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Loading Coils; was : Vincent antenna
John Smith wrote:
"So, a summary of your point?" The velocity of the wave traveling on the turns of a coil is slightly less than 300 million meters per second. Divide the number of meters of wire in your coil by 300,000,000 and you get the number of seconds required for the signal to get from one end to the other on the coil, almost. Actual delay is slightly more because material surroundings slow the wave a little more than a vacuum does. There is no magic instantaneous transfer of energy from one turn to another within a coil. If there were, Terman would have told us so. Best regards, Richard Harrison, KB5WZI |
blah, blah, blah... was Loading Coils; was : Vincent antenna,superposition, etc.
Dave wrote:
[usual chit] Better yet, why don't you go and found rec.radio.amateur.conventional-antennas ??? Your donkey would be sorely missed here; But, we would get by, as you bored yourself and others to death ... Oh yeah, make sure you unsubscribe from this news thread. :-) Regards, JS |
Loading Coils; was : Vincent antenna
On 1 Dec, 13:44, Owen Duffy wrote:
"AI4QJ" wrote : Hi Owen, First of all I said in the post that I was using EE101. Skin effect is somewhere in EE201; it is not generally considered necessary to consider RF skin effect when explaining fundamental principles. After Tom reported the measured Q of the coil... you didn't need to calculate R from first principles. you brought it up I merely went on to illustrate that no matter what worse case skin effect you could resonably think of, the phase angle No, you guessed could it be twice, quadruple. A Max Smart approach, "would you believe... ". Tom's measurements suggest over ten times. Sure, even at ten times, it doesn't affect your result, but it does speak to the rigour of your analysis. will still be essentiall 90 degrees for all practical purposes. When talking about the COIL (not a mobile antenna system at 4MHz), it was important for the sake of discussion to be talking about 90 degrees because a true amateur antenna will be not be so perfect. The discussion at hand was W8JI's coil, not an antenna. At the end of the day, it appears to me you are working up the relationship between the phase of the current through the coil with voltage across the coil, and you seem to regard the phase of the current to be uniform at all points in the coil. If I understood Tom's article correctly (and it too is short on detail), he is comparing the phase of the current at one end of the coil with the phase of the current at the other end of the coil. You are not on the same page! But, as I said, the rigour isn't there for what is being touted as just a maths problem. Agreed, it is not an unfamiliar technique to make reasonable assumptions when illustrating a point. Thank you for the opportunity to confirm my assumptions valid in this case. No, I did not confirm anything. Now that you force the issue, I disagree with most of what you said in the posting to which I responded. Owen Cecil, Nobody here is willing to say they were wrong. It is not education that they demand, just a place on the net where they can complain. If collectively they debated point by point and resolving as they move along things could be solved. But that is not on the agenda or addresses their needs. All just want to be on the majority side if a poll is taken for security. Art |
Loading Coils; was : Vincent antenna
On Sat, 1 Dec 2007 18:45:52 -0500, "AI4QJ" wrote:
"Richard Clark" wrote in message .. . I am not convinced of that you know how to read at all. So the answer is "no", you cannot verbalize the discussion in English. Hi Dan, This is, after all, a written communication. In English, verbalization is an auditory utterance, which is completely impossible to perceive in this forum. There are other meanings which allow for you to be asking me to submit a script written entirely in verbs. I don't think that would be any more productive. What I have written certainly isn't in French (unless it would aid your comprehension). Let's face it, you don't stand a chance in head-to-head competition over deconstructing English. I note you continue to assign me my response when what I've offered does not fit the script. Emotion still dominates your forced logic here. You might be surprised (and it surprises me if you are surprised) to find few to none here would ever label me as being unable to -um- verbalize. I believe we are discussing the delay characteristic of current in a coil. Would you be surprised if Cecil and Art diverged even at this point? What would be the point of supporting them when they abandon you? I dearly would like to see them sign on to the notion that a coil has some inherent, fixed delay characteristic such as you describe (you are describing that aren't you, now's the time to correct this mistake of mine if I have made one). I would assume if I was as far off in what I think the topic is supposed to be, you or others would have jumped in to tell me AND TOLD ME WHAT THE ACTUAL CONTROVERSY IS ALL ABOUT. As already having done that, what purpose would repeating it serve? After all, if you once asked what my point was, and then you went on to ignore my explicit answer, what faith would I have that even more repetition would spare us? IF I am guilty misunderstanding the nature of the controversy, you may not believe this but it actually will not make me lose confidence in myself (shudder). Melodrama suitable for day-time TV now that the writers are on strike. You are ready to throw me out of the sacred RRAA nesting place? Not me, you have to satisfy Art and Cecil. Do you really think you are out of the woods with straining to explain what they have to offer? Frankly, Dan, you don't have the slightest understanding of what they are talking about. Now, that is not a flame because no else does either, and neither do they. If this was first principles from them (or you), the thread would be only three postings long. Just look at the single sentence of yours quoted above that survives from my reflection of your question back to you. I see absolutely no discussion of Cecil's centerpiece of Velocity Factor. You are entirely silent when it comes to how the impedance discontinuity between the coil and stinger contributes the rest of the 90 degrees of electrical length. Dare you discuss how as long as the frequency is kept constant, the VF and Z0 of coil stock will be relatively constant? [This last quote drawn from Cecil is one of those zingers that says nothing using a lot of words - if the frequency doesn't change, wouldn't the frequency determinate characteristics stay the same anyway?] So, you misunderstand what this is all about? You haven't even touched the surface! Basically, catch up, get a move on, or move over, because this isn't a math problem. I invite you to flesh out your explanation if you have more to offer than the stale 3.5nS myopic target of opportunity. Proving Tom was/is/might be wrong there doesn't change the basic flaw of this thread. 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
On Sat, 1 Dec 2007 17:15:05 -0800 (PST), art
wrote: All just want to be on the majority side if a poll is taken for security. What could be more revered than a minority of three on Calvary? 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
On Sat, 1 Dec 2007 16:49:44 -0800 (PST), art
wrote: Yup. He was found to be insane and put in the Tower. You must've burnt your history books when you left. This is not a reference about Heß (do you really believe he was going to lead a Putsch against Hitler?). Rudolph Heß parachuted into Scotland 2 years after Chamberlain returned from Munich. Germany did not want interference by Gt Britain. Hitler and the Nazi party didn't, certainly. Reasonable (not insane) Germans went to Chamberlain for support. Iran came to us in 2003 ready to abandon their nuclear program, we have our own Chamberlains that decided that we weren't going to negotiate that. The same Chamberlains abandoned the North Korean protocols of 1993 to de-nuclearize; after 7 years, and one bomb test, they have since decided to write up new treaties for less guarantees. Our Chamberlains were informed by India that they were going to ramp up their nuclear program, our Chamberlains asked if we could help. There are several countries in the world that, with existing stockpiles, are only weeks away from deliverable munitions. They are watching our power evaporate. Our Chamberlains shrug their shoulders in the standard Munich salute: "Learn to live with it" as Rummy would say. 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
On Sat, 1 Dec 2007 17:01:17 -0800 (PST), art
wrote: On 1 Dec, 13:11, Richard Clark wrote: On Sat, 1 Dec 2007 12:28:06 -0800 (PST), art wrote: On 1 Dec, 11:46, Richard Clark wrote: On Sat, 1 Dec 2007 14:15:14 -0500, "AI4QJ" wrote: Even Richard the Guru agreed that this could not be true. Hi Dan, I did? .................................................. ......................... Such is the seduction of confirmatory bias over the explicit answer to . an explicit question. I warned you about overly elaborate questions. . . Imagine, many here wail over my exacting answers demanding something . shorter. The same crowd wails when I comply! Clearly their grief is . because either response plunges a stake into the corpse of logic they . have been trying to revive. . .................................................. .........................-.. REMOVED FOR THE SAKE OF BREVITY.....NOT SURE WHY THAT WAS INCLUDED Not agreeing is NOT the same as disagreeing. .................................................. .........................-..... . Does my status as Guru follow the ephemeral tide of celebrity for . supporting a cause? I could be called a fool for the same reason. I . willingly allow either to be attached to me (it is a conceit of . others, not mine; mine are far above that ordinary rank). . . posters stay humble, even decimal point errors, should they . be so bold as to actually back up their statements with "math" (a black art . for many) ;-) . . English is much more difficult than math. That is why this is not a . math problem. It isn't exactly an English problem, but both language . and math have been prostituted to serve a clumsy argument with loading . coils. Cecil is especially prone to tripping over pebbles in the road . and exclaiming they are intellectual boulders. . . It is fun to watch, however. Tragedy viewed from a distance is called . comedy. Without it, lurkers would evaporate, discussion would wither, . and this group would flicker out. . .................................................. .........................-..... REMOVED FOR THE SAKE OF BREVITY DON'T KNOW HOW THAT GOT IN TO THIS DEBATE Se Richard, two lines got the job done.Next time concentrate on technical substance if you are aware of any Hi Arthur, You simply reposted my entire reply. Which two lines did you actually read? (I won't comment on your sense of brevity.) 73's Richard Clark, KB7QHC- Hide quoted text - - Show quoted text - No,I enclosed all but two lines as not being relavent to the subject at hand, This quote above obviously reveals otherwise - twice now! Would a third time be a charm? This is like a drawing for the lottery. Which two lines was it? I look forward to seeing if my ticket wins. ;-) 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
Art wrote:
"He was found to be insane and put in the tower." Rudolph Hess was thought to be insane and put away for life after piloting an aircraft to London. I had never heard that Hess was a messenger from the German High Command. Considering the message, he should have been respected. Ambassador Joe Kennedy`s assessment wasn`t far off the mark. Without massive foreign help, Hitler`s disregard of his general staff, and his premature panic attack of the Soviet Union, when his forces were already fully occupied, the Battle of Brittain would have been lost by the British. The apes on Gibralter and the crows in the Tower of London would have been of little help. Hitler`s forces had excellent training and equipment. They were also accustomed to winning and quickly too. Thankfully, Hitler made mistakes which doomed his enterprise. Best regards, Richard Harrison, KB5WZI |
Loading Coils; was : Vincent antenna
Richard Harrison wrote:
... There is no magic instantaneous transfer of energy from one turn to another within a coil. If there were, Terman would have told us so. Best regards, Richard Harrison, KB5WZI Richard: Thanks, got you now, and of course, no disagreement here. However, if anyone has a view to the contrary, I would be interested in the specifics ... However, there is something akin "special case" which does come to my mind: Say a two turn coils' configuration was changed to two single turns ... somehow, even if insignificant, this same interaction of what is occurring in one turns must be "felt" by the two turn coil. (crud, I hope you can "decode" that ...) What say you? Regards, JS |
Loading Coils; was : Vincent antenna
"AI4QJ" wrote in
: "Owen Duffy" wrote in message ... "AI4QJ" wrote in : I say that the phase relation MUST be the same everywhere on the coil. That does not seem to me to support Cecil's proposition at all, I understand Cecil to argue that there is a substantial phase change in the coil current along the coil. That didn't come out very clearly. As I understand it, Cecil argues that there is substantial phase change in the forward and reflected wave components when considering the helix as a transmission line. Owen |
Loading Coils; was : Vincent antenna
On Sat, 1 Dec 2007 21:47:47 -0500, "AI4QJ" wrote:
I dearly would like to see them sign on to the notion that a coil has some inherent, fixed delay characteristic such as you describe (you are describing that aren't you, now's the time to correct this mistake of mine if I have made one). In an inductor, current lags voltage. If you connect a resitor and a coil in parallel and apply AC, EE101 tells you that, although the phase of the voltage across them stays the same, the current is "delayed" by the phase angle in the inductor when compared to current in the resistor. So, yes, in this very fundamental sense there is a fixed delay. If this weren't so, I assure you the world we live in just wouldn't be the same and there would be no such thing as ham radio ;-)) Hi Dan, I will then proceed to interpret this as to mean I made no mistake, and a coil (not a coil and resistor, nor a coil and something else, I did not ask about externalities) exhibits a fixed delay. Elaboration is equally unnecessary. Correct me if you meant something else; but, please and again, do not inject other issues into what I have written. If you feel that you must, I have to say this is not what is being discussed and that your concerns are not representative of the topic. I have no interest in belaboring the obvious. Do you, or can you (as has Cecil, and presumably Arthur) assign an immutable angle (at one frequency) value that is inherent in Tom's or Cecil's coil? I care little if it is correct, demonstrable, or can be derived from any principles - simply can you offer a fixed quantifiable? If you find this a strange request, then I would again suggest you have missed the boat. This is not a flame, because it sank a long time ago with all hands on board. 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
On 1 Dec, 18:03, (Richard Harrison) wrote:
Art wrote: "He was found to be insane and put in the tower." Rudolph Hess was thought to be insane and put away for life after piloting an aircraft to London. I had never heard that Hess was a messenger from the German High Command. Considering the message, he should have been respected. Ambassador Joe Kennedy`s assessment wasn`t far off the mark. Without massive foreign help, Hitler`s disregard of his general staff, and his premature panic attack of the Soviet Union, when his forces were already fully occupied, the Battle of Britain would have been lost by the British. From a vantage point afar from danger you under estimate the British. You would have all surrender without a fight? Your admiration of the german army in its quest to deny freedom to the masses is certainly a shock to me. You have lost all respect by thumbing your nose at those who gave of their lives for the cause of freedom while others stood by aloof. Not once did I see a mustang in the air as the luftwaffe excersed their might during those early years. In fact, I did not see one plane from the army air force during those years,only hurricains and spitfires. But I am glad the U.K. was free and able to supply landing space when the enemy turned its eyes away from our shores and thus dashed your hopes. The enemy airforce by that time had become just a shadow of it's former self when the battle of Britain was decided leaving them nothing to provide a blitzcreeg prior to any advance that had proved succesful before. To cross the English channel in a time of war has never been easy no matter which direction one is travelling, history proves that. The apes on Gibralter and the crows in the Tower of London would have been of little help. Hitler`s forces had excellent training and equipment. They were also accustomed to winning and quickly too. Were you wearing a uniform supplied by Germany at that time? Thankfully, Hitler made mistakes which doomed his enterprise. Best regards, Richard Harrison, KB5WZI |
Loading Coils; was : Vincent antenna
*Here is another way of looking at the coil current.* Every wave must start with a wave front, some kind of initial small step increase in the voltage and current. This initial increase in voltage and current must enter the coil by charging the space around the wire to some voltage, which requires current to complete. This requires power and effectively 'charges' some length of coil wire to some energy level, identical to charging a capacitor. The initial wave front is moving, so we can think of the capacitor (wire) behind the wave front as being charged and the capacitor in front of the wave front as being uncharged. As the wave front enters the coil, a small initial length of the coil will be charged, with the stored energy located at a radial distance from the wire. Within close radial distance of a coiled wire, we have the adjacent coils and the wire on the other side of the coil. Both are within the radial energy field expansion from the small initial length of coil freshly charged by the initial wave. The layers of coils can be considered as a series of capacitors, each spaced at a distance equal to the coil turn spacing. The initial field charges this series of capacitors at a velocity of field propagation. The length of time required to charge the series of capacitors is the time it takes for a wave traveling at the speed of light to travel the length of the coil, not the wire length contained within the coil. This explains the short time required for the initial pulse to be detectable across the coil. Obviously, this series of capacitors is shorted together by a path much longer than the distance between coil windings. The wave front continues down and around this longer path, taking a period of time equal to time of travel of light traveling the length of the wire as if it were stretched straight. Again obviously, while part of the energy of the wave front has been stored in the capacitors of the adjacent coils resulting in a wave front with diminished power, the reduction would be a division between the series capacitors and the forward path along the wire. We must consider the magnetic field in this analysis. The initial step voltage that is picked will determine the current which flows as a result of the wire size and the surrounding materials, just as it does for a transmission line. The initial step current will be steady (DC) once the wave front has passed any point on the coil. The increasing magnetic field in the axis of the coil is a result of the increasing distance traveled by the wave front along the coiled wire, leaving a steady state current and voltage (and unchanging magnetic and electrical field) in place at points on the wire passed by the wave front. The establishment of the steady magnetic field must be accompanied by a changing magnetic field at the wave front. This magnetic field passes the wire on the opposite side of the coil and induces a back voltage before the initial wave front can follow the wire around the coil circumference to reach the far side. As a result, the wave front encounters a back voltage and current after the initial front has passed a very short distance into the curved coil wire. Please notice that the wave front described is equivalent to a square wave on the forward face of the wave. A complete sine wave would be made of successive rectangular waves, each of the appropriate length and magnitude needed to compose a smooth sine wave as a final construction. Assuming that the wave front will be traveling on a straight wire before it enters the curved wires of the coil, the impedance of the wire will change at the junction of straight and bent where the wire comes close to the adjoining coil. This will cause a small reflection. There will be a second reflection when the wave front encounters the reverse voltage generated by the magnetic field that has crossed the coil, which acts to cause a change in the impedance of the wire. Once traveling in a relatively steady state along the curved portion of the coil wire, the impedance would continue to change slowly as the wire winds between environments from one coil end to the other. (Remember, the impedance of the wire is the ratio of voltage to current detectable on the wire.) Eventually the wave front will reach the far end of the coil where it will encounter a new environment. A reflection will occur or not, depending upon the end conditions. The amount of power stored in the coil when the wave front reaches the coil end is the steady state voltage X current X time. The time term is the time required for the wave front to travel the length of wire in the coil. 73, Roger, W7WKB |
Loading Coils; was : Vincent antenna
"AI4QJ" wrote in
: "Owen Duffy" wrote in message ... .... That didn't come out very clearly. As I understand it, Cecil argues that there is substantial phase change in the forward and reflected wave components when considering the helix as a transmission line. I don't know if this is too simplistic but here goes: The forward wave maintains it's phase as it encounters a new purely resitive medium (like a straight copper wire or PCB trace). The reflected wave that goes back into the helix transmission line refects as a mirror image of the forward wave, just as light would reflect from a partial mirror. This indeed would be a phase change relative to the incident wave, approx. 90 degrees TIME or about 62.5 nsec at 4MHz in the example under consideration. From here we can go on to discuss the amplitude of the reflected wave and what it takes to cause resonance and a 1:1 standing wave to appear. The standing wave will not have a time phase shift so it cannot be used to measure delay, but voltage and current will of course have a 90 degrees distance phase shift across the transmission line. I am open to correction on this. The seems to me a bit confused, and I can't really understand it. Looking at the coil Tom used: If you use the inductance calculator at http://hamwaves.com/antennas/inductance.html to determine Beta, you get 2.008 rad/m. The coil is .254m long, so that suggests a one-way phase delay of 0.51 rad, or 29.2°. Some suggest that this coil will replace the equivalent electrical length in a quarter wave monopole to shorten it with inductive loading, and irrespective of the position of the loading coil... which is not consistent with experience that a larger loading coil is needed the further it is from the base. One of the proponents posted on eham, the following solution to a loading coil for 160m: "The VF of a 6" dia., 4 TPI coil on 160m would be about 0.02. Whatever number of degrees you want the coil to occupy, wind it accordingly.", note the independence of coil size and location on the monopole. Owen |
Loading Coils; was : Vincent antenna
"AI4QJ" wrote in
: .... Owen, What I did was use the basic impedance calculations: .... You are performing lumped analysis where the current is uniform through the coil, and there is no propagation delay. The other solution that is being discussed is to treat the helix as a transmission line with distributed R, L, G and C. That is what the calculator that I gave the link to does. It implements the technique described by the Corums and others, see the links. The key thing is that the transmission line solution passes to lumped elements when the coil length is sufficiently short, so they are not inconsistent. It is questionable whether the transmission line solution is worth the trouble for short coils. Another practice by some is to assert that the helix substitutes Beta*CoilLength radians of unloaded conductor... but I have not seen a proof of why that can be done, nor does it seem sensible in the general case. Owen |
Loading Coils; was : Vincent antenna
On Sat, 01 Dec 2007 20:28:27 -0800, Roger wrote:
*Here is another way of looking at the coil current.* Every wave must start with a wave front Hi Roger, That, in a sense, sums up what Tom offers at his page (although I am heavily editing you and outrageously paraphrasing him). To go even further, and to the matter of measurement, especially in the problematic use of leads that introduce error; there are TWO ways for your "wave front" to arrive at the other end of the coil. One is conduction, the other radiation. To this point in the discussion, conduction has been the sole consideration (strange too, given the hysterical outrage over treating the coil as a lumped load that so often attends this topic). Clearly radiation arrives by a more direct route, and given the disproportionate size of the wavelength in comparison to the size of the coil, the coil is for all intents and purposes transparent to the propagation of the wave. This is not so for the helix of a TWT, nor for the deliberate coil design of the helical antenna. However, at 80 meters, any point at the other end of a 10 inch coil is going to be steamrollered into oblivion. Tom's commentary hints at this, although the measurement provided is lacking in detail to support this thesis. 73's Richard Clark, KB7QHC |
Loading Coils; was : Vincent antenna
art wrote:
On 1 Dec, 12:44, Richard Clark wrote: On Sat, 1 Dec 2007 11:56:55 -0800 (PST), art wrote: You pick a very poor place to talk about cowardice! At that time Mr Kennedy Snr stated that islands of Britain could not possibly stave off the armies that had overun Europe Hi Arthur, This week in class I learned from Ambassador Thomas Graham that Hitler's second in command came to England and asked Neville Chamberlain to reject Hitler's conditions for moving into Czechoslovakia. He informed Chamberlain that the German High Command was ready to topple Hitler if England showed strength. We all know the rest of the story.... Yup. He was found to be insane and put in the Tower. Germany did not want interference by Gt Britain. In September 3rd 1939 Gt Britain was alone in declaring war against Germanies gigantic armies. That is what you have to do if you are the Worlds policeman. Doing what is right regardless of the consequences Pity the U.S. is unable to do the same. Think how many countries the US government has invaded since they took on the job and it looks like there is more to come. Freedom fighters from all over the World knew that there was a place to go for the defence of freedom,and they came and joined with us. Front and centre were the Polish fighters with out which the British homeland was in danger.The American ambassador fled to home soil while the King and Queen stayed put. It was a couple of years before the U.S. had to join the fray and there was a Country still there that they could join to carry on the fight. It wasn't easy during those times but the British held fast and resolute. And nobody can take those proud times away that away. Art Unwin KB9MZ....XG (uk) Art, You are a historical revisionist. Dave K8MN |
Loading Coils; was : Vincent antenna
On Dec 2, 12:19 am, "AI4QJ" wrote:
"AI4QJ" wrote in message The location on the monopole may make a difference. Since a standing wave is present, the location on the antenna will define the amount of current in the coil. Mounting near the feedpoint is at a high current point and this will increase ohmic losses. At approximately the center of the whip, the current (and ohmic loss) will be minimal. However, more inductance will be needed in the center location. thus more wire. More wire means more resistance. In spite of that, many say that the most efficient location is at near the center of the whip and intuitively I think this generally correct as long as you use heavy wire. It does make quite a difference. And this one one part that bugs me about the taper/delay dilemma. A coil loaded antenna actually needs more wire than the comparison 1/4 wave monopole. I used one of Reg's programs to churn some numbers up. "Vertload" The program is metric. I started with a 3m whip, and used a ..3 meter long loading coil, 100 mm diameter, which is close to four inches. The antenna was tuned for 3.800 mhz, and used 2 ohms as the ground loss. The coil came out to a 171 turns per meter, or a .17 dia/pitch ratio. This first example gave the total height of 3.3m tall overall, and the coil was at .01m from the base, and the stinger above the .3m long coil was 2.990m tall. I used 3m of whip regardless of the coil height. The base load version needed 51 turns of coil, which was 16.31 m of wire plus the 3m of the whip. 19.31 m of wire total. The efficiency was appx 14.49% vs the 1/4 wave. Then I tried a center load. To keep the same turn ratio, I had to use a longer coil. ..44m vs the .3m of the base load. Needed 75 turns, with a coil wire length of 23.92m. 26.92m total wire with the whip. The efficiency was 24.89 %. Then I tried an appx 2/3 coil level with 2m base whip, and 1m stinger. Again, to use the same coil stock, you would have to lengthen the coil to .53m vs the .3m of the base load. Would need 90 turns, with a wire length of 28.69m. 31.69m total wire length with the whip. The efficiency was 28.02 %. You actually need more wire than the equal 1/4 wave whip. Say a monopole at 3.8 mhz is 61.57 ft tall. The appx 9.84 ft whip base loaded needs 63.35 ft of wire. The center load needs 88.32 ft of wire. The 2/3 load needs 103.97 ft of wire. But it's the still most efficient of the three assuming no overly high coil resistance. To me, the coil current taper/delay, etc issue is basically a non issue. It doesn't really matter to me one way or the other as the design of the antennas will not change a whit. Of course, it's nice to know exactly how it happens, but it's not going to change the design of the short verticals as far as coil placement, etc. The optimum locations for those are already well known, and will not be effected no matter how thick the lather is whipped up on this NG.. :/ BTW, the optimum coil locations match the "lumped" theory so close as to make me wonder why anyone wastes so much energy worrying about it.. But.. That's just me. I have many things to do and worry about besides radios and antennas. So I choose what I do worry about with some care. :) This "problem" isn't one of them.. lol.. MK |
Loading Coils; was : Vincent antenna
AI4QJ wrote:
In an inductor, current lags voltage. If you connect a resitor and a coil in parallel and apply AC, EE101 tells you that, although the phase of the voltage across them stays the same, the current is "delayed" by the phase angle in the inductor when compared to current in the resistor. No, it isn't - the phase of the current around the circuit has to stay the same. Think of the simplest possible circuit: an AC voltage source (of zero internal impedance) with one terminal wired to R, lumped L in series, and directly back to the other terminal of the AC source. If the phase of the current were delayed through L as you suggest, there would then be a difference in phase between the two terminals of the AC source... which is obviously not true. It's the magnitude and phase of the voltage that varies at different points around the circuit; but the magnitude and phase of the current has to remain the same all the way around the loop. In more formal terms, Kirchhoff's current law applies all around the circuit; and it most certainly applies between the two terminals of a lumped inductance. If this weren't so, I assure you the world we live in just wouldn't be the same Well, you're certainly right about that :-) What isn't sufficiently understood is that loading by pure lumped inductance is responsible for almost all the properties of a physically short loaded vertical. This is easy to see for base loading, where lumped inductance at the feedpoint is simply compensating for the capacitive reactance of the physically short whip. The same remains true when the loading inductance is moved further up the whip (progressively increasing the inductance, of course, in order to maintain a zero reactance at the feedpoint). Loading by pure lumped inductance explains all the well-known observations: the need for more inductance if the coil is located further up the whip; the relatively constant magnitude and phase of the current in the part of the whip below the loading inductance; the large step increase in voltage across the inductance itself; and the very rapid decrease in current in the section above the loading inductance, tapering to zero current at the top and accompanied by a very large electric field. Note again: all the above is explained using the classic behaviour of lumped inductance, with ZERO difference in current magnitude and phase between its two terminals. Now what changes when we replace a theoretical lumped inductance with a physically realizable coil? The main difference is that the real-life coil occupies a significant fraction of the total physical height of the antenna. In addition to providing inductance, the coil is now behaving to some extent like a helically-wound section of the complete antenna. Now it is completely reasonable to expect some 'antenna-like' behaviour from the coil: there will be some radiation from the coil itself, accompanied by some decrease in current with distance along the coil. We also expect some phase shift in current between its two ends. This 'antenna-like' behaviour in a physically long loading coil is completely reasonable and to be expected. However, it will be difficult to explain in detail because the 'antenna-like' properties of the coil will be strongly influenced by the other parts of the antenna. (This also means that measurements made on a coil in isolation will have very limited relevance to the behaviour of the coil as part of a complete antenna.) There may be several different valid explanations, each looking at the problem from a different viewpoint - no problem about that, of course. But there will also be several INvalid explanations... so how do we tell the difference? All the valid explanations will have at least one thing in common. They will ALL be able to handle the boundary condition that, when the physical size of the coil tends towards zero, every part of its behaviour tends towards the classic behaviour of pure lumped inductance. In particular for this part of the discussion, the phase shift in current between its two terminals MUST tend to zero. Now that the loading has become pure inductance, any valid explanation must still be able to explain all the major features of the loaded whip, as identified above. In other words, any explanation MUST be able to handle that boundary condition smoothly and effortlessly, without any need for a sudden change in its own rules and assumptions. If it cannot do that, then logic tells us that explanation cannot be correct. For example, if at the boundary it is still demanding a phase shift in current between the two terminals of a lumped inductance, that cannot be correct. If it demands that lumped inductance behaves differently in antennas than it does in any other circuit, then again it cannot be correct. It's not me making these rules, by the way - just recognising that they exist, and insisting that they apply. Boundary conditions that join up with existing knowledge are a very useful 'logical razor' to slice and dice ideas that fail to pass those tests. In classical logic this method is called 'reductio ad absurdum', but that's only the Latin for something that everybody knows: "If it don't make sense, it kain't be right." Unfortunately, some people seem to be immune to this, or want to negotiate waivers for their own particular ideas. Progress comes from recognising that there are no exceptions, and being prepared to let go of cherished ideas if it is shown that they don't work. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
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On Dec 2, 2:46 am, wrote:
On Dec 2, 12:19 am, "AI4QJ" wrote: "AI4QJ" wrote in message The location on the monopole may make a difference. Since a standing wave is present, the location on the antenna will define the amount of current in the coil. Mounting near the feedpoint is at a high current point and this will increase ohmic losses. At approximately the center of the whip, the current (and ohmic loss) will be minimal. However, more inductance will be needed in the center location. thus more wire. More wire means more resistance. In spite of that, many say that the most efficient location is at near the center of the whip and intuitively I think this generally correct as long as you use heavy wire. BTW, if you raise the coil, you generally will see maximum current at the coil, not at the base. This is another thing that bothers me about the taper/delay theory.. Myself, I think the usual "short" loading coil acts pretty much as in lumped theory. To me, it acts more as a single unit, rather than the many feet of wire acting as a mere extension to the whip. These two things kind of blow the "90 degrees of wire theory" in my mind at least.. If that were the case, you would think the amount of wire, coil turns should stay the same no matter the location. But also, even with the physical length of wire being coiled up, I would also still expect to see maximum current at the base of the whip, same as a 1/4 monopole. But this is not the case. Seems to me it's been shown many times that if you elevate the coil, the current distribution is fairly linear up the lower whip, and you will see a slight current maximum at the coil, not at the base. I don't think you would see that current max at the coil if it were not acting pretty much as a lumped inductor. But thats just my take part 2.. MK |
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Gene Fuller wrote:
A proper "quote" does not include any extra analysis. Yet another diversion devoid of any technical content. You will not find "4.5 degrees" in quotes anywhere in my article indicating that I did NOT quote W8JI. W8JI did not say "4.5 degrees", you did. There are 17 different definitions of "say" in my Webster's. Two of those definitions are used in the following sentence. When W8JI *said* "3 ns", he *said* a mouthful, indicating that there is a 4.5 degree delay through the test coil. -- 73, Cecil http://www.w5dxp.com |
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AI4QJ wrote:
62.5nsec delay. It is correct. Measurement would easily prove it. Maybe on monday when I go to the lab I will make such a coil and put it on a scope, take a picture and prove it. However, my peers would be wondering why I was trying to prove such a thing; it's sort of like proving gravity exists is it not? What would be the point? Sort of like not having to measure the delay in order to know it is impossible for it to be 3 ns. So it cannot be 2-4nsec. My point exactly. The erroneous measurement was made using current devoid of any phase shift. -- 73, Cecil http://www.w5dxp.com |
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Gene Fuller wrote:
As far as I can tell, W8JI did not do any math or other type of analysis to come up with the 3 ns delay. There was some surrounding discussion, but the delay itself was simply read from an instrument. So let me repeat my earlier questions. I previously answered your question in capital letters. What went wrong? Why is that number incorrect? This is about the 20th time that I have explained the error that W8JI made. The signal he used to measure phase shift didn't possess a phase shift. W7EL made the same mistake in his "delay through a loading coil" measurements. When the phase of the total current changes hardly at all from one end of a 1/2WL dipole to the other, that current CANNOT even be used to measure the delay through the wire. Why do you, W8JI, and W7EL think a current with an essentially unchanging phase can be used to measure phase shift? This is all explained on my web page. -- 73, Cecil http://www.w5dxp.com |
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On Dec 2, 7:46 am, "Jimmie D" wrote:
When you shorten an antenna dont you(shouldnt you) have to replace the C along with the L? Jimmie Well, if you have less C, you would need more L. Depends where you shorten the whip. Below or above the coil.. Shortening the whip below the coil does not effect the tuning near as much as shortening the stinger above the coil. IE: take my 11 ft mobile whip tuned to 80m. I can add a 3 ft extension to the base, and it will shift the tuning a fairly small amount in the band.. But add 3 ft to the stinger, and the shift will be quite large.. You will be way out of the ham band. Of course, if you have a choice, it's always better to add more C, than it is to add more L. I'm not sure if this is exactly what you are asking... MK |
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On Sun, 2 Dec 2007 09:59:24 +0000, Ian White GM3SEK
wrote: (This also means that measurements made on a coil in isolation will have very limited relevance to the behaviour of the coil as part of a complete antenna.) Hi Ian, Your parenthetical is EXACTLY what devastates the logic of forcing the real inductor to observe a constant angular length according to Cecil's misapplication of the so-called Corum rule. It also reveals the problem with Tom's measurement. However, negating Tom does not validate Cecil - and vice versa. As for the implicit (or explicit) expectation of Kirchhoff being satisfied, that is a lose-lose proposition from the get-go as these discussions violate the necessary zero scale of wavelength, something you also covered quite well: The main difference is that the real-life coil occupies a significant fraction of the total physical height of the antenna. 73's Richard Clark, KB7QHC |
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On Sun, 2 Dec 2007 14:24:42 -0500, "Jimmie D"
wrote: If the delay in the coil Cecil has talked about is measured without the appropriate C and R would not this affect the normal parameters of the coil. The delay through a delayline or a loading coil is dependent on more than just L. Hi Jimmie, The Corum math is available. Can you find the delay contribution of externalities to the coil in those equations? 73's Richard Clark, KB7QHC |
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Richard Harrison wrote:
Surely the signal follows the path of the turns on a coil. Not entirely as adjacent turns do have an effect on each other so there is a grain of truth in what W8JI is saying. W8JI's error was in taking that grain of truth and rationalizing that small grain into an explanation that is off by at least a magnitude. It looks like a reasonable rule of thumb is that the velocity factor of a coil is approximately half what it would be if the signal followed the wire entirely. In other words, if one calculates the delay in the length of wire used to wind the coil, the actual delay through the coil is likely to be half of that value. -- 73, Cecil http://www.w5dxp.com |
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Owen Duffy wrote:
I say that the phase relation MUST be the same everywhere on the coil. That does not seem to me to support Cecil's proposition at all, I understand Cecil to argue that there is a substantial phase change in the coil current along the coil. Please understand exactly what I am saying, Owen. 1. There is a *substantial* phase change in the *traveling-wave* current along the coil. Traveling-wave current is hard to measure in a standing-wave antenna but its phase yields complete and accurate phase/delay information. 2. There is virtually *no* phase change in the *standing-wave* current along the coil. Standing-wave current is easy to measure in a standing-wave antenna but its phase yields close to *zero phase/delay information*. 3. In a standing-wave antenna, the total current is primarily standing-wave current. In a loaded mobile antenna, the standing- wave current is approximately 90% of the total current thus tending to mask the traveling-wave current. W8JI's and W7EL's "measurements" were made using standing- wave current. They should have instead used traveling-wave current. It's an easy mistake to make but one would think, after five years, it is time to admit the mistake. -- 73, Cecil http://www.w5dxp.com |
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Tom Donaly wrote:
That is when it is electrically close to 90 degrees in length. In length? You still don't get it. Yes, in electrical length, not physical length. You still just don't get it. I gave an example of a stub that is 45 degrees in physical length yet 90 degrees in electrical length. You really should take time to verify that stub. -- 73, Cecil http://www.w5dxp.com |
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Art wrote:
"Were you wearing a uniform supplied by Germany at that time?" Fortunately not. I was wearing a uniform supplied by the U.S. Navy in the Pacific theater at that time. We had no choice when attacked by the Japanese. The U.S. had interrupted oil to Japan to try to curb their agression and they responded with an attack on Pearl Harbor. The English proved their grit during the Battle of Britain. But, it would have been lost had not lend-lease been provided by the U.S.A. Even Hermann Goering gave slight praise to British industry when asked if he needed something else for his Luftwaffe and he replied: "A couple of Spitfire squadrons would be very nice." The Luftwaffe`s failure to gain control of the skies during the Battle of Britain was Hitler`s first defeat and it stained Goering`s reputation. Hermann`s nephew was raised in Salt Lake City and commisioned a Captain in the U.S. Army Airforce where he was considered a uniquely qualified B-17 pilot assigned to the 303rd Bombardment Group (Hell`s Angels) of the 8th Air Force based in Molesworth, England, flying missions against Nazi Germany. His name was Werner G. Goering. Remember that Eisenhower said that at least 1/3 of his forces were of German descent. The only mission Werner was not eager to perform was when he had to bomb Cologne where his grandmother lived. Hermann`s younger brother, Albert Goering was notable for helping Jews and other dissidents survive in Germany throughout the war. He sometimes called upon Herman and received help in this idealogical problem. Mostly war is bad sttuff no matter which side you are on. One of my predecessors, named Harrison signed the Declaration of Independance and lost his fortune as a result. Best regards, Richard Harrison, KB5WZI |
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AI4QJ wrote:
You are ready to throw me out of the sacred RRAA nesting place? The next step by the gang of gurus will be to "ploink" you which means they will program their newsreaders to shield themselves from your postings of technical facts which disagree with their old wives' tales. A few of them believe there is no reflected energy in a reflected wave. -- 73, Cecil http://www.w5dxp.com |
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Richard Harrison wrote:
There is no magic instantaneous transfer of energy from one turn to another within a coil. It's not magic and it cannot occur at faster than light speed. Magnetic coupling between air-core coils does exist. It is just not of the magical magnitude asserted by W8JI. You wouldn't use the same argument on an iron-core coil, would you, where virtually all of the coil#1 flux does indeed link with coil#N? -- 73, Cecil http://www.w5dxp.com |
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"AI4QJ" wrote in
: "AI4QJ" wrote in message ... note the independence of coil size and location on the monopole. The location on the monopole may make a difference. Since a standing wave is present, the location on the antenna will define the amount of current in the coil. Mounting near the feedpoint is at a high current Yes, the complete picture is that: 1. more inductance is needed the further that a single small loading coil is located from the base; and 2. loss is due to I^2*R, so locating the coil further up decreases current, but increases required inductance and inherent R. The above mean that the optimum efficiency is often from a coil located closer to the middle than to the top or bottom. It seems reasonable that a stand alone coil can be characterised as a transmission line having a delay that equates to an electrical length in degrees, radians, wavelengths or a velocity factor. In fact the inductance calculator at http://hamwaves.com/antennas/inductance.html is based on that approach and shows the calculated value of Beta. But, it is the suggestion by some that the coil simply replaces an equivalent electrical length of the monopole conductor irrespective of the coil's location that is inconsistent with 1 above. A further issue is the accuracy of the estimate of the coil's electrical length when represented as a transmission line. Using the length of the wire in the coil (as is sometimes done) is too simplistic. The Corum paper referenced at the calculator above describes a method that appears to be more reliable. Owen |
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art wrote:
Cecil, Nobody here is willing to say they were wrong. Art, nothing in this posting was written by me. And I, for one, admitted that "power waves" is a wrong concept about ten years ago. No ethical person would post an assertion that I still believe in such. -- 73, Cecil http://www.w5dxp.com |
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Richard Clark wrote:
"AI4QJ" wrote: I believe we are discussing the delay characteristic of current in a coil. Would you be surprised if Cecil and Art diverged even at this point? What would be the point of supporting them when they abandon you? I don't know about Art, Richard, but I detest your trying to mind fornicate with me. Who is religiously supporting who is obviously important to you but to some of us, only technical facts are important. If I believe AI4QJ to be technically correct, I will support him and vice versa. I do believe we are discussing the delay characteristic of current in a coil. -- 73, Cecil http://www.w5dxp.com |
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Cecil Moore wrote:
Richard Harrison wrote: Surely the signal follows the path of the turns on a coil. Not entirely as adjacent turns do have an effect on each other so there is a grain of truth in what W8JI is saying. W8JI's error was in taking that grain of truth and rationalizing that small grain into an explanation that is off by at least a magnitude. It looks like a reasonable rule of thumb is that the velocity factor of a coil is approximately half what it would be if the signal followed the wire entirely. In other words, if one calculates the delay in the length of wire used to wind the coil, the actual delay through the coil is likely to be half of that value. I follow you and am in some degree of agreement--now let toss there stones at two of us ... LOL This is most likely a gray area because of the lack of apparatus available to most "normal" amateurs, which can do meaningful measurements ... Regards, JS |
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John Smith wrote:
However, if anyone has a view to the contrary, I would be interested in the specifics ... In a coil wound on an iron-core toroid, do you believe the flux follows the wire in the coil and ignores the iron in the toroid? Coupling is, of course, not nearly that good in an air- core coil but coupling exists nonetheless. Some of the current generated in a coil is through the air-core transformer action between coils. -- 73, Cecil http://www.w5dxp.com |
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Cecil Moore wrote:
John Smith wrote: [said, "gray areas exist!] In a coil wound on an iron-core toroid, do you believe the flux follows the wire in the coil and ignores the iron in the toroid? At designed freqs, permeability of core material, turns size/spacing--the core OVERWHELMS all other forms of magnetic coupling--I cannot even begin to think how I would measure EM coupling between turns in such an environment ... Coupling is, of course, not nearly that good in an air- core coil but coupling exists nonetheless. Some of the current generated in a coil is through the air-core transformer action between coils. Air core, EM coupling between turns exists, in what degree--I simply cannot, probably, afford the equipment to measure ... As I stated, for at least the most part, we are in agreement ... it seems only logical ... however, things are not always as they seem (now, how's that for "wiggle room?" ;-) ) Regards, JS |
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Owen Duffy wrote:
That didn't come out very clearly. As I understand it, Cecil argues that there is substantial phase change in the forward and reflected wave components when considering the helix as a transmission line. Yes, and there's hardly any phase change in the resultant standing wave when they are superposed because their phasors are rotating in opposite directions at the same angular velocity. -- 73, Cecil http://www.w5dxp.com |
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