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#1
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What is going on?
Many hams have just gone thru an ice storm where many have lost the end
portions of their elements due to the weight of ice. Strange thing is that many of those hams who suffered damage are confinced that they see NO difference in their shortened antennas and a few were adamant that the performance had IMPROVED One local guru who had many books on radio thought that maybe the real world was different to what he read in books! He then took out his ARRL book and right there is said that gain of two dipoles side by side increases gain in proportion to the spacing between the ends of the dipole. Since this revelation was in a book it was obvious that what other hams were experiencing with their damaged antennas must be true. So the guru purchased two dipole and put them side by side and then remove the ends just as the ice storm would and thus increased the gap between the two dipoles, which the A.R.R.L BOOK said would produce more gain. The guru is now befuddled He listened to experiences in the REAL WORLD and merged it with what must be right because it was in a BOOK but did not get all this extra gravy he was looking for !. What is going on between the real world and what is written in books.? He He! Regards Art |
#2
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Art, KB9MZ wrote:
"What is going on between the real world and what is written in books?" Ever heard: "It`s all Greek to me!"? Prerequisite education is needed to understand books which are likely accurate. An interpretation may be needed by those lacking the prerequisites. ARRL books do a pretty good job of simplification for many hobbiests. Best regards, Richard Harrison, KB5WZI |
#3
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" Art Unwin KB9MZ" wrote in message news:KVAOb.93878$8H.136929@attbi_s03... Many hams have just gone thru an ice storm where many have lost the end portions of their elements due to the weight of ice. Strange thing is that many of those hams who suffered damage are confinced that they see NO difference in their shortened antennas and a few were adamant that the performance had IMPROVED One local guru who had many books on radio thought that maybe the real world was different to what he read in books! He then took out his ARRL book and right there is said that gain of two dipoles side by side increases gain in proportion to the spacing between the ends of the dipole. Since this revelation was in a book it was obvious that what other hams were experiencing with their damaged antennas must be true. So the guru purchased two dipole and put them side by side and then remove the ends just as the ice storm would and thus increased the gap between the two dipoles, which the A.R.R.L BOOK said would produce more gain. The guru is now befuddled He listened to experiences in the REAL WORLD and merged it with what must be right because it was in a BOOK but did not get all this extra gravy he was looking for !. What is going on between the real world and what is written in books.? He He! Regards Art ART, I too have lost portions of my antenna due to ice storms, I was able to retune and still operate my station with the damaged antenna. Howeever ther is no way I could tell you if it was better or worse as no reference had benn previously established for comparison. I seriously doubt if those others that this has happened to had a chance to establish some meaningful reference either. I too am familar with the statement reguarding spacing between the ends of the antenna. I find it both amusing and incredible that anyone could take this to mean that cutting off the ends of the antenna will cause an increase in gain. |
#4
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Jimmy wrote:
"I too am familiar with the statement regarding spacing between the ends of the antenna." Yes, The 19th edition of the "ARRL Antenna Book" has Fig 39 on page 8-35 which shows "Gain of two collinear 1/2-WAVE elements as a function of spacing between the adjacent ends." It says nothing of cutting off your ends to spite your array! You actually get about 3 dBd gain from two !/2-wave dipoles when there is a 1/2-wave space between their adjacent ends versus only a 1.5 dBd gain when there is only the space of a short insulator between the ends of the 1/2-wave dipoles. Best regards, Richard Harrison, KB5WZI |
#5
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On Fri, 23 Jan 2004 20:36:54 GMT, "Jimmy"
wrote: ART, I too have lost portions of my antenna due to ice storms, I was able to retune and still operate my station with the damaged antenna. Howeever ther is no way I could tell you if it was better or worse as no reference had benn previously established for comparison. I seriously doubt if those others that this has happened to had a chance to establish some meaningful reference either. I too am familar with the statement reguarding spacing between the ends of the antenna. I find it both amusing and incredible that anyone could take this to mean that cutting off the ends of the antenna will cause an increase in gain. Hi Jimmy, Anecdotal evidence is what sells antennas like the eh, even in the face of their higher efficiency claims resulting in 30dB poorer signals. The argument for clipping off "unused" parts of antennas (especially yagis) is a howler. It is much like a suggestion to paint out the parts of the telescope lens that you don't look through. Would the telescope still work? On the boresight perhaps (no field of view, but with no more magnification for it though), with less light (you can only use it at local noon), and more fringing (artifacts due to BW restriction). No doubt there would be someone to offer glowing testimonial to that advance in science that so confounds the experts. (And waiting for a Patent publication for special telescope enhancement paint.) 73's Richard Clark, KB7QHC |
#6
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Richard Clark wrote: On Fri, 23 Jan 2004 20:36:54 GMT, "Jimmy" wrote: ART, I too have lost portions of my antenna due to ice storms, I was able to retune and still operate my station with the damaged antenna. Howeever ther is no way I could tell you if it was better or worse as no reference had benn previously established for comparison. I seriously doubt if those others that this has happened to had a chance to establish some meaningful reference either. I too am familar with the statement reguarding spacing between the ends of the antenna. I find it both amusing and incredible that anyone could take this to mean that cutting off the ends of the antenna will cause an increase in gain. Hi Jimmy, Anecdotal evidence is what sells antennas like the eh, even in the face of their higher efficiency claims resulting in 30dB poorer signals. The argument for clipping off "unused" parts of antennas (especially yagis) is a howler. It is much like a suggestion to paint out the parts of the telescope lens that you don't look through. Would the telescope still work? On the boresight perhaps (no field of view, but with no more magnification for it though), with less light (you can only use it at local noon), and more fringing (artifacts due to BW restriction). No doubt there would be someone to offer glowing testimonial to that advance in science that so confounds the experts. (And waiting for a Patent publication for special telescope enhancement paint.) Well Richard, have you not heard of the famous aperture mask? Reduces the aperture of the telescope, and there are people that swear by them! And, they don't work either. Your analogy is quite correct. At best they can improve apparent contrast. But at a reduction in detail. - Mike KB3EIA - |
#7
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Richard Harrison wrote:
You actually get about 3 dBd gain from two !/2-wave dipoles when there is a 1/2-wave space between their adjacent ends versus only a 1.5 dBd gain when there is only the space of a short insulator between the ends of the 1/2-wave dipoles. Too bad coils don't have a phase shift through them. :-) If they did, a phase-reversing coil could be used in that "short insulator space" to bring the gain back to about 3 dBd as described by Kraus in _Antennas_for_all_Applications_, vol 3. -- 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! =----- |
#8
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Cecil wrote,
Richard Harrison wrote: You actually get about 3 dBd gain from two !/2-wave dipoles when there is a 1/2-wave space between their adjacent ends versus only a 1.5 dBd gain when there is only the space of a short insulator between the ends of the 1/2-wave dipoles. Too bad coils don't have a phase shift through them. :-) If they did, a phase-reversing coil could be used in that "short insulator space" to bring the gain back to about 3 dBd as described by Kraus in _Antennas_for_all_Applications_, vol 3. -- 73, Cecil http://www.qsl.net/w5dxp What value coil does Kraus recommend, Cecil, for, say, a pair of forty meter dipoles to make them do what you want at forty meters? 73, Tom Donaly, KA6RUH |
#9
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Tdonaly wrote:
What value coil does Kraus recommend, Cecil, for, say, a pair of forty meter dipoles to make them do what you want at forty meters? It's a textbook, not a cookbook, so he doesn't recommend a specific "value". The requirement is that the coil be self- resonant at the operating frequency. Quoting Kraus: "Here the (1/2WL) elements present a high impedance to the coil which may be resonated without an external capacitance due to its distributed capacitance." He says a 2-element array of 1/2WL elements has a gain of 3.8 dBi, a 3-element array a gain of 5.3 dBi, and a 4-element array a gain of 6.4 dBi. -- 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! =----- |
#10
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Cecil wrote,
Tdonaly wrote: What value coil does Kraus recommend, Cecil, for, say, a pair of forty meter dipoles to make them do what you want at forty meters? It's a textbook, not a cookbook, so he doesn't recommend a specific "value". The requirement is that the coil be self- resonant at the operating frequency. Quoting Kraus: "Here the (1/2WL) elements present a high impedance to the coil which may be resonated without an external capacitance due to its distributed capacitance." He says a 2-element array of 1/2WL elements has a gain of 3.8 dBi, a 3-element array a gain of 5.3 dBi, and a 4-element array a gain of 6.4 dBi. -- 73, Cecil http://www.qsl.net/w5dxp So he didn't give an analysis, but just wrote that a self-resonant coil would do the job. Thanks, Cecil. 73, Tom Donaly, KA6RUH |