-c sample outputs. Thank you for this concise summary. Except it is actually an incorrect concise summary. The directional coupler adds RF voltage from a sampling across the line directly to a sampling of RF current past that point. It is only after the voltages, one proportional to current and one proportional to voltage, are added that the resulting voltage is rectified and used to drive a meter. The directional effect can be analyzed using wave theory or simple circuit theory. The results are the same. 73 Tom |
Current through coils
Tom wrote, "The directional effect can be analyzed using wave theory or
simple circuit theory. The results are the same." Of course, "the directional effect" depends completely on having the sampler calibrated to the impedance of the line into which it's inserted. Otherwise, it's just resolving "forward" and "reverse" _as_if_ the signal is in a line that has a characterisitc impedance equal to the sampler's calibration impedance. To the extent the samples are accurate for instantaneous currents and voltages, the sampler does NOT depend on sinusoidal excitation. The result is accurate for the current and voltage that exist at each instant in time. Some directional couplers are very broadband; others are not. We made the ones in the 8753 that Tom uses to be accurate over a wide frequency range. And of course, if you don't just rectify the output, you can extract phase information from it as well as amplitude. Cheers, Tom |
Current through coils
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Current through coils
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. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
John Popelish wrote: I appreciate the correction. I am weak in the area of RF instrumentation, but am learning fast. It is an area I have somehow avoided for a long time, but am getting interested in it, lately. Good. It is an interesting area of electronics. If you are comfortable with RF circuitry, RF instrumentation is only a small additional step. I would very much like to see a more complete report on the measurements you have made, in relation to this thread. The problem is always time. I'm at the busiest time of the year for me, so everything that isn't a fore is sitting. I really swore I wouldn't get involved in an ungoing three year debate, but here I am anyway. I guess I needed a break from a constant string of projects all with tight deadlines. I am sure I would learn from seeing that. I tried to find an operating manual or application note on the network analyzer you used, but found little that was helpful to teach me how it works, and how one applies it. It seems to have 4 signal connectors (if I am interpreting what I have found, correctly) and I can interpret your web account to mean several possible things, so I am still under a bit of a cloud, here. Your tutelage is much appreciated. This is the closest manual I could find. http://www.home.agilent.com/cgi-bin/...OUNTRY_CODE=US For this: http://www.home.agilent.com/USeng/na...881282/pd.html Agilent seems to obsolete things after seven years. I have some useful equipment. Including an Impedance test set I paid about 20K for in the 90's. It directly measures almost anything you would every want to know. The nice thing about having test gear is being able to build almost anything. I have it because of work. You can do a lot with almost nothing except a vector voltmeter and a test fixture, but the automated measurements save me time. 73 Tom |
Current through coils
Tom, W9JI wrote:
"It is only after the voltages, one proportional to current and one proportional to voltage, are added that the voltage is rectified and used to drive the meter." Obviously a power determination must use voltage and current samples taken at the same place at the same time. We can`t use today`s voltage and yesterday`s current nor can we use the voltage over here and the current over there. Everything happens simultaneously and at the same sampling point. A single loop terminated in a diode is coupled to the center conductor of the coax. Its magnetic coupling produces the current sample. Its capacitive coupling produces the voltage sample. These are tweaked for identical deflection of the power meter. Best regards, Richard Harrison, KB5WZI |
Current through coils
Cecil Moore wrote: is only 40% shortening. I think the lumped inductor crossover point is probably pretty far below 4 MHz. 73, Cecil http://www.qsl.net/w5dxp There isn't any "crossover point". That point has been made several times by different people. There is a gradual transition over a very wide frequency range, and a rapidly increasing change as self-resonace is approached. |
Current through coils
chuck wrote:
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? You understand, Chuck, for example, my 75m bugcatcher coil, base- mounted on my GMC pickup with no whip is 1/4WL self-resonant at 6.6 MHz, i.e. it is 90 degrees on 6.6 Mhz. By ratio and proportion, the height on 4 MHz is 90(4/6.6) = ~54.5 degrees, 3.6 times the transition height for passing to the lumped element regime. One would have to divide the self-resonant frequency by 6 to get down to the 15 degree maximum for the lumped element regime so 1.1 MHz would be the highest frequency for which the lumped element regime could be considered valid. As the paper says: "Of course, the uniform current assumption has no validity for coils operating anywhere near self-resonance." Even the 100 uH test coil, 90 degrees self-resonant at 16 MHz, when used on 4 MHz is 90(4/16) = ~22.5 degrees, still above the 15 degree limit. One would have to go down to 2.7 MHz for the lumped element regime to be valid for that 100 uH coil and that is for an excellent coil with a Q of around 300. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
John Popelish wrote: (snip) I would very much like to see a more complete report on the measurements you have made, in relation to this thread. The problem is always time. I'm at the busiest time of the year for me, so everything that isn't a fore is sitting. I really swore I wouldn't get involved in an ungoing three year debate, but here I am anyway. I guess I needed a break from a constant string of projects all with tight deadlines. I can appreciate that. I have recently gotten sucked into a wide ranging study of ferrite rod antenna basics, and am having trouble finding time to go to work or to bed. Almost every preconceived notion I had about them I have been able to disprove by direct measurement. Very educational. I am sure I would learn from seeing that. I tried to find an operating manual or application note on the network analyzer you used, but found little that was helpful to teach me how it works, and how one applies it. (snip) This is the closest manual I could find. http://www.home.agilent.com/cgi-bin/...OUNTRY_CODE=US For this: http://www.home.agilent.com/USeng/na...881282/pd.html I'll take a good look at these. Agilent seems to obsolete things after seven years. I have some useful equipment. Including an Impedance test set I paid about 20K for in the 90's. It directly measures almost anything you would every want to know. (snip) So far, I am working with an RF volt meter, a signal generator or two, and an antique Boonton 160A Q meter. But I am finding lots of ways to put them to use. I would love to have a vector volt meter or vector impedance meter. A network analyzer is way beyond my budget. |
Current through coils
wrote:
Cecil Moore wrote: is only 40% shortening. I think the lumped inductor crossover point is probably pretty far below 4 MHz. There isn't any "crossover point". That point has been made several times by different people. One of those people supporting a "crossover point" is Dr. Corum in his IEEE peer reviewed paper at: http://www.ttr.com/TELSIKS2001-MASTER-1.pdf (page 6) Dr. Corum is pretty clear about 15 degrees, i.e. 4% of a wavelength, being the "crossover point". He considers 15 degrees to 90 degrees to require a distributed network analysis while below 15 degrees, "one passes to the lumped- element regime ..." The "crossover point" would be the same rule as for a transmission line. How long does a transmission line with reflections have to be before it is no longer valid to consider it a lumped piece of wire. 15 degrees is 4% of a wavelength and sounds reasonable. However, under the right conditions, one could arrange a current node at the halfway point of that 15 degrees of feedline thus causing current to flow into both ends of the feeline at the same time. 1/2 cycle later, current would be flowing out of both ends. How would a lumped-circuit model handle those conditions? The "crossover point" is obviously arbitrary but if one locates it very far above 15 degrees, according to Dr. Corum, one risks invalid analysis results such as have been reported here. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
(No smiley faces this time. No trolls or tricks either.) The assertion that there is some important difference between a standing wave and its component traveling waves has been made on a number of occasions in this thread. Indeed, that concept seems pretty central to the entire issue. It may be worth examining the importance of this distinction further. Basic assumptions: * System is linear, with no diodes, saturating cores, etc. * System is steady-state, with no startup transients. * System is lossless, including a lack of radiation * Superposition applies, i.e., scaling works and we can add subcomponent functions without error. The whole is precisely equal to the sum of the parts, no more and no less. If any of these assumptions are not operative, then what follows may not be correct. 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) The key question then becomes, what information has been lost in adding the traveling waves to form a standing wave? All of the parameters and variables are still in the standing wave equation, namely, k, z, w, t. The numerical values and definitions for these terms have not changed. One can add constant phase offsets in the traveling wave equations, but those don't really add any new information, and in any case they are not lost in converting to the standing wave format. Are there some hidden variables that have not been considered? If so, what are they, and where do they show up in the original traveling wave equations? If not, why does the analysis and measurement of the traveling wave components give one iota more information than the analysis and measurement of the standing wave? There is little doubt that real world conditions will violate some of the assumptions, but that does not seem to be the issue in the debate at this time. Again, what extra information would be gained if somehow the traveling wave components could be measured? 73, Gene W4SZ Cecil Moore wrote: wrote: [snip] Current is current. On the contrary, one can look at the formula for standing wave current and see that standing wave current is NOT like traveling wave current. Traveling wave current is of the form f(z+wt) or f(z-wt) depending upon the direction of travel. Standing wave current is of the form f(z) + f(wt) so they are quite different and therefore have *different* characteristics. As you can see from the functions, magnitude and phase are interlocked for a traveling wave. Magnitude and phase are unlocked for a standing wave. With a phasor fixed at zero degrees, how does a standing wave phasor manage to flow? |
Current through coils
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. -- 73, Cecil http://www.qsl.net/w5dxp |
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