Re: Topband: Grounding the ends of radials
I generally agree with you, Bob - especially with regard to not grounding the far ends of 1/4 wave radials!! After all what we are trying to establish is a low-impedance image plane for the vertical radiator to be fed against! A 1/4 wave wire, grounded at the far end would have a high impedance to ground at the base, or feed-point, of the antenna! Makes no sense! Would not result in a very favorable driving-point impedance! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Bob Eldridge Sent: Saturday, January 25, 2014 3:46 PM To: topband@contesting.com Subject: Topband: Grounding the ends of radials I posted this on TowerTalk and I got a couple of responses as to why the ends of ground radials should not be grounded. Isn't it dependent on whether you want the radials resonant or not? And if you do want them resonant, on the length of the radial? It doesn't make sense to ground the far end of a quarter wave radial if you want a low impedance at the base of the antenna. It does make sense if you have short radials and want to intercept the return current. Bob VE7BS _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Grounding the ends of radials
It seems to me that whether or not one grounded the far end of a radial would make no difference. I don't see why one would want to ground the end of their radial, but if it was done with a ground rod that's not really much of a ground for rf. Think about it: a single ground rod at the base of a vertical isn't going to provide much of a ground -- that's why we need radials. A ground rod at the far end of a radial will provide a similar crummy rf ground thus limiting any effect it would have on that radial at rf. Also, for any reasonable number of radials resonance doesn't really matter since its providing a ground screen (for on- or under-ground radials). The radial network is a non-resonant counterpoise. -Bill Sent from my iPhone On Jan 25, 2014, at 3:58 PM, Charlie Cunningham charlie-cunning...@nc.rr.com wrote: I generally agree with you, Bob - especially with regard to not grounding the far ends of 1/4 wave radials!! After all what we are trying to establish is a low-impedance image plane for the vertical radiator to be fed against! A 1/4 wave wire, grounded at the far end would have a high impedance to ground at the base, or feed-point, of the antenna! Makes no sense! Would not result in a very favorable driving-point impedance! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Bob Eldridge Sent: Saturday, January 25, 2014 3:46 PM To: topband@contesting.com Subject: Topband: Grounding the ends of radials I posted this on TowerTalk and I got a couple of responses as to why the ends of ground radials should not be grounded. Isn't it dependent on whether you want the radials resonant or not? And if you do want them resonant, on the length of the radial? It doesn't make sense to ground the far end of a quarter wave radial if you want a low impedance at the base of the antenna. It does make sense if you have short radials and want to intercept the return current. Bob VE7BS _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Grounding the ends of radials
If I lay my 1/4 wavelength bare radials several inches below ground; is that not the same as if the radials were grounded along their length? Doug -Original Message- True, I expect, Carl. Just don't ground it! If you think about it, a more-or-less ideal image - plane for the vertical would be a circular metallic sheet a 1/2 wave in diameter ( although infinite extent would be better). 73, Charlie, K4OTV -Original Message- From: ZR [mailto:z...@jeremy.mv.com] Sent: Saturday, January 25, 2014 4:43 PM To: Charlie Cunningham; 'Bob Eldridge'; topband@contesting.com Subject: Re: Topband: Grounding the ends of radials OTOH connecting all the ends together with a wire that can handle the total current would help balance the field..Yes or no? Carl KM1H --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Grounding the ends of radials
I am guessing that Bob is talking about insulated wire on the ground. But some specifics from him would be useful. Frequently mentioned specific radial implementations, in no specific order: 1) Raised radials 2) Radials of insulated wire laying on ground or embedded in lawns, etc. 3) Bare wire on, or in the ground. I suspect, but do not know that he is referring to 2). 1) would not be an issue as everyone treats these as needing attention to resonance issues. 3) in reasonably conductive ground, together with very fuzzied velocity factor issues, the radials can be part of a far reaching ground of many wavelengths, whose appearance of any resonance can be anywhere between non-existent and mild. Buried radials are as grounded as the ground permits. 2) will have significant modification by velocity factor issues, which have been *measured* anywhere between 45 and 85 percent. The actual distance from the conductive earth is highly variable in individual installations, as is the nature of the earth itself. Anything laying on the ground is severely modified by velocity factor. If he is talking about very dense radials, ~60 plus, the capacity at and near the ends to earth of all the wires is quite high and can easily blunt resonance effects, depending on ground conductivity. I posted this on TowerTalk and I got a couple of responses as to why the ends of ground radials should not be grounded. Isn't it dependent on whether you want the radials resonant or not? And if you do want them resonant, on the length of the radial? It doesn't make sense to ground the far end of a quarter wave radial if you want a low impedance at the base of the antenna. It does make sense if you have short radials and want to intercept the return current. Bob VE7BS _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Grounding the ends of radials
Yes. And the operative words there are along its length - very different from grounding at its end! The nastiest, and most difficult case to model and analyze is the case of radials laid on the ground! I would take a few elevated resonant radials over that arrangement, most any time!! BTW - dirt may be good but it ain't that good! :) 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Doug Renwick Sent: Saturday, January 25, 2014 5:32 PM To: topband@contesting.com Subject: Re: Topband: Grounding the ends of radials If I lay my 1/4 wavelength bare radials several inches below ground; is that not the same as if the radials were grounded along their length? Doug -Original Message- True, I expect, Carl. Just don't ground it! If you think about it, a more-or-less ideal image - plane for the vertical would be a circular metallic sheet a 1/2 wave in diameter ( although infinite extent would be better). 73, Charlie, K4OTV -Original Message- From: ZR [mailto:z...@jeremy.mv.com] Sent: Saturday, January 25, 2014 4:43 PM To: Charlie Cunningham; 'Bob Eldridge'; topband@contesting.com Subject: Re: Topband: Grounding the ends of radials OTOH connecting all the ends together with a wire that can handle the total current would help balance the field..Yes or no? Carl KM1H --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: grounding the ends of radials
but if it was done with a ground rod that's not really much of a ground for rf. It isn't there to provide a ground. It is there to intercept return rf, which flows not far below the surface. So a ground spike is a more appropriate term. Ground rods are good for safety purposes. Yes, I am assuming insulated wire laid on or near the surface. But grounding the far end of buried bare radials doesn't do any harm. A single ground rod at the base of a vertical isn't going to provide much of a ground. True. But a ring of short grounding spikes, connected together and back to the base (U.S. Army tactical grounding system), provides a reasonable alternative to a metal plate. The radial network is a non-resonant counterpoise. Sometimes, but not always. Bob VE7BS _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: grounding the ends of radials
But why ground the end of a bare buried radial that's already buried in the ground?? Probably be more effective to just soak the area with Calcium Chloride or something! A radial network of elevated resonant radials is NOT a non-resonant counter-poise. In fact an 80m 1/4 wave vertical or a 160m inverted L each with a few elevated resonant radials are just a ground-plane antennas, for Pete's sake! And its properties are well known and documented and have been for decades! (but some people much prefer dirt!) If you believe- no proof is necessary. If you don't believe - no proof is possible! FWIW 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Bob Eldridge Sent: Saturday, January 25, 2014 6:53 PM To: topband@contesting.com Subject: Topband: grounding the ends of radials but if it was done with a ground rod that's not really much of a ground for rf. It isn't there to provide a ground. It is there to intercept return rf, which flows not far below the surface. So a ground spike is a more appropriate term. Ground rods are good for safety purposes. Yes, I am assuming insulated wire laid on or near the surface. But grounding the far end of buried bare radials doesn't do any harm. A single ground rod at the base of a vertical isn't going to provide much of a ground. True. But a ring of short grounding spikes, connected together and back to the base (U.S. Army tactical grounding system), provides a reasonable alternative to a metal plate. The radial network is a non-resonant counterpoise. Sometimes, but not always. Bob VE7BS _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Grounding the ends of radials
Elevated radial wires perform much differently than buried radial wires. Elevated, horizontal radial wires having self-resonant 1/4 wavelength used as all, or part of an elevated counterpoise for a monopole, tee, or inverted L should NOT have a low-Z (direct) path to the earth at the operating frequency at either end of those horizontal conductors -- such as provided by wired connections using ground rods. If so, then those elevated, horizontal conductors no longer will have the characteristics of opposing, end-fed 1/4-wave conductors -- which have about zero r-f current at the ends opposite their feedpoints and maximum r-f current at their feedpoints, and which produce the best radiation efficiencies from such antenna systems. The reason for this is that the r-f current flowing in to and out of the ground plane from the end(s) of such grounded, elevated radials constitutes loss that otherwise would add to the fields radiated by that antenna system. _ Depending on their wavelengths, number, and geometry, buried radial wires concentric with the base of a monopole provide a relatively low loss path for r-f currents flowing in the earth within about 1/2 wavelength of the monopole (due to its near-field radiation into the ground plane) to flow between the r-f ground connection of the transmit system and the feedpoint of the monopole. The lower the r-f losses in that path, the greater the radiation efficiency of that antenna system. As shown by well-documented physical experiments going back to 1937 and many subsequent real-world tests and measurements also accepted by the FCC, a monopole of about 55-deg electrical height or more driven against a set of ~120 buried horizontal radials at equal azimuth spacing and each having a free-space wavelength of about 90 degrees produces a peak inverse-distance groundwave field at 1 km that is within several percent of the maximum theoretical field possible for that applied power when radiated by a perfect monopole of such electrical heights when driven against a perfect ground plane. R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Grounding the ends of radials
I generally agree with you, Bob - especially with regard to not grounding the far ends of 1/4 wave radials!! After all what we are trying to establish is a low-impedance image plane for the vertical radiator to be fed against! A 1/4 wave wire, grounded at the far end would have a high impedance to ground at the base, or feed-point, of the antenna! Makes no sense! Would not result in a very favorable driving-point impedance! The issue is complicated by the number of radials, the soil, and the radial length. Even buried radials directly in contact with soil are resonant, the extent of which depends on the shallow and deep characteristics of the earth. In most soils, bare wires are not grounded for RF as well as people probably think. Measuring buried 40 meter radials here, I could get a fairly high base impedance with some radial lengths and numbers. This did **not** affect the field strength. With about a dozen radials the base impedance of a 40M vertical with long radials was about 50-60 ohms. It had about the same measured field strength as 4 elevated resonant radials that had a base impedance down in the upper 30 ohm range. People used to use ground rods at the ends of radials when they had to truncate the radials. Also, some people used ground rods and no radials at all. They swore by those systems, wrote articles about those systems, and even bragged about all the DX they worked. Opinions, contacts, or feelings tells us more about how difficult it is to tell how well something really works than it tells us how the systems actually work. That's why this stuff rages on and on for decades. Even the AM BC stuff was mostly meaningless nonsense. People would pull radials in over other radials while guessing not many of the old radials were still there, make measurements with 3 dB of wobble in the readings and pick the numbers they liked, and call it conclusive evidence. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Grounding the ends of radials
All true, of course. Aside from the rocky condition of my lot, one of the main reasons that I rely on elevated radials is that I can model those antennas handily and I get good measurable results that compare and agree pretty well with my EZNEC models. Especially useful in parasitic or phased arrays! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Saturday, January 25, 2014 8:47 PM To: topband@contesting.com Subject: Re: Topband: Grounding the ends of radials I generally agree with you, Bob - especially with regard to not grounding the far ends of 1/4 wave radials!! After all what we are trying to establish is a low-impedance image plane for the vertical radiator to be fed against! A 1/4 wave wire, grounded at the far end would have a high impedance to ground at the base, or feed-point, of the antenna! Makes no sense! Would not result in a very favorable driving-point impedance! The issue is complicated by the number of radials, the soil, and the radial length. Even buried radials directly in contact with soil are resonant, the extent of which depends on the shallow and deep characteristics of the earth. In most soils, bare wires are not grounded for RF as well as people probably think. Measuring buried 40 meter radials here, I could get a fairly high base impedance with some radial lengths and numbers. This did **not** affect the field strength. With about a dozen radials the base impedance of a 40M vertical with long radials was about 50-60 ohms. It had about the same measured field strength as 4 elevated resonant radials that had a base impedance down in the upper 30 ohm range. People used to use ground rods at the ends of radials when they had to truncate the radials. Also, some people used ground rods and no radials at all. They swore by those systems, wrote articles about those systems, and even bragged about all the DX they worked. Opinions, contacts, or feelings tells us more about how difficult it is to tell how well something really works than it tells us how the systems actually work. That's why this stuff rages on and on for decades. Even the AM BC stuff was mostly meaningless nonsense. People would pull radials in over other radials while guessing not many of the old radials were still there, make measurements with 3 dB of wobble in the readings and pick the numbers they liked, and call it conclusive evidence. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
