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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 |
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