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On Wed, 22 Jun 2005 16:12:28 -0500, (Richard
Harrison) wrote: Ian White wrote: "The real technical question is how many, and how long, will be "just enough" for "here"?" Reminds me of the trailer house designer pulling out reaces until the whole projkect collapses, then rebuilding with only the last brace removed reinstalled. Sounds like the guy works for Fleetwood. Here's an example of their fine American craftsmanship used on my fifth-wheel trailer. Actually I think they probably have a crew of illegal aliens doing the work but who knows. http://users.triconet.org/wesandlind...yFleetwood.jpg The awning upright kept the sheet from tearing off completely and landing in the middle of I-10 (75 mph limit). Adding insult to injury, I had just increased my insurance deductable before the trip from $200 to $1K to "save money." |
Wes Stewart wrote:
. . . Publish the paper Walt, the authors are all gone (I think, but you know better than I) the IRE is gone too; what are they going to do, come back from the grave and sue you? The authors didn't own the copyright. (If they did, it would be the property of their heirs if still valid.) But the IRE isn't gone -- it merged with the IEE, back in the '60s as I recall, to become the IEEE. If the copyright is valid, they're its owner. And they might sue. Roy Lewallen, W7EL |
Wes, N7WS wrote:
"Sounds like the guy who works for Fleetwood." Did not expect to hit a nerve with my story of "Value Engineering". Fleetwood could be called Fleetaluminum after Wes` skin peeled and sailed down I-10 at 75 mph. When you are making many examples of a product it makes sense to minimize cost if you don`t compromise the product. A guy in my college class was hired by a car radio manufacturer. He spent most of his first 18 months with the company eliminating a single nut and bolt in a vibrator. His starting salery probably wasn`t much, but I doubt they ever produced enough vibrators to recoup the cost of their design improvement which saved a single fastener. His work must have been akin to that of T.A. Edison finding the right stuff for the filament of an incandescent lamp, finding a thousand things that didn`t work before finding one which did. Best regards, Richard Harrison, KB5WZI |
In article ,
Roy Lewallen wrote: 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's the first thing to check - see if there's any record of the renewal actually taking place in 1964 or 1965. If it didn't, then the work would have entered the public domain effective 1/1/1966, I believe. That would put it in the public domain after 1993. Here's where I differ with you. The copyright law which went into effect on 1/1/78 automatically extended the second (renewal) term of copyright, for works which had been originally copyrighted before 1950 and on which the copyright had been renewed before 1/1/78. The second (28-year) term was automatically lengthened to 67 years, giving a total of 95 years of protection. So: if the work's original 28-year copyright was not renewed, then it fell into the public domain in 1966. If the work's original 28-year copyright *was* renewed in its last ear, then the second 28-year term was effective, was automatically extended to 67 years by the Copyright Act of 1976, and is still in force today. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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On Wed, 22 Jun 2005 17:56:52 -0700, Roy Lewallen
wrote: Wes Stewart wrote: . . . Publish the paper Walt, the authors are all gone (I think, but you know better than I) the IRE is gone too; what are they going to do, come back from the grave and sue you? The authors didn't own the copyright. (If they did, it would be the property of their heirs if still valid.) But the IRE isn't gone -- it merged with the IEE, back in the '60s as I recall, to become the IEEE. If the copyright is valid, they're its owner. And they might sue. All true, but... Suppose that the IEEE has a staff of lawyers sitting around picking their collective noses and they get wind of some ham (who actually knew the authors) posting a copy of a document published in 1937 and practically incorporated by reference in every FCC licensed broadcast station's proof of performance. They can't prove any financial harm, except maybe they didn't sell a copy of the document for $25 and even at that there is some possibility that the usage is "fair" in that it's for "research purposes", do you think they will sue? Section 107 of the Copyright Act of 1976. Limitations on exclusive rights: Fair Use Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified in that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. |
Walter Maxwell, W2DU proposed a fast way to determine earth loss at
radio frequencies without digging into the earth. "Earth Constants", conductivity and permittivity, affect ground wave propagation and terrestrial reflections.. They may predict or explain some propagation. They al;so affect operation of nearby antennas. Earth permittivity is the ratio of a capacitor`s capacitance using an earth sample as a dielectric, to its capacitance using air as the dielectric. Under "permittivity" my dictionary says: "-See Dielectric Constant.". Earth conductivity is defined as the conductance between opposite faces of a unit cube (usually 1.0 cubic meter) of a given earth material, e.g. rock, sand, clay, loam, water, etc. Hoe do you measure this without changing its value? Conductivity and permittivity are affected by chemical and physical composition, moisture, and temperature (especially freezing). Earth constants are functions of frequency and antenna polarization. R.F. determination seems best. Best regards, Richard Harrison, KB5WZI |
"Wes Stewart" wrote in message ... On Wed, 22 Jun 2005 17:56:52 -0700, Roy Lewallen wrote: Wes Stewart wrote: . . . Publish the paper Walt, the authors are all gone (I think, but you know better than I) the IRE is gone too; what are they going to do, come back from the grave and sue you? The authors didn't own the copyright. (If they did, it would be the property of their heirs if still valid.) But the IRE isn't gone -- it merged with the IEE, back in the '60s as I recall, to become the IEEE. If the copyright is valid, they're its owner. And they might sue. All true, but... Suppose that the IEEE has a staff of lawyers sitting around picking their collective noses and they get wind of some ham (who actually knew the authors) posting a copy of a document published in 1937 and practically incorporated by reference in every FCC licensed broadcast station's proof of performance. They can't prove any financial harm, except maybe they didn't sell a copy of the document for $25 and even at that there is some possibility that the usage is "fair" in that it's for "research purposes", do you think they will sue? Section 107 of the Copyright Act of 1976. Limitations on exclusive rights: Fair Use Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified in that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. Seems to me, Wes, that our use on the group could be considered criticism, comment and teaching. So far I haven't received anything from the library, so we'll see what happens. Walt |
"Richard Harrison" wrote Earth constants are functions of frequency and antenna polarization. R.F. determination seems best. ================================= You seem to know something about it Rixhard. How is it done? ---- Reg |
On Thu, 23 Jun 2005 11:37:34 -0400, "Walter Maxwell"
wrote: Seems to me, Wes, that our use on the group could be considered criticism, comment and teaching. So far I haven't received anything from the library, so we'll see what happens. Hi Walt, Do you have a BailPal account that we can chip into? 73's Richard Clark, KB7QHC |
"Richard Clark" wrote in message ... On Thu, 23 Jun 2005 11:37:34 -0400, "Walter Maxwell" wrote: Seems to me, Wes, that our use on the group could be considered criticism, comment and teaching. So far I haven't received anything from the library, so we'll see what happens. Hi Walt, Do you have a BailPal account that we can chip into? 73's Richard Clark, KB7QHC Sorry Richard I don't know what a BailPal is. Or are you yankin my leg? Or on the other hand are you being a compassionate soul in case I get sued? In the meantime I've only had a short time to review the Mathcad info, but I'll have some questions on it for you shortly. Walt |
Reg, G4FGQ wrote:
"How is it done?" We have to do it within the USA broadcast frequencies with the following method. The site of the transmitting antenna is plotted on a very accurate map. Pick map sites along radiaal lines from the antenna which are accessible and free from possible reradiation sources (hard to do within a city) but many sites along a radial will work. For a single-tower, the nearest measurement site should be at least 5x the tower height away. For a directional array, the nearest measurement site should be at least 10x the widest gap between towers in the array. You need to be far enough away so the antenna system appears to be a point source. You need to make a log of the measurements you make, showing the site distance from the transmitter, measured field strength, time and conditions which influence the measurement. You need to be able to duplicate the measurements. You would prefer to make the first set of measurements with the antenna operating in a nondirectional mode even if it normally does not operate nondirectionally, so you can determine efficiency very simply. The more sites and measurements, the better. 25 measurements along each radial is often considered enough for a nondirectional antenna. 40 or 50 would be required 9in a directional array, as the number of radial measurements needed depends on the complexity of antenna system and its pattern. After completing measurements along a single radial, they should be analyzed to determine the effective field at one mile from the antenna, and the effective ground conductivity. Fortunately, the FCC publishes charts are made a part of the rules in Part 73 of the FCC Rules. You have likely seen reproductions in many textbooks. I have an old copy of all the groundwave field intensity versus conductivity charts which divide the AM broadcast band into frequency segments. These FCC charts contain more information than we can use, but they also have what we need. At the top of the chart is a straight line that shows how the signal would be attenuated over perfectly conducting earth. The field strength value at one mile is 100 mV / m. At 2 miles, it`s 50 millivolts / m, and so on. This is as expected as over perfedt earth the signal varies inversely with distance from the transmitter. Beliw the straight line on the chart is a family of curves, each dedicated to a particular soil conductivity. There is a curve for sea water, 5.000 millisiemens (millimhos) and there is a curve for about as nonconductive soil as is found (0.5 millisiemens), and there are several curves in between those extremes. All of the FCC curves are based on 100 mV / m at 1 mile, but can be scaled. If your transmitter delivers 500 mV / m at 1 mile, aimply multiply all points on the curve by 5. We want to find the conductivity of our earth. It can be different on every radial parh from the antenna.We find conductivity by plottibg our measured field intensities on translucent graph paper with grid lines which match the fcc graph. Then we line them up and place them over a light source. We can see which of the FCC curves our points most closely follow. It`s labeled ewith its conductivity. Best regards, Richard Harrison, KB5WZI |
"Richard Harrison" wrote in message ... Reg, G4FGQ wrote: "How is it done?" We have to do it within the USA broadcast frequencies with the following method. The site of the transmitting antenna is plotted on a very accurate map. Pick map sites along radiaal lines from the antenna which are accessible and free from possible reradiation sources (hard to do within a city) but many sites along a radial will work. For a single-tower, the nearest measurement site should be at least 5x the tower height away. For a directional array, the nearest measurement site should be at least 10x the widest gap between towers in the array. You need to be far enough away so the antenna system appears to be a point source. You need to make a log of the measurements you make, showing the site distance from the transmitter, measured field strength, time and conditions which influence the measurement. You need to be able to duplicate the measurements. You would prefer to make the first set of measurements with the antenna operating in a nondirectional mode even if it normally does not operate nondirectionally, so you can determine efficiency very simply. The more sites and measurements, the better. 25 measurements along each radial is often considered enough for a nondirectional antenna. 40 or 50 would be required 9in a directional array, as the number of radial measurements needed depends on the complexity of antenna system and its pattern. After completing measurements along a single radial, they should be analyzed to determine the effective field at one mile from the antenna, and the effective ground conductivity. Fortunately, the FCC publishes charts are made a part of the rules in Part 73 of the FCC Rules. You have likely seen reproductions in many textbooks. I have an old copy of all the groundwave field intensity versus conductivity charts which divide the AM broadcast band into frequency segments. These FCC charts contain more information than we can use, but they also have what we need. At the top of the chart is a straight line that shows how the signal would be attenuated over perfectly conducting earth. The field strength value at one mile is 100 mV / m. At 2 miles, it`s 50 millivolts / m, and so on. This is as expected as over perfedt earth the signal varies inversely with distance from the transmitter. Beliw the straight line on the chart is a family of curves, each dedicated to a particular soil conductivity. There is a curve for sea water, 5.000 millisiemens (millimhos) and there is a curve for about as nonconductive soil as is found (0.5 millisiemens), and there are several curves in between those extremes. All of the FCC curves are based on 100 mV / m at 1 mile, but can be scaled. If your transmitter delivers 500 mV / m at 1 mile, aimply multiply all points on the curve by 5. We want to find the conductivity of our earth. It can be different on every radial parh from the antenna.We find conductivity by plottibg our measured field intensities on translucent graph paper with grid lines which match the fcc graph. Then we line them up and place them over a light source. We can see which of the FCC curves our points most closely follow. It`s labeled ewith its conductivity. Best regards, Richard Harrison, KB5WZI Hi Richard, you deserve an A+ for your excellent presentation on the use of the FCC charts of signal level vs distance and conductivity. You've described the method exactly as I have used it for single tower BC antennas. I still have a complete set of the charts from 550 KHz to 1600 KHz that I used during the late 1940s, when I was doing AM BC antenna work. Walt, W2DU |
"Ian White GM3SEK" wrote That was an administrative policy decision rather than a technical one. From the technical viewpoint, everybody agrees that 120*0.25wl is more than enough to override the local ground conditions under the tower irrelevant. ==================================== - - - - and since soil resistivity decreases with increasing frequency, and the impedance due to soil capacitance also decreases with increasing frequency, everybody agrees that 1/8th wavelength or less is more than long enough. And if that isn't enough, the velocity of propagation along buried wires is considerably slower than the free-space value. It depends on moisture content and permittivity. The attenuation due to skin effect and wire inductance along lossy radial wires is rather high. There's negligible current flowing in them at distances greater than 1/4-wavelength at their own velocity. The wires may just as well not be there. Finally, as the wires spread apart, at appreciable distance practically all the remaining current flows in the soil because the cross-sectional area of the soil is far greater than that of the wire. The longitudinal impedance of the wire is greater than that of the soil. The foregoing applies to low and medium resistivity soils. In arid, sandy, rocky, cactus-growing soils, with resistivities greater than 5,000 or 10,000 ohms-metres, buried wires have low attenuation, they become resonant and develop standing waves. It is then a good idea to consider changing from vertical antennas to horizontal dipoles. The effects can be estimated by calculations on model radial systems. It may have been noticed that ground loss is least at low and very high resistivities. So there must be a maximum loss at some resistivity. I wonder if maximum loss occurs around 377 ohm-metres after taking the reflecting angle into account? If B. L & E, made any errors, they made sure they erred on the safe side regarding numbers. ---- Reg, G4FGQ |
"Reg Edwards" wrote in message ... "Ian White GM3SEK" wrote That was an administrative policy decision rather than a technical one. From the technical viewpoint, everybody agrees that 120*0.25wl is more than enough to override the local ground conditions under the tower irrelevant. ==================================== - - - - and since soil resistivity decreases with increasing frequency, and the impedance due to soil capacitance also decreases with increasing frequency, everybody agrees that 1/8th wavelength or less is more than long enough. Reg, do you really mean what you said above, 'soil resistivity decreases with increasing frequency'? Are you sure you didn't mean soil conductivity decreases with increasing frequency? In my experience with AM BC antennas I've found that conductivity decreases, not resistivity. The FCC charts showing signal level vs conductivity and frequency overwhelmingly show conductivity decreasing with frequency. So you ask, what proof is there that the FCC charts are correct? Well, Reg, soil conductivity measurements of thousands of AM antenna systems world wide have proved them correct. As an example that I posted a few days ago, consider the coverage area from afforded by a single 1/4wl vertical radiating 250 watts at 550 KHz with a signal strength of 1 mv/meter at one mile and a conductivity of 8. If the frequency were raised to 1500 KHz with a 1/4wl vertical at that frequency, the power required to cover the same area is 47 KW. Does this example indicate a decreasing soil resitivity with increasing frequency or a decreasing soil conductivity? Walt, W2DU |
Walter,
Your ancient charts, which I think I have once seen but don't now have ready access to, apply to LF. Permittivity was ignored when they were calculated. The curves were intended to be used as a guide, better than nothing, rather than the Bible on the subject. But amateurs are concerned with what happens at HF. There are a lot of MHz between 16 KHz, 500 KHz and 40 MHz I think the discrepancy about conductivity vs frequency is due to simplification of the equivalent circuit of soil which, in its most simple form, is a resistor in shunt with a capacitor. As frequency increases the capacitative impedance decreases and drags the equivalent resistive component down with it. There is a significant decrease at around 7 MHz. At 30 or 40 MHz the soil has changed from being mainly resistive at LF to being mainly capacitative and not nearly so lossy. The capacitance between a pair of 1 metre square plates, spaced 1 metre apart, is only 8.8 pF. But when muliplied by the permittivity of damp soil the impedance at 30 MHz is quite low. The permittivity of water is 80. Simple conductivity does not apply. We are not talking about the same things. Actually, its not worth arguing about. The uncertainty in soil characteristics is plus or minus 30 or 40 percent. And it makes less than 1 S-unit difference to the performance of radials and Eznec take off angles at HF. No doubt Roy will disagree as a matter of Boston Tea Party principles. And Richard, KB7QHC, will spin off at a tangent into Shakesperian verse. Hope this clarifies my Altzeimer's thoughts on the matter. ---- Reg, G4FGQ |
On Sat, 25 Jun 2005 05:42:31 +0000 (UTC), "Reg Edwards"
wrote: Richard, KB7QHC, will spin off at a tangent into Shakesperian verse. Hi Reg, Let's draw a chord between 3 soil samples to see how fruitless knowing "How to measure soil constants at HF" really is: You are in farm country where the annual rainfall is 835mm. Where the mean temperature is 12.8°C. Where the soil is 20% sand, 65% silt, and 15% clay. What is the Conductivity in the 80M band? You are in farm country where the annual rainfall is 360mm. Where the mean temperature is 4.9°C. Where the soil is 65% sand, 20% silt, and 15% clay. What is the Conductivity in the 80M band? You are in farm country where the annual rainfall is 790mm. Where the mean temperature is 6.9°C. Where the soil is 31% sand, 33% silt, and 36% clay. What is the Conductivity in the 80M band? OR We return to our regularly scheduled "More Les Dames d'Escoffier Recipes with your host Punchinello." Today we discuss packing coaxial tubes with meringue to measure propagation delay for custards. 73's Richard Clark, KB7QHC |
"Richard Clark" wrote in message ... On Sat, 25 Jun 2005 05:42:31 +0000 (UTC), "Reg Edwards" wrote: Richard, KB7QHC, will spin off at a tangent into Shakesperian verse. Hi Reg, Let's draw a chord between 3 soil samples to see how fruitless knowing "How to measure soil constants at HF" really is: You are in farm country where the annual rainfall is 835mm. Where the mean temperature is 12.8°C. Where the soil is 20% sand, 65% silt, and 15% clay. What is the Conductivity in the 80M band? You are in farm country where the annual rainfall is 360mm. Where the mean temperature is 4.9°C. Where the soil is 65% sand, 20% silt, and 15% clay. What is the Conductivity in the 80M band? You are in farm country where the annual rainfall is 790mm. Where the mean temperature is 6.9°C. Where the soil is 31% sand, 33% silt, and 36% clay. What is the Conductivity in the 80M band? OR We return to our regularly scheduled "More Les Dames d'Escoffier Recipes with your host Punchinello." Today we discuss packing coaxial tubes with meringue to measure propagation delay for custards. 73's Richard Clark, KB7QHC ==================================== I don't know. And neither do you or anybody else. If you DID know you would not have the foggiest idea what to do with the data anyway. I might! Havn't I recently said the uncertainty in ascertaining soil characteristics is in the order of 30 to 40 percent and not worth arguing or making yourself appear ridiculous about. There's missing data. You forgot the iron oxide content and soil permeability. ---- Punchinello. |
Reg Edwards wrote:
. . . The attenuation due to skin effect and wire inductance along lossy radial wires is rather high. There's negligible current flowing in them at distances greater than 1/4-wavelength at their own velocity. The wires may just as well not be there. . . . I'm afraid your oversimplified model of how radials work has once again led you astray. B, L, & E's measurements show the following: For an 88 degree high vertical, where n is the number of radials, the following fraction of the current at the center is flowing in the radial 1/4 wavelength (at a velocity factor of 0.2, the approximate VF in the radial's environment), from Fig. 42 of their paper: n Fraction 15 0.67 30 0.68 60 0.90 113 ~ 1.0 1/4 *free space* wavelength from the center: n Fraction 15 0.19 30 0.14 60 0.26 [This is a minimum; it rises then drops further out] 113 0.61 " " Note that the results are quite different when the radiator is only 22 degrees high (Fig. 43) -- the resonant effects apparent on the 60 and 113 radial measurements are absent, and the currents decay monotonically. There isn't nearly as much difference between 15 and 113 radials. But with 15 radials, the current 1/4 in-ground wavelength from the center is still about 67% of the current at the center. Again I see evidence that your analysis overlooks the interaction among radials. There's less interaction when there are only a few, but even with 15 your analysis has led you badly astray. And does it account for the considerable differences with different radiator heights? But I've pointed this out to you before yet you keep promoting this myth, so I guess you just don't want to be confused by the facts. If B. L & E, made any errors, they made sure they erred on the safe side regarding numbers. One of their key results is that ". . .the ground system consisting of only 15 radial wires need not be more than 0.1 [free space] wave length long, while the system consisting of 113 radials is still effective out to 0.5 [free space] wave length." Their results agree reasonably well with NEC-4 modeling. But I'm sure glad we've got you to set us straight about how well they did and how they could have improved their methods. You've surely got a clearer perspective, not having been prejudiced by actually reading their paper. Oops, here I am nitpicking again -- pointing out that .67 doesn't equal zero. Roy Lewallen, W7EL Certified Reg's Old Wife and Nit-Picker |
Reg, G4FGQ wrote:
"Your ancient charts, which I think I have once seen but don`t now have access to, apply only to LF. Permittivity was ignored when they were calculated." True, they are not for HF. My edition was reprinted by the Seabrooke Printing Company, Inc. and covers the range ftom 540 KHz to 1600 KHz. Dielectric constant (permittivity) is assumed to be 15 in all cases. The reason there are graphs for frequency segments such as 1560 kc to 1640 kc is that loss increases with frequency. Skin effect is an important faxtor. The higher the frequency, the less it penetrates the earth, so the crust carrying the r-f is thinner. The decline of field intensity versus distance from the transmitter is steeper at HF. My set of curves has a page which gives the formulas used to construct "surface wave field intensity versus numerical distance over plane earth". It has separate sets of formulas for vertical and horizontal polarizations. Curves in the book are for vertical polarization, the only thing of interest to a broadcaster. One option would be to construct your own set of curves. Another would be to find some curves which have already been constructed. I don`t know of any but expect that they exist. Best regards, Richard Harrison, KB5WZI |
On Sat, 25 Jun 2005 07:56:38 +0000 (UTC), "Reg Edwards"
wrote: "Richard Clark" wrote in message .. . You are in farm country where the annual rainfall is 835mm. Where the mean temperature is 12.8°C. Where the soil is 20% sand, 65% silt, and 15% clay. What is the Conductivity in the 80M band? Answer: 30 mS You are in farm country where the annual rainfall is 360mm. Where the mean temperature is 4.9°C. Where the soil is 65% sand, 20% silt, and 15% clay. What is the Conductivity in the 80M band? Answer: 30 mS You are in farm country where the annual rainfall is 790mm. Where the mean temperature is 6.9°C. Where the soil is 31% sand, 33% silt, and 36% clay. What is the Conductivity in the 80M band? Answer: 15 mS ==================================== I don't know. And neither do you or anybody else. Such answers above have been know for decades. If you DID know you would not have the foggiest idea what to do with the data anyway. I might! You might? With emphasis too. Now if that isn't a firm declaration to end the pursuit in "How to measure soil constants at HF." In point of fact, you simply validate my premise: Let's draw a chord between 3 soil samples to see how fruitless knowing "How to measure soil constants at HF" really is As you struggled on: There's missing data. You forgot the iron oxide content and soil permeability. There is so much missing information as: What is it to an average of one skin depth in YOUR garden, old son? To this point all method and no results. By contrast, Walt provided both, and his data shows a continuity to your pronouncement about the wavelength shortening of radials adjacent to the ground - something you proclaimed no antenna measurement could achieve. Walt's method necessarily includes one skin depth (and more) that your scraping at the veneer of soil could never model. He doesn't have to worry about temperature, moisture, time of day, season, iron oxide content, or permeability - it comes free with the attempt and you don't have to haul mud into the kitchen. Do I hear John Cleese muttering something about the Bloody Obvious? 73's Richard Clark, KB7QHC |
Roy, surely you realise that all depends on soil conductivity and
permittivity which B, L & E forgot to determine before leaving the site. 30 years previously, around 1905, Sommerfeld (and others) had produced a significant report showing the importance of ground characteristics on radiation and propagation at LF and below. Which B, L, & E ought to have been aware of if they had known what they were about. You should concentrate your thoughts on HF and above, not on LF and VLF distractions. Different characteristics prevail at HF at which frequencies amateurs are most concerned. ---- Reg |
Reggie,
The following is so full of glaring contradictions - well, you can rely on me to point them out. :-) On Sat, 25 Jun 2005 18:34:17 +0000 (UTC), "Reg Edwards" wrote: Roy, surely you realise that all depends on soil conductivity and permittivity which B, L & E forgot to determine before leaving the site. You have thoroughly refuted any intimate knowledge of their paper, it goes unread by you, and yet you "know" this for a fact. Or perhaps that is elevating your prose upon to an unwarranted pedestal. 30 years previously, around 1905, Sommerfeld (and others) had produced a significant report showing the importance of ground characteristics on radiation and propagation at LF and below. Which B, L, & E ought to have been aware of if they had known what they were about. However, your earlier reference to LF from Sommerfeld (and others) is then wholly negated by you with: You should concentrate your thoughts on HF and above, not on LF and VLF distractions. Different characteristics prevail at HF at which frequencies amateurs are most concerned. Back in 1905, they called the frequencies above 1MHz VHF.... So, our trio, B,L, & E could just as easily had dismissed this work as you have? Such legerdemain. Sir Kelvinator asks, "Got any data, Reggie?" This quality of fence sitting - arguing both sides against the middle - is classic Punchinello. 73's Richard Clark, KB7QHC |
Reg Edwards wrote:
Roy, surely you realise that all depends on soil conductivity and permittivity which B, L & E forgot to determine before leaving the site. It just isn't sinking in, is it? It depends on the conductivity and permittivity to a skin depth or more, which was impossible for them to determine. A surface measurement wouldn't have provided the necessary information. Measurement of ground wave attenuation to another location would have included ground with a variety of possible characteristics different from those in the immediate vicinity. 30 years previously, around 1905, Sommerfeld (and others) had produced a significant report showing the importance of ground characteristics on radiation and propagation at LF and below. Which B, L, & E ought to have been aware of if they had known what they were about. I'm sure they were. But the paper has nothing to do with propagation. What makes you think it does? They certainly did know about the effect of conductivity. In a theoretical analysis at the beginning of their paper they calculated expected radial ground currents for several different ground conductivities, and explain how current is distributed in the ground with conductivity being a factor. The radial ground current analysis was later found to be in error(*), but it's still considerably closer than the results I've seen from your analysis and program. You should concentrate your thoughts on HF and above, not on LF and VLF distractions. Different characteristics prevail at HF at which frequencies amateurs are most concerned. That's a bizarre admonition from someone constantly harping about how many radials American AM broadcasters use. I am indeed most interested in HF, where skin depth is on the order of 12 feet for average soil, and measurement of surface conductivity and permittivity is pretty useless. Incidentally, since you haven't read their paper, you probably don't know that the BL & E measurements were done at 3 MHz, which is HF. (*) To my knowledge, no one has developed a method of calculating radial currents or ground system losses with even approximate accuracy other than with numerical analysis such as used by NEC-4. Many years ago I spent a couple of years of spare time in a technical library looking for just such an analysis without success. Reg's method is delightfully simple but gives results which are very wrong. Roy Lewallen, W7EL |
I wrote:
"Another (option) would be to find some curves which have already been constructed." Found some curves in Pete Saveskie`s "Radio Propagation Handbook" on pages 15, 17, and 19. They are from CCIR and may be available from them. They are for field strengths over sea water, good earth, and poor earth at 16 frequencies from 100 KHz to 10 MHZ. Best regards, Richard Harrison, KB5WZI |
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