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Very, very good Reg. If you can get them to understand
what you have said, it would be a cakewalk to understand the underpinnings of my antennas. My aproach of explaining what you have said is to refer to 'complex circuitry', where in general use this is used to SIMPLIFY circuits. If one understood the basics of what you are pointing out then one could easily understand how one can translate lumped circuits to circuits that RADIATE in an efficient manner. It should not be difficult to understand that a matching circuit which is desirable in a lot of cases, is a circuit of lumped items. There is absolutely no reason whatsoever to prevent one from transforming the lumped items to radiating circuits which not only radiate but also provide the same impedance to a transmitter that the original matching unit supplied. Also very importantly it shows how little the frequency dominates the antenna size Thanks a bunch for your posting and I wish you luck in your education pursuit in the area that I met failure Cheers Art. "Reg Edwards" wrote in message ... Peter, I am somewhat surprised to receive such questions from your good self. They are not so far from the realms of Ohm's Law as to cause YOU any difficulties. Perhaps after the festivities you are feeling too lazy to satisfy your own curiosity by exercising your brain cells. ;o) You must be aware, even without thinking about it, a lumped radiation resistance must always be associated with a definite location on an antenna at which the current is known. This by no means need be at the feedpoint. But I guess this is the first occasion on which you have been confronted with the *distributed* variety and have been brought to a sudden dead stop. Let's stay with the well-known resonant 1/2-wave dipole. The objective is to directly compare radiation resistance with wire loss resistance. To do this means the same current must flow through both just as if they were in series with each other. { Many people are familiar with the simple equation, efficiency = Rrad / ( Rrad + Rloss ) and state it whenever an appropriate occasion arises. It sounds very learned of course. But in the whole of North America I venture to say hardly a single radio amateur knows from where Rloss and Rrad can be obtained (except perhaps ground loss with verticals) and what its value is. It follows that few have ever used the equation presented in Handbook articles, etc. } We have a choice. 1. Lump both the radiation resistance and conductor resistance together at one point after transforming from the distributed to lumped value of wire loss. Or 2, leave the wire resistance where it is and distribute the radiation resistance along the wire. We have no choice about the type of istribution - it must be the same as the wire resistance is distributed - i.e., uniformly. Whatever we do we cannot avoid transforming from a lumped to distributed resistance value, or vice-versa. Electrical engineers do it all the time. In the case of a dipole there are several ways. But its a simple process and the result is amazingly even more simple. I prefer to begin with the accurate assumption of a sinewave distribution of current along the dipole wire with the maximum of 1 amp at the dipole centre. Then integrate P = I squared R from one end of the wire to the other to find the total power dissipated in the wire. The equivalent lump of resistance located at the centre (where 1 amp flows) turns out to be exactly half of uniformly distributed end-to-end resistance of the wire. In fact, that's exactly how the radiation resistance of the usual 70-ohm lump got itself into a dipole's feedpoint. It is exactly half of 140 ohms. If radiation resistance itself had any say in the matter I am sure it would prefer to be nicely spread along the length of the wire instead of being stuck in a lump next to the feedpoint. If the end-to-end wire loss resistance is R ohms then the ficticious equivalent lump at the centre feedpoint is exactly R/2 ohms. So easy to remember, eh? Another way of obtaining exactly the same result is to calculate the input impedance of a 1/4-wave, open-circuit, transmission line, which of course is the same as half of a half-wave dipole. It even has a 1/4-sinewave current distribution along its length. The input resistance at resonance is always half of the conductor loss resistance. With a good impedance bridge this can be measured to keep Roy happy. In fact, it is the pair of 1/4-wave, open-circuit, single-wire lines constituting the dipole which transform the uniformly distributed wire loss resistance to the equivalent lumped 1/2-value input resistances as measured at the dipole centre. And, of course, the antenna performs exactly the same transformation on an antenna's uniformly distributed radiation resistance. I sometimes feel sorry for things which find themselves securely locked in, constrained for ever to obey the irresistible laws of nature, helpless to do othewise, for ever. See how the interlocking bits of the jig-saw puzzle now fit very nicely together. Your general question - yes it would be possible to 'assume' any arbitrary mathematical distribution of radiation or loss resistance and then find an equivalent lumped value which would radiate/dissipate the same power when located at a particular current point. But it would not be of any practical use - it would never correspond to an actual antenna. When calculating efficiency of wire antennas it seems only a uniform distribution of resistance is of any use. An investigator has no choice in the matter. Calculating the efficiency of coil loaded antennas gets complicated. The current distributions of the upper and lower sections are different and so are their efficiencies. But efficiencies are so high in the conductors themselves ball-park guesses are good enough. However it is still necessary to transform various effects, including those due to the coil, to the common base feedpoint in order to calculate input impedance. --- Best Wishes, Reg, G4FGQ =================================== Reg: [snip] For calculating convenience, we assume the radiation resistance, Rrad, is uniformly distributed along the length of the wire and is 140 ohms which has been calculated from its dimensions. It only has two - Length and Diameter. But for a half-wave dipole it is always about 140 ohms. Wire diameter has a relatively small effect on Rrad. [snip] Reg, in your model, is your *assumption* "for calculating convenience" that radiation resistance is uniformly distributed along the antenna structure, i.e. the transmission line that represents the antenna in your model, supported by any theory or is it just a mathematical *fit* to the data? For example, one could *assume* literally any analytic distribution of radiation resistance along an antenna's length, for instance sinusoidal, catenary, exponential, triangular, etc... and come up with a value/function for that particular distribution that has the equivalent effect of a lumped value placed at the antenna feedpoint. What is so unique about uniform? Why do you think *uniform* is any better than any other distribution of Rrad? I have no axe to grind here, just curiosity... Best Regards for the New Year. -- Peter K1PO Indialantic By-the-Sea, FL. |
#2
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"Art Unwin KB9MZ" wrote
Very, very good Reg. ========================== Art, nice to hear from a representative of the few who agree with what is the bleeding obvious. I am aware of your long outstanding problems about convincing folks of the properties of your loop-coupled antenna proposals. But I am too exhausted and too long-in-the-tooth to take part in the (by far) unecessarily convoluted arguments. Try KISS. Provide a precise, unambiguous picture of all dimensions and submit it to a program capable of analysing it - if you can find one. I am unable to provide any assistance myself in that direction. May you and yours enjoy life in 2004 to the full. ---- Yours, Reg, G4FGQ. |
#3
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"Reg Edwards" wrote in message ... "Art Unwin KB9MZ" wrote Very, very good Reg. ========================== Art, nice to hear from a representative of the few who agree with what is the bleeding obvious. I am aware of your long outstanding problems about convincing folks of the properties of your loop-coupled antenna proposals. But I am too exhausted and too long-in-the-tooth to take part in the (by far) unecessarily convoluted arguments. Try KISS. Provide a precise, unambiguous picture of all dimensions and submit it to a program capable of analysing it - if you can find one. Reg, no need for help as it is all completed with success. I may add. I used AO PRO to do the final wrap up as well as making the antennas which in uncompromising fashion proved what you are stating but what other people have been unable to understand . And I have made many different antennas of this family.! I might add that with shorting either capacitor one can change a "T match style antenna "to other forms that provide for high or low impedance at the antenna feed point. to meet requirements of the transmitter.as well as providing a ' loss less' interface, a subject that has been bandied around for years but in isolation. I am sure glad however, to see a dissertation such as yours that was unsolicitated even tho it may finish up as a 'Plonk" on this side of the Pond as many times the obvious is ignored until it apears in a book Hopefully you will able to withstand the junk that will now be thrown at you for stating such an outrageous thing. Cheers Art I am unable to provide any assistance myself in that direction. May you and yours enjoy life in 2004 to the full. ---- Yours, Reg, G4FGQ. |
#4
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Art:
[snip] Reg, no need for help as it is all completed with success. I may add. I used AO PRO to do the final wrap up as well as making the antennas which in uncompromising fashion proved what you are stating but what other people have been unable to understand . [snip] Art, you can't blame others for not understanding! What? It is your responsibility and your's alone to help others to understand your ideas, concepts, inventions. Any failure of others to understand is your responsibility alone! There are three important things in science: Communications, communications and communications. Clearly *you* have failed to communicate. If you communicate clearly and succinctly without whining and do so clearly and unequivocally and stop complaining that no one understands you, why... then you may succeed! I for one certainly wish you well in that regard. [snip] I am sure glad however, to see a dissertation such as yours that was unsolicitated even tho it may finish up as a 'Plonk" on this side of the Pond as many times the obvious is ignored until it apears in a book [snip] Not true at all. Reg is quite capable of explaining himself and no one that I know of feels that Reg's contributions to the NG are "plonk". Apparently you might! [snip] Hopefully you will able to withstand the junk that will now be thrown at you for stating such an outrageous thing. Cheers Art [snip] Reg has proven that he can withstand criticism, questioning, and examination, he has demonstrated that many times over on this NG... he needs no help or appeals to the lack of ability of readers and listeners. Art, wake up and smell the roses and practice: Communicatons, communications, communications... :-) You are doing better, but... you have come very close to whining again here... If no one understands you, it is your fault! "Perception is Reality" -Tom Peters Best regards for the New Year, -- Peter K1PO Indialantic By-the-Sea, FL. |
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