|
Ground rods.at HF
I post the following as a copy of a reply I made to the uk.amateur
radio newsgroup. ===================================== I am considering the using some army surplus aluminium alloy poles as part of the rf ground for an inverted L antenna. They are thick walled 4ft tubes able to withstand stand being driven into the ground, and are lying around waiting to be used for something. The issues which come to mind are corrosion through contact with the earth and electrolytic reaction where a copper cable is attatched with steel bolt and eylet connector. Has anyone on here tried this? John m1jta ==================================== John, I have used 3 or 4 feet alumininium alloy tubes as earth rods, on and off, for many years. I have found them just the same as any other or metals - ie., no bloody good. Electrically, at HF, a 3 or 4-feet earth rod is no better than a single, thin, radial, shallow-buried, horizontal wire of the same length which is much easier to install. The resistance to ground has nothing whatsoever to do with the conductivity of the metal or surface corrosion products. It has everything to do with the resistivity of the soil in which the rod is embedded. ie., the soil in the immediate vicinity of the rod. Resistance to ground depends almost entirely on rod length and is only very slightly dependent on rod diameter. Only old wives believe resistance is related to surface area of the rod or electrode and dig great holes in their back gardens to bury unwanted, scrap, hot-water cylinders. They would do better by approaching their local scrap metal merchant. A 3 or 4 feet rod in typical garden soil has a resistance to ground of the order of 100 to 200 ohms and by itself is useless. To locate one rod immediately next to another does next to nothing regarding ground connection resistance. A pair of rods must be spaced apart by at least twice their length before the resulting ground resistance approaches half the resistance of one rod. A collection of a number of rods must be spaced apart by many times greater than their depth of burial to obtain the full benefit of all being connected in parallel. Consequently, the connecting wires from rods to a focal point themselves constitute a good system of shallow-buried radials and the short rods at the ends of the radial wires can be dispensed with. Exactly the same result can be achieved just by extending the radials by another, insignificant 3 feet. The rods are both wasted effort and wasted copper (or aluminium). ---- Reg, G4FGQ |
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. |
I sent too soon.
The problem with ground rods at high radio frequencies is that depth of earth renetration may be low as compared with length of the ground rod. Contact that counts is that which connects with the current path. There is a special problem with the aluminum material itself of the ground rods mentioned by the questioner. Aluminum, zinc, and magnesium are galvanic anodes used for cathodic protection of less active metals. A copper ground rod is likely to last forever in the soil. An aluminum ground rod is likely to soon be sacrificed in its attempt to protect other connected metals in the same galvanic soup. Best regards, Richard Harrison, KB5WZI |
|
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 |
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 |
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 |
|
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 |
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 |
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 |
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/ |
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 |
"Walter Maxwell" wrote Back on the subject of radials, unless the FCC has changed the requirements since I was involved, the requirement is for 90 radials. However, most of the AM BC stations I'm familiar with use 120, even tho not required. ======================================== Walt, Has it taken 70 years for the old wives of the FCC to return to Earth, disregarding B.L & E who forgot to measure ground conductivity, not to mention permittivity, and think again about economics? ---- Reg. |
Has it taken 70 years for the old wives of the FCC to return to Earth,
disregarding B.L & E who forgot to measure ground conductivity, not to mention permittivity, and think again about economics? The only stations that the FCC is concerned about is commercial. And the reason they stick with the standard number is for stability and getting the max bang for buck, and an easily expected performance level. Buying a load of wire will beat using more transmitter power over the long run. If they use 120 radials, they know they will be getting close to maximum performance. If they don't, it's a crap shoot. 120 radials *will* outperform 16 of them. There is no question, unless they are over sea water. I'm not saying hams have to run that many. In fact, I think 60 will do for most, except the most hard core for good results. Even less for the more casual user. But I have no problems with the FCC wanting a certain level of performance for commercial stations. I have no problems seeing why they do it either. Wire is cheap compared to todays level of monthly light bill. With some stations, the radials, or lack of , in certain directions gives them a controlable pattern with no surprises in f/s over a period of time with changing ground conditions. The main thing is stability of performance over periods of time. Or thats my take anyway. MK |
MK,
How satisfying it is to read your message, written in plain, easy to understand, well-punctuated English, without any undeciferable coded abbreviations. I agree with what you say although I am unfamiliar with exactly how the FCC fits into the scheme of things. Amateurs and commercial broadcasters have a common fundamental requirement. There is a service area to be covered with a given field strength. Depending on frequency, requirements then diverge. But the design methods used to satisfy requirements are all confined (or should be) to the principles of engineering economics. Inevitably, the Dollar, Pound, Frank, Mark, Rouble and the Yen rule the roost. Both commercial broadcasters and amateurs do a cost-befit analysis. The broadcaster takes into account the revenue acruing from selling the service. The amateur, whether he likes it or not, has to ask himself what the satisfaction of using the station is worth. Amateurs' bank accounts are not unlimited. Field strength at the limits of the service area depends on the power efficiency of the radiating system. If engineering economics dictate use of a set of buried ground radials then the peformance of the ground radials must be included. Considering the system as a whole, it may be economical NOT to achieve the maximum possible radiating efficiency. Indeed, the maximum is seldom the target. If there is an economical choice in the matter, once the location of the station is decided, everybody agrees that efficiency depends on soil resistivity at the site. To estimate efficiency it is necessary, at the very least, to make a guess at soil resistivity. Perhaps just by looking at the type of weeds growing in it. Or it can be measured. Depending on how far it enters into station economics, it is possible to numerically estimate efficiency from the number and length of radials AND FROM SOIL RESISTIVITY. B.L & E and the FCC don't enter into it. ---- Reg. ======================================== MK wrote, The only stations that the FCC is concerned about is commercial. And the reason they stick with the standard number is for stability and getting the max bang for buck, and an easily expected performance level. Buying a load of wire will beat using more transmitter power over the long run. If they use 120 radials, they know they will be getting close to maximum performance. If they don't, it's a crap shoot. 120 radials *will* outperform 16 of them. There is no question, unless they are over sea water. I'm not saying hams have to run that many. In fact, I think 60 will do for most, except the most hard core for good results. Even less for the more casual user. But I have no problems with the FCC wanting a certain level of performance for commercial stations. I have no problems seeing why they do it either. Wire is cheap compared to todays level of monthly light bill. With some stations, the radials, or lack of , in certain directions gives them a controlable pattern with no surprises in f/s over a period of time with changing ground conditions. The main thing is stability of performance over periods of time. Or thats my take anyway. MK |
On Wed, 7 Sep 2005 14:07:39 +0000 (UTC), "Reg Edwards"
wrote: MK, How satisfying it is to read your message, written in plain, easy to understand, well-punctuated English, without any undeciferable coded abbreviations. I agree with what you say although I am unfamiliar with exactly how the FCC fits into the scheme of things. Amateurs and commercial broadcasters have a common fundamental requirement. There is a service area to be covered with a given field strength. Depending on frequency, requirements then diverge. But the design methods used to satisfy requirements are all confined (or should be) to the principles of engineering economics. Inevitably, the Dollar, Pound, Frank, Mark, Rouble and the Yen rule the roost. Both commercial broadcasters and amateurs do a cost-befit analysis. The broadcaster takes into account the revenue acruing from selling the service. The amateur, whether he likes it or not, has to ask himself what the satisfaction of using the station is worth. Amateurs' bank accounts are not unlimited. Field strength at the limits of the service area depends on the power efficiency of the radiating system. If engineering economics dictate use of a set of buried ground radials then the peformance of the ground radials must be included. Considering the system as a whole, it may be economical NOT to achieve the maximum possible radiating efficiency. Indeed, the maximum is seldom the target. If there is an economical choice in the matter, once the location of the station is decided, everybody agrees that efficiency depends on soil resistivity at the site. To estimate efficiency it is necessary, at the very least, to make a guess at soil resistivity. Perhaps just by looking at the type of weeds growing in it. Or it can be measured. Depending on how far it enters into station economics, it is possible to numerically estimate efficiency from the number and length of radials AND FROM SOIL RESISTIVITY. B.L & E and the FCC don't enter into it. ---- Reg. Sorry to disagree, Reg, but it appears you're overlooking an important point--the difference between the efficiency of the radiating system itself, versus the efficiency of the ground area external to the radiating system. BL&E shows that when 90 - 120 (actually 113) radials of 0,4 w/l form the ground system for a 1/4 wl radiator, the efficiency is 98.7% efficient, REGARDLESS OF THE SOIL RESISTIVITY UNDER THE RADIALS. This is shown by obtaining the field strength of 192 mv/meter at 1 mile for 1000 watts delivered to the antenna under the conditions described above, compared to 194.5 mv/meter with a perfect ground having an efficiency of 100% It is only the soil resistivity of the ground external to the radial system that determines the field stength external to the radial system. Consequently, the soil resistivity (or conductivity, if you like) is significant only in the areas external to the radial system. Walt, W2DU |
On Wed, 07 Sep 2005 11:41:33 -0400, Walter Maxwell
wrote: Sorry to disagree, Reg, but it appears you're overlooking an important point--the difference between the efficiency of the radiating system itself, versus the efficiency of the ground area external to the radiating system. Walter, my friend, you're beating a dead horse. It would appear that Reg's mind is made up and no amount factual proof is going to change it. Had BL&E been Englishmen I sure things would be different.G 73, Danny, K6MHE |
On Wed, 07 Sep 2005 09:39:28 -0700, Dan Richardson wrote:
On Wed, 07 Sep 2005 11:41:33 -0400, Walter Maxwell wrote: Sorry to disagree, Reg, but it appears you're overlooking an important point--the difference between the efficiency of the radiating system itself, versus the efficiency of the ground area external to the radiating system. Walter, my friend, you're beating a dead horse. It would appear that Reg's mind is made up and no amount factual proof is going to change it. Had BL&E been Englishmen I sure things would be different.G 73, Danny, K6MHE Good point, Danny, how true. Walt |
| Sorry to disagree, Reg, but it appears you're overlooking an
important | point--the difference between the efficiency of the radiating system | itself, versus the efficiency of the ground area external to the | radiating system. | | BL&E shows that when 90 - 120 (actually 113) radials of 0,4 w/l form | the ground system for a 1/4 wl radiator, the efficiency is 98.7% | efficient, REGARDLESS OF THE SOIL RESISTIVITY UNDER THE RADIALS. This | is shown by obtaining the field strength of 192 mv/meter at 1 mile for | 1000 watts delivered to the antenna under the conditions described | above, compared to 194.5 mv/meter with a perfect ground having an | efficiency of 100% | | It is only the soil resistivity of the ground external to the radial | system that determines the field stength external to the radial | system. Consequently, the soil resistivity (or conductivity, if you | like) is significant only in the areas external to the radial system. | | Walt, W2DU Walt, What if the ground outside the radial system was comprised of 30-1000 feet of sand and rock overlying any conductive soil below? Would we then be able to measure 192 mv/meter at one mile with our 113 radials of 0.4 w/l? Ron, WA4IWN |
dansawyeror wrote:
All, A fundamental basic question, which is the primary purpose of radials: 1. is it to create a ground, that is a as close as possible to zero ohm virtual reference for the 'real' vertical half of the dipole? There is no such thing as "creating a ground". As for a "virtual reference", you can declare any point on any conductor a "reference" and for that matter "ground" that you wish. 2. Or are they to create a real resonant half of a dipole? There's no need to try to make a dipole. If the radials are on or very near the ground, their sole purpose is to reduce the amount of loss due to current returning to the base of the antenna. The current entering the antenna at the base equals the current flowing into the source through the ground. This ground current results in I^2 * R loss; radials reduce the R and therefore the loss. In the case of a "ground plane" antenna with highly elevated radials, the radials provide a path for the base current to flow (again, current out of the source -- into the antenna -- has to equal the current into it -- from the radials). Because of the physical configuration, it's sometimes more convenient to build an antenna this way instead of making a dipole. The radials radiate very little, and the vertical section radiates twice as much per unit length as a dipole, resulting in the same overall gain and pattern. If it is the first then what does the 'efficiency' curve look like for a shortened, loaded, vertical? That is if the vertical element is loaded to resonate at 1/5 of a half wave length what does the ground resistance profile look like for 120 radials at various lengths of 1/20 wave, 1/10 wave and 1/5 wave? The answer to this depends on the ground conductivity and frequency. But the radiation resistance of the shortened antenna will be less than that of a full-height one. Therefore, if the ground resistance is fixed and determined by the ground system (not completely true -- it does depend some on the antenna height -- but close enough for discussion), the efficiency of the short antenna will be less than for a full-height one. I recommend finding and reading "The W2FMI Ground-Mounted Short Vertical", by Jerry Sevick, W2FMI in March 1973 QST. He built several antennas very much like you describe and made extensive measurements. The question I am really driving at is if mesh is layed down at 100% coverage about what fraction of a wave length needs to be covered to create a 2.5, 5, and 10 ohm equivalent ground for the vertical above? Sorry, I don't know the answer to that one right off the bat. It could be determined with NEC-4 modeling, but I don't have time to do that. I suggest that you locate a copy of Brown, Lewis, and Epstein's paper "Ground Systems as a Factor in Antenna Efficiency", now posted on the web. You should be able to get a fairly good idea from their measurements of 113-radial systems. In the paragraph above is the mesh simulating a ground or is it fact operating as a ground. I really don't know what "simulating a ground" and "operating as a ground" means. But the radial field doesn't act like either real Earth or a perfect infinite plane, if that's what you mean. If sufficiently fine, a mesh will act like a solid conductor the size of the mesh. Roy Lewallen, W7EL |
"Walter Maxwell" wrote in message ... On Wed, 7 Sep 2005 14:07:39 +0000 (UTC), "Reg Edwards" wrote: MK, How satisfying it is to read your message, written in plain, easy to understand, well-punctuated English, without any undeciferable coded abbreviations. I agree with what you say although I am unfamiliar with exactly how the FCC fits into the scheme of things. Amateurs and commercial broadcasters have a common fundamental requirement. There is a service area to be covered with a given field strength. Depending on frequency, requirements then diverge. But the design methods used to satisfy requirements are all confined (or should be) to the principles of engineering economics. Inevitably, the Dollar, Pound, Frank, Mark, Rouble and the Yen rule the roost. Both commercial broadcasters and amateurs do a cost-befit analysis. The broadcaster takes into account the revenue acruing from selling the service. The amateur, whether he likes it or not, has to ask himself what the satisfaction of using the station is worth. Amateurs' bank accounts are not unlimited. Field strength at the limits of the service area depends on the power efficiency of the radiating system. If engineering economics dictate use of a set of buried ground radials then the peformance of the ground radials must be included. Considering the system as a whole, it may be economical NOT to achieve the maximum possible radiating efficiency. Indeed, the maximum is seldom the target. If there is an economical choice in the matter, once the location of the station is decided, everybody agrees that efficiency depends on soil resistivity at the site. To estimate efficiency it is necessary, at the very least, to make a guess at soil resistivity. Perhaps just by looking at the type of weeds growing in it. Or it can be measured. Depending on how far it enters into station economics, it is possible to numerically estimate efficiency from the number and length of radials AND FROM SOIL RESISTIVITY. B.L & E and the FCC don't enter into it. ---- Reg. Sorry to disagree, Reg, but it appears you're overlooking an important point--the difference between the efficiency of the radiating system itself, versus the efficiency of the ground area external to the radiating system. BL&E shows that when 90 - 120 (actually 113) radials of 0,4 w/l form the ground system for a 1/4 wl radiator, the efficiency is 98.7% efficient, REGARDLESS OF THE SOIL RESISTIVITY UNDER THE RADIALS. This is shown by obtaining the field strength of 192 mv/meter at 1 mile for 1000 watts delivered to the antenna under the conditions described above, compared to 194.5 mv/meter with a perfect ground having an efficiency of 100% It is only the soil resistivity of the ground external to the radial system that determines the field stength external to the radial system. Consequently, the soil resistivity (or conductivity, if you like) is significant only in the areas external to the radial system. Walt, W2DU ======================================= Walt, just what is it you cannot agree with? You appear to be making an argument where none exists. It is obvious there must be a distant point beyond which a large number of radials will approach 100% efficiency regardless of ground resistivity. B.L & E and the FCC arbitraliry decided on 1/2-wavelength and 120. Both nice round figures. I'm sorrry to say you appear unable to agree that for the remaining 99.9% of all possible cases, ie., for cases less than 1/2-wavelength and fewer than 120 radials, that GROUND RESISTIVITY in the immediate vicinity of the antenna DOES HAVE A SIGNIFICANT EFFECT ON EFFICIENCY and it cannot be disregarded. My only criticism of B.L & E is that they forgot to measure soil resistivity before leaving the site. And apparently, nobody has ever bothered to go back and do it for them. The only mention of their work occurs on this newsgroup. When laying radials, 99% of amateurs forget B.L & E (if they have ever heard of them) and the magic number of 120. Hasan Schiers has recently given a blow-by-blow account of a sensible way to lay a set of radials with the reasoning behind it. ---- Reg. |
Reg, G4FGQ wrote:
"The broadcaster takes into account the revenue accruing from selling the service." Yes, and he takes into account the ease of compliance with FCC Riles in the USA. Although 90 radials is a minimum requirement for the U.S. AM broadcaster, here is the rule quoted by John Edward Cunningham in his 1977 "The Complete Broadcast Antenna Handbook", from page 311: "The current FCC Rules specify that the radials should be at least 1/4 wavelength long and that there should be as many as practicable, but in no case less than 90. The Rules add that a system of 120 radials spaced every 3-degrees and extending 0.35-0.4 wavelength from the tower is considered an excellent ground system. In addition, a square ground screen 24 or 48 on a side is often provided at the base of the tower, particularly when the tower height is such as to cause a high voltage. Whenever a less than optimum ground system is used, the FCC requires a complete field-intensity survey to establish that the effective field at one mile meets minimum requirements." Best regards, Richard Harrison, KB5WZI |
Reg Edwards wrote:
. . . My only criticism of B.L & E is that they forgot to measure soil resistivity before leaving the site. And apparently, nobody has ever bothered to go back and do it for them. What would you suggest as a method of measuring the RF ground resistivity to a depth of 17 - 100 feet (3 skin depths at 3 MHz for the range of likely resistivities)? Assuming it's very likely that the resistivity would be quite different at different depths within that range, how should they have used that information? How would you use that information if someone "bothered to go back and do it for them"? Reg, all signs point to your being seriously in need of a holiday. How about a little trip to New Jersey to show us Yanks how it should have been done? For less than the price of a couple of bottles of decent wine, you can buy everything you'll need -- bucket, pocket DVM, trowel -- right there, so you won't even have to carry any equipment with you. Roy Lewallen, W7EL |
Dear Roy,
I'm sorry to say your worthless comments constitute an abject admission of defeat in an argument which exists only in your imagination. By the way, are you still using your S-meter as the North American Standard of signal strength? ---- Reg. |
Dan Richardson wrote - Had BL&E been Englishmen I sure things would be different.G ==================================== They sure would! They would have been instructed to go back and finish the job. ---- Reg. |
Dan Richardson wrote -
Had BL&E been Englishmen I sure things would be different.G ==================================== They sure would! They would have been instructed (by their employers) to go back and finish the job. ---- Reg. ===================================== I am reminded of the military engineer who was dispatched by Napolion, an engineer himself, in connection with standardisation of the Metre, to measure the distance between the Earth's Equator and the North Pole. Measurements began, but the further the engineer departed from his beautiful lady friend in Paris the more difficult it became to make progress along the route. Eventually, he couldn't withstand the mental and physical stress. He returned to her Parisian boudoir and resorted to cooking the books in what time he had to spare. So, the International Standard of Length, The Metre, held in Paris, France, carefully guarded by the German occupying forces during WW2, may or may not be equal to 39.37 English inches. Actually, the most fundamental physical measurement standard is the Mass of the Standard Kilogram on which everything else depends. But it is quite an arbitrary quantity. I have just finished a bottle of Blossom Hill, Californian, white wine. Makes a pleasant change to arguing about what 'amateurs' BL&E might, or might not have done before leaving the site. ---- Reg. |
Reg Edwards wrote:
Dan Richardson wrote - Had BL&E been Englishmen I sure things would be different.G ==================================== They sure would! They would have been instructed (by their employers) to go back and finish the job. ---- Reg. ===================================== I am reminded of the military engineer who was dispatched by Napolion, an engineer himself, in connection with standardisation of the Metre, to measure the distance between the Earth's Equator and the North Pole. Measurements began, but the further the engineer departed from his beautiful lady friend in Paris the more difficult it became to make progress along the route. Eventually, he couldn't withstand the mental and physical stress. He returned to her Parisian boudoir and resorted to cooking the books in what time he had to spare. So, the International Standard of Length, The Metre, held in Paris, France, carefully guarded by the German occupying forces during WW2, may or may not be equal to 39.37 English inches. Actually, the most fundamental physical measurement standard is the Mass of the Standard Kilogram on which everything else depends. But it is quite an arbitrary quantity. I have just finished a bottle of Blossom Hill, Californian, white wine. Makes a pleasant change to arguing about what 'amateurs' BL&E might, or might not have done before leaving the site. ---- Reg. All the above is/maybe true but remember that all the formule work using the values represented in the METRE and the KILOGRAM. Something must be correct here.... Dave WD9BDZ |
On Thu, 8 Sep 2005 16:09:23 +0000 (UTC), "Reg Edwards"
wrote: I have just finished a bottle of Blossom Hill, Californian, white wine. Makes a pleasant change to arguing about what 'amateurs' BL&E might, or might not have done before leaving the site. ---- Reg. I hate to say this, Reg, but calling BL&E 'amateurs' is insulting to me. I knew them well, and worked with B and E in the RCA Laboratories antenna lab, and they are anything but 'amateurs'. I think you finished off the Blossom Hill to rapidly. Perhaps you should take a look at the long list of IRE articles published by Dr. G.H. Brown, reporting his work that shaped the present design of all AM BC antennas. Did you ever wonder what happened to the diamond-shaped AM towers? And why the AM towers constructed since 1940 have a uniform cross section? And did you know that Dr. Brown gave John Kraus, W8JK, the idea of close spaced elements that culminated in the 'W8JK Beam' antenna? L, (Bob Lewis) is also a fine engineer, although he is also a ham, W2EBS. Walt |
David G. Nagel wrote:
SNIPPED for readability All the above is/maybe true but remember that all the formule work using the values represented in the METRE and the KILOGRAM. Something must be correct here.... Dave WD9BDZ Yep! Everything simply requires adjustments to proportionality constants, Reynolds numbers, Plankian constants, etc. |
| All times are GMT +1. The time now is 11:35 PM. |
Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
RadioBanter.com