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I don't think it's unreasonable to discuss their performance, and
consider the findings Yuri has presented as being both reasonable and viable. 73, Jim AC6XG I am just amazed that with all the "theoretical" arguing going on, why none of the "learned" experts measure, answer or explain the following REAL effects or show where I (we) are wrong: We are assuming quarter wave electrical (90 deg) antenna with loading coil inserted from 50 - 70% of the radiator length. 1. As I mentioned and got only fuzzy arguments (poor coils, metal caps, poor connection, which do not jive with observations), having let's say 80m mobile Hustler antenna (many of them around) with coil. Put 100W to it (no obstructions, meters, things to detune it) for about 30 secs. Go feel the coil, or if you have thermal strips, watch the color from bottom to top. You will notice warmer bottom. Put 500W to it, you will "reshrink" the tubing, heatshrink tubing will start curling from the bottom, insulation on wire will start blistering. I have done it, I saw it, I melted the bottom of the coil. K0PP is sending picture of similarly fried Minooka Special. Why coils melt at the bottom and not all along if the current is uniform across the coil? Explanation: Uniform coil, with uniform wire, on uniform form, same caps on top and bottom, the resistance is the same along the coil. If R is the same, and there is more heat developed in part of the coil, then according to I2R formula, current MUST be HIGHER in the part of the coil that heats more - at the bottom. If the current is higher at the bottom part of the coil, it cannot be the SAME at both ends. Do not believe me? Everybody can do the test with mobile coil and verify it. You don't need meters and nothing disturbs the setup. This demonstartes that current is not uniform accross the coil, it larger at the bottom than on top. Where are we wrong here? 2. As I quoted on my page http://www.k3bu.us/loadingcoils.htm results of W9UCW test and measurements, Barry measured in the controlled environment, (60 radials, good coil, RF ammeters) that current in loading coil varies between top and bottom in the range of 40 - 60%,. which confirms the effect described above and puts some figures on it. It was done on different bands, with different positions of the coil and generally follows the pattern. RF ammeters are designed for this particular type of measurements. We get the same conclusion and confirm the effect - the current in the loading coil varies across the coil, it is not the same. What is wrong with those measurements and results? Again anyone can verify them. Did anyone measured anything different? 3. Lets look at the RF choke. Coil the piece of coax into a coil with enough inductance to suppress RF current. Is the current same at both ends? 4. W9UCW used toroid loading coil and got the same results. How could that be? It was MEASURED not "figured" out. 5. Cecil explained the reflected wave situation and delay in the coil, which supports and explains the mechanism of the phenomena. 6. ON4UN in his Low Band DXing book for years has shown and explained the distribution of current in various configurations of loading coils, hats, stubs and clearly shows that current across the coil decreases in proportion to the electrical degrees of the radiator that it replaces. Where is he wrong? Another engineer that "knows nothing"? 7. How could it be if the voltage (neon bulb test) is increasing along the coil towards the top, current has to be decreasing. Can we see some other (better) measurements, anyone? Or is all the above fantasy, because EZNEC says so? Can we have some REASONS instead of ridicule? Point by point please. Yuri, K3BU.us |
Roy Lewallen wrote:
I'm not sure why anyone would think that you can treat an antenna, or a loading coil of significant length, as a lumped element and expect to get anything resembling accurate results. Roy, have you read the arguments that started this discussion? They are at: http://www.k3bu.us/loadingcoils.htm Please tell us if you agree with John Devoldere's "Bible" - "ON4UN's Low Band DXing", 3rd Edition, on page 9-34: -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Ian White, G3SEK wrote:
This brings us back to the question of practical loading coils, and how much radiation (and therefore current variation along the length) we can expect. For the feedpoint impedance to be purely resistive in an electrical 1/4WL shortened vertical, the current must undergo a round trip phase shift of 360 degrees and the voltage must undergo a round trip phase shift of 180 degrees. The loading coil must provide the phase shift that the antenna doesn't provide. For a typical 75m 8 ft mobile antenna, the coil must provide approximately 80 degrees of phase shift. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Art Unwin KB9MZ wrote:
If reactance can be seen as a "{missing" part of a radiator how should we view what a capacitor represents? Grin A series cap has the opposite effect of a series coil. I have seen such antennas made out of end to end caps but I've never really understood their claim to fame. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Roy Lewallen wrote in message ...
No, I will make one more comment. After a bit of reflection, I think this might be at the core of some people's problem in envisioning a lumped inductor. When a current flows into an inductor, it doesn't go round and round and round the turns, taking its time to get to the other end. An inductor wound with 100 feet of wire behaves nothing like a 100 foot wire. Why? It's because when the current begins flowing, it creates a magnetic field. This field couples to, or links with, the other turns. This is the way I view it, and why I couldn't automatically endorse the fairly large difference they saw. Unless the coil is very long, say as in a helical whip, I see it acting pretty much as a lumped inductor. Sure, the current may vary some through the coil when it's a foot or so long bugcatcher coil, but I don't see it being a major issue. I wouldn't normally expect to see a sharp current taper across the coil. I see that type of coil acting much as a "one piece" lumped inductor, not as a many turned rf roller coaster ride. Not a perfect lumped inductor, but close enuff for average gov work. MK |
Cecil Moore wrote in message
A bugcatcher coil on a 75m mobile antenna also does not meet the definition of a lumped circuit. Dunno. I think it does. Not perfect by any means, but I still think it "acts" pretty much like a lumped inductor. MK |
Cecil Moore wrote:
Ian White, G3SEK wrote: This brings us back to the question of practical loading coils, and how much radiation (and therefore current variation along the length) we can expect. For the feedpoint impedance to be purely resistive in an electrical 1/4WL shortened vertical, the current must undergo a round trip phase shift of 360 degrees and the voltage must undergo a round trip phase shift of 180 degrees. The loading coil must provide the phase shift that the antenna doesn't provide. For a typical 75m 8 ft mobile antenna, the coil must provide approximately 80 degrees of phase shift. I'm sure you'll find the answer in Balanis, if you read it with an open mind instead of trying to force him to agree with you. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
Mark Keith wrote:
This is the way I view it, and why I couldn't automatically endorse the fairly large difference they saw. Unless the coil is very long, say as in a helical whip, I see it acting pretty much as a lumped inductor. Sure, the current may vary some through the coil when it's a foot or so long bugcatcher coil, but I don't see it being a major issue. I wouldn't normally expect to see a sharp current taper across the coil. I see that type of coil acting much as a "one piece" lumped inductor, not as a many turned rf roller coaster ride. Not a perfect lumped inductor, but close enuff for average gov work. MK The round trip current phase shift in an electrical 1/4WL vertical must total 360 degrees. If the coil doesn't perform part of that phase shift, what does? -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Mark Keith wrote:
Cecil Moore wrote in message A bugcatcher coil on a 75m mobile antenna also does not meet the definition of a lumped circuit. Dunno. I think it does. Not perfect by any means, but I still think it "acts" pretty much like a lumped inductor. MK Where does the rest of the necessary phase shift in the round trip current come from if not from the coil? -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Ian White, G3SEK wrote:
Cecil Moore wrote: For the feedpoint impedance to be purely resistive in an electrical 1/4WL shortened vertical, the current must undergo a round trip phase shift of 360 degrees and the voltage must undergo a round trip phase shift of 180 degrees. The loading coil must provide the phase shift that the antenna doesn't provide. For a typical 75m 8 ft mobile antenna, the coil must provide approximately 80 degrees of phase shift. I'm sure you'll find the answer in Balanis, if you read it with an open mind instead of trying to force him to agree with you. Ian, I learned the above in the class I took from Balanis at ASU in 1995 while I worked for Intel in Chandler, AZ. I asked him a lot of questions about center-loaded antennas as they are not covered well in his book. The fact that none of the resident gurus on this newsgroup will touch the above simple question with a ten foot pole speaks volumes. A very bright engineer has been in email contact with me over this deductive reasoning problem. So far, he has not attempted to resolve the conflict between a lumped inductor and the absolutely necessary phase shift. Here is the answer to the question presented by Devoldere in "ON4UN's Low Band DXing". For convenience sake, I will draw the vertical mobile antenna as one half of a dipole but the same logic applies. Note the coil is drawn in electrical degrees, not in proportional physical length. wire coil wire -----------////////////////////////---------- 22.5 deg 45 deg 22.5 deg We know from the end result that this is what has to happen. An electrical 1/4WL antenna simply must cause a 90 degree phase shift in the current from end to end. Otherwise, it wouldn't be an electrical 1/4WL antenna. Until someone can explain exactly how a lumped inductor causes a 45 degree phase shift in the current, I am going to assume that a lumped inductor is incapable of that feat. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Ian White, G3SEK wrote:
I don't know what the full detailed explanation is. But I do know that, in order to be correct for all possible cases, it *must* include the feature that as the physical dimensions of the coil tend towards zero, the difference in current between its two ends falls towards zero also. Any "explanation" that denies this fundamental physical fact is guar-an-teed to be wrong. So let's agree on that, and then we can move forward to find an explanation. OK, let's agree on that and take another look at the example I just presented on another thread involving half a dipole. wire coil wire ---------------////--------------- 22.5 deg ? deg 22.5 deg Assuming a lumped inductance, presumably the current into the coil will have the same phase as the current out of the coil. Zero phase shift through the coil means this antenna has the same current phasing as a 40m dipole used on 75m, i.e. the feedpoint current is at a current minimum point. We know that is NOT the case in reality. So what's the answer? -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
G3SEK wrote:
But first we all need to agree that for an ideal lumped loading coil, the current at the top and bottom terminals will be the same. If the current is not the same at both ends, then the coil cannot be behaving as an ideal lumped inductor. We are back to this line of "reasoning": ......and if we rip all four legs off the frog and say "Frog jump", frog doesn't jump. The "conclusion" is - Froggie is deaf :-) Is it a big science secret that coils can cause delay, phase shift? Can anyone also measure the fricken thing and THEN argue???? We have the effect, W9UCW measured it, ON4UN and W5DXP provided explanations, what's missing? Being wrong, recognizing it and admitting? (Sorry) Just because software (for now?) cannot digest it, it can't be? This is becoming amusing to see how serious this misconception was out there and who is on the bandwagon. Let's see "better" explanation. The difference is THERE doesn't matter how anyone denies it!!! Knowing about it will help to design and optimize the crippled antennas, including fricken fracktals (with coils). I am gathering material for test setup allowing to measure RF current in every foot of the loaded antenna, I have two 8 amp meters, so I will have to use some power for full deflection, but it will be just another level of the same thing. You are all invited to witness! I will document it, take pictures and video. If there are no answers, pointing wrong to the points I have raised in my other posting, then I am done, can't do anything more, just will do the measurements and present the results. Yuri, K3BU.us |
Cecil Moore wrote:
OK, let's agree on that and take another look at the example I just presented on another thread involving half a dipole. wire coil wire ---------------////--------------- 22.5 deg ? deg 22.5 deg Assuming a lumped inductance, presumably the current into the coil will have the same phase as the current out of the coil. Zero phase shift through the coil means this antenna has the same current phasing as a 40m dipole used on 75m, i.e. the feedpoint current is at a current minimum point. Sorry, I don't understand that last statement... -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
Ian White, G3SEK wrote:
Cecil Moore wrote: OK, let's agree on that and take another look at the example I just presented on another thread involving half a dipole. wire coil wire ---------------////--------------- 22.5 deg ? deg 22.5 deg Assuming a lumped inductance, presumably the current into the coil will have the same phase as the current out of the coil. Zero phase shift through the coil means this antenna has the same current phasing as a 40m dipole used on 75m, i.e. the feedpoint current is at a current minimum point. Sorry, I don't understand that last statement... A 40m 1/4WL vertical used on 40m is 90 degrees long. A 40m 1/4WL vertical used on 80m is 45 degrees long and we know its characteristics. If the coil above has zero phase shift, the antenna above is also 45 degrees long and will exhibit the feedpoint characteristics of a 40m 1/4WL vertical used on 80m but we know it doesn't exhibit those characteristics. ERGO, the phase shift through the coil is not zero. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
"Ian White, G3SEK" wrote in message ...
Yuri wrote: I am just amazed that with all the "theoretical" arguing going on, why none of the "learned" experts measure, answer or explain the following REAL effects or show where I (we) are wrong: [...] Yuri is making some fair points - those practical observations do need to be explained. But first we all need to agree that for an ideal lumped loading coil, the current at the top and bottom terminals will be the same. If the current is not the same at both ends, then the coil cannot be behaving as an ideal lumped inductor. I believe that Tom took this stance early on when he explained variances of slight current change by virtue of the capacitive component of the real world inductor when wound on a scale that is used on a vertical radiator. I suspect that if he brought Q into the equation /discussion people would not of gotten off track so quickly in the first place! People have become so enamourd with modeling technics they are willing to let their guard down and accept what their results show and throw caution to the wind. I think I will follow Roy and get out of this one Art Now the vainess of man does not allow one to admit error, so the hole digging continues with faces pointed down despite pleas from the faces above Art That tells us that the explanation has to involve the non-zero physical dimensions of the coil. In other words, the coil is no longer just a pure inductor - it also has some antenna-like distributed properties, which do allow (and indeed require) a current variation along the length. I don't know what the full detailed explanation is. But I do know that, in order to be correct for all possible cases, it *must* include the feature that as the physical dimensions of the coil tend towards zero, the difference in current between its two ends falls towards zero also. Any "explanation" that denies this fundamental physical fact is guar-an-teed to be wrong. So let's agree on that, and then we can move forward to find an explanation. |
Cecil Moore wrote:
Ian White, G3SEK wrote: Cecil Moore wrote: OK, let's agree on that and take another look at the example I just presented on another thread involving half a dipole. wire coil wire ---------------////--------------- 22.5 deg ? deg 22.5 deg Assuming a lumped inductance, presumably the current into the coil will have the same phase as the current out of the coil. Zero phase shift through the coil means this antenna has the same current phasing as a 40m dipole used on 75m, i.e. the feedpoint current is at a current minimum point. Sorry, I don't understand that last statement... A 40m 1/4WL vertical used on 40m is 90 degrees long. A 40m 1/4WL vertical used on 80m is 45 degrees long and we know its characteristics. If the coil above has zero phase shift, the antenna above is also 45 degrees long and will exhibit the feedpoint characteristics of a 40m 1/4WL vertical used on 80m but we know it doesn't exhibit those characteristics. ERGO, the phase shift through the coil is not zero. OK, I see what you're getting at, but by changing the frequency you are losing sight of some important points. Let's stay on the *same* frequency, halve the physical height of the antenna and insert a lumped loading coil at the midpoint. Instead of being 90deg tall, our vertical monopole is now only 45deg tall (physically). Drawn on its side, and fed against ground at one end, it now looks like: wire coil wire ---------------////--------------- 22.5 deg ? deg 22.5 deg (just as you drew it) Where you're going astray (I suspect) is in believing that the coil literally "replaces" the 45deg of antenna that was lost when we halved the height. It doesn't - the loading coil drastically changes the current distribution. Fed with 1.0A at the base, the original quarter-wave has a roughly cosine-shaped current distribution, so the current at a point 22.5deg from the top is 1A * cos(90-22.5) = 0.38A. Now feed the loaded antenna with 1.0A at the base. The current distribution is now radically different: in the bottom 22.5deg of the antenna, the current hardly changes - let's say it's 0.9A at the bottom of the loading coil. Since we have assumed a lumped loading coil, the current at the top of the coil is the same 0.9A. But now the current distribution in the top 22.5deg is very different from the full-size case: it tapers much more sharply, from 0.9A down to zero at the very top. This is all standard stuff. My reason for walking through it is to emphasize that shortening the antenna and loading it changes many things about the current distribution, both above and below the loading coil. And here are two other important differences: the feed impedance of the loaded antenna is much lower than that of the full-size; and the much sharper reduction in current is associated with a much higher E-field over the same length of top section. To sum up, shortening and loading the antenna creates so many important differences that you're misleading *yourself* if you say that the loading coil simply "replaces" the missing length of antenna. Two footnotes: 1. The diagram for current distribution with center loading in 'Low Band DXing' is based on the same incorrect assumption that loading coil somehow fully "replaces" the missing 45deg of antenna. (Fortunately the method later in the same chapter for calculating the inductance of loading coils is still OK, because it doesn't depend on any assumptions about current distribution.) 2. I haven't thought about an answer to Cecil's problems of what happens to the "missing" 45deg, and what happens to the forward and reflected waves of voltage and current. Since it's Cecil who chooses to think about antennas in such ways, he'll have to solve his own problems! My only point is that a correct solution can *not* involve a difference in the currents at the two ends of an idealized lumped inductor. Such a difference simply cannot be... so the true solution will be that bit harder for Cecil to find. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
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Cecil Moore wrote in message ...
Mark Keith wrote: This is the way I view it, and why I couldn't automatically endorse the fairly large difference they saw. Unless the coil is very long, say as in a helical whip, I see it acting pretty much as a lumped inductor. Sure, the current may vary some through the coil when it's a foot or so long bugcatcher coil, but I don't see it being a major issue. I wouldn't normally expect to see a sharp current taper across the coil. I see that type of coil acting much as a "one piece" lumped inductor, not as a many turned rf roller coaster ride. Not a perfect lumped inductor, but close enuff for average gov work. MK The round trip current phase shift in an electrical 1/4WL vertical must total 360 degrees. If the coil doesn't perform part of that phase shift, what does? What if it does though? If the coil is still a fairly small portion of the overall length, I don't see the change as severe. Heck, if current is supposed to be the same on each end of the coil, it should be the same going in both directions..:) Seems to me it would pretty much equal out in the overall scheme of things. Even if one ends up with a bit more current, being the coil is not that large overall, the difference should not be drastic. Or to my thinking anyway..I think it's quite possible a coil mounted higher than 1/2 the total length shows a sharper cutoff of current at it's end. To me , it's because of the shorter overall length of the stinger above the coil. The current taper at the top of the coil and above is more abrupt than if the coil were center loaded. Or thats the way I see it. Whether it's right or wrong remains to be seen... MK |
However, we get into issues of your having done work at the 100mA levels and we thus turn to my earlier comments about accuracy. 100mA on an 8 Ampere full scale 3.5 inch meter is slightly more than 1% deflection (less than the width of the needle). Richard, you got the "wires crossed" - mixing two cases. W9UCW measured data I have been quoting in my article at K3BU.us, he SET the power for the bottom meter to read full scale on his 100 mA meter. Then he read the top meter which showed readings in the 40 to 60 % down. I have not done my measurements besides "hand test" and frying the Hustler coils. Just brief test to see how much deflection I get with 100W on 8A meter. I know a thing or two about measurements, done my years at IBM Test Engineering Dept. I will document my tribulations and if get it, use infrared camera too. If W9UCW lied, deceived us I will be the first one to choke him :-) So far he put figures on what I knew and they jive. Why don't you guys that know pitfalls of measurement do it and report ????? Hello???? Yuri. K3BU.us I am not as dumb as Reg portrays me. Got highest IBM Award - Outstanding Contribution Award signed by then chairman Frank Cary for Design and Development Excellence. BTW this was doing something that "experts" at IBM Endicott lab said it couldn't be done. This coil stuff is trivial in comparison. |
"Ian White, G3SEK" wrote: Since we have assumed a lumped loading coil, the current at the top of the coil is the same 0.9A. But now the current distribution in the top 22.5deg is very different from the full-size case: it tapers much more sharply, from 0.9A down to zero at the very top. Right. But the discussion is about whether the lumped loading coil model is accurate. Any conclusions based upon inaccurate assumptions would probably also be inaccurate. 73, Jim AC6XG |
Ian White, G3SEK wrote:
Where you're going astray (I suspect) is in believing that the coil literally "replaces" the 45deg of antenna that was lost when we halved the height. It doesn't - the loading coil drastically changes the current distribution. No, I do NOT claim that the coil literally replaces the 45 degree of antenna that was lost. The feedpoint impedance drops which indicates that it is not a literal replacement. The decrease in the feedpoint impedance indicates that the antenna is not radiating as much energy in one cycle as a full 1/4WL vertical since the reflected current has increased. This is consistent with field strength tests. Since we have assumed a lumped loading coil, the current at the top of the coil is the same 0.9A. But now the current distribution in the top 22.5deg is very different from the full-size case: it tapers much more sharply, from 0.9A down to zero at the very top. I propose that it cannot do that. Seems to me, the impedance looking toward the end of the antenna is approximately the same for a six foot whip Vs the base of a six foot whip mounted atop a coil. I don't see any reason to suspect otherwise. Please provide me a reason. the feed impedance of the loaded antenna is much lower than that of the full-size; .... which proves my point above. That indicates that it is not as efficient a radiator as a full size 1/4WL vertical. In fact, the less efficient it becomes as a radiator, the lower the feedpoint impedance. This fits in exactly with the fact that a good 75m mobile antenna has a ~12 ohm feedpoint impedance. To sum up, shortening and loading the antenna creates so many important differences that you're misleading *yourself* if you say that the loading coil simply "replaces" the missing length of antenna. I never said that so I assume that is your straw man. If that is not a straw man, I apologize but it walks and talks like a straw man. 1. The diagram for current distribution with center loading in 'Low Band DXing' is based on the same incorrect assumption that loading coil somehow fully "replaces" the missing 45deg of antenna. Please prove that a shortened antenna that is electrically 90 degrees doesn't replace the missing number of degrees in the physical antenna. 2. I haven't thought about an answer to Cecil's problems of what happens to the "missing" 45deg, and what happens to the forward and reflected waves of voltage and current. That's more than obvious, Ian. :-) How about thinking about those nagging questions and providing us an answer? This is what happens when one ignores the basics. The steady-state shortcut strikes again. My only point is that a correct solution can *not* involve a difference in the currents at the two ends of an idealized lumped inductor. Such a difference simply cannot be... so the true solution will be that bit harder for Cecil to find. Since there is no such thing in reality as an idealized lumped inductor, there is no real solution to the problem. Please allow me to suggest that you guys are just engaging in mental masturbation. Was it good for you? :-) -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Mark Keith wrote:
Cecil Moore wrote in message ... The round trip current phase shift in an electrical 1/4WL vertical must total 360 degrees. If the coil doesn't perform part of that phase shift, what does? What if it does though? If the coil is still a fairly small portion of the overall length, I don't see the change as severe. Heck, if current is supposed to be the same on each end of the coil, it should be the same going in both directions..:) Seems to me it would pretty much equal out in the overall scheme of things. May I suggest that you think about the problem for awhile longer? If the current doesn't undergo a 360 degree phase shift in its round trip, that will *decrease* the feedpoint current. But we know the feedpoint current *increases* when a loading coil is installed. This is a clear indication that the reflected current is still in phase with the forward current. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Yuri Blanarovich wrote:
I am not as dumb as Reg portrays me. What Reg needs is some Bella Sera Merlot. Dang, that's good stuff. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Jim Kelley wrote:
"Ian White, G3SEK" wrote: Since we have assumed a lumped loading coil, the current at the top of the coil is the same 0.9A. But now the current distribution in the top 22.5deg is very different from the full-size case: it tapers much more sharply, from 0.9A down to zero at the very top. Right. But the discussion is about whether the lumped loading coil model is accurate. Any conclusions based upon inaccurate assumptions would probably also be inaccurate. The discussion has had to take a step back, because we quickly discovered that there isn't agreement about the properties of an idealized lumped inductor. Without that shared fundamental understanding of what "the lumped model" is, it's hopeless to discuss whether or not that model is accurate for a practical coil. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
Cecil Moore wrote:
[More wriggling, followed by] Please allow me to suggest that you guys are just engaging in mental masturbation. Was it good for you? :-) I'm finished with you. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
"Ian White, G3SEK" wrote:
The discussion has had to take a step back, because we quickly discovered that there isn't agreement about the properties of an idealized lumped inductor. There's been some blustery speculation about that, but I think the issue is more whether or not an idealized inductor can actually tell us the whole story. It doesn't seem to. Without that shared fundamental understanding of what "the lumped model" is, it's hopeless to discuss whether or not that model is accurate for a practical coil. Perhaps so. I haven't seen anyone actually share their fundamental understanding of the model with the group yet. 73, Jim AC6XG |
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Jim Kelley wrote:
There's been some blustery speculation about that, but I think the issue is more whether or not an idealized inductor can actually tell us the whole story. It doesn't seem to. If a loading coil has no effect on the current or the electrical length of the antenna, exactly what effect does it have? -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Ian White, G3SEK wrote:
Cecil Moore wrote: Please allow me to suggest that you guys are just engaging in mental masturbation. Was it good for you? :-) I'm finished with you. Ian, I apologize if my humor offended you. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Cecil, W5DXP wrote:
"Until someone can explain exactly how a lumped inductor causes a 45-degree phase shift in the current, I`m going to assume that a lumped inductor is incapable of that feat." There are base loading coils in shielded boxes which don`t radiate but do have significant inductance which make too-short antennas seem long enough for impedance matching purposes. How to get 45-degrees? Make te reactance equal to the total resistance in the circuit. Pythagoras showed how about 2500 years ago. You have a 1:1 ratio between resistance and reactance which are at right-angles to each other. Thus, the resultant impedance is the vector sum which is the square root of 2 times the resistance or reactance which are equal. Pythagoras said: c sq = a sq + b sq. c = impedance a = resistance b = reactance Resistance and reactance are at right angles to each other. When they are equal, their resultant impedance bisects the right-angle of 90-degrees, so the impedance is at 45-degrees. In a resistance, the voltage drop is instantaneous with the current through the resistance. In a pure inductance, current lags the voltage by 90-degrees. In a circuit containing both resistance and inductive reactance, the current lag is somewhere between 0 and 90-degrees. In fact, the current makes the same angle with the applied voltage as impedance in the circuit makes with the resistance because volts and amps are in-phase in the resistance. An inductor which radiates brings an extra to the impedance calculation, its radiation resistance. Best regards, Richard Harrison, KB5WZI |
Ian White, G3SEK wrote:
Cecil Moore wrote: Ian, I apologize if my humor offended you. It wasn't the "humor" (which was too feeble to offend anyone) but your talent for turning any technical discussion into a total waste of time. Imaginary circuits impossible to achieve in reality are not a waste of time? What is the agenda for diverting the discussion away from reality to something that cannot possibly exist in reality? I may be wrong, but it seems to me that agenda simply seeks to avoid the truths that will be uncovered by limiting the discussion to things that are possible. Since lumped inductors are impossible to achieve in reality, one might assert that they can sit up and spit cider in your eye. (From an old Dean Martin movie) How could you ever prove otherwise since the assertion cannot be tested? -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Richard Harrison wrote:
Cecil, W5DXP wrote: "Until someone can explain exactly how a lumped inductor causes a 45-degree phase shift in the current, I`m going to assume that a lumped inductor is incapable of that feat." There are base loading coils in shielded boxes which don`t radiate but do have significant inductance which make too-short antennas seem long enough for impedance matching purposes. But the point is, those loading coils in shielded boxes are NOT *lumped inductors*. We have been told that lumped inductors have zero phase shift. Apparently, a 45-degree phase shift in the current through a lumped inductor would violate the rules of usage for lumped inductors. I have no doubt that real-world inductors provide a phase shift in the current. My statement was limited entirely to lumped inductors, a purely imaginary conceptual model. Sorry if that wasn't clear. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
KB7QHC wirtes:
As this is your party, the burden of proof is upon you. I supplied you with a litany of trip-points and you in fact responded to none. I appreciate your points, some are valid, I know about them, some were off target, some are in the area of nitpicking, when we are overlooking bigger picture. I explained that your previous posting was based on wrong assumptions (not reading carefully the threads?) - the 100mA on 8A meter, measurement techniques, etc. I will do my tests and measurements, first I will do that on my Radiomobile, to test the real life typical mobile situation. Next it would be to replicate W9UCW setup with radials. I keep getting "arguments" that are nitpicking in the .01 area of significance vs. 50% and the facts. I presented 7 points of proof and asked if anyone can debunk them, prove wrong, so far not a single "overthrow". Let me try to summarize again briefly: The temperature test, feeling or thermal strips prove that there is not .1 difference in current accross the loading coil but around 50%. W9UCW measured it and showed 40 - 60% differences. W5DXO explained mechanics of the effect. Are the FACTS in the way of coil "must" have the same current theory? This is not enough proof that current is significantly different at both ends of the coil rather than miniscule, hardly measureable? That IS the argument. As has been demonstrated, there is a camp that believes the current is the same. We know it is not and are bringing it to their attention in hope that it will set the record and knowledge straight. If they choose not to believe it, then let them be happy with their calculated world. Anyone measured it yet? Yuri, K3BU.us |
Yuri Blanarovich wrote:
Are the FACTS in the way of coil "must" have the same current theory? This is not enough proof that current is significantly different at both ends of the coil rather than miniscule, hardly measureable? That IS the argument. As has been demonstrated, there is a camp that believes the current is the same. We know it is not and are bringing it to their attention in hope that it will set the record and knowledge straight. One more data point. Assuming a 102 inch base-loaded mobile antenna on 75m, the impedance looking into the whip is around 0.5-j2000. If we assume a current of 1.5 amp into the bottom of the coil and also out of the top of the coil, the voltage at the top of the coil will be around 3000 volts. With a base loaded 75m antenna, the voltage at the top of the coil should not be extremely difficult to measure and could be viewed with an oscilloscope. This is an experiment that I can do at reduced power. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Cecil Moore wrote:
We have been told that lumped inductors have zero phase shift. I think the claim is that there is zero current differential in magnitude across a lumped inductor. It's certainly true of a pure inductor. Presumably, one in which radiation is not a factor, and for which the electrical length is short compared to wavelength. 73, Jim AC6XG |
Cecil, W5DXP wrote:
"My statement was limited entirely to lumped inductors, a purely imaginary conceptual model." Sorry I didn`t get the picture. An inductor that provides no phase shift is similar to a capacitor that holds no charge. Inductors and capacitors store energies in their magnetic and electric fields. Current lags in the inductor and leads in the capacitor. Pure reactances have a 90-degree phase shift between applied voltage and resulting current by definition. An inductor sans phase shift is salt without savor or sugar without sweetness. Lumped inductance means coiled in place of straight wire, to me. Reference to toroidal coils in this thread implied to me an absence of external field, for which I chose a shielded coil with a straight-axis for my example. I agree with Cecil that a 90-degree antenna which includes only a 45-degree length of wire needs another 45-degree phase-shift in its length to reach the full 90-degrees. As the coil is in series with a resistance, and the resistance the coil experiences depends upon its position between drivepoint (low-resistance) and far end (high resistance) at the end of the element, the inductance required to produce the same required phase shift, varies with its position in the element. Where the resistance is low, so is the required inductance. Where the resistance is high, so is the required inductance, and it is all for the same number of degrees that the antenna is short. Best regards, Richard Harrison, KB5WZI |
Cecil Moore wrote:
If a loading coil has no effect on the current or the electrical length of the antenna, exactly what effect does it have? Apparently the correct answer is "loading". 73, Jim AC6XG |
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Yuri, K3BU wrote:
"Are the FACTS in the way of coil "must" have the same current theory?" Sure. Power traveling along a radiator is absorbed in resistance, both loss and radiation resistance, so it is diminished by the time it gets to a reflection point, the tip of the antenna. This is not like a coil without an opportunity to radiate or which is small in terms of wavelength. Often an extreme example is more impressive than the mediocre. For instance, complete reflections on a lossless line make clearer examples of phase patterns than slight mismatches on a lossy line. For a coil, use the example of the "normal helix antenna". At one of the radio broadcast stations where I worked in 1949, was an operator, James L. Davis, W5LIT who wrapped a bamboo fishing pole completely from end to end with wire in the form af a solenoid, using it as his rear bumper mounted 75-meter phone mobile antenna. When he modulated, the corona at its tip echoed his voice. Obviously, there was a huge difference in the drivepoint current (high) of this antenna, a continuous coil, and the current at the tip (low). The voltage was the reverse of its end currents, being high where the current was low and being low where the current was high. J.L. Davis was very pleased with his mobile operation. Best regards, Richard Harrison, KB5WZI |
Jim Kelley wrote:
Cecil Moore wrote: We have been told that lumped inductors have zero phase shift. I think the claim is that there is zero current differential in magnitude across a lumped inductor. It's certainly true of a pure inductor. Presumably, one in which radiation is not a factor, and for which the electrical length is short compared to wavelength. For a lumped inductance, the electrical length is zero. Presumably, that has a zero effect on the current. Assuming that only the voltage is affected, the phase relationship between the voltage and current is blown compared to an unloaded antenna. But the relationship is somehow (magically?) restored by the time the end of the antenna is encountered. Exactly how is that relationship restored? -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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