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#1
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Radial straight down
Has anyone ever bored a hole into the ground and dangled a radial or
counterpoise down it instead of burying a radial 6" horizontally under the ground or stringing out a counterpoise? Any promise in doing this? Or is it a non-starter? |
#2
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Radial straight down
Richard wrote:
Has anyone ever bored a hole into the ground and dangled a radial or counterpoise down it instead of burying a radial 6" horizontally under the ground or stringing out a counterpoise? One of my textbooks says such a configuration dissipates half of the incident power. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
#3
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Radial straight down
"Richard" wrote in message ... Has anyone ever bored a hole into the ground and dangled a radial or counterpoise down it instead of burying a radial 6" horizontally under the ground or stringing out a counterpoise? Any promise in doing this? Or is it a non-starter? Well, I have a 1/2 wave inverted L for 160 that I use with a remotely tuned L network on 160, 80 and 40. The matching network sits on top of a 6 inch well casing that goes down 90 feet and is grounded to that. That was initially my only ground. The 160 meter impedance was 2600 Ohms and 1800 on 80 and 700 on 40. I later installed a counterpoise under the horizontal portion of the antenna, 160 feet at 10 foot elevation. Of course, I didn't notice any change in operational reports or anything, but the feedpoint impedance went to 1900, 1200 and 450 Ohms respectively. I suppose the earthworms think that global freezing is taking place, but no other effects noted. It's been a very effective LF antenna for over 20 years both ways. W4ZCB |
#4
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Radial straight down
Richard wrote:
Has anyone ever bored a hole into the ground and dangled a radial or counterpoise down it instead of burying a radial 6" horizontally under the ground or stringing out a counterpoise? Any promise in doing this? Or is it a non-starter? Radials basically serve the purpose of improving the apparent conductivity of the soil at the base of the antenna (e.g. less loss than a simple stake in the ground). A goodly portion of the loss of an antenna like a vertical is in the IR losses of the RF current flowing in the surface of the soil (where "surface" depends on the RF properties of the soil, skin effect and all that). So, burying deeper probably doesn't help this (e.g. you want to improve the conductivity at the surface). |
#5
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Radial straight down
On May 11, 8:23*am, "Richard" wrote:
Has anyone ever bored a hole into the ground and dangled a radial or counterpoise down it instead of burying a radial 6" horizontally under the ground or stringing out a counterpoise? Any promise in doing this? Or is it a non-starter? Letter from June 1949 QST: Dear Editor: I have followed with great interest your articles and correspondence on underground antennas. I tried several directive beams buried in four feet of moist earth. After several reports from various hams I found I had no more power than with the old skywire. I dug deeper - even tried rhombics - but reports were still the same ('Nice sig, OM, but some guy in Califormia has 10kw right on you.')!!! I consulted the old faithful ARRL Handbook and decided to try a multiple-wavelength vertical on ten meters. I did not have to look far for a suitable antenna site. We have a 200- foot well right in our basement. I hooked a variometer to the final tank and from same connected a No. 6 stranded wire to a pipe running into the well. I was delighted to raise a C2 in Hankow, China, on my first CQ. Chinese stations were heard that pinned the S-meter on the receiver. I soon discovered that all I could work were Chinese amateurs. Now wouldn't this bear out the Handbook theory that 'the more wavelengths an antenna has, the more it tends to radiate straight off the end'? - W7LLE |
#6
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Radial straight down
On May 11, 7:23*am, "Richard" wrote:
Has anyone ever bored a hole into the ground and dangled a radial or counterpoise down it instead of burying a radial 6" horizontally under the ground or stringing out a counterpoise? RF currents needing to travel a lengthy path through the earth to reach such a vertical buried wire would encounter high losses. The function of buried radials is to provide a low loss return path for the r-f conduction currents induced in the earth near a monopole, which result from displacement currents generated by radiation from the monopole. Almost all of these currents lie within a radius of 1/2 of a free-space wavelength (regardless of the monopole height). So the most efficient collection of these ground currents means the radials should extend about 1/2 of a free-space wavelength from the base of the monopole -- so that the currents won't have to travel very far through the lossy earth before they are "captured" by a radial wire. The electrical length of buried radials with respect to the reduced v.p. in their environment has no real bearing on how effective the radials are at reducing the r-f loss in the ground system. The r-f loss present in the radial ground system doesn't affect the shape of the relative field pattern generated by the monopole, or the propagation of the fields launched by the monopole. But as that ground system loss is in series with antenna current, it will affect the radiation efficiency of the antenna system. A benchmark, real-world study of this subject was made by Brown, Lewis & Epstein of RCA Labs in 1937. It showed showed that 113 evenly- spaced, buried radials each 0.412 free-space wavelengths long and used with monopoles from ~70 to 90 degrees in height produced measured surface-wave fields at 3/10 of a mile that were within 2% of those generated by a perfect monopole with a zero-loss r-f ground, over a zero-loss ground plane. This corresponds to an antenna system efficiency of about 96%, or 960 watts radiated for 1,000 watts applied to the feedpoint. For a monopole with a radiation resistance of 36 ohms this 96% efficiency means that the r-f resistance in the ground system is about 1.5 ohms. There wouldn't be much practical benefit gained by using more/longer radials. The BL&E tests were conducted in the sandy soil of New Jersey, where earth conductivity is rather poor. RF |
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