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#1
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#2
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The best answer I've seen, based on current research is:
N=(SQRT(2*PI*L))/A N equals the square root of the quantity 2*PI*L divided by A, whe N = optimum number of radials for high efficiency L = amount of wire available in meters A = distance between wire tips at the far end (a measure of radial density) A = 1.3 for 95% or greater efficiency (approximation) read article for more precise values. A = 2.6 for 85% efficiency (approximation) Example 1: You have 500 meters of wire available. How many and how long for the two values of A? N = (SQR(2*pi*500))/1.3 = 43 radials. Length = 500/43 = 11.6 meters N= (SQR(2*pie*500))/2.6 = 22 radials. Length = 500/22 = 18 meters Example 2: (you have space constraints and the max radial length available is 15 meters) How many radials are required and how much wire is required? The circumference of a circle with a radius of 15 meters is 2*PI*15 or 94.2 meters. With the tips of the radials seperated by 1.3 meters we have 94.2/1.3 = 72 radials. If we go for slightly more loss, we have 94.2/2.6 or 36 radials, 15 meters long. Now you can plug in your own limitations for radial length, and get a feel for how many of them you will need for 95% efficiency (A=1.3 meters) and 85% (A=2.6 meters). This info was presented in some ARRL publication, as I recall, and is also presented in the 4th Edition of "Low-Band DXing" by John Devodere. ....hasan, N0AN "Walter Maxwell" wrote in message ... On Sun, 4 Sep 2005 22:24:24 -0500, (Richard Harrison) wrote: Reg, G4FGQ wrote: "The rods are both wasted effort and wasted copper (or aluminum)." Likely so. Radials are placed to capture displacement current to and from the vertical radiator, to prevent its travel at a high densitY in the earth where it would cause high loss. B, L, & E found that more radials were better than longer radials. More radials put the displacement current capture closer to the vertical radiator where its density is higher. Radials need extend outward only as far as there is any current or until a point of diminishing returns is reached. At great distance from the vertical radiator, the earth`s crust, which may be affected, has a great cross section, so current density is low and so are losses. There is much less displacement current to deal with near the ends of radials. Displacement current is low near the ends of the radials and the earth out there has a large cross section and a low resistance. Due to skin effect, the closer to the surface, the higher the current. This is especially true at high frequencies. Hi Richard, You've just presented the best abstract of BL&E I've seen ever seen. It should be must reading for anyone who asks questions concerning the purpose of radials, how many, and how long. Walt, W2DU |
#3
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I appreciate Walt, W2DU`s kind words regarding my posting about ground
rods and radials. I did not recommend any particular number or length of radials. RCA`s Brown, Lewis, and Epstein examined how many and how long ground radials should be in the 1930`s. The FCC accepted their experimental work, conducted at 3 MHz, and used it to set ground system standards for broadcasting in the medium wave band. These standards are still applicable. B.L.&E. did good work. Another RCA alumnus, E.A. Laport, abstracted some of B.L.&E.`s work in "Radio Antenna Engineering". Figs. 2.17, 2.18, and 2.19 on pages 119 and 120 show field strength as a function of the number of radials. All the Figs. show near perfection with 113 radials, so it seems the FCC rounded up to 120 radials and made it the rule. It`s worked well, giving us good broadcast reception when the earth is dry and sandy or wet and swampy. Laport`s figures show performance with 1/2 and 1/4 the ideal number of radials. As Walter flattered me, I`ll reciprocate. Get hold of the April 1973 issue of QST. Look on page 35. Walter is pictured there. He is a real good looking fellow! Best regards, Richard Harrison, KB5WZI |
#5
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On Mon, 05 Sep 2005 14:25:09 -0700, Dan Richardson wrote:
On Mon, 5 Sep 2005 15:31:18 -0500, (Richard Harrison) wrote: [snip] As Walter flattered me, I`ll reciprocate. Get hold of the April 1973 issue of QST. Look on page 35. Walter is pictured there. He is a real good looking fellow! [snip] If you don't have that QST handy you can see Walter he http://users.adelphia.net/~k6mhe/BLE_de_W2DU.html 73, Danny, K6MHE Well, Danny, ya had to go and do it din't ya? Now people who see my face in post offices will know how to trace me through my mug shot you just posted. I thought I'd gotten away with it. Somebody hire you to post it? CSI? Law & Order? At least after I'm sent away to Attica everybody, including you, will be able to find me. Ya wanna know sumptin? I don't even have any remorse! Walt |
#6
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On Mon, 05 Sep 2005 21:32:45 -0400, Walter Maxwell
wrote: Well, Danny, ya had to go and do it din't ya? Now people who see my face in post offices will know how to trace me through my mug shot you just posted. I thought I'd gotten away with it. Somebody hire you to post it? CSI? Law & Order? At least after I'm sent away to Attica everybody, including you, will be able to find me. Ya wanna know sumptin? I don't even have any remorse! Walt The devil made me do it! G Danny |
#7
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On Mon, 05 Sep 2005 14:25:09 -0700, Dan Richardson wrote:
On Mon, 5 Sep 2005 15:31:18 -0500, (Richard Harrison) wrote: [snip] As Walter flattered me, I`ll reciprocate. Get hold of the April 1973 issue of QST. Look on page 35. Walter is pictured there. He is a real good looking fellow! [snip] If you don't have that QST handy you can see Walter he http://users.adelphia.net/~k6mhe/BLE_de_W2DU.html 73, Danny, K6MHE Danny, I was just perusing the data in the post re the above url and found a typo. In the ground radial data in the line showing 30 radials, the data for 0.4/wl indicating 158 mv/meter should read 185 mv/meter. I've searched through my files for the one I sent to you containing this data, but I can't find it. I'm assuming you simply copied my data, so it's probably my error, which I'd like to fix in the original. I guess all I can do is ask you to place a correction on that incorrect piece of data to avoid giving the impression that the remaining data may be suspect. Walt, W2DU |
#8
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On Mon, 05 Sep 2005 22:22:37 -0400, Walter Maxwell
wrote: On Mon, 05 Sep 2005 14:25:09 -0700, Dan Richardson wrote: On Mon, 5 Sep 2005 15:31:18 -0500, (Richard Harrison) wrote: [snip] As Walter flattered me, I`ll reciprocate. Get hold of the April 1973 issue of QST. Look on page 35. Walter is pictured there. He is a real good looking fellow! [snip] If you don't have that QST handy you can see Walter he http://users.adelphia.net/~k6mhe/BLE_de_W2DU.html 73, Danny, K6MHE Danny, I was just perusing the data in the post re the above url and found a typo. In the ground radial data in the line showing 30 radials, the data for 0.4/wl indicating 158 mv/meter should read 185 mv/meter. I think you mean the line for 60 radials? Anyway I changed that one to the 185 figure. Please double check it for me. Thanks, Danny, K6MHE email: k6mheatarrldotnet http://users.adelphia.net/~k6mhe/ |
#9
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On Mon, 05 Sep 2005 19:33:38 -0700, Dan Richardson wrote:
If you don't have that QST handy you can see Walter he http://users.adelphia.net/~k6mhe/BLE_de_W2DU.html 73, Danny, K6MHE Danny, I was just perusing the data in the post re the above url and found a typo. In the ground radial data in the line showing 30 radials, the data for 0.4/wl indicating 158 mv/meter should read 185 mv/meter. I think you mean the line for 60 radials? Anyway I changed that one to the 185 figure. Please double check it for me. Thanks, Danny, K6MHE email: k6mheatarrldotnet http://users.adelphia.net/~k6mhe/ Ya done good, Danny, thanks. Walt |
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