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Cecil Moore, W5DXP wrote:
"For instance, a coil might be 10+j300 ohms or a cap might be 2-j500 ohms." A small loop antenna with a perimeter only a small fraction of a wavelength has almost uniform current throughout. Its impedance is an inductive reactance in series with a resistance. The U.S. Bureau of Standards published inductance formulas for single-turn and several-turn loops in Bulletin 74. Results can`t take into account loss from radiation so they are approximate. Arnold King gives an approximate formula for the radiation resistance of a small one-turn loop in "Transmission Lines, Antennas, and Wave Guides": Re = 20(Beta)to the 4th power times A squared Beta=2pi/lambda A=area enclosed by the loop. Best regards, Richard Harrison, KB5WZI |
Cecil Moore wrote:
Or maybe not. EZNEC apparently won't properly model the Lattin antenna. www.g3ycc.karoo.net/lattin.htm . . . I took a look at it, and sure enough, it can't. The antenna is constructed from tubular 300 ohm twinlead, and EZNEC has no way to account for the dielectric between conductors. In that antenna, it looks like the velocity factor of the differential mode field between conductors would be important to its operation, and without the ability to model the dielectric between conductors, EZNEC wouldn't get the velocity factor right. When I see a claim that EZNEC can't model a particular antenna, I often find that the reason for the claim is that the antenna's inventor or seller has dreamed up some magical property to explain the impossibly good performance he's claiming for the antenna. EZNEC models the antenna just fine, it just doesn't model the magical property and validate the claims -- that is, it shows how the antenna really works, not how the huckster claims it works. But there are, certainly, some kinds of antennas which it really can't model properly for one reason or another. The Lattin antenna is one of those. Roy Lewallen, W7EL |
On Thu, 07 Apr 2005 10:05:04 -0700, Roy Lewallen
wrote: But there are, certainly, some kinds of antennas which it really can't model properly for one reason or another. The Lattin antenna is one of those. Hi Roy, Having model dozens of variations of this antenna, as well as what was described in the patent - I cannot think of one reason why it should work except through haphazard luck. Certainly the offered "theories" are no more credible than those for other antennas that defy modeling such as the single or double bazooka, the eh, the cfa. This antenna has many reports of its confounding expectation and then in the same breath those who are confounded expressing their sincere belief it works. It's one of those situations where the builder can't get it to sing, but has a brother-in-law who knows this fellow who lives next door to one who can, but who took it down ten years ago because it was so hard to tune. Perhaps you could widen your customer base if you added a "belief scale" to the available control settings for EZNEC. It could range from "agnostic" to "I believe in miracles." 73's Richard Clark, KB7QHC |
John Smith wrote:
Cecil: Take a look at this folded wave monopole... I am playing with a reflector and director to sandwich this driven element between.... This is the design I have in mind, NO groundplane radials when used as a stand-alone vertical monopole/end-fed. There are warnings in EZNEC about segments not lining up between close spaced wires. My 29 dBi omnidirectional antenna is an example of what happens when one ignores the segment alignment between closely spaced segments. I have modified your segmentation to try to follow the EZNEC guidelines and that file is attached. There is quite a change in the results. The feedpoint impedance went from 2.787+j15.47 to 0.7587+j22.69, the gain went from 7.23 dBi to 3.16 dBi, and the TOA went from 6 deg to 9 deg. I standardized on one foot per segment. I don't really understand what you are trying to do and am just the messenger. -- 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! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Cecil:
Did you remember to attach the file? I don't see it, but would love to study your changes... At ~2.7 ohms I can use a 1:16 balun (reversed direction from conventional use) to mate the antenna with 50 ohms, and get an acceptable SWR... Cecil, try to hear this in a positive manner: If I must conform to EZNEC, then any creativity must be abandoned... If I conform to all the rules of the past and the "Absolute Truths" encompassed by any application--how could I ever hope for a new discovery of geometry or configuration, or the possible use of un-used manipulations of existing rules? If one travels the same road, takes the same plane, rides the same rail, boards the same boat, walks the same path--he sees only the same sights, that which is common place.... even futile paths invoke my curriosity--as just a change of scenery can be enjoyed many times. If that argument is carried out to its nth degree, only one question would remain, "Why should I bother with any of this?", it would be quite easy for a programmer to create a program which quizzes you on ant type (monopole, dipole, yagi, 1/2 wave, 1/4 wave, center loaded, bottom loaded, etc, etc), the freq etc... then constructs the antenna for you. Including suggesting height, mounting brackets and a host of other varibles and conditions that tasks the mind to consider... In other words, once I give control and authority to EZNEC, why should it not "do it all?" But then, even if it did, I would still dilly around with these copper, aluminum and stainless bits and pieces. grin You have talked me back into abandoning EZNEC.... Regards, John -- I would like to point out, I do appreciate the "Been there--done that!" posts. Indeed, now your observations, comments and discourse should be filled with wisdom--I am listening!!! "Cecil Moore" wrote in message ... John Smith wrote: Cecil: Take a look at this folded wave monopole... I am playing with a reflector and director to sandwich this driven element between.... This is the design I have in mind, NO groundplane radials when used as a stand-alone vertical monopole/end-fed. There are warnings in EZNEC about segments not lining up between close spaced wires. My 29 dBi omnidirectional antenna is an example of what happens when one ignores the segment alignment between closely spaced segments. I have modified your segmentation to try to follow the EZNEC guidelines and that file is attached. There is quite a change in the results. The feedpoint impedance went from 2.787+j15.47 to 0.7587+j22.69, the gain went from 7.23 dBi to 3.16 dBi, and the TOA went from 6 deg to 9 deg. I standardized on one foot per segment. I don't really understand what you are trying to do and am just the messenger. -- 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! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Richard H:
Do you happen to have a URL handy where I could view "Bulletin 74?" Thanks in advance, warmest regards, John -- I would like to point out, I do appreciate the "Been there--done that!" posts. Indeed, now your observations, comments and discourse should be filled with wisdom--I am listening!!! "Richard Harrison" wrote in message ... Cecil Moore, W5DXP wrote: "For instance, a coil might be 10+j300 ohms or a cap might be 2-j500 ohms." A small loop antenna with a perimeter only a small fraction of a wavelength has almost uniform current throughout. Its impedance is an inductive reactance in series with a resistance. The U.S. Bureau of Standards published inductance formulas for single-turn and several-turn loops in Bulletin 74. Results can`t take into account loss from radiation so they are approximate. Arnold King gives an approximate formula for the radiation resistance of a small one-turn loop in "Transmission Lines, Antennas, and Wave Guides": Re = 20(Beta)to the 4th power times A squared Beta=2pi/lambda A=area enclosed by the loop. Best regards, Richard Harrison, KB5WZI |
John Smith wrote:
"Do you happen to have a URL handy where I could view "Bulletin 74?" I searched the web unsuccessfully, including some NIST sites which dictated schedules for clearing their files at certain file ages. But, I did find a reference to the famous bulletin in Keith Henney`s 1950 edition of "Radio Engineering Handbook". On page 132, Keith writes: "It is possible to calculate the true (l-f) inductance of some types of air-cored coils with a fair degree of accuracy. National Bureau of Standards Circular 74 has long been the most authorative source of such information. Some of the most useful contained therein are reproduced here." Pages of information follow which include design charts which I can`t reproduce due to my limitations. Such information is not copyrighted as it is assumed the taxpayer has paid for collection of the information already, and should not have to pay for it a second time. That was pre Bush policy, of course. You can probably borrow a copy of Keith Henney`s book in a library near you and delight ijn designing your own antenna coil. The publisher was McGraw-Hill. Best regards, Richard Harrison, KB5WZI |
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On Sat, 9 Apr 2005 23:39:15 -0500, (Richard
Harrison) wrote: I searched the web unsuccessfully http://www.hills2.u-net.com/private/...4/CONTENTS.HTM contains partial page transcriptions. Employing the search term "Radio Instruments and Measurements" at: http://www.kartoo.com/ you can make use of an unique, cluster based search engine that represents the next wave of sifting information on the Web. You will find references to this tome (hardly a circular or bulletin) of more than 600 pages (you will also find book venders ready to sell this work for $20-$30). One NIST site contains a quote from Edison: " . . . This is the greatest book on this subject that I have ever read, and I want to congratulate you and your Bureau on its production." There are multiple authors. I cited one, George Clark Southworth, another was J. Howard Dellinger. There are hard copies available through NIST's Historical Archives (try to get one though). 73's Richard Clark, KB7QHC |
Richard:
Could these be them; or, are these not the same? http://www.fcc.gov/mb/audio/decdoc/r...bulletins.html Regards -- I would like to point out, I do appreciate the "Been there--done that!" posts. Indeed, now your observations, comments and discourse should be filled with wisdom--I am listening!!! "Richard Clark" wrote in message ... On Sat, 9 Apr 2005 23:39:15 -0500, (Richard Harrison) wrote: I searched the web unsuccessfully http://www.hills2.u-net.com/private/...4/CONTENTS.HTM contains partial page transcriptions. Employing the search term "Radio Instruments and Measurements" at: http://www.kartoo.com/ you can make use of an unique, cluster based search engine that represents the next wave of sifting information on the Web. You will find references to this tome (hardly a circular or bulletin) of more than 600 pages (you will also find book venders ready to sell this work for $20-$30). One NIST site contains a quote from Edison: " . . . This is the greatest book on this subject that I have ever read, and I want to congratulate you and your Bureau on its production." There are multiple authors. I cited one, George Clark Southworth, another was J. Howard Dellinger. There are hard copies available through NIST's Historical Archives (try to get one though). 73's Richard Clark, KB7QHC |
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