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Information about my experience with Magnetic Loop antenna's onmy homepage
On 28 feb, 20:53, Richard Clark wrote:
On Sun, 27 Feb 2011 23:14:34 -0600, John - KD5YI wrote: Wimpie is right, Richard. I presume Wimpie can speak for himself. *As he offered musings that were done on the back of a handy envelope, there is every chance he is not right. *I offered a similar chance that I was not right either, but I offered complete (two in fact) equations that no one has disputed, and none have faulted for computation. *I admitted a misapplication of one - which also passed without comment. Considering Wimpie's work was not done for the antenna under consideration (the size of his being much smaller where radiation resistance varies by the FOURTH POWER of size) - what does "right" mean? 73's Richard Clark, KB7QHC Hello Richard, Your formulas can be disputed: When using (from http://www.ece.msstate.edu/~donohoe/ece4990notes5.pdf): Rr_loop = 320*(pi)^4*A^2/lambda^4 for f = 3.6 MHz, Dloop = 1.27m (so A = 1.27 m^2), Rr_loop = 0.001 mOhm. This result agrees the number in my previous calculation (for the same situation). From the same source, but for a dipole of 1.27m with large end- plates, Rr_dipole = 80*(pi)^2*le^2/lambda^2 = 0.18 Rr_dipole = 0.045 Ohm (without large end-plates). This is roughly a factor 45 or 180 more (for the dipole). Maybe somebody can confirm the above calculations. The actual efficiency depends on the required (space consuming) reactive component to cancel the capacitive (dipole) or inductive (loop) behavior. The advantage of the loop (especially for reception) is that you need a variable capacitor instead of a variable loop, and matching / balun function can be made easily. He also mentioned the vertical radiation component (NVIS operation) together with the nulls in the horizontal plane. Regarding claims, Norbert didn't make claims about the high efficiency. Please read his conclusion that starts with "despite the low efficiency of 3%….". His stated 3% reasonably agrees with my 3% (though you think that the calculation may be wrong). The claim with regards to performance comparable to a half wave or vertical antenna is for higher frequencies (where the loop's efficiency increases significantly). Of course I have serious doubts about the conclusions regarding general noise cancelling properties, but the conclusions can be right for that special RF-environment. Whether they apply for another situation, can be food for the radio amateur experimenter (or professional?). With kind regards, Wim PA3DJS www.tetech.nl |
Information about my experience with Magnetic Loop antenna's onmy homepage
|
Information about my experience with Magnetic Loop antenna'son my homepage
On 2/28/2011 1:53 PM, Richard Clark wrote:
On Sun, 27 Feb 2011 23:14:34 -0600, John - wrote: Wimpie is right, Richard. I presume Wimpie can speak for himself. As he offered musings that were done on the back of a handy envelope, there is every chance he is not right. I offered a similar chance that I was not right either, but I offered complete (two in fact) equations that no one has disputed, and none have faulted for computation. I admitted a misapplication of one - which also passed without comment. Considering Wimpie's work was not done for the antenna under consideration (the size of his being much smaller where radiation resistance varies by the FOURTH POWER of size) - what does "right" mean? 73's Richard Clark, KB7QHC I didn't mean Wimpie was right about his technical response. I meant he was right about a part of his message which you cut: "I agree with you that several statements on Norbert's site will not hold when scientifically reviewed. However I think the way you respond will likely not result in better statements." "As the name of the newsgroup indicates; this is a radio amateur group and Norbert site starts with "Dutch amateur radio station". This may require another approach then you should use in a professional environment. If you prefer that, Edaboard.com (just an example) is a more suitable place." John |
Information about my experience with Magnetic Loop antenna's onmy homepage
On 28 feb, 20:53, Richard Clark wrote:
On Sun, 27 Feb 2011 23:14:34 -0600, John - KD5YI wrote: Wimpie is right, Richard. I presume Wimpie can speak for himself. *As he offered musings that were done on the back of a handy envelope, there is every chance he is not right. *I offered a similar chance that I was not right either, but I offered complete (two in fact) equations that no one has disputed, and none have faulted for computation. *I admitted a misapplication of one - which also passed without comment. Considering Wimpie's work was not done for the antenna under consideration (the size of his being much smaller where radiation resistance varies by the FOURTH POWER of size) - what does "right" mean? 73's Richard Clark, KB7QHC Hello Richard, you used r = 1m (as you have r in your formulas), that is D = 2m, 6.28m circumference. I used D = 1.27m (4m perimeter), that is r = 0.635 m. Quote from Norbert's site: "When a magnetic loop antenna is used for 3.5 MHz with a perimeter of 4 meter (13.3 foot) , it has an efficiency of approximately 3%." Maybe this helps you to explain the difference between your and my result, Wim PA3DJS www.tetech.nl Don't forget to remove abc in case of PM. |
Information about my experience with Magnetic Loop antenna's on my homepage
On Mon, 28 Feb 2011 15:36:27 -0600, John - KD5YI
wrote: I didn't mean Wimpie was right about his technical response. I meant he was right about a part of his message which you cut: I selectively quote to make the response specific to the point being responded to (like I am right now). It saves room, is not ambiguous, and serves the technical community by confining discussion to technical matters. 73's Richard Clark, KB7QHC |
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Information about my experience with Magnetic Loop antenna'son my homepage
On 2/28/2011 7:24 PM, Richard Clark wrote:
On Mon, 28 Feb 2011 15:36:27 -0600, John - wrote: I didn't mean Wimpie was right about his technical response. I meant he was right about a part of his message which you cut: I selectively quote to make the response specific to the point being responded to (like I am right now). It saves room, is not ambiguous, and serves the technical community by confining discussion to technical matters. 73's Richard Clark, KB7QHC Then I'll just have to put the "point" back in Quote Wim I agree with you that several statements on Norbert's site will not hold when scientifically reviewed. However I think the way you respond will likely not result in better statements. As the name of the newsgroup indicates; this is a radio amateur group and Norbert site starts with "Dutch amateur radio station". This may require another approach then you should use in a professional environment. If you prefer that, Edaboard.com (just an example) is a more suitable place. /Quote |
Information about my experience with Magnetic Loop antenna's on my homepage
On Mon, 28 Feb 2011 14:13:29 -0800 (PST), Wimpie
wrote: you used r = 1m (as you have r in your formulas), that is D = 2m, 6.28m circumference. It is the specified diameter/radius of the 80M antenna at the link of the antenna manufacturer. I stated that quite clearly. I choose to go to the source rather than rely on possible transcription errors in amateur postings. I used D = 1.27m (4m perimeter), that is r = 0.635 m. That antenna does not exist. Quote from Norbert's site: "When a magnetic loop antenna is used for 3.5 MHz with a perimeter of 4 meter (13.3 foot) , it has an efficiency of approximately 3%." There is no Ciro Mazzoni antenna with that dimension. I specifically asked if this statement was for the MIDI loop antenna with a 2 meter diameter (and is designed for 80M operation). To this point no one has affirmed or denied this my natural selection from the manufacturer. The page quite clearly reveals three photos of the distinctive design. The Mazzoni antennas also come in distinctive 1m, 2m, 4m integral sizes. There is no 1.27m diameter tuned loop offering. Maybe this helps you to explain the difference between your and my result, The original page (2) contains errors or misattribution (same thing), that is why I am careful to trim away the textual noise and restate what I perceive to be the model under investigation. 73's Richard Clark, KB7QHC |
Information about my experience with Magnetic Loop antenna's on my homepage
On Tue, 1 Mar 2011 02:25:00 +0000, ka7niq
wrote: This has been a good thread, I have little room for an antenna, a mag loop may be just the ticket for my small Tampa QTH ? Hi OM, Well, as you can imagine (barring the numerous errors and moral judgments), it all depends upon the band you want to operate - with the 40M and higher frequencies quite well served. A lot of myth surrounds what are called "magnetic loops" and this thread has corralled some of them - including from Norbert as his page which forces the argument that fairly agrees that below 40M performance dives. However, through sloppy bookkeeping, the Ciro Mazzoni line is not one I would walk away from for stated "inefficiencies." The principle consideration is the ratio between radiation resistance (power that is expressed into making contacts) and Ohmic loss (bulk metal conductivity power that is expressed into making heat). Wimpie's choice of 20mm diameter stock (how that arrived in the mix is a mystery) compares poorly with the Ciro Mazzoni 50mm tubing for its smallest design. The 80M design from the vendor uses 75mm stock for good reason and this should be a selection guide for your application. Their second 80M design uses 140mm stock! Pushing this further with conductance now nailed down, you want a large loop because the radiation resistance varies by the fourth power of dimension. That is to say, if you double the loop radius, you obtain 16 times the radiation resistance. Small changes in loop radius can quickly escalate or emasculate efficiency. Radiation resistance is the beneficial characteristic of how we manage to couple a signal out into space and which is typically thought of as being 50 Ohms (although this is rarely the actual value that more often varies between 35 and 70 Ohms for simple wire antennas of conventional length). As you can see from these resistance figures, the difference between a radiation resistance in the thousandths of an Ohm, and typical values in the tens of Ohms is a hallmark for caution. When paired with metal resistance in the Ohms (something that ordinarily only comes with using wire-wrap wire for long runs), you want to boost radiation resistance as high as possible. When paired with metal resistance that is in the thousandths of Ohms, there is every chance you are looking at 50% efficiency for 1 meter diameter loops. Bigger radius comes with its own problem, however. It limits the high band of operation as these designs are optimized for being a small portion of wavelength. Observe the various design options from Ciro Mazzoni, and you will observe they are specified over only two octaves for any particular design. That should give you a clue if you want to homebrew your own, because you will encounter the same limitations of coverage regardless of construction method. So, this returns us to the first statement above: it all depends on which band(s) you want to work. It further depends upon your pain threshold for poor efficiency if you choose to push beyond the coverage limits. Professionals describe this in terms of a cost/benefit ratio. If we restrict discussion to non-professional qualitative expressions of benefit: super, great, fantastic, maximum and peg escalating dollar amounts to each with corresponding breathless emphasis - then there are many deals for sale on those terms for the gullible. 73's Richard Clark, KB7QHC |
Information about my experience with Magnetic Loop antenna's onmy homepage
On 1 mar, 03:25, ka7niq wrote:
'Wimpie[_2_ Wrote: ;734551']On 28 feb, 20:53, Richard Clark wrote:- On Sun, 27 Feb 2011 23:14:34 -0600, John - KD5YI wrote: - Wimpie is right, Richard.- I presume Wimpie can speak for himself. *As he offered musings that were done on the back of a handy envelope, there is every chance he is not right. *I offered a similar chance that I was not right either, but I offered complete (two in fact) equations that no one has disputed, and none have faulted for computation. *I admitted a misapplication of one - which also passed without comment. Considering Wimpie's work was not done for the antenna under consideration (the size of his being much smaller where radiation resistance varies by the FOURTH POWER of size) - what does "right" mean? 73's Richard Clark, KB7QHC- Hello Richard, you used r = 1m (as you have r in your formulas), that is D = 2m, 6.28m circumference. I used D = 1.27m (4m perimeter), that is r = 0.635 m. Quote from Norbert's site: "When a magnetic loop antenna is used for 3.5 MHz with a perimeter of 4 meter *(13.3 foot) , it has an efficiency of approximately 3%." Maybe this helps you to explain the difference between your and my result, Wim PA3DJS www.tetech.nl Don't forget to remove abc in case of PM. This has been a good thread, I have little room for an antenna, a mag loop may be just the ticket for my small Tampa QTH ? -- ka7niq Hello Chris, Which antenna will fit your needs depends on many factors (tuning range, indoor/outdoor, aesthetics, local regulations, your experience/ preference, available volume, house construction, buy or homebrew, available materials, local or DX use, etc). So I can't judge whether a loop is good solution in your situation. In addition, "the" best antenna for the transmitting case will very likely not be the best one for the reception case. Best regards, Wim PA3DJS www.tetech.nl |
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