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"Tom Donaly" wrote in message m... Cecil Moore wrote: Tom Donaly wrote: Who said anything about a circuit model? I'm going to present an example, step by step. Please contribute something technical in response. It's a simple lossless quarter-wave matching section example. ------50 ohm feedline---+---1/4WL 600 ohm feedline---7200 ohm load Pfor1=100w-- Pfor2=352w-- 100w --Pref1=0w --Pref2=252w Vfor1=70.7v-- Vfor2=460v-- Vload=849v --Vref1=0v --Vref2=389v Ifor1=1.414A-- Ifor2=0.766A-- Iload=0.118A --Iref1=0A --Iref2=0.648A Vref2 is 180 degrees out of phase with Vfor2 and thus they subtract. Iref2 is in phase with Ifor2 and thus they add. The impedance at '+' is (Vfor2-Vref2)/(Ifor2+Ifor1) The impedance at '+' is (460v-389v)/(0.766A+0.648A) = 70.7V/1.414A = 50 ohms Note that the impedance seen at the match point is: Vfor1/Ifor1 = (Vfor2-Vref2)/(Ifor2+Iref2) So Tom, do you find anything wrong with this network analysis? If so, please be technically specific. (Sorry, your feelings don't matter.) -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Cecil, if I had a dollar for every time you challenged someone to solve a quarter wavelength transmission line transformer problem I could eat a meal in the best restaurant in San Francisco and still have change left over to pay a 20% tip. The question is not whether or not the theory you made up in your head is right or not, but whether the length, shape, volume, whatever of a loading coil on a short antenna makes any substantial difference in the efficiency of the antenna. The problem of increasing the total current on a short antenna was solved so many years ago the fellows who solved it are old enough to be Richard Harrison's grandparents. If Yuri would spend more time researching his subject and less time with his fish thermometers and his diatribes against Tom Rauch he would learn that. 73, Tom Donaly, KA6RUH Tom You would have enough money to own the restaurant. sigh Here goes--- Any difference in current between the ends of a compact loading coil in the center of a short whip is due to radiation from the coil. The same people have been making the same arguments here for years. sheesh! OTOH is has been entertaining. 73 H. |
Tom Donaly wrote:
The question is not whether or not the theory you made up in your head is right or not, but whether the length, shape, volume, whatever of a loading coil on a short antenna makes any substantial difference in the efficiency of the antenna. No, that's not the question at all. You have diverted the issue from current through the coil to efficiency. The question is whether the current at each end of a real-world loading coil is the same or not the same. Efficiency is irrelevant. Diverting the issue is an obvious tactic employed by someone who is losing the argument. If one doesn't understand standing waves on a transmission line, one cannot understand standing-wave antennas. The ignorance of how standing- wave antennas work is the basic problem. I am attempting to alleviate that ignorance. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
H. Adam Stevens, NQ5H wrote:
Any difference in current between the ends of a compact loading coil in the center of a short whip is due to radiation from the coil. That's an old wives' tale. But don't feel bad. Kurt N. Sterba made essentially that same mistake in his Nov. 2004 article in "Worldradio". Anyone who believes that the current is zero at the tip end of a standing-wave antenna because it has been radiated needs a refresher course in standing waves. ************************************************** ******************* * Any difference in forward current between the ends of a loading * coil is due to radiation from the coil. * * Any difference in reflected current between the ends of a loading * coil is due to radiation from the coil. ************************************************** ******************* Please read those two statements until they soak in because they agree with you about component currents but disagree with you about superposed currents. The main difference between the net superposed current at each end of the coil is caused by the phase shift through the coil acting on each of those current components in opposite phase-rotation since they are traveling in opposite directions. Is any difference in current between the ends of a section of transmission line due to radiation from the transmission line? Yes, but most of the difference is due to phase shifts between the forward and reflected waves. Exactly the same concepts apply both to a transmission line with standing waves and a standing-wave antenna. In fact, a horizontal wire antenna is nothing more than a "lossy" transmission line losing energy to radiation. A mobile antenna is a standing-wave antenna possessing a Z0, just like a transmission line. There's a forward current and a reflected current. The superposition of those two component currents causes the main difference in the magnitude of the net current at each end of the coil. When Roy, W7EL, measured the phase of the current at each end of the coil, he measured the phase of the NET superposed current, not the phase of the forward current or reflected current. The phase shift of the NET superposed current is only a couple of degrees max from feedpoint to end as asserted by Kraus in "Antennas for all Applications", page 464. In the ARRL Antenna Book is an equation for the characteristic impedance of a single wire over ground. It is 138*log(4h/d) where 'h' is the height of the antenna and 'd' is the diameter of the wire. The Z0 for a piece of #16 wire positioned 24 feet above ground is about 600 ohms. A quarter wavelength of that wire used as an antenna responds essentially the same as a quarter wavelength of lossy transmission line. There is a large reflected current component at the tip of a mobile (standing-wave) antenna. In fact, my earlier quarter-wavelength matching section plus its 100w load acts similar to a quarter-wavelength antenna radiating 100w. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Cecil Moore wrote:
Tom Donaly wrote: The question is not whether or not the theory you made up in your head is right or not, but whether the length, shape, volume, whatever of a loading coil on a short antenna makes any substantial difference in the efficiency of the antenna. No, that's not the question at all. You have diverted the issue from current through the coil to efficiency. The question is whether the current at each end of a real-world loading coil is the same or not the same. Efficiency is irrelevant. Diverting the issue is an obvious tactic employed by someone who is losing the argument. If one doesn't understand standing waves on a transmission line, one cannot understand standing-wave antennas. The ignorance of how standing- wave antennas work is the basic problem. I am attempting to alleviate that ignorance. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- Cecil, I'll believe you know something about loading coils when you go back to school and learn something about basic classical electromagnetic theory. As it stands, all you can do is make one unsupported statement after another and hope someone is gullible enough to believe you. 73, Tom Donaly, KA6RUH (P.S. How do you know what the subject was? You didn't read all the posts.) |
Tom Donaly wrote:
Cecil, I'll believe you know something about loading coils when you go back to school and learn something about basic classical electromagnetic theory. Been there - done that - even got the T-shirt with Maxwell's equations on it. I suspect that your university never taught the real thing. As it stands, all you can do is make one unsupported statement after another and hope someone is gullible enough to believe you. I supported my statements with examples. Strangely enough, you haven't posted any technical disagreement with my examples. All you do is take potshots based on nothing except your feelings. It's impossible to argue with you on a technical basis because you have not posted anything technical. Do you disagree that the Z0 of a single #16 wire located 24 ft. above ground is ~600 ohms? Do you disagree that such a wire can support standing waves whether used as a transmission line or as an antenna? Please post what you find technically wrong with my examples (all based on valid distributed network reflection models) which I learned in the 50's from "Field and Waves in Modern Radio" by Ramo and Whinnery and a later edition of the same book in graduate school. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
"Cecil Moore" wrote in message ... Jimmie wrote: What, Coililng the wire has nothing to do with how well it does or does not radiate, only with how the radiation is summed into the total field. The current distribution in a loading coil should be very similar to the current distribution in the secton of antenna it is replacing. Actually, coiling the wire tends to reduce the far-field radiation because much of the near-field(s) cancel each other. The currents on each side of the coil are traveling the opposite direction in much the same way they do in a transmission line. However, that doesn't mean the currents at the bottom and top of the coil are identical. The magnitude of the total current at the bottom and top of the coil depends in large amount on the phase shift through the coil. -- 73, Cecil http://www.qsl.net/w5dxp Just because it is canceld in the far field does not mean the coil did not radiate. I would not even say it is canceled in the far field although this is a convenent way of looking at radiation. All you can really say for sure is that the out of phase voltages in the receiving antenna combine destructively. ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
"Richard Harrison" wrote in message ... Jimmie wrote: "Coiling the wire has nothing to do with how it does or does not radiate,---." Good. Just leave your antenna rolled up. Best regards, Richard Harrison, KB5WZI And it will radiate, assuming no other changes but the geometry of the antenna.. When the out of phase componts of the radiation reach a receiving antenna they will destructivly combine. |
Cecil Moore wrote:
Tom Donaly wrote: Cecil, I'll believe you know something about loading coils when you go back to school and learn something about basic classical electromagnetic theory. Been there - done that - even got the T-shirt with Maxwell's equations on it. I suspect that your university never taught the real thing. As it stands, all you can do is make one unsupported statement after another and hope someone is gullible enough to believe you. I supported my statements with examples. Strangely enough, you haven't posted any technical disagreement with my examples. All you do is take potshots based on nothing except your feelings. It's impossible to argue with you on a technical basis because you have not posted anything technical. Do you disagree that the Z0 of a single #16 wire located 24 ft. above ground is ~600 ohms? Do you disagree that such a wire can support standing waves whether used as a transmission line or as an antenna? Please post what you find technically wrong with my examples (all based on valid distributed network reflection models) which I learned in the 50's from "Field and Waves in Modern Radio" by Ramo and Whinnery and a later edition of the same book in graduate school. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- I'm not going to waste my time arguing with you , Cecil; as you say, been there, done that. I know there are people in the past who have attempted to characterize antennas as transmission lines. It's an old, hoary method. You have a copy of Balanis. He has references you can look up to see how close your ideas are to the truth. Nope, I don't need to argue. I have a wife who is always willing and ready to provide arguing services whenever I need them. I don't need you. 73, Tom Donaly, KA6RUH |
Jimmie wrote:
Just because it is canceld in the far field does not mean the coil did not radiate. It is generally accepted that if RF energy doesn't escape to the far- field, that energy is not "radiated". Energy can appear in the near- field around a wire without being "radiated". I would not even say it is canceled in the far field although this is a convenent way of looking at radiation. All you can really say for sure is that the out of phase voltages in the receiving antenna combine destructively. If the fields combine destructively in the near-field, that field energy is returned to the system and never reaches the receiving antenna in the far field. That's how transmission lines are supposed to work and why the spacing between the two conductors needs to be negligible compared to a wavelength. The near-balanced currents on each side of a coil, traveling in opposite directions, cause destructive interference in the near field, thus limiting the amount of energy radiated by the coil. An electrical 1/4WL helical antenna radiates slightly less RF than does a 1/4WL straight wire. That implies the amount of radiation from an air-core coil is slightly less than from a wire the same overall length as the coil. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Jimmie wrote:
And it will radiate, assuming no other changes but the geometry of the antenna.. When the out of phase componts of the radiation reach a receiving antenna they will destructivly combine. If it actually radiates and if that radiation destructively combines at one receiving antenna, then radiation must constructively combine at another (potential) receiving antenna, or else the conservation of energy principle would be violated. Any far-field destructive interference event must be exactly balanced by an equal magnitude constructive interference event at some other location in the far-field. If there is a receiving antenna there, it will experience gain over the first location. And a coiled up antenna is likely to experience a lot of I^2*R losses. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
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