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#1
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"Roy Lewallen" wrote in message ... Ian White GM3SEK wrote: . . . The real technical question is: how many, and how long, will be "just enough" for "here"? That obviously requires a lot more knowledge and engineering judgement. . . . Well, Ian, the BLE paper reports data allowing one to make that engineering judgement. It's unfortunate that my copy of the paper is in my library in Florida, and I won't be back there until November to scan it for the group. However, I have ordered a copy from the Michigan State U library. The BLE experiments were conducted to determine what combination of radials would form the best simulation of a perfect ground, i.e., what combination would achieve a field strength closest to the ideal calculated value. One factor they considered is that when the spacing between adjacent wires in a grid structure is 1/20 lambda or less, the effect is that of a continuous reflecting surface. The spacing between radials is not exactly the same as a grid structure, but the effect is similar. BLE found that the optimum length of the radials in the ground is not related to resonant length as it is with elevated radials. They found that the principal reason for the optimum length concerns the volume containing the significant energy in the electromagnetic fields in the space surrounding the radiator that intersects the ground. They found that at a distance of 0.4 lambda from the radiator the energy in the fields has reduced to the level of diminishing returns, where collecting the currents at a greater distance would yield no significant decrease in loss resistance, and therefore no further increase in field strength. Indeed, the field strength obtained with at least 90 radials 0.4 lambda in length was found to be insignificantly less than that of a perfect ground. This fact was unknown prior to BLE's experiments. I can't remember the exact difference shown in the graph, but it is inconsequential. With the radials simulating a near-perfect reflecting ground plane the skin depth of the earth beneath the radials is of no consequence, because the RF energy is nearly totally reflected, with only an insignificant amount transmitted through the ground plane. Consequently, the soil conditions directly beneath the ground plane are irrevelant. However, the soil conditions immediately external to the ground plane are important to the intensity of the ground wave propagation from vertical radiators. The poorer the soil conductivity the greater the loss at low angles of elevation. And as we all know, propagation of the ground wave is frequency sensitive. Many years ago, using the FCC propagation charts of field strength vs distance for a conductivity of 8, the geographical area covered with a field strenght of 1 mv/meter at 1 mile for a 250 watt station at 550 KHz would require 47 kilowatts at 1500 KHz to cover the same area with the same signal level. When I receive the requested copy of the BLE paper I'll scan it and publish it for all to see. Walt, W2DU |
#2
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"Walter Maxwell" wrote in message ... "Roy Lewallen" wrote in message ... Ian White GM3SEK wrote: . . . The real technical question is: how many, and how long, will be "just enough" for "here"? That obviously requires a lot more knowledge and engineering judgement. . . . Well, Ian, the BLE paper reports data allowing one to make that engineering judgement. It's unfortunate that my copy of the paper is in my library in Florida, and I won't be back there until November to scan it for the group. However, I have ordered a copy from the Michigan State U library. The BLE experiments were conducted to determine what combination of radials would form the best simulation of a perfect ground, i.e., what combination would achieve a field strength closest to the ideal calculated value. One factor they considered is that when the spacing between adjacent wires in a grid structure is 1/20 lambda or less, the effect is that of a continuous reflecting surface. The spacing between radials is not exactly the same as a grid structure, but the effect is similar. BLE found that the optimum length of the radials in the ground is not related to resonant length as it is with elevated radials. They found that the principal reason for the optimum length concerns the volume containing the significant energy in the electromagnetic fields in the space surrounding the radiator that intersects the ground. They found that at a distance of 0.4 lambda from the radiator the energy in the fields has reduced to the level of diminishing returns, where collecting the currents at a greater distance would yield no significant decrease in loss resistance, and therefore no further increase in field strength. Indeed, the field strength obtained with at least 90 radials 0.4 lambda in length was found to be insignificantly less than that of a perfect ground. This fact was unknown prior to BLE's experiments. I can't remember the exact difference shown in the graph, but it is inconsequential. With the radials simulating a near-perfect reflecting ground plane the skin depth of the earth beneath the radials is of no consequence, because the RF energy is nearly totally reflected, with only an insignificant amount transmitted through the ground plane. Consequently, the soil conditions directly beneath the ground plane are irrevelant. However, the soil conditions immediately external to the ground plane are important to the intensity of the ground wave propagation from vertical radiators. The poorer the soil conductivity the greater the loss at low angles of elevation. And as we all know, propagation of the ground wave is frequency sensitive. Many years ago, using the FCC propagation charts of field strength vs distance for a conductivity of 8, the geographical area covered with a field strenght of 1 mv/meter at 1 mile for a 250 watt station at 550 KHz would require 47 kilowatts at 1500 KHz to cover the same area with the same signal level. When I receive the requested copy of the BLE paper I'll scan it and publish it for all to see. Walt, W2DU In my previous post above I forgot to mention that the displacement currents that enter the ground between the radials don't follow the lossy ground to the center of the radial system. Instead, they quickly diffract to the nearest radial and thus continue toward the center along the radial wire. Consequently, the more radials the shorter distance the diffracted current has to travel to reach the higher conductivity of the wire. The last I knew the FCC requires only 90 radials (every 4°) to comply with the regulations, but many BC antenna engineers use 120 (every 3°). I discussed this issue in Chapter 5 in both the 1st and 2nd editions of Reflections, with a diagram of the diffraction phenomenon in Fig. 1. Walt, W2DU |
#3
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Walter Maxwell wrote:
In my previous post above I forgot to mention that the displacement currents that enter the ground between the radials don't follow the lossy ground to the center of the radial system. Instead, they quickly diffract to the nearest radial and thus continue toward the center along the radial wire. Consequently, the more radials the shorter distance the diffracted current has to travel to reach the higher conductivity of the wire. The last I knew the FCC requires only 90 radials (every 4°) to comply with the regulations, but many BC antenna engineers use 120 (every 3°). I discussed this issue in Chapter 5 in both the 1st and 2nd editions of Reflections, with a diagram of the diffraction phenomenon in Fig. 1. This interaction among radials has quite a dramatic effect on the effective ground conductivity. I noticed and reported quite some time ago that Reg's ground radial program produced answers which disagree strongly with both BLE and NEC-4 modeling (which agree with each other reasonably well), and speculated that he didn't account for this interaction in his program. (I haven't checked since to see if the program has been modified.) All he says about having to trust the writer of the program if you don't have access to the source code is true. Roy Lewallen, W7EL |
#4
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Walter Maxwell wrote:
. . . When I receive the requested copy of the BLE paper I'll scan it and publish it for all to see. Is the publishing of copyrighted papers on the Web generally permitted under fair use rules? The IEEE and other publishers of professional papers charge around $25 for downloaded reprints, and I'd think that would cut into their income. Or does the IEEE specifically permit publishing of their papers on the Web? Roy Lewallen, W7EL |
#5
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On Wed, 22 Jun 2005 08:57:00 -0700, Roy Lewallen
wrote: Walter Maxwell wrote: . . . When I receive the requested copy of the BLE paper I'll scan it and publish it for all to see. Is the publishing of copyrighted papers on the Web generally permitted under fair use rules? The IEEE and other publishers of professional papers charge around $25 for downloaded reprints, and I'd think that would cut into their income. Or does the IEEE specifically permit publishing of their papers on the Web? Unless I'm mistaken, the copyright would have had to been renewed to remain in effect. According to this link: http://www.scils.rutgers.edu/~lesk/copyrenew.html it was not. |
#6
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On Wed, 22 Jun 2005 09:33:33 -0700, Wes Stewart
wrote: According to this link: http://www.scils.rutgers.edu/~lesk/copyrenew.html it was not. Hi Wes, You should take care to observe the proviso offered: "This file does not contain listings for music, movies, or periodicals." The practice of many journals is that your material, offered for publication, is accepted only with the explicit rights of ownership being transferred to that society. In fact, if you were to cite your own work without giving a reference to that society's publication, then you could be held accountable for plagiarism. The "Open Source" movement has sparked a debate in this regard and academic authors are being better versed on methods that allow them to both publish and retain rights. 73's Richard Clark, KB7QHC |
#7
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Wes Stewart wrote:
Unless I'm mistaken, the copyright would have had to been renewed to remain in effect. According to this link: http://www.scils.rutgers.edu/~lesk/copyrenew.html it was not. Thanks for the URL - it looks like it'll come in handy. Unfortunately, the fourth sentence on that page is "This file does not contain listings for music, movies, or periodicals." The BLE paper was published in the _Proceedings of the IRE_, a periodical. Roy Lewallen, W7EL |
#8
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"Roy Lewallen" wrote in message ... Walter Maxwell wrote: . . . When I receive the requested copy of the BLE paper I'll scan it and publish it for all to see. Is the publishing of copyrighted papers on the Web generally permitted under fair use rules? The IEEE and other publishers of professional papers charge around $25 for downloaded reprints, and I'd think that would cut into their income. Or does the IEEE specifically permit publishing of their papers on the Web? Roy Lewallen, W7EL Hasn't the copyright expired on material published in 1937? Walt |
#9
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On Wed, 22 Jun 2005 13:49:11 -0400, "Walter Maxwell"
wrote: Hasn't the copyright expired on material published in 1937? Hi Walt, You cannot imagine how difficult it is to track down rights' holders. The presumption does not lie in copyright having expired automatically. Many organizations hire lawyers for no other purpose than this paper chase. The author's name is becoming increasingly irrelevant in this age of information. 73's Richard Clark, KB7QHC |
#10
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Walter Maxwell wrote:
Hasn't the copyright expired on material published in 1937? Hm. The way I read http://www.copyright.gov/circs/circ1.html#hlc, it has. It looks to me like the original copyright was good for 28 years and for copyrights originally issued in 1937, renewal (if done) was good for another 28. That would put it in the public domain after 1993. I'd sure appreciate comments from someone who's actually familiar with the law -- it's pretty convoluted and I'm not at all confident about my interpretation. Roy Lewallen, W7EL |
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