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Radials for a Vertical ?
I'm thinking of buying a used Hustler 6BTV vertical ( 80 thru 10
coverage) and was wondering about how many radials I'd need and how long they should be ? If I do get it, I'd be ground mounting the vertical and planting the radials about 1 - 2 inches deep in soil that's mainly clay. Thanks in advance. 73 Gary |
"Gary" wrote in message ... I'm thinking of buying a used Hustler 6BTV vertical ( 80 thru 10 coverage) and was wondering about how many radials I'd need and how long they should be ? If I do get it, I'd be ground mounting the vertical and planting the radials about 1 - 2 inches deep in soil that's mainly clay. Thanks in advance. 73 Gary You might want to think about hardware cloth - - half inch screen dipped in zinc - - virtually one continuous sheet, solderable and resistant to weather and moisture. It comes in a 36" width, and I bought about 100 ft of it for my ground-mounted 6-band Butternut. The results have been excellent. People use cars and trailers for their counterpoise - - but this makes a much bigger one, with a lot more capacitance to ground. You can then sod over it or put in plastic sheeting and pebbles - - whatever you like. The only thing you need to settle is to get your sprinklers arranged ahead of time so you don't have to trench through under the hardware cloth. 73, Chuck W6PKP |
Gary,
The general 'generic' answer is as many as you can stand to put in, and as long as you can make them. Usually, the length is a 1/4 wave (or sort of close) for the lowest frequency of use. Don't have that much room? Then make them as long as possible. The more you put down the 'better' it'll be. That's where the 'as many as you can stand' comes in. At some point you'll be ready to quit, so quit... 'Doc PS - The 'text book' answer? Not really, but probably the average one. |
On Wed, 29 Jun 2005 18:27:54 -0700, "Chuck Olson"
wrote: "Gary" wrote in message .. . I'm thinking of buying a used Hustler 6BTV vertical ( 80 thru 10 coverage) and was wondering about how many radials I'd need and how long they should be ? If I do get it, I'd be ground mounting the vertical and planting the radials about 1 - 2 inches deep in soil that's mainly clay. Thanks in advance. 73 Gary You might want to think about hardware cloth - - half inch screen dipped in zinc - - virtually one continuous sheet, solderable and resistant to weather and moisture. It comes in a 36" width, and I bought about 100 ft of it for my ground-mounted 6-band Butternut. The results have been excellent. People use cars and trailers for their counterpoise - - but this makes a much bigger one, with a lot more capacitance to ground. You can then sod over it or put in plastic sheeting and pebbles - - whatever you like. The only thing you need to settle is to get your sprinklers arranged ahead of time so you don't have to trench through under the hardware cloth. 73, Chuck W6PKP Ok, thanks Chuck ... 73 Gary K8IQ |
On Thu, 30 Jun 2005 03:37:48 GMT, 'Doc wrote:
Gary, The general 'generic' answer is as many as you can stand to put in, and as long as you can make them. Usually, the length is a 1/4 wave (or sort of close) for the lowest frequency of use. Don't have that much room? Then make them as long as possible. The more you put down the 'better' it'll be. That's where the 'as many as you can stand' comes in. At some point you'll be ready to quit, so quit... 'Doc PS - The 'text book' answer? Not really, but probably the average one. Thanks Doc ! .... 73 Gary K8IQ |
On Thu, 30 Jun 2005 14:24:52 GMT, Jim Higgins wrote:
On Wed, 29 Jun 2005 21:02:02 -0400, in , Gary wrote: I'm thinking of buying a used Hustler 6BTV vertical ( 80 thru 10 coverage) and was wondering about how many radials I'd need and how long they should be ? If I do get it, I'd be ground mounting the vertical and planting the radials about 1 - 2 inches deep in soil that's mainly clay. 5BTV here, ground mounted. I found that 4 radials cut for 40M and buried as you paln to do gave a marked improvement on all bands. More and longer if you can. You'll need to readjust the antenna for best SWR after installing radials. Thanks for the info Jim. 73 Gary |
Here is an additional question.
I have to mount my 40/80 vertical in a place where it can be hidden by trees, which means against the back fence in my yard. I can only put radials to cover 180 degrees. I assume my signal will radiate best in that direction. What kind of radiation will I get toward the side of the antenna without the radials? Mark, KJ7BS |
RF
"Mark" wrote in message news:Cs0xe.14415$ro.8260@fed1read02... Here is an additional question. I have to mount my 40/80 vertical in a place where it can be hidden by trees, which means against the back fence in my yard. I can only put radials to cover 180 degrees. I assume my signal will radiate best in that direction. What kind of radiation will I get toward the side of the antenna without the radials? Mark, KJ7BS |
Mark,
This month's edition of QEX (July/Aug. 2005) has an article addressing your question with a simulation matching your question exactly. Bottom line: put as many radials as long as possible in your yard and don't worry about it. The simulation with 60 1/4 wavelength radials in a 180 degree arc only resulted in a 1.67dB difference in signal strengths from the radial direction to the no radial direction. 73, Larry, W0QE Mark wrote: Here is an additional question. I have to mount my 40/80 vertical in a place where it can be hidden by trees, which means against the back fence in my yard. I can only put radials to cover 180 degrees. I assume my signal will radiate best in that direction. What kind of radiation will I get toward the side of the antenna without the radials? Mark, KJ7BS |
Mark,
Good question! There will be ~some~ gain/loss of signal in various directions. Probably won't be much gain or loss, just depends on 'other' things (how near the fence, fence made of wood/metal, and other mysterious things). Wouldn't worry too much about it, and if it really bothers you, sneak a radial or two under the fence for a ways. Hide it well and don't get caught running stuff in your neighbor's yard! 'Doc |
Thanks for the input. I will check out the QEX article.
The fence is block and my "neighbor's yard" is a horse exercise pasture. The horse farm behind me breeds and trains race horses. Mark, KJ7BS "'Doc" wrote in message m... Mark, Good question! There will be ~some~ gain/loss of signal in various directions. Probably won't be much gain or loss, just depends on 'other' things (how near the fence, fence made of wood/metal, and other mysterious things). Wouldn't worry too much about it, and if it really bothers you, sneak a radial or two under the fence for a ways. Hide it well and don't get caught running stuff in your neighbor's yard! 'Doc |
Mark wrote:
Thanks for the input. I will check out the QEX article. The fence is block and my "neighbor's yard" is a horse exercise pasture. The horse farm behind me breeds and trains race horses. A friend has just buried a large amount of chicken-wire under the surface of his wife's new horse-schooling area, so it can double as his antenna testing range. You might at least be able to persuade your neighbor to let you slot in a few radials with a spade. -- 73 from Ian G/GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
I have read Al Christman's QEX article, and though he mentions radial systems
used in AM BC stations, I doubt if he's read Brown, Lewis and Epstein, else I also doubt if he would have made some of the statements that appear in the article The Brown, Lewis and Epstein paper is a must read for anyone contemplating the installation of radials for a vertical radiator. Fortunately, Richard Harrison has supplied the paper in the thread below 'Brown Lewis and Epstein'. My post below has also been added to the above mentioned thread. However, I apologize for the problem in making the tabular data come out right--I tried, but was unsuccessful, so I hope you can interpret the data to be useful to you. Now to the mail I posted in the above mentioned thread. Walt,W2DU Thanks to Richard Harrison, he has supplied us with the renowned Brown, Lewis and Epstein paper, reporting the voluminous and enlightening experimental data concerning the length and number of ground radials required in approaching the condition of perfect ground underneath a vertical radiator. This paper has long been well known and highly respected in the communications engineering community, and since 1938 has become the standard for engineering the radial systems for AM BC stations Worldwide. The FCC requirement for radials in US BC stations is based on data in the BLE paper. The tragedy here is that BLE paper has gone practically unknown in the amateur community, as witnessed by so many continual questions and incorrect answers concerning the length and number of radials required to achieve the desired performance of our vertical radiators. So let me present a short, but definitive abstract of the pertinent numbers taken from the paper, that answer some of the pertinent questions correctly. As a reference on which to base the radiated field strength, the industry standard has traditionally used millivolts per meter to describe field strength. Specifically, the field strength of 194.5 millivolts per meter at one mile, radiated from a quarter-wavelength radiator over perfect ground with 1000 watts input, is the industry standard. In other words, this field strength is the maximum attainable under ideal conditions. The data below, obtained directly from measurements made at 3 MHz by Brown, Lewis and Epstein in 1937, provide definitive answers to those who ask how many radials of what length are necessary to provide a suitable ground plane. When comparing the fields strengths below, remember that 194.5 mv/meter is the field strength obtained with perfect lossless ground. Number of Field Strength Loss in dB Relative Radials in mv/meter to Perfect Ground Length Length 0.4 wl 1/4 wl 1/8 wl 0.4 wl 1/4 wl 1/8 wl 113 192 180 152 0.112 0.673 2.14 60 185 176 150 0.435 0.868 2.26 30 174 162 150 0.967 1.59 2.26 15 158 153 1.81 2.08 2 126 120 118 3.77 4.19 4.39 When reviewing these data, please keep in mind that as the field strength approaches 194.5 mv/meter the effective ground is approaching perfect ground, which means that the conductivity of the ground in which the radials are planted is irrelevant, only the ground external to the radial system is relevant with respect to conductivity. It should also be kept in mind that the energy in the EM fields surrounding the vertical radiator diminishes with distance from the radiator. Thus the displacement currents entering the ground diminish proportionately with distance. Consequently, there is a distance from the radiator after which the currents become too small to be significant to the conservation of power radiated. This fact determines the maximum length of the radials necessary to reach the point where the law of diminishing returns prevails. The measurements reported in the BLE paper show this distance to be between 0.4 and 0.5 wavelengths. As noted above, this distance is relative to the amount of energy in the displacement currents at this distance from the radiator, and is in no way relevant to any resonant length of the radial. It is well known that radials buried in the ground lose all sense of resonance. Walt, W2DU |
Man, O, Man, do I have some apologizing to do to Danny Richardson, K6JHE. Danny
is the one who supplied the data on the Brown, Lewis and Epstein paper, not Richard Harrison. I'm sorry, Danny, it was a senior moment at age 86 that's responsible. Walt, W2DU |
"Walter Maxwell" wrote in message ... Man, O, Man, do I have some apologizing to do to Danny Richardson, K6JHE. Danny is the one who supplied the data on the Brown, Lewis and Epstein paper, not Richard Harrison. I'm sorry, Danny, it was a senior moment at age 86 that's responsible. Walt, W2DU Dang, I can't seem to get anything right today. Can't even spell Danny's call sign correctly. Repeat after me, it's K6MHE, it's K6MHE, it's K6MHE. Walt, W2DU |
I only wish I had contributed B, L, and E`s findings on antenna radials.
My information has always come 2nd hand from its reprinting by Ed Laport in "Radio Antenna Engineering. Ed has formulas to use in choosing your ground system. I can`t find my copy of Ed`s excellent book at the moment. Laport, like Walter, W2DU, is an RCA alumnus and has associated with the famous pioneers. K6JHE did us a favor by posting the original data. Common sense says that earth closest to a vertical tower gets most of the capacitive current between the tower and the earth. It is important that density of the ground radials be high close to the tower to reduce current in the lossy soil. I think there is more to it. The area of a circle around a tower is (pi)(r)(r), where r=distance from the tower. Area grows as the square of the distance from the tower. Assume a unit depth for the earth crust, and cross-section becomes equal to the surface area. The resistance of a conductor is its resistive coefficient times its length divided by its cross-sectional area. Total resistance seen by a ground wave traveling away from a tower is an inverse function of the distance from the tower`s highly conducting ground system. The farther from the tower you get, the more cross-aection there is, so the less resistance there is in the earth. This must be in textbooks, but I don`t recall seeing it. I once asked what a-c resistance to use for the earth at 60 Hz, 50 some years ago, in a student problem and was told to use 25 ohms, no matter what the distance through earth was. That`s when I noodled out the above explanation for the earth`s resistance. It should work at r-f too except for skin effect which if I recall causes an increase in resistance proportional to the square root of the frequency. The skin thickness is proportional to the reciprocal of the square root of the frequency. The point is that high conductivity is only needed very close to the tower for the ground wave. For a sky wave, you need high conductivity at the reflection point for a vertically polarized wave. Best regards, Richard Harrison, KB5WZI |
Richard Harrison wrote:
. . . It should work at r-f too except for skin effect which if I recall causes an increase in resistance proportional to the square root of the frequency. The skin thickness is proportional to the reciprocal of the square root of the frequency. . . That's an approximation which is true only for a good conductor. A poor conductor like ground acts like a conductor only up to a particular frequency, above which it acts like a dielectric in which the skin depth stays constant with frequency. Of course, there isn't an abrupt change, but the characteristic transitions from one to the other much like the frequency response of a highpass filter transitions from a fixed rising characteristic to flatten at the break frequency. Here are the transition frequencies for some common types of ground, where the first number in parentheses is the conductivity in S/m, the second is the relative permittivity (dielectric constant): Very good (0.0303, 20): 27.2 MHz Average (0.005, 13): 6.9 MHz Poor (0.002, 13): 2.8 MHz For many purposes involving electromagnetics including determining skin depth, the ground acts like a conductor below the transition frequency and like a dielectric above it. For example, here's the skin depth in feet for average soil at various frequencies: Freq MHz Skin Depth Ft 0.5 34.2 1 25.1 3.5 15.9 7 13.8 10 13.2 30 12.6 100 12.6 A very good treatment of this can be found in Kraus' _Electromagnetics_. Roy Lewallen, W7EL |
Dear Richard:
Your last paragraph (quoted below) is a good summary. It, or something like it, should be an introductory paragraph in every vertical's data sheet and advertisement. Well done. To have a vertical perform well for the important (for DX) angles between 2 and 12 degrees (above the horizon) one would like to have a copper sea starting one or two wavelengths from the antenna. I have worked 10 watt backpack stations in the UK when they were by the sea side. No hope to do so when they are inland. 73, Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: "Richard Harrison" wrote in snip The point is that high conductivity is only needed very close to the tower for the ground wave. For a sky wave, you need high conductivity at the reflection point for a vertically polarized wave. Best regards, Richard Harrison, KB5WZI |
I have worked 10 watt
backpack stations in the UK when they were by the sea side. No hope to do so when they are inland. Three or four weeks ago I drove down to the beach to do some fishing, bbqing, and general r&r. Of course, I had my radio. I pulled my truck right up next to the water. Didn't bother throwing a "water" ground wire out. Just ran normal with my "extended" 14 ft mobile whip. The coil 8 ft above the base of the whip. 100w. Was yakking on 40m late at night, and among all the stations, mostly home stations, some running power, I was one of the loudest ones on the freq. Can't beat a good sal****er location. :) Also, a mobile late at night on 40m, generally is as good as most normal height dipoles, etc. In fact, I had one guy do a test. He was in the house in FLA, and I wagered that his signal would increase if he went to his mobile. He did, and it did. MK |
I was at Quintana beach, at the mouth of the river.
Basically Freeport TX. I was parked on the beach, right where the beach makes the turn north at the river, on the east side of the river. Anywhere on the gulf coast is a good place to play radio. It's all rated the top "30" rating as far as ground conductivity. If you are nearly on the water like I was, you can really brown the food with a good vertical. I had to keep moving the truck up, as the tide kept coming up. Almost got stuck once... :( BTW...The fishing that night was lousy... I did much better at the BBQ and the radioing..MK |
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