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Antenna ground - how can you tell if it's good
Everybody acknowledges that a good ground is required for any amateur
work, especially for a vertical. When I'm putting in an RF ground for either my station or for an antenna system, how do I know when I've achieved "good enough"? What works? Thanks - Mark Sheffield/N0LF |
Everybody acknowledges that a good ground is required for any amateur work, especially for a vertical. When I'm putting in an RF ground for either my station or for an antenna system, how do I know when I've achieved "good enough"? What works? =================================== Anything will work! To summarise, begining with 1 radial, all you can do is keep laying more radials until performance ceases to improve. Then that's the best which can be done at your QTH. Performance can be judged by measuring the strength of fixed, stable, not too distant, MF and lower frequency HF radio stations in daylight. There's an effect known as "Reciprocity" which means that an antenna with its ground system is just as good or bad on transmit as it is on receive. If you increase the number of shallow-buried radials by 50 percent and there's no noticeable improvement then stop laying. Depending on the type of soil you will end up with a number which, in general, will be fewer than what you thought of before you started. With a vertical, much depends on the lowest frequency of interest. Opinions differ but in my opinion, in average garden soil, there's not much point in laying shallow buried radials longer than 1/10th of a wavelength. They can be shorter in very fertile, fine, damp soil and longer in dry sandy or rocky soil. Fertility is the key. Increase their number according to the above 50 percent guidline. Layout and bends in the wires are unimportant as are varying lengths. Just spread them out fairly uniformly over the area available. A 180-degree missing sector because the house gets in the way is not of great consequence. Wire diameter has little electrical effect. Choose wire diameter according to type of soil and wire durability. Forget about ground rods. A ground rod is little better electrically than a horizontal radial of about the same length. A short ground rod can be used as a common connecting point. If you like amusing yourself with numbers, and for crude predictions of what to expect, download programs EARTHRES and RADIALS2 from website below. A little knowledge of your local soil resistivity can add much to the interest and help you to forget the lumbago. --- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
Mark Sheffield, N0LF wrote:
"When I`m putting in an RF ground for either my station or for an antenna system, how do I know when I`ve achieved "good enough"?" Measurement accuracy is sometimes overestimated as Reg Edwards, G4FGQ has often declared in this group. But, you know your RF ground is good enough when expanding the system brings very little improvement. You need no RF ground for a properly balanced antenna system. For an unbalanced antenna, the ground system is 1/2 of the total antenna system. This system has a total resistance that is the sum of its desired radiation resistance and its undesired loss resistance. Nearly all the undesired loss is in the ground system. So, it`s very important to minimize ground loss in an unbalanced antenna system. There are two ways to determine that you`ve rid your unbalanced antenna system of loss resistance. If the loss resistance is zero, the driving impedance of the 1/4-wave monopole against ground should measure 36.5 ohms (from 1950 Kraus "Antennas" page 315). The second way is to measure the field intensity along the earth`s surface at a distance of one mile from the antenna. With 1 watt into the antenna, the field intensity at one mile is 6.5 millivolts/meter with a lossless system (from Kraus as above). Best regards, Richard Harrison, KB5WZI |
I should have mentioned. When measuring signal strengths as a measure of
performance there's safety in numbers. Take the average of a fair number of transmissions, all well above the noise level, at about the same time each day, using your most stable S-meter with the receiver gain turned down such that the meter deflection is on the most sensitive sector of its scale. Allow the receiver to warm up for the same length of time on each occasion it is used. S-meter calibration doesn't matter two hoots. And once set, don't ever touch the receiver gain control. You should take all these precautions from the time when you have laid only one radial. You will not wish to dig up already laid radials in order to re-measure the earlier ones you forgot to treat in the standard manner. It will be appreciated, to make tests during radial-laying operations by asking for signal strength reports from your many friends, using THEIR S-meters, will result in you losing them. Incidentally, when "I" used this method of testing antenna efficiency I stopped at 8, 10 feet, radials with a 3 feet rod at the end of each. This included the domestic incoming main water pipe which made no difference when THAT was connected. So I stopped. But my soil resistivity is only about 70 ohm-metres. I can grow anything in my garden. At present it is covered with a dense growth of 3 feet high weeds except for a small patch which I use to feed the birds. As if they didn't get enough to eat anyhow. With the trees and overgrown bushes it is a wild-life sanctuary for frogs, rats, squirrels and hedgehogs. The only complaints I get are from the neighbours. But its stopped them complaining about TVI. --- Reg, G4FGQ |
Thank you very much - these are very helpful ways to approach the problem. Best Regards, Mark Sheffield/n0lf |
instead of radials, you COULD just make the grounded side vertical - into a
well, I THINK??? (I'm assuming that would work - but never tried it - my post-hole digger handles were too short) "MarkS" wrote in message om... Everybody acknowledges that a good ground is required for any amateur work, especially for a vertical. When I'm putting in an RF ground for either my station or for an antenna system, how do I know when I've achieved "good enough"? What works? Thanks - Mark Sheffield/N0LF --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.744 / Virus Database: 496 - Release Date: 8/24/2004 |
Nice Site,
John-WA4JM -- |
Hal Rosser wrote:
"Instead of radials, you dould just make the ground side vertical into a well, I think?" Not at HF, efficiently, because the ground penetration depth decreases for an RF wave as frequency increases. It is "skin effect" which decreases the depth with the square root of the frequency. A steel well casing may make a good ground return at LF but not at HF. Best regards, Richard Harrison, KB5WZI |
"Richard Harrison" wrote in message
... Hal Rosser wrote: "Instead of radials, you dould just make the ground side vertical into a well, I think?" Not at HF, efficiently, because the ground penetration depth decreases for an RF wave as frequency increases. It is "skin effect" which decreases the depth with the square root of the frequency. A steel well casing may make a good ground return at LF but not at HF. Best regards, Richard Harrison, KB5WZI Keep them earthworms warm at nite. 73 H. NQ5H |
"Bill Turner" wrote
If you have an impedance analyzer you can trust, and if you are using a 1/4 wave vertical (full size, not loaded), and if your ground is perfect, you should measure about 36 ohms at the feedpoint. Any measurement higher than that is due to ground loss. _________ But in practical terms, how do you get a "perfect" earth ground reference for the analyzer to use when making the measurement? RF |
But in practical terms, how do you get a "perfect" earth ground reference
for the analyzer to use when making the measurement? =================================== You don't need a "perfect earth" because that is precisely the quantity you are trying to measure. The only "perfect" thing is the 36 ohms which is the calculated value of the 1/4-wave antenna's radiation resistance. But it is not essential to have an antenna as tall as a quarterwave to find the earth-loss resistance. There's not many people who can erect a 1/4-wave vertical at 160 meters. The 'perfect' radiation resistance of an antenna shorter than 1/4-wave is given with sufficient accuracy by - Rrad = Square( 24 * Height / Wavelength ) ohms. Of course, an antenna shorter than 1/4-wave has reactance. But this can be tuned out with any coil which has a negligible loss resistance compared with antenna resistance. Make the measurement at the resonant frequency of coil + antenna whatever it may be. The antenna analyser will tell you when you are at resonance. Vary frequency for the minimum pure resistance. And that is the resistance you are looking for. The lower the measurement frequency the more easy and accurate the measurement provided it is not overdone. The earth resistance measurement doesn't have to be made at the same frequency the antenna is to be used at. It can be appreciably lower. The great advantage of these one-hand held, battery-driven, antenna analysers is that the connecting wires can be kept very short, ie., much shorter than a 1/4-wavelength. They are sufficiently accurate for this sort of job. And don't be afraid of lying on your belly to read the meter. The best things since sliced bread. --- Reg, G4FGQ. |
"Reg Edwards" wrote in message ... I should have mentioned. When measuring signal strengths as a measure of performance there's safety in numbers. Take the average of a fair number of transmissions, all well above the noise level, at about the same time each day, using your most stable S-meter with the receiver gain turned down such that the meter deflection is on the most sensitive sector of its scale. Allow the receiver to warm up for the same length of time on each occasion it is used. S-meter calibration doesn't matter two hoots. And once set, don't ever touch the receiver gain control. You should take all these precautions from the time when you have laid only one radial. You will not wish to dig up already laid radials in order to re-measure the earlier ones you forgot to treat in the standard manner. It will be appreciated, to make tests during radial-laying operations by asking for signal strength reports from your many friends, using THEIR S-meters, will result in you losing them. Incidentally, when "I" used this method of testing antenna efficiency I stopped at 8, 10 feet, radials with a 3 feet rod at the end of each. This included the domestic incoming main water pipe which made no difference when THAT was connected. So I stopped. But my soil resistivity is only about 70 ohm-metres. I can grow anything in my garden. At present it is covered with a dense growth of 3 feet high weeds except for a small patch which I use to feed the birds. As if they didn't get enough to eat anyhow. With the trees and overgrown bushes it is a wild-life sanctuary for frogs, rats, squirrels and hedgehogs. The only complaints I get are from the neighbours. But its stopped them complaining about TVI. --- Reg, G4FGQ Sounds a little like my counterpoise. 12 wires 12ft long, Short ground rod at far end of each wire just to pin it down. 10ft 2inch pipe in the middle for ground/ mount. You can get an idea of resistance to ground by connecting 120 VAC to the ground system through a fuse and see how big of a fuse you can blow. I rigged a fuse holder with a neon blown fuse indicator to a piece of PVC pipe. last time I checked mine it would pop a 10amp fuse. |
"Bill Turner" wrote in message ... On Fri, 03 Sep 2004 17:19:26 GMT, "Jimmie" wrote: You can get an idea of resistance to ground by connecting 120 VAC to the ground system through a fuse and see how big of a fuse you can blow. I rigged a fuse holder with a neon blown fuse indicator to a piece of PVC pipe. last time I checked mine it would pop a 10amp fuse. __________________________________________________ _______ Remember the movie "Dumb and Dumber"? This is the electronic version. -- Bill, W6WRT QSLs via LoTW Thats what I thought the first time I saw it done but this is the way the power company checks grounds. It can be done in a safe manner. Also there is equipment commercially made for doing this test. Ideally one should use this approved equipment but there is no reason it cant be done with improvised equipment with no more risk than taking a voltage measurement in a hot chassis. Of course there are those who lack the ability to safely perform a test like this and should not even be allowed in their service panel to reset a breaker. |
"Bill Turner" wrote in message ... On Wed, 08 Sep 2004 14:51:10 GMT, "Jimmie" wrote: Thats what I thought the first time I saw it done but this is the way the power company checks grounds. __________________________________________________ _______ I can't believe a power company could be dumb enough to blow a fuse to measure (?) ground resistance. A much better way would be to use either a variac or a current-limited source and calculate the resistance with Ohm's law. In what way better, They are not interested in a specific value in most cases. Just a go -no go test. Plug the tester into an outlet, touch it to the ground stake after isolating ground from neutral. Fuse pops or it doesnt, Ground meets spec or it doesnt. Apparently there are lot of people who think this idea is not so dumb since the tester they use is commercially available, a fact that I mentioned in the previous post that you chose to ignore. -- Bill, W6WRT (founder of the Society to Prevent Fuse Abuse) QSLs via LoTW |
On Wed, 08 Sep 2004 21:24:53 GMT, "Jimmie"
wrote: They are not interested in a specific value in most cases. .... Ground meets spec or it doesnt. Without a specific value, how do they (we) know it meets spec? 73's Richard Clark, KB7QHC |
Richard Clark wrote:
On Wed, 08 Sep 2004 21:24:53 GMT, "Jimmie" wrote: They are not interested in a specific value in most cases. ... Ground meets spec or it doesnt. Without a specific value, how do they (we) know it meets spec? For a mains safety ground, the bottom line is: is the ground resistance low enough to blow a fuse in the live rail? If the answer is no, you're heading for a fire, so there is some surety in verifying that a fuse really will blow. On the other hand, for an RF ground it's a lousy test. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
"Ian White, G3SEK" wrote in message ... Richard Clark wrote: On Wed, 08 Sep 2004 21:24:53 GMT, "Jimmie" wrote: They are not interested in a specific value in most cases. ... Ground meets spec or it doesnt. Without a specific value, how do they (we) know it meets spec? For a mains safety ground, the bottom line is: is the ground resistance low enough to blow a fuse in the live rail? If the answer is no, you're heading for a fire, so there is some surety in verifying that a fuse really will blow. On the other hand, for an RF ground it's a lousy test. True enough on the RF , but no worse than any other test meant for primary power. While this test alone does not insure a good RF ground and it is a good first test to let you know you are going in the right direction. If this test is bad for 60Hz AC then RF ground is probably a lot worse. VSWR reading for my antenna is 1.25:1 at the resonant frequency of my antenna. Given the inaccuracies of SWR meters I figure I have a ground resistance some where between 3 and 10 ohms. Maybe one day I will try to to get a more accurate reading when other things in my life take less priority. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
On Thu, 09 Sep 2004 13:11:02 GMT, "Jimmie"
wrote: VSWR reading for my antenna is 1.25:1 at the resonant frequency of my antenna. Given the inaccuracies of SWR meters I figure I have a ground resistance some where between 3 and 10 ohms. Hi Jimmie, How do you figure that? 73's Richard Clark, KB7QHC |
"Richard Clark" wrote in message ... On Thu, 09 Sep 2004 13:11:02 GMT, "Jimmie" wrote: VSWR reading for my antenna is 1.25:1 at the resonant frequency of my antenna. Given the inaccuracies of SWR meters I figure I have a ground resistance some where between 3 and 10 ohms. Hi Jimmie, How do you figure that? 73's Richard Clark, KB7QHC Mostly an educate guess, my AC test blows a 10 amp fuse to smithereens so I figure less than 10. SWR is 1.25 to 1 This equates to about 40 ohms impedance seen at the antenna base. This also agrees with my antenna analyzer. Antenna is a full length 1/4 wl antenna on 20m. I was figuring 37 or soo for this. I know its a lot of by guess and by golly and I am aware that there are better ways of finding out what the ground loss really is but I'm not so anal that I reallly care. Given the SWR reading I figure closer to 3 and a neighbor recently had lightning rods installed and the installers measured theire ground resistance at 2.5 ohms so I am pretty confident of my educated guess . When I get my tower up 20 meters will be on a beam on top of the tower and I plan to use the ground plane with a 40 M vetical 1/4 wave antenna. Ground plane is made of 12 wires 12ft long connected to a 10 ft ground rod at the base of the antenna. Do you think I should modify the ground plane. I was thinking of at least adding 4 wires 1/4 wl long for 40, I really think this may be a waste of time though. Also would existing ground plane be good for 80M. |
On Thu, 09 Sep 2004 19:42:41 GMT, "Jimmie"
wrote: This equates to about 40 ohms impedance seen at the antenna base. This also agrees with my antenna analyzer. Antenna is a full length 1/4 wl antenna on 20m. I was figuring 37 or soo for this. Hi Jimmie, So you have no radials? 73's Richard Clark, KB7QHC |
"Richard Clark" wrote in message ... On Thu, 09 Sep 2004 19:42:41 GMT, "Jimmie" wrote: This equates to about 40 ohms impedance seen at the antenna base. This also agrees with my antenna analyzer. Antenna is a full length 1/4 wl antenna on 20m. I was figuring 37 or soo for this. Hi Jimmie, So you have no radials? Yes I alreaady described it once in this thread. 73's Richard Clark, KB7QHC |
"Richard Clark" wrote in message ... On Thu, 09 Sep 2004 19:42:41 GMT, "Jimmie" wrote: This equates to about 40 ohms impedance seen at the antenna base. This also agrees with my antenna analyzer. Antenna is a full length 1/4 wl antenna on 20m. I was figuring 37 or soo for this. Hi Jimmie, So you have no radials? Described the radials once but that text has been snipped. 12 12f t wires, Center ground stake 10 ft long, far end of each wire has a stake about 3 ft long. These are used more to just hold the wires in place. 73's Richard Clark, KB7QHC |
On Fri, 10 Sep 2004 14:25:15 GMT, "Jimmie"
wrote: 12 12f t wires, Center ground stake 10 ft long, far end of each wire has a stake about 3 ft long. These are used more to just hold the wires in place. Hi Jimmy, Modeling concurs with your description, measurements and conclusion. 73's Richard Clark, KB7QHC |
Jimmie wrote -
12 12f t wires, Center ground stake 10 ft long, far end of each wire has a stake about 3 ft long. These are used more to just hold the wires in place. =============================== Jimmie, For amusement and my education, would you mind letting us have a few more crude details of your ground radial system please. TYPE OF SOIL (A) Is it high quality, fertilised garden loam, perhaps very slightly sandy which can grow flowers and shrubs of which you can be proud when you try. Perhaps used to be farm or orchard or agricultural land. (B) Is it slightly gritty, stoney, but ample body which can still make a nice flower garden. Quite fertile even though it may be overgrown with profuse, dense, robust weeds. (Like mine.) (C) Is it sandy, clayey, with small stones or pebbles? Needs attention with fertilisers to grow nice flowers. But a lawn might do very well. (D) Does it contain stones, sand, grit and small rocks with only 75% of good soil but still needs hoeing and weeding to keep looking presentable.? (E) Is it poor soil, smewhat infertile, difficult to manage as a flower garden? Could be turned into a rock garden. Even the weeds don't do very well. (F) Thin layer of mediocre soil over bedrock. MOISTURE CONTENT (G) Fairly wet. (H) Nicely moist. (I) Slightly damp. (J) Well drained, dry. (K) Dusty. (L) Arid. ROUGH DEPTH OF WIRE BURIAL. In tenths of an inch if very shallow. Zero if just trodden in, in good contact with soil surface. Thank you. ---- Reg. |
"Reg Edwards" wrote in message ... Jimmie wrote - 12 12f t wires, Center ground stake 10 ft long, far end of each wire has a stake about 3 ft long. These are used more to just hold the wires in place. =============================== Jimmie, For amusement and my education, would you mind letting us have a few more crude details of your ground radial system please. TYPE OF SOIL (A) Is it high quality, fertilised garden loam, perhaps very slightly sandy which can grow flowers and shrubs of which you can be proud when you try. Perhaps used to be farm or orchard or agricultural land. (B) Is it slightly gritty, stoney, but ample body which can still make a nice flower garden. Quite fertile even though it may be overgrown with profuse, dense, robust weeds. (Like mine.) XXXX (C) Is it sandy, clayey, with small stones or pebbles? Needs attention with fertilisers to grow nice flowers. But a lawn might do very well. (D) Does it contain stones, sand, grit and small rocks with only 75% of good soil but still needs hoeing and weeding to keep looking presentable.? (E) Is it poor soil, smewhat infertile, difficult to manage as a flower garden? Could be turned into a rock garden. Even the weeds don't do very well. (F) Thin layer of mediocre soil over bedrock. MOISTURE CONTENT (G) Fairly wet. (H) Nicely moist. X (I) Slightly damp. (J) Well drained, dry. (K) Dusty. (L) Arid. ROUGH DEPTH OF WIRE BURIAL. 1 inch In tenths of an inch if very shallow. Zero if just trodden in, in good contact with soil surface. Thank you. ---- Reg. Soil is kind of a strang brew. when the house was built there was quite a hill here that was leveled off. When the top soil was put back they put down the top soil with about a foot of clay over it. So I have a foot of clay a foot or so of top soil and more clay. Top layer of clay can get faily dry while the layer of topsoil and underlying clay stay fairly moist. Grass and trees grow fairl well and I never have to water them. Sometimes the grass browns when we have drought conditions but the fruit trees always seem to do well. I susppect this is because they can reach the underlying moisture. |
On Fri, 10 Sep 2004 14:25:15 GMT, "Jimmie"
wrote: "Richard Clark" wrote in message .. . On Thu, 09 Sep 2004 19:42:41 GMT, "Jimmie" wrote: This equates to about 40 ohms impedance seen at the antenna base. This also agrees with my antenna analyzer. Antenna is a full length 1/4 wl antenna on 20m. I was figuring 37 or soo for this. 12 12f t wires, Center ground stake 10 ft long, far end of each wire has a stake about 3 ft long. These are used more to just hold the wires in place. Hi Jimmie, My last post responding to this included a mistaken analysis. I had picked up the sample vertical and did not notice it was using MININEC ground, which is unsuitable for this question. On using the particulars you supply above, the results are very much different. With the default ground (0.005/13): Impedance = 57.96 + J 0.1116 ohms With extremely poor ground (0.001/3): Impedance = 65.24 - J 0.1441 ohms SWR (50 ohm system) = 1.305 With poor ground (0.002/13): Impedance = 55.64 + J 0.1153 ohms SWR (50 ohm system) = 1.113 With "Pastoral" ground (0.01/14) Impedance = 56.62 + J 0.1475 ohms SWR (50 ohm system) = 1.132 With very good ground (0.0303/20) Impedance = 54.38 + J 0.3596 ohms SWR (50 ohm system) = 1.088 For each change of ground I drove out reactance by trimming the radiatior to |
On Fri, 10 Sep 2004 14:25:15 GMT, "Jimmie"
wrote: "Richard Clark" wrote in message .. . On Thu, 09 Sep 2004 19:42:41 GMT, "Jimmie" wrote: This equates to about 40 ohms impedance seen at the antenna base. This also agrees with my antenna analyzer. Antenna is a full length 1/4 wl antenna on 20m. I was figuring 37 or soo for this. 12 12f t wires, Center ground stake 10 ft long, far end of each wire has a stake about 3 ft long. These are used more to just hold the wires in place. Hi Jimmie, My last post responding to this included a mistaken analysis. However, it has been now thrice plagued. Originally I had picked up the sample vertical and did not notice it was using MININEC ground, which is unsuitable for this question. Then in doing the suite of grounds, I had truncated the radials by half in a frequency translation. Then I fumbled the wrong key -sigh- On using the particulars you supply above, the results offer the low end of ground resistance by your estimate. However this depends on several things (not surprisingly - ground). Does your analyzer read real resistance, or simply SWR? What does it read with a 50 Ohm resistor (taking the average of several, all with close trimmed leads)? Anyway, by your SWR reading it appears your situation corresponds to an "extremely poor ground." Curious thing about the nature of "extremely poor," is that what does this mean? There is every indication that it offers the least loss, and yet it also offers the poorest signal out (at 10° as an indicator of DX). With extremely poor ground (0.001/3 Zground = 209 Ohms): Impedance = 39.46 + J 0.234 Ohms SWR (50 ohm system) = 1.267 -6.01 dBi @ 10° With poor ground (0.002/13 Zground = 104 Ohms): Impedance = 42.34 + J 0.1014 Ohms SWR (50 ohm system) = 1.181 -3.25 dBi @ 10° With the default ground (0.005/13 Zground = 99 Ohms): Impedance = 43.64 + J 0.03538 Ohms SWR (50 ohm system) = 1.146 -3.36 dBi @ 10° With "Pastoral" ground (0.01/14 Zground = 87 Ohms) Impedance = 44.93 + J 0.515 Ohms SWR (50 ohm system) = 1.113 -3.00 dBi @ 10° With very good ground (0.0303/20 Zground = 57 Ohms): Impedance = 44.5 + J 0.3779 Ohms SWR (50 ohm system) = 1.124 -1.11 dBi @ 10° For each change of ground I drove out reactance to less than one Ohm by trimming the radiator to what you describe as a full size quarterwave antenna. Going back to the nature of ground, we return to the descriptions of conductivity and how a "very good" conducting soil is NOT what you want nearby in terms of matching. A "very good" conducting soil is injecting several ohms more resistance into your feed than an "extremely poor" quality soil. However, when we consider the Z of ground, we observe that it is the ratio of this impedance to the æther that is the better indicator of achieving good low angle launch characteristics. Consistent here are the SWR of 6.6 for "very good" soil compared to the SWR of 1.8 for "extremely poor" soil. There is less conductive loss (but more capture of power) in the "extremely poor" soil and there is more conductive loss (but less capture of power) in the "very good" soil. Clearly it is the REFLECTIVE attributes of the media interface that is the more compelling characteristic than with the so-called boon of conductivity. Two more points of practical consideration he 1. With 12 radials laid out as you have, there is very little variation over "average" grounds (no point in trying harder); 2. The DX angle is driven by ground characteristics many wavelengths out (no point in worrying about ground either way). 73's Richard Clark, KB7QHC |
I have lost all previous contributions to this thread.
But Jimmie gave the description of his radial system - 12 12f t wires, Center ground stake 10 ft long, far end of each wire has a stake about 3 ft long. These are used more to just hold the wires in place. plus a brief description of type of soil and moisture content. I guessed at wire diameters. From which I deduce the following input impedances - AT 1.9 MHz AT 7.0 MHz ---------------- ---------------- 10 + j0 13 + j11 ohms. Uncertainty = +/- 3 ohms which is adequate for the intended purpose. The above figures have been obtained using programs ENDFEED and RADIALS2 (two different modelling methods) and averaging the results at soil resistivities of 100 and 300 ohm metres. Programs can be downloaded in a few seconds from website below. Calculating time no longer than needed to enter the simple data. In practice, only the resistances matter because the reactances are tuned out simultaneously with the antenna, equivalent to minor readjustments of the tuner. The resistance values, in conjunction with calculated radiation resistance can be used to calculate radiating efficiency. If Jimmie should ever measure input resistance with similar uncertainty (not too difficult) then I should be pleased to hear his results. ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
On Sun, 12 Sep 2004 16:31:12 +0000 (UTC), "Reg Edwards"
wrote: From which I deduce the following input impedances - AT 1.9 MHz AT 7.0 MHz This is a 20M system. |
"Reg Edwards" wrote in message ... I have lost all previous contributions to this thread. But Jimmie gave the description of his radial system - 12 12f t wires, Center ground stake 10 ft long, far end of each wire has a stake about 3 ft long. These are used more to just hold the wires in place. plus a brief description of type of soil and moisture content. I guessed at wire diameters. From which I deduce the following input impedances - AT 1.9 MHz AT 7.0 MHz ---------------- ---------------- 10 + j0 13 + j11 ohms. Uncertainty = +/- 3 ohms which is adequate for the intended purpose. The above figures have been obtained using programs ENDFEED and RADIALS2 (two different modelling methods) and averaging the results at soil resistivities of 100 and 300 ohm metres. Programs can be downloaded in a few seconds from website below. Calculating time no longer than needed to enter the simple data. In practice, only the resistances matter because the reactances are tuned out simultaneously with the antenna, equivalent to minor readjustments of the tuner. The resistance values, in conjunction with calculated radiation resistance can be used to calculate radiating efficiency. If Jimmie should ever measure input resistance with similar uncertainty (not too difficult) then I should be pleased to hear his results. I had really not given it a whole lot of thought unti gettin invovled in this thread but I am beginning to think that my sort of unique soil conditions may effect my ground system considerably. With the moist, top soil and clay at the lower levels I am getting a good primary power ground, but now I dont think my RF connection to earth is very good at all ass the counter poise is in some fairly dry sandy clay. Wife says that when I installed this thing back in '94 that she remembered me putting in some longer wires than the 12 12 ft wires. At this point I am thinking maybe is was 8 12 ft wires and 4 1/4 wl 20m wires. I know the origonal plan waas to put in the 12 ft wires and 1/4 wl wires for several bands out to 80m with 3 or 4 wires for each band. I know I didnt do it for 80M but now I must admit I am not sure about other bands. I may have put in other radials for 20 and 40 meters. Shortly after this I almost totally gave up radio until recently. |
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