|
Current across the antenna loading coil - from scratch
John Popelish wrote:
Go back and ponder what I wrote. Too much has been clipped for my elaboration to have any continuity. Sorry, I don't respond well to primrose paths. What keeps you from simply stating your point? It is a koan. Sorry, I don't respond well to "nonsensical questions". What keeps you from simply stating your point? Is it, if your point turns out to be wrong, you want me to take the heat? If you have no interest in anything but butting heads with the people who have disagreed with you, then, please stop responding to my posts. If you are into playing games, you are responding to the wrong person. Try W8JI or W7EL instead. -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
John Popelish wrote:
Cecil Moore wrote: For instance, what is the current at the end of 200 feet of RG-58 terminated by a 50 ohm antenna used on 446 MHz when the source current is 2 amps? Somewhat less then 2 amps. Does "somewhat" cover 24 dB of losses? :-) The point is that the current "drops" by exactly the same amount as the voltage. That's a characteristic of distributed networks as opposed to lumped circuits. In a Z0 RF environment, the current has to "drop" by exactly the same amount as the voltage to maintain the Z0 ratio. There are really no "across" and "through" concepts as exist in DC circuitry. I guess I'm so dense that I need help in proving what you think I can prove with that information. Right now, I am apparently missing something, maybe because of too much California Merlot. Sounds like something I might do, this afternoon. Which, helping or imbibing? :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
wrote in message oups.com... Yuri Blanarovich wrote: Yuri wrote: You agree that impedance along the radiator changes, being low at the bottom, around tens of ohms, to being high at the top, around thousands of ohms. )Tom replied: )I never said that. What do you mean by reactance? The X can be very )high but radiation resistance very low even near the open end. I really give up. What's the point. This is a typical example of Tom's response to technical argument or trying to go step by step. I am talking impedance, he "knows" I mean reactance. As I said, I get better response from a brick wall. No wonder he duntgetit! Oh well! Yuri, Part of communicating is understanding the words the other person is using. I'm only trying to understand what you intend the words you use mean. Please don't blame me for trying to sort out what you are saying. If you mean "reactance", say "reactance" and not "impedance". If you mean "through", say "through" and not "across". Really good one Tom! Why twist and dance? If you don't know what the impedance is please read 2005 ARRL Handbook: page 4.42 Impedance (re Inductance) and page 22.1 Impedance (re Antennas) If we measure current drop from one end of the the coil to the other, we see current drop across the coil. (You would love "through" because you can then "prove" that if it flows through it has to be the same, right?) When you use "across", I guessed and thought you really meant "through" or "at each end". When you used "impedance", I couldn't guess and figure out if you meant the scalar impedance, vector impedance, resistance, reactance, or what. It could mean too many things. I meant freakantance, just could not express it :-) Nice try! Keep on twisting. Before you didn't get it, now you don't want to get it. Let's back off one more giant step back to measurements. Show where W9UCW was "cheating" in his test setup, pictures and comments at http://www.k3bu.us/loadingcoils.htm where he shows clearly that RF current drops significantly across (through) the loading coil, just like it drops across (through) the resonant antenna (piece of wire or tubing) from max at the base, to zero at the tip. I venture to say that (most) everybody knows that impedance of such resonant radiator is low, about few ohms, at the base to thousands of ohms at the tip. If you don't know or get that, no point of discussing current magnitude at the ends of the loading coil. 73 Tom 73 Yuri, K3BU |
Current across the antenna loading coil - from scratch
Cecil Moore wrote:
John Popelish wrote: Cecil Moore wrote: For instance, what is the current at the end of 200 feet of RG-58 terminated by a 50 ohm antenna used on 446 MHz when the source current is 2 amps? Somewhat less then 2 amps. Does "somewhat" cover 24 dB of losses? :-) The point is that the current "drops" by exactly the same amount as the voltage. That's a characteristic of distributed networks as opposed to lumped circuits. In a Z0 RF environment, the current has to "drop" by exactly the same amount as the voltage to maintain the Z0 ratio. There are really no "across" and "through" concepts as exist in DC circuitry. I guess I'm so dense that I need help in proving what you think I can prove with that information. Right now, I am apparently missing something, maybe because of too much California Merlot. Sounds like something I might do, this afternoon. Which, helping or imbibing? :-) Merlot is what we Californians ship to out of state Republicans in hopes of poisoning them into not voting in the next election. 73, Tom Donaly, KA6RUH |
Current across the antenna loading coil - from scratch
Cecil, W5DXP wrote:
"There is no phase information in standing wave current phase." Kraus and Terman agree with Cecil. Kraus writes on page 239 of his 1950 edition of "Antennas": "It is generally assumed that current distribution of an infinitesimally thin antenna (l/a=infinity) is sinusoidal, and that the phase is constant over a 1/2-wavelength interval, changing abruptly by 180-degrees between intervals." This agrees with Terman who writes on page 94 of his 1955 edition of "Electronic and Radio Engineering": "When the load impedance does not equal the characteristic impedance (as at the open-circuit at the standing-wave antenna tip), the phase relations are complicated by the presence of the reflected wave. The phase of the resulting voltage (or current) then oscillates about the phase of the voltage (or current) of the incident wave , as illustrated in Fig. 4-5.The phase shift under these conditions tends to be concentrated in regions where the voltage (or current) goes through a minimum;----." Pity the fool who argues with Kraus or Terman. Best regards, Richard Harrison, KB5WZI |
Current across the antenna loading coil - from scratch
John Popelish wrote:
Roy Lewallen wrote: John Popelish wrote: A point of clarification to John's posting: When a standing wave exists on a transmission line, the phase of the voltage or current is fixed (other than periodic phase reversals) with position only if the end of the line is open or short circuited. Otherwise, the phase of voltage and current will change with position. Is that because the result is not a pure standing wave (superposition of two equal and oppositely traveling waves), but a superposition of a pair of traveling oppositely traveling waves of different amplitudes? Yes, but I wouldn't put it quite that way. I prefer to say that this is simply a special case of the more general result you get when you sum forward and reverse waves. Nothing magical or abrupt happens when the two traveling waves are equal in amplitude -- if they're slightly different, you get a little phase shift of the total current with position along the wire, the current minima aren't quite zero, and the spatial shape of the amplitude of the total current -- that is, the shape of the standing wave -- isn't quite sinusoidal. Making the amplitudes more and more different smoothly transitions the nature of the total current until in the special case of the reverse traveling wave being zero you have the distribution of a pure traveling wave. Roy Lewallen, W7EL |
Current across the antenna loading coil - from scratch
Cecil Moore wrote:
Tom Ring wrote: wrote: Answer the question Cecil, how can we have charge movement over a small length of conductor (in terms of the wavelength) in two directions at the same time, or a drift velocity in two directions at once? Cecil and Co. are not interested in real physics, math, or engineering. They have made up their own. As I said to Roy, you may as well give up. Tom, I learned this stuff at Texas A&M in the 50's and it was decades old already, having been developed before I was born. Are you also willing to deny the existence of simultaneous forward and reflected EM waves? Nope, but that's not what you're arguing about. tom K0TAR |
Current across the antenna loading coil - from scratch
Tom Donaly wrote:
Merlot is what we Californians ship to out of state Republicans in hopes of poisoning them into not voting in the next election. What do you ship out to Libertarians? -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
Yuri Blanarovich wrote: Let's back off one more giant step back to measurements. Show where W9UCW was "cheating" in his test setup, pictures and comments at http://www.k3bu.us/loadingcoils.htm where he shows clearly that RF current drops significantly across (through) the loading coil, just like it drops across (through) the resonant antenna (piece of wire or tubing) from max at the base, to zero at the tip. Displacement currents in the inductor and the very high reactance of the very short antenna above the coil explain current difference. Current cannot vanish Yuri. It has to have an alternative path. I can change current difference at each end of the inductor all over the place depending on the design of the loading coil, with NO change in the loading coil position or antenna lengths. It is the theory you have, that the current is tied to the "missing degrees", that is wrong. Without displacement currents there is no current difference at each end of the coil, it is not caused by "missing degrees. It is caused by the capacitance above the coil being very low and the capacitance of the coil to the outside world being much larger. The current is not all gone in the first few turns either. It is a series reactance/shunt reactance problem. 73 Tom |
Current across the antenna loading coil - from scratch
Cecil Moore wrote:
Tom Donaly wrote: Merlot is what we Californians ship to out of state Republicans in hopes of poisoning them into not voting in the next election. What do you ship out to Libertarians? Libertarians don't believe in handouts. 73, Tom Donaly, KA6RUH |
Current across the antenna loading coil - from scratch
John Popelish wrote:
If we assume the coil is an idealized lumped inductance with no stray capacitance at all (not a real inductor) then it would have the same instantaneous current at each end and that current would be zero, since it has zero size. In other words it would fit entirely in the point that holds the node. Real inductors with stray capacitance and imperfect magnetic coupling for all parts of its internal current path, would have a phase shift in the current at opposite ends, so they would have current at their ends that was 180 degrees out of phase, if they were centered on the node points. For half of each cycle, current would be entering each end, and for the other half of each cycle, current would be leaving each end. Both those currents would detour out the sides f the inductor into displacement current through the stray capacitance of the surface of the inductor to its surroundings. I think (with very little actual knowledge of the software) this conceptual model is how EZNEC handles current through a modeled inductor and how it can have different currents at the inductor ends, without being aware of whether those currents are driven by traveling or standing waves. It is all based on current through inductor segments and voltage across capacitive segments. If the segments are small enough, it is a good approximation of a distributed solution. There are two ways of modeling an inductor in EZNEC. One is by using an inductive "load". This is a pure lumped inductance, which takes up zero physical space and whose currents are equal at its two terminals. It does not couple or react at all to its surroundings other than via its terminals, and its voltage-current characteristics are dictated by that of a pure inductance, v = L di/dt. For a number of reasons discussed many times here, this isn't a good model for many or most typical loading coils. The other way of modeling an inductor in EZNEC is by making it from conductors -- "wires" -- arranged in a polygonal helix. (EZNEC v. 4.0 provides an automated way to generate this structure.) These wires are treated exactly the same as all other wires in the model. As long as the turns aren't too close together (conservatively, closer than several wire diameters, but in practice good results are usually obtained with spacing as close as one diameter air space between wires), it does a very good job of calculating the inductor currents and radiation. (It's a little generous about loss if the turns are close because it doesn't account for proximity effect.) EZNEC calculates the total current by first calculating the self and mutual impedances of every segment in the model from a fundamental equation, then using Ohm's law to find the total current in each segment from those impedances and the voltages from the user specified sources.(*) It's not aware of traveling or standing waves. The presence or absence of standing waves -- that is, a changing magnitude of current with position -- can be seen by viewing its output. Displacement current is a consequence of mutual coupling between segments -- in a dipole, the dominant coupling is to the other half of the dipole, and in a grounded monopole, to ground. However, each segment couples to every other, even on its own wire, and it's this coupling which brings about the current distribution that ultimately occurs. EZNEC deals only with total currents and makes no effort to detect, use, or break up total current into individual traveling waves. It isn't aware of whether currents are "driven by traveling or standing waves" if for no other reason that no currents are ever "driven by" traveling or standing waves. Voltage differences cause currents which can be described as traveling waves. When multiple traveling waves are summed to find a total current, the amplitude of the sinusoidal current varies with position along the line, and this envelope is called a "standing wave". A standing wave is simply a description of the magnitude distribution of the total current along a wire or transmission line. It doesn't drive or cause anything -- it's a description of an effect, not a cause. All the fuss about standing waves is a diversion which confuses the issue and deflects attention from the salient issues involved in understanding the topic under discussion. (*) This is a simplified explanation. For details, see Part I of the NEC-2 manual. Roy Lewallen, W7EL |
Current across the antenna loading coil - from scratch
This is freakin unbelievable.
You think you are making fool of me and rest of us? You are not answering questions, nor engaging in the exchange. You keep pulling out crap, like first the current is equal, then "" I can change current difference at each end of the inductor all over the place depending on the design of the loading coil, with NO change in the loading coil position or antenna lengths." You are getting tangled in your own webs!!! Tell us what is wrong with W9UCW setup and results. Where did he screw up, what is wrong, and show what you have measured in THE SAME type of setup. Not freakin W8JI coils, not at the base, no weird frequency, not twist and dance. Just take 40m shorted vertical, make it resonant with DECENT coil like he has about 2/3 up the mast, stick the RF ammeters at both ends and give us the readings. You have the pictures, you should be able to replicate the setup. Then you tell us that the current is the same at both ends, show us the pictures and describe your setup, meters, frequency and results. This goes for the rest of the "gurus" that insist on the same. Then model the loading coil as a solenoid or loading stub of same inductance in EZNEC and show us what you get. Cecil did it, and the silence is deafening!!! Can you explain what is "wrong" with Cecil's examples? Looks like Belrose should get another pHDuuhh for starting all this misconception and misinformation in ham literature. Pathetic is that some of the "gurus" that should know better, are on the same bandwagon to la-la land. Stop crap and twist and dance, answer the freakin questions or say nothing. We are not idiots that you BS with "you don't know what I mean by impedance". So what happened to impedance? Now you know what it is, or is pink electron displacement capacitance current phasor phase mumbo jumbo? wrote in message ps.com... Yuri Blanarovich wrote: Let's back off one more giant step back to measurements. Show where W9UCW was "cheating" in his test setup, pictures and comments at http://www.k3bu.us/loadingcoils.htm where he shows clearly that RF current drops significantly across (through) the loading coil, just like it drops across (through) the resonant antenna (piece of wire or tubing) from max at the base, to zero at the tip. Displacement currents in the inductor and the very high reactance of the very short antenna above the coil explain current difference. Current cannot vanish Yuri. It has to have an alternative path. Have you heard of standing waves? I can change current difference at each end of the inductor all over the place depending on the design of the loading coil, with NO change in the loading coil position or antenna lengths. That is the progress, first current can't change, now you can make it. It is the theory you have, that the current is tied to the "missing degrees", that is wrong. Without displacement currents there is no current difference at each end of the coil, it is not caused by "missing degrees. It is caused by the capacitance above the coil being very low and the capacitance of the coil to the outside world being much larger. The current is not all gone in the first few turns either. It is a series reactance/shunt reactance problem. 73 Tom PRICELESS!!!!! So WHAT IS THE CURRENT AT THE TOP OF THE RESONANT 90 deg (any) VERTICAL? Same as at the base, because "Current can not vanish Yuri"? You are jerking our chain or have a real problem. Suggestion: do some reading on impedance, resonance, standing waves, current and voltage distribution along the antennas, and look at the current curves in books and as produced by EZNEC. Looks like you have no clue how antennas work. You can have another "last word" that will "show" that you "know" what you are talking about. 73 Yuri |
Current across the antenna loading coil - from scratch
wrote:
Current cannot vanish Yuri. It has to have an alternative path. Forward current is one amp at zero degrees. Reflected current is one amp at 180 degrees. That creates a standing wave current node where net current is zero. It has "vanished" due to superposition. -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
Roy Lewallen wrote:
EZNEC deals only with total currents and makes no effort to detect, use, or break up total current into individual traveling waves. Then, without effort, EZNEC accurately reports the presence of traveling waves or standing waves as can be seen from the graph of the EZNEC results at: http://www.qsl.net/w5dxp/travstnd.GIF The graph on the left is for traveling wave current. Its magnitude is fixed and its phase varies with wire length. Traveling wave phase can be used to determine the phase shift through the wire (or through a coil). The graph on the right is for standing wave current. Its phase is fixed and its magnitude varies with wire length. Standing wave magnitude can be used to determine the phase shift through the wire (or through a coil) by taking the arc-cosine of the magnitude. -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
Yuri Blanarovich wrote:
Just take 40m shorted vertical, make it resonant with DECENT coil like he has about 2/3 up the mast, stick the RF ammeters at both ends and give us the readings. You have the pictures, you should be able to replicate the setup. What is it you are after? I already posted, years ago, measurements at: http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm Then you tell us that the current is the same at both ends, show us the pictures and describe your setup, meters, frequency and results. I think what is happening here is you are getting angry and not paying attention to what people are saying. I've already said it is possible to have different currents at each end of a loading coil. What I disagree with you about is you seem to attribute that difference to some magical property related to the distribution of current based on electrical degrees the loading coil replaces or standing waves, and that is very simply and clearly wrong. Current cannot "drop" or be "dropped". It can be divided between paths, but it cannot vanish into thin air. The mechanism that allows current to change in an antenna is displacement current, and it comes from capacitance. The only thing wrong with Barry's setup is he uses large meters compared to the size of the coil, and they are invasive. The meter requires cutting the leads and adding a fairly large bulk into the system. I'd never use thermocoupler meters to measure high impedance systems, magnetic-field coupling systems can be smaller, have less distributed capacitance, and don't require rerouting leads. Current transformer systems are also more accurate and can have much better resolution, and can even be used to determine phase. Let's not let the measurement method overshadow the real disagreement, however. The real disagreement is you seem to be saying the missing area of antenna replaced by the inductor and standing wave patterns of current distribution in the antenna are what causes the loading coil to behave as it does. Barry also proposed that, if I am not mistaken. That is not true. The single thing that allows an inductor to have a current difference and phase shift in current along the coil or at each terminal is the capacitance of the coil to the outside world. That is why we would have to be very careful NOT to disturb the coil by mounting other large measurement devices on the coil. This goes for the rest of the "gurus" that insist on the same. The "gurus" you despise go back to Maxwell, who described displacement current: http://maxwell.byu.edu/~spencerr/websumm122/node72.html The term displacement current is not an invention of those you call "gurus". It is part of physics dating way back to the 19th century. THAT is why so many people are trying to tell you about displacement currents, it isn't to make you feel bad. You have to include displacement currents in any model, or you cannot have a current taper along the length of a conductor. Then model the loading coil as a solenoid or loading stub of same inductance in EZNEC and show us what you get. Cecil did it, and the silence is deafening!!! Can you explain what is "wrong" with Cecil's examples? Sure. His explanation of what is happening and the fact he picked a very special conditions just to satisfy a twisted theory. Roy showed in his models why Cecil's conclusions were wrong. Practical measurements will show the same thing. The ONLY thing that allows a conductor to have current taper along its length is displacment current. That is a function of the capacitance from that conductor to the world around that conductor compared to the impedance presented by the system beyond that point. It is NOT determined by standing waves. It is not determined by "missing length replaxed by coil". Looks like Belrose should get another pHDuuhh for starting all this misconception and misinformation in ham literature. Pathetic is that some of the "gurus" that should know better, are on the same bandwagon to la-la land. I'm not sure what motivates you to attack everyone, but at least you universally seem to hate almost everyone. Jack Belrose is a great guy and has contributed a great deal with his work. If you finmd something wrong with what he is saying, tell us what it is. Don't attack the person, point out the error. Stop crap and twist and dance, answer the freakin questions or say nothing. We are not idiots I suppose everyone has a right to their own opinions on that topic. I've done my best to answer the questions. I hope this post helps clarify things. Calm down, there is no need to get upset. Did this help answer your questions? 73 Tom |
Current across the antenna loading coil - from scratch
wrote:
I already posted, years ago, measurements at: http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm Those are RMS standing wave measurements. To see what is wrong with using RMS standing wave measurements please see: http://www.qsl.net/w5dxp/travstnd.GIF I think what is happening here is you are getting angry and not paying attention to what people are saying. I've already said it is possible to have different currents at each end of a loading coil. And there phase information in those standing wave current magnitudes. There is no phase information is standing wave current phase. What I disagree with you about is you seem to attribute that difference to some magical property related to the distribution of current based on electrical degrees the loading coil replaces or standing waves, and that is very simply and clearly wrong. No, it is your misconceptions about standing wave current that are very simply and clearly wrong. Current cannot "drop" or be "dropped". RF current drops with the attenuation factor, just like RF voltage does. Clinging to the lumped circuit model presuppositions is what causes you to make silly assertions like the above. Standing wave current periodically drops to zero in unterminated transmission lines. The single thing that allows an inductor to have a current difference and phase shift in current along the coil or at each terminal is the capacitance of the coil to the outside world. Is capacitance to the outside world also what allows a wire to have zero current at one point and two amps of current 90 degrees away. Of course not! The degrees of delay through the coil is primarily responsible for the difference in current. That, and where it is places on the standing wave current curve. You have to include displacement currents in any model, or you cannot have a current taper along the length of a conductor. We are talking about displacement current to earth ground and there is zero displacement current to the outside world ground yet there's SWR current taper on coaxial transmission lines. Maybe it's time for you to learn how to add phasors? Sure. His explanation of what is happening and the fact he picked a very special conditions just to satisfy a twisted theory. Roy showed in his models why Cecil's conclusions were wrong. Practical measurements will show the same thing. Roy used standing wave current phase to try to measure the delay through a coil. That's an invalid measurement. None of my conditions are special. They just seem special to your lumped circuit model. The distributed network model works for all conditions. -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
Roy Lewallen wrote:
Jack Belrose, VE2CV, is a highly respected engineer and scientist with an extensive and distinguished professional history. So are a lot of people who disagree with you. No one is always right, ... You have known for a year now that standing wave current phase cannot be used to determine the delay through a coil yet you continue to post those invalid results. Guess you are proof of your own statement. -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
Tom, W8JI wrote:
"The ONLY thing that allows a conductor to have current taper along its length is displacement current." In a-c circuits, added to ordinary conduction current there is displacement current, at right angles to the direction of propagation, determined by the rate at which the field energy changes. Also at right angles to the direction of propagation, and determined by the rate at which energy changes, there is a changing magnetic field, in addition to the changing electric field. Together the electric and magnetic fields exchange energy and produce radiation. Displacement current which is the a-c current through a capacitor, that has no d-c conduction, is not the"ONLY" thing that allows a conductor to have a current taper along its length.. A conductor can lose energy through dissipation and radiation forever, not just relocate it temporarily through storage in a reactance. The dissipation line at the end of a rhombic antenna does not handle the entire output of the transmitter at its other end. Most of the energy is already radiated by the time it reaches the dissipation line. Best regards, Richard Harrison, KB5WZI |
Current across the antenna loading coil - from scratch
Cecil Moore wrote:
We are talking about displacement current to earth ground and there is zero displacement current to the outside world ground yet there's SWR current taper on coaxial transmission lines. Maybe it's time for you to learn how to add phasors? Cecil, Sorry, you cannot pick and choose which displacement currents to consider. It might be helpful to go back to review the fundamentals of Maxwell's equations, including the continuity equation for current, before making these inane comments. 73, Gene W4SZ |
Current across the antenna loading coil - from scratch
Richard Harrison wrote:
Displacement current which is the a-c current through a capacitor, that has no d-c conduction, is not the "ONLY" thing that allows a conductor to have a current taper along its length.. Richard, That is incorrect, and even Terman never said such a thing. Charge is not created or destroyed. It either keeps moving as current, or it is stored. Charge storage is the equivalent of displacement current. The terminology is slightly confusing at times, but it has not changed for over 100 years. Detailed discussions of this topic are found in virtually every intermediate and advanced textbook on electricity and magnetism. 73, Gene W4SZ |
Current across the antenna loading coil - from scratch
Speaking as a lurker, I find Roy's and Tom's postings very educational and I
appreciate the time they take to do it. I am a little dense, but I think I have learned four key points (at least, key for me) from this material: 1. One can discuss transmission lines and antennas using pulse analysis or steady-state analysis. When these two are mixed together the results can be a mess. 2. When discussing "phase difference" we need to specify the two components that have the difference. (I.e., phase difference between the current into and out of an inductor is a different animal than the phase difference between current and voltage at a specific point.) 3. Superposition ("adding together") of power computations is not valid in reactive circuits. 4. Displacement current is as real as any other current when dealing with antennas and their components. (I cannot remember "displacement current" ever being mentioned back in the dark ages when I was in EE school. Perhaps the school should remain nameless.) Bill - W2WO |
Current across the antenna loading coil - from scratch
I'm very glad to hear that our postings are being read and considered.
Bill Ogden wrote: Speaking as a lurker, I find Roy's and Tom's postings very educational and I appreciate the time they take to do it. I am a little dense, but I think I have learned four key points (at least, key for me) from this material: 1. One can discuss transmission lines and antennas using pulse analysis or steady-state analysis. When these two are mixed together the results can be a mess. True. You can actually translate from one to the other, but it requires an FFT or its inverse. Attempts to mix the two nearly always leads to invalid conclusions. 2. When discussing "phase difference" we need to specify the two components that have the difference. (I.e., phase difference between the current into and out of an inductor is a different animal than the phase difference between current and voltage at a specific point.) Yes, although we can use an arbitrary reference as long as it's the same for all components. For example, if one current has a phase angle of 50 degrees relative to some arbitrary reference and the other has a phase angle of 30 degrees relative to that same reference, we know that the phase of the first relative to the second is 20 degrees. 3. Superposition ("adding together") of power computations is not valid in reactive circuits. It's never valid. Let me give you an example. Consider two AC or DC voltage sources, each of 10 volts amplitude, with their negative terminals connected together. (If they're AC, have them be of the same frequency and in phase.) Connect a 10 ohm resistor between their positive terminals. Superposition says that we can analyze the circuit with each source individually and the other one turned off (short circuited in the case of a voltage source), and add the results. What we get should be the same answer as a full analysis with both the sources on at the same time. So let's do it. Turn off source #2. The current from source #1 through the resistor is 1 amp. The voltage across the resistor is 10 volts. Now turn source #1 off and #2 on. The current through the resistor is 1 amp going the other way than before, or -1 amp. The voltage across the resistor is 10 volts, but in the opposite direction as before, or -10 volts. Adding the results gives a total of 0 amps through and 0 volts across the resistor. That's the right answer -- it's what we have when both sources are on. But now look at the power dissipated by the resistor. With only source #1 on, it's I^2 * R = 1^2 * 10 = 10 watts. With only source #2 on, it's (-1)^2 * 10 = 10 watts. The sum of the two is 20 watts, which is not the dissipation with both sources on. Superposition does not apply to power, period. If it ever seems to, it's only because of coincidence. Don't be confused by the "forward" and "reverse" power concept. This is not superposition and the concept must be used with great care to avoid reaching invalid conclusions. 4. Displacement current is as real as any other current when dealing with antennas and their components. (I cannot remember "displacement current" ever being mentioned back in the dark ages when I was in EE school. Perhaps the school should remain nameless.) It's a useful concept, but also has to be used with care because it isn't a real current consisting of movement of electrons. Current in one conductor creates a field which induces current in another conductor, making the current appear to have "flowed" from one conductor to the other. The classic example is of course current flow "through" a capacitor. "Displacement current" is a widely used term; it's in the index of the first four EM texts I grabbed from the bookshelf. Of an example of a parallel RC circuit in Kraus' _Electromagnetics_, he says, "The current through the resistor is a *conduction current*, while the current 'through' the capacitor may be called a *displacement current*. Although the current does not flow through the capacitor, the external effect is as though it did, since as much current flows out of one plate as flows into the opposite one." Displacement current appears in Ampere's law, one of the four Maxwell equations. In one formulation it has the quantity i + d(phi)e/dt on one side. The i is conduction current, and the derivative quantity is known as the displacement current. Roy Lewallen, W7EL |
Current across the antenna loading coil - from scratch
Not that I could fan the flames any more anyhow, but just what was the
original discussion about anyhow? As in Cecil says what, and those disagreeing with him say what? I'm curious how something that doesn't seem that complex can generate so many weeks of acrimony and vitriol! I don't know the answer - but then again, I'm not really sure what the question is. But I do know where to look it up.... - 73 de Mike KB3EIA - |
Current across the antenna loading coil - from scratch
Roy Lewallen wrote:
I'm very glad to hear that our postings are being read and considered. Bill Ogden wrote: Speaking as a lurker, I find Roy's and Tom's postings very educational and I appreciate the time they take to do it. I am a little dense, but I think I have learned four key points (at least, key for me) from this material: 1. One can discuss transmission lines and antennas using pulse analysis or steady-state analysis. When these two are mixed together the results can be a mess. True. You can actually translate from one to the other, but it requires an FFT or its inverse. Attempts to mix the two nearly always leads to invalid conclusions. 2. When discussing "phase difference" we need to specify the two components that have the difference. (I.e., phase difference between the current into and out of an inductor is a different animal than the phase difference between current and voltage at a specific point.) Yes, although we can use an arbitrary reference as long as it's the same for all components. For example, if one current has a phase angle of 50 degrees relative to some arbitrary reference and the other has a phase angle of 30 degrees relative to that same reference, we know that the phase of the first relative to the second is 20 degrees. 3. Superposition ("adding together") of power computations is not valid in reactive circuits. It's never valid. Let me give you an example. Consider two AC or DC voltage sources, each of 10 volts amplitude, with their negative terminals connected together. (If they're AC, have them be of the same frequency and in phase.) Connect a 10 ohm resistor between their positive terminals. Superposition says that we can analyze the circuit with each source individually and the other one turned off (short circuited in the case of a voltage source), and add the results. What we get should be the same answer as a full analysis with both the sources on at the same time. So let's do it. Turn off source #2. The current from source #1 through the resistor is 1 amp. The voltage across the resistor is 10 volts. Now turn source #1 off and #2 on. The current through the resistor is 1 amp going the other way than before, or -1 amp. The voltage across the resistor is 10 volts, but in the opposite direction as before, or -10 volts. Adding the results gives a total of 0 amps through and 0 volts across the resistor. That's the right answer -- it's what we have when both sources are on. But now look at the power dissipated by the resistor. With only source #1 on, it's I^2 * R = 1^2 * 10 = 10 watts. With only source #2 on, it's (-1)^2 * 10 = 10 watts. The sum of the two is 20 watts, which is not the dissipation with both sources on. Superposition does not apply to power, period. If it ever seems to, it's only because of coincidence. Don't be confused by the "forward" and "reverse" power concept. This is not superposition and the concept must be used with great care to avoid reaching invalid conclusions. 4. Displacement current is as real as any other current when dealing with antennas and their components. (I cannot remember "displacement current" ever being mentioned back in the dark ages when I was in EE school. Perhaps the school should remain nameless.) It's a useful concept, but also has to be used with care because it isn't a real current consisting of movement of electrons. Current in one conductor creates a field which induces current in another conductor, making the current appear to have "flowed" from one conductor to the other. The classic example is of course current flow "through" a capacitor. "Displacement current" is a widely used term; it's in the index of the first four EM texts I grabbed from the bookshelf. Of an example of a parallel RC circuit in Kraus' _Electromagnetics_, he says, "The current through the resistor is a *conduction current*, while the current 'through' the capacitor may be called a *displacement current*. Although the current does not flow through the capacitor, the external effect is as though it did, since as much current flows out of one plate as flows into the opposite one." Displacement current appears in Ampere's law, one of the four Maxwell equations. In one formulation it has the quantity i + d(phi)e/dt on one side. The i is conduction current, and the derivative quantity is known as the displacement current. Roy Lewallen, W7EL Not everyone is happy with the term "displacement current." Albert Shadowitz, in his book _The Electromagnetic Field_, has a chapter entitled "The So-called Displacement Current." The term isn't in the index to Feynman's _Lectures on Physics_. (At least I couldn't find it.) All that is academic to the fact that AC current seems to be able to make its way through a capacitor with no more opposition than the capacitive reactance. Fortunately, no one on this newsgroup has any objection to the way the term is commonly used. 73, Tom Donaly, KA6RUH |
Current across the antenna loading coil - from scratch
Check my article that describes the controversy, shows some proof of reality
and then efforts of the "gurus" to deny it and "reason" why it can't be so. http://www.k3bu.us/loadingcoils.htm The problem is that back in 1953 in QST article there was erroneous conclusion/statement made, which propagated through the books, until W9UCW measured the current across the loading coils and found that there is significant drop from one end to the other, and the rest is (ongoing) history Yuri, K3BU.us "Michael Coslo" wrote in message ... Not that I could fan the flames any more anyhow, but just what was the original discussion about anyhow? As in Cecil says what, and those disagreeing with him say what? I'm curious how something that doesn't seem that complex can generate so many weeks of acrimony and vitriol! I don't know the answer - but then again, I'm not really sure what the question is. But I do know where to look it up.... - 73 de Mike KB3EIA - |
Current across the antenna loading coil - from scratch
Richard Harrison wrote:
A conductor can lose energy through dissipation and radiation forever, not just relocate it temporarily through storage in a reactance. The dissipation line at the end of a rhombic antenna does not handle the entire output of the transmitter at its other end. Most of the energy is already radiated by the time it reaches the dissipation line. For instance, consider 100 ft. of 50 ohm coax with losses of 3 dB driving a 50 ohm load from a source of 200 watts. At the source, we have 100 volts at 2 amps. At the load, we have 70.7 volts at 1.414 amps. The current dropped by exactly the same amount as the voltage. Hint: The V/I ratio must be maintained at 50 ohms for flat lines. Anyone who doesn't understand RF H-field (current) drop in a lossy transmission line has probably been so seduced by his lumped circuit model that he thinks the model dictates reality instead of vice versa. -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
Gene Fuller wrote:
Sorry, you cannot pick and choose which displacement currents to consider. Why not? All I (and probably Yuri) have ever been considering are displacement currents to earth ground from the coil. That is the only current flowing sideways from the coil to ground. -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
Tom Donaly wrote:
Not everyone is happy with the term "displacement current." Albert Shadowitz, in his book _The Electromagnetic Field_, has a chapter entitled "The So-called Displacement Current." The term isn't in the index to Feynman's _Lectures on Physics_. (At least I couldn't find it.) All that is academic to the fact that AC current seems to be able to make its way through a capacitor with no more opposition than the capacitive reactance. Fortunately, no one on this newsgroup has any objection to the way the term is commonly used. 73, Tom Donaly, KA6RUH That's interesting. It prompted me to look at my other electromagnetics texts. Of the eight I have (Johnk, Jordan & Balmain, Kraus, Ida, Majid, Holt, Ramo et al, and King), all include displacement current in the index and all discuss the concept. Only King objects to its use, although he notes that "The second term [in Ampere's law] was called the 'displacement current' by Maxwell, and this name continues to be used." He goes on to say that "Actually this terminology is unfortunate because the word displacement belongs to the old ether model and because the word current means specifically moving charge." He adds further reasons for his objection in the following paragraphs. With a copyright date of 1945, King's book (_Electromagnetic Engineering_, Vol. I) is the oldest of the texts I have. Perhaps the term has become more acceptable as time has passed. I do see why physicists such as Feynman wouldn't be accepting of the term. As I mentioned in my earlier posting, it does need to be used with care. We have to always keep in mind that it isn't a real current and therefore doesn't always behave like one. But it is a useful concept as long as we stay aware of its limitations. Roy Lewallen, W7EL |
Current across the antenna loading coil - from scratch
Michael Coslo wrote:
Not that I could fan the flames any more anyhow, but just what was the original discussion about anyhow? As I realized what the actual misconception really is, the discussion shifted from coils to standing waves. Seems to me, W8JI and W7EL do not understand the difference implied by these two different equations (assuming |Ifor|=|Iref|). Ifor = I1*cos(kx+wt) and Iref = I1*cos(kx-wt) Istnd = I1*cos(kx+wt) + I1*cos(kx-wt) = I2*cos(kx)*cos(wt) Gene Fuller has kindly explained the difference but W8JI and W7EL seemed to have ignored his explanation. Gene says there is no phase information in standing wave current phase and I agree. As in Cecil says what, and those disagreeing with him say what? Looking at: http://www.qsl.net/w5dxp/travstnd.GIF I say the RMS standing wave current's unchanging phase on the right hand graph, cannot be used to measure phase. W7EL continues to report those phase measurements as valid indicators of delay through coils when installed in standing wave environments. I say all the phase information in the standing wave current is in its magnitude which is a cosine function as explained in Kraus and Terman. W8JI and W7EL both dismiss the phase information in the standing wave magnitude and insteadtrust the standing wave phase to yield valid delay measurements. I'm curious how something that doesn't seem that complex can generate so many weeks of acrimony and vitriol! I don't know the answer - but then again, I'm not really sure what the question is. But I do know where to look it up.... Now you know what the argument is about. Seems to me, W8JI, W7EL, and others possess misconceptions caused by assuming the unproven presuppositions of their lumped circuit model. They "prove" their misconceptions by making measurements known to be invalid. I can't tell if they are aware of what they are doing or not. If you know where to look for the answer, please tell us. I have looked and only found a clear explaination in "Optics" by Hecht. A side argument is whether standing wave current can drop to zero at a node in an unterminated transmission line. W8JI continues to assert that current cannot drop without some imagined third path. -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
Tom Donaly wrote:
Not everyone is happy with the term "displacement current." Albert Shadowitz, in his book _The Electromagnetic Field_, has a chapter entitled "The So-called Displacement Current." The term isn't in the index to Feynman's _Lectures on Physics_. (At least I couldn't find it.) All that is academic to the fact that AC current seems to be able to make its way through a capacitor with no more opposition than the capacitive reactance. Fortunately, no one on this newsgroup has any objection to the way the term is commonly used. Here's an associated quote from "Electromagnetic Engineering" by R.W.P King: "an adequate representation of the reactance of a coil with a nonuniformly distributed current is NOT POSSIBLE in terms of a coil with a uniform current [a lumped- element inductance] connected in parallel with a lumped capacitance." -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
Cecil Moore wrote:
Gene Fuller has kindly explained the difference but W8JI and W7EL seemed to have ignored his explanation. Cecil, Give it up on this line of baloney. There is not the slightest bit of disagreement on the nature of traveling waves and standing waves. The only person who was ever appeared to be confused was you. I am happy that you seem to now have at least partial understanding. 73, Gene W4SZ |
Current across the antenna loading coil - from scratch
Gene Fuller wrote:
"This is incorrect, and even Terman never said such a thing." I had written: "Displacement current which is the a-c current through a capacitor, that has no a-c conduction, is not the "ONLY" thing that allows a conductor to have a current taper." It was Tom, W8JI who shouted: "The ONLY thing etc." I just said displacement current is NOT the only thing. Energy level often declines between ends of a wire or coil due to losses from radiation or dissipation in the wire or coil. Tom is mistaken. I don`t find the subject of "displacement current" listed in my Terman`s index. I think its definition is accepted. but I gave mine in case someone did not understand what it is. J.C. Maxwell unlocked the secret of radiation when he speculated displacement current would produce magnetic lines of force the same as conduction current does, thus a traveling E-field produces an H-field and vice versa. It`s been proved correct. Terman writes on page 1 of his 1955 edition: "Electrical energy that has escaped into free space exists in the form of electromagnetic waves. These waves, which are commonly called radio waves, travel with the velocity of light and consist of magnetic and electric fields that are at right angles to each other and at right angles to the direction of travel." Terman writes on page 866 of his 1955 edition in his chapter on "Antennas": "A wire antenna is a circuit with distributed constants; hence the current distribution on a wire antenna that results from application of a localized voltage follows the principles discussed in Chapt. 4, (titled"Transmission Lines") and depends upon the antenna length; mesured in wavelengths; the terminations at the ends of the antenna wire; and the losses in the system." Nothing I wrote conflicts with Terman. That`s not the kind of fool I am. Best regards, Richard Harrison, KB5WZI |
Current across the antenna loading coil - from scratch
Yuri Blanarovich wrote: Check my article that describes the controversy, shows some proof of reality and then efforts of the "gurus" to deny it and "reason" why it can't be so. http://www.k3bu.us/loadingcoils.htm Yuri, I know you aren't going to like to hear this, but your article incorrectly claims the current difference (you call it current drop) is related to the electrical degrees the coil replaces. That is not accurate. ON4UN's book was initially incorrect. Consider a short vertical antenna. If the current is uniform through toploading, radiation resistance is higher and current lower throughout the radiator. If it is base loaded, current becomes nearly triangular in distribution. Current into the vertical actually doubles so we have the same number of ampere-feet. It always requires the same number of ampere feet to radiate the same power as EM radiation. The job of the inductor in either system is simply power factor correction, to bring voltage and current into phase. We have a large voltage drop across the coil, but current does not change. phase shift and delay of current through the inductor will also be very small, zero in a perfect coil. That is in an ideal antenna with very small stray capacitance to the outside world compared to the antenna area above the coil. If we have a physically large coil, the coil MIGHT have significant capacitance compared to the antenna area above the coil. In this case there would be a difference in current between the bottom and top terminal of the coil, and there would be phase difference in the current entering and leaving the coil, but it is a result of current being shunted off through displacement currents. The exact amount would depend on the physical size of the coil and the capacitance compared to the antenna above the coil. There is not any magic to any of this, and we don't need to have standing waves. It is incorrect to consider the coil behavior and antenna currents by making the coil "act like" it has the missing electrical dgrees or replaces a section current curve in the antenna. I can have one antenna and use a good coil design that has essentially no current difference at each terminal, and replace it with a very large (or poorly designed) diameter coil that has large differences in current at each end. Probably the ultimate in poor coil design for base loading is a linear loading system or stub, while the best would be a compact coil with nearly equal diameter to length. The very fact we can change distribution all over the place with only a change in loading inductor design proves your theory incorrect. Please try to not extract certain sentences from long explainations to distort the overall picture of what really happens, and of what I am describing. The fact is, we cannot model or predict the behavior of a loading system without knowing the displacement currents. Neither wave theory nor "missing antenna length" theory will paint the correct picture of what is going on, and neither will give an accurate answer to a wide variety of real world systems. By the way, this did not start with Belrose and it is not a QST or Handbook problem. The Antenna Engineering Handbook by Jasik and dozens of other college or engineering textbooks all deal with the problems the same way. If you are looking to libel anyone, you need to go all the way back to James C. Maxwell in the 19th century. It was before the Civil War that the "big error" you and Barry found started. I guess it all comes down to if Barry and Yuri are right, or if nearly every professor, scientist, and engineer from Maxwell to today are correct. I can measure ANY antenna and prove things behave as I described. Can you do the same? 73 Tom |
Current across the antenna loading coil - from scratch
Mike,
The question changes continuously. As soon as one myth is exploded Cecil slides right into another. The original topic dealt with currents in a loading coil for a mobile antenna. However, the technical part of that discussion ended a long time ago. Only the sniping remains. 73, Gene W4SZ Michael Coslo wrote: Not that I could fan the flames any more anyhow, but just what was the original discussion about anyhow? As in Cecil says what, and those disagreeing with him say what? I'm curious how something that doesn't seem that complex can generate so many weeks of acrimony and vitriol! I don't know the answer - but then again, I'm not really sure what the question is. But I do know where to look it up.... - 73 de Mike KB3EIA - |
Current across the antenna loading coil - from scratch
Gene Fuller wrote:
Cecil Moore wrote: Gene Fuller has kindly explained the difference but W8JI and W7EL seemed to have ignored his explanation. Give it up on this line of baloney. There is not the slightest bit of disagreement on the nature of traveling waves and standing waves. On the contrary, you must not have read W7EL's recent posting where he again presented his coil delay "measurements" using the standing current phase as a measurement reference. Remember, the current you said contains no phase information? Maybe you should share your knowledge with W7EL? The only person who was ever appeared to be confused was you. I am happy Regarding the cos(kz)*cos(wt) term in a standing wave: When you made your posting, you reinforced my argument better than any other reference. I am very happy with your posting and cannot thank you enough. I will continue to use it as one of my best references for the invalidity of W7EL's coil delay measurements. Gene Fuller, W4SZ wrote: In a standing wave antenna problem, such as the one you describe, there is no remaining phase information. Any specific phase characteristics of the traveling waves died out when the startup transients died out. Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be seen again. The only "phase" remaining is the cos (kz) term, which is really an amplitude description, not a phase. -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
wrote:
I know you aren't going to like to hear this, but your article incorrectly claims the current difference (you call it current drop) is related to the electrical degrees the coil replaces. That is not accurate. The current drop in a wire with standing waves is indeed related to the number of degrees occupied by the wire. Why shouldn't the same thing be true for a coil? Consider a short vertical antenna. Consider a 1/4WL vertical antenna. The current drop is a function of the cosine of the number of degrees one moves away from the source. The same thing is true for a helical antenna. The same thing is true for a half helical - half wire antenna. I guess it all comes down to if Barry and Yuri are right, or if nearly every professor, scientist, and engineer from Maxwell to today are correct. I can measure ANY antenna and prove things behave as I described. Can you do the same? 1. You assume the unproven presuppositions of your lumped circuit model with a religious-like fervor. 2. You make invalid measurements using standing wave current whose phase contains no phase information. All the phase information is known to be in the magnitude measurement, but you dismiss any of the proven arc-cosine calculations as bogus. With misconceptions and invalid measurements, it is no wonder that you can prove anything in the world even when it violates the laws of physics. -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
Gene Fuller wrote:
The question changes continuously. As soon as one myth is exploded Cecil slides right into another. Would you rather discuss something for which no disagreement exists, or discuss the real point of disagreement? It is apparent to me that the problem is not with coils. The same point of disagreement exists whether a coil is present or not. That point of disagreement involves standing waves, not coils. Take away the coil and the misconception still exists when discussing only a straight wire. W8JI is still maintaining that the current cannot drop to zero at a standing wave current node when the forward current and reflected current are of the same magnitude. That is obviously the point of misconception and it has been clear ever since he refused to discuss zero amps at the bottom of the coil and 2 amps at the top of the coil. Replace the coil with a straight wire and W8JI still has that same misconception. So you see the coil is not the source of the disagreement. -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
Hi Richard,
My point is in complete agreement with Tom, W8JI. The only thing that allows "current taper" is displacement current. Conservation of charge is one of the most fundamental laws in nature. The historical basis for referring to storage of charge in a capacitor as "displacement current" is considered incorrect today. However, the underlying physical science remains intact. "Current taper" means that charge stops moving as current and becomes stored in a capacitor. (Everything has capacitance; there is no requirement for a little lump with two leads on it.) It is this charge storage phenomenon that is known as displacement current. Energy levels and losses have nothing to do with this question. 73, Gene W4SZ Richard Harrison wrote: Gene Fuller wrote: "This is incorrect, and even Terman never said such a thing." I had written: "Displacement current which is the a-c current through a capacitor, that has no a-c conduction, is not the "ONLY" thing that allows a conductor to have a current taper." It was Tom, W8JI who shouted: "The ONLY thing etc." I just said displacement current is NOT the only thing. Energy level often declines between ends of a wire or coil due to losses from radiation or dissipation in the wire or coil. Tom is mistaken. |
Current across the antenna loading coil - from scratch
Cecil,
Your own calculations would appear to support Tom's assertion. I believe after a long series of EZNEC models and RRAA messages you came to the conclusion that the 75 meter bugcatcher coil at 4 MHz had a traveling wave phase shift of around 10 degrees. I won't get into the discussion about whether this has any bearing on a standing wave antenna; let's just assume it does. This same coil resonated an antenna with a whip length of 10 feet or so. A quarter wavelength at 4 MHz is around 60 feet. The phase shift that could be attributed to the whip is therefore around 15 degrees. The phase shift of the missing 50 feet of wire for a plain quarter wave antenna would be around 75 degrees. Is 10 degrees the same amount as 75 degrees? Is this problem stated incorrectly? Why is Tom wrong? 73, W4SZ Cecil Moore wrote: wrote: I know you aren't going to like to hear this, but your article incorrectly claims the current difference (you call it current drop) is related to the electrical degrees the coil replaces. That is not accurate. The current drop in a wire with standing waves is indeed related to the number of degrees occupied by the wire. Why shouldn't the same thing be true for a coil? |
| All times are GMT +1. The time now is 07:01 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com