Re: Topband: Modeling Ground and losses
Is it conventional to compare the surface wave fields at a distance so near the Radial length and the wave length? I chose a horizontal plane distance that would be just a bit into the far field radiation of that system, so as to minimize groundwave propagation loss. Greater distances would show lower fields, but their ratio would still be the same as at 0.1 km -- as would the difference in radiated power. R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Reply to W8JI post of Sat, 28 Feb 2015 19:14:07 -0500: The source of the r-f current flowing on buried radials is the r-f current flowing in the earth as a result of radiation from the vertical monopole. (etc) It seems to me that answer ignores other effects. 1.) If we remove the earth, the radials still have current. Yes, but then the origin of that current is via a direct, metallic path back to the 2nd terminal of the source (transmitter), using either balanced or coaxial transmission line. That operating configuration is different than when the radials are buried. 2.) If we place a conductor almost anywhere near any antenna, connected or not, it has current. If the wire is long and at 45 degrees or less, it can have very high current. But if those conductors are not buried, then the source of that current did not incur losses by traveling from the monopole to, and through the lossy earth around the base of the monopole -- to reach those radials. 3.) With the same applied power, a single radial in earth, despite being in the same dirt, has more current than the same radial with just one opposing radial. It's collecting from the same dirt. A single buried radial may have more current as you suggest (I'd have to model this), but that might be expected because a relatively small amount of the earth current flowing near the location where an opposing radial might have been can then collected by the remaining radial. No doubt the total current collected using both radials in this scenario is greater than when using either one of them, alone. 4.) Groundplanes still have current in radials See comment to 1.) above. Reply to KR9U post of Sat, 28 Feb 2015 21:23:50 -0500: ... If I add an imperfect ground with the radial buried just below the ground, I would expect that the efficiency of the antenna would drop. NEC4 shows it loses about 10 dB vs. free space, with about 6 dB of directivity in the direction of the radial wire using average ground. If I use dry sandy ground, then we gain back about 3 dB with a very similar pattern. ... Wouldn't that tend to show that a monopole system using a very high-loss ground plane should have greater gain than when driven against a very low-loss ground plane? Given that your NEC4 model is a 160-meter monopole system and other things equal, what does it show when only one 0.5-meter radial wire is used, and it is buried several centimeters below the surface of 0.1 mS/m d.c. 5 earth? If you are correct, then we should all be using uninsulated wires for radials. ?? EM radiation/current passes through the insulation of buried radial wires as easily as it does through the insulation of aerial wires. R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
If the total energy flowing into the monopole system with buried radials is dictated only by its hard-wired connection through the transmission line back to the transmitter, then what is accounting for the reduction of its radiated power? Nothing I said even remotely implies loss would be the same as things are changed, so the question or exercise is completely meaningless to the topic. I said the system is complex. I said radial current comes from more than one cause. I said it is far more than just a simple transference of current from soil to the radials. The radials are directly exposed to antenna fields. The radials are directly connected to the antenna feedline. If they are anywhere near soil or in soil, they are coupling to the soil. The soil is part of the system. A fence near the radials is part of the system. Unconnected wires are part of the system. A lake or ocean near the antenna is part of the system. It is a huge mix of things interacting, not just a boy and his radial, with the radial collecting currents only from the soil. By definition, soil or not, the radials have current. By definition, connected to the feedpoint or not, the radials (like any conductor around an antenna) will have current. But if that isn't enough, the field strength change of a model doesn't even prove what physically happens. The model just estimates or calculates a result. It might be spot on, but it just is a calculated summary of results of many things. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Richard-- Is it conventional to compare the surface wave fields at a distance so near the Radial length and the wave length? 0.1 km Sounds like a lot, but it is only 100m, which is low, in Lambda terms.. Bill--W4BSG -Original Message- From: Richard Fry Sent: Sunday, March 01, 2015 12:08 PM To: topband@contesting.com Subject: Re: Topband: Modeling Ground and losses The feedpoint connection, in all cases of vertical antennas, whether the system is shunt fed or series fed, or even if it is an end-fed half wave, ties one feed terminal to the ground or counterpoise system. It has to be that way, and the current out into that counterpoise (whatever the counterpoise is) has to be equal to the common mode current at the junction flowing up into the radiator. The link below leads to a NEC4 comparison of a 1/4WL vertical monopole using four 1/4WL radial wires at 90-deg horizontal intervals. In one case the radials are buried. In the other case they (and the monopole) are elevated 1 meter above the earth, and not connected to the earth by any metallic path. Applied power in both cases is 100 watts, and earth conductivity in both cases is 5 mS/m, d.c.5. The surface wave fields at 0.1 km from these two configurations differ by about 1.15 dB, which means that their radiated powers differ by about 30%. If the total energy flowing into the monopole system with buried radials is dictated only by its hard-wired connection through the transmission line back to the transmitter, then what is accounting for the reduction of its radiated power? http://s20.postimg.org/453nz5vn1/160_M_QTR_WV_MONOPOLE_Flds.jpg R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
The source of the r-f current flowing on buried radials is the r-f current flowing in the earth as a result of radiation from the vertical monopole. (etc) It seems to me that answer ignores other effects. 1.) If we remove the earth, the radials still have current. Yes, but then the origin of that current is via a direct, metallic path back to the 2nd terminal of the source (transmitter), using either balanced or coaxial transmission line. I doubt any system is 100% pure with a boundary condition like a hard switch. Dirt is not the same everywhere, even at one location. It probably is almost never the same at the surface as it is a few inches down. Arbitrarily declaring the method current gets into the wire is a single method determined entirely by contact or no contact is completely illogical. The feedpoint connection, in all cases of vertical antennas, whether the system is shunt fed or series fed, or even if it is an end-fed half wave, ties one feed terminal to the ground or counterpoise system. It has to be that way, and the current out into that counterpoise (whatever the counterpoise is) has to be equal to the common mode current at the junction flowing up into the radiator. It can't be any other way. Contact with the earth isn't like suddenly flipping a light switch, where all of a sudden all of the current is magically collected from the dirt all around the antenna, and then moving the wire .01 wavelengths up suddenly flips the switch the other way. The only true case I can think of where virtually all of the current is returned from the soil would be where the radial wire is buried several soil skin depths below the surface. We can certainly have creative license to **say** it is collected from the soil for any buried radial, but it pretty clearly isn't factual unless the wire is infinitely deep in the soil so far as skin depth goes. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
The feedpoint connection, in all cases of vertical antennas, whether the system is shunt fed or series fed, or even if it is an end-fed half wave, ties one feed terminal to the ground or counterpoise system. It has to be that way, and the current out into that counterpoise (whatever the counterpoise is) has to be equal to the common mode current at the junction flowing up into the radiator. The link below leads to a NEC4 comparison of a 1/4WL vertical monopole using four 1/4WL radial wires at 90-deg horizontal intervals. In one case the radials are buried. In the other case they (and the monopole) are elevated 1 meter above the earth, and not connected to the earth by any metallic path. Applied power in both cases is 100 watts, and earth conductivity in both cases is 5 mS/m, d.c.5. The surface wave fields at 0.1 km from these two configurations differ by about 1.15 dB, which means that their radiated powers differ by about 30%. If the total energy flowing into the monopole system with buried radials is dictated only by its hard-wired connection through the transmission line back to the transmitter, then what is accounting for the reduction of its radiated power? http://s20.postimg.org/453nz5vn1/160_M_QTR_WV_MONOPOLE_Flds.jpg R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Comments to two earlier posts by separate posters (clips below): But if indeed a less lossy ground means that fewer radials are needed to be placed in the field, then the coupling to the less lossy ground is greater which I would expect to mean more loss in the radial field which would then require more radials to reduce the effect. I agree that radials shield the field from the earth; however it seems that it is not quite as simple as it first seems. I agree with Tom's analysis -- a good radial system SHIELDS the field from the earth, returning the field and the IN PLACE OF the lossy earth. Studying N6LF's excellent work lit up the light bulb for me in several ways. First, by noting that current in a radial inductively couples to the lossy earth underneath it, which dissipates power. _ The source of the r-f current flowing on buried radials is the r-f current flowing in the earth as a result of radiation from the vertical monopole. Current is not lost to the earth from the buried radials. Instead, current _ enters_ the radials from the earth around them, because the radial wires provide a lower resistance path back to the 2nd terminal of the antenna system than does the earth. The r-f resistance of a set of buried radials is a circuit element in series with the r-f current flowing on a monopole. That is why it is important to system radiation efficiency for that r-f resistance to be as low as possible. The concepts in my statements above are not original to me. They are based on the publications of Dr. George H. Brown, Dr. Frederick E. Terman, Edmund Laport, and other authors of antenna engineering textbooks and papers. Below are some supporting clips from the textbooks of G. Brown, F. Terman and E. Laport. Please note that none of these authors writes that the function of buried radial wires is to act as a shield. From G. Brown et al, Ground Systems as a Factor in Antenna Efficiency, Proceedings of the Institute of Radio Engineers, Volume 25, Number 6 -- June 1937, page 757: \\ The earth currents are set up in the following manner. Displacement currents leave the antenna, flow through space, and finally flow into the earth where they become conduction currents. If the earth is homogeneous, the skin effect phenomena keep the current concentrated near the surface of the earth as it flows back to the antenna along radial lines. Where there are radial ground wires present, the earth current consists of two components, part of which flows in the earth itself and the remainder of which flows in the buried wires. As the current flows in toward the antenna, it is continually added to by more displacement currents flowing into the earth. It is not necessarily true that the earth currents will increase because of this additional displacement current, since all the various components differ in phase. // From F. Terman, Radio Engineers' Handbook, First Edition (1943), page 842: \\ Loss Resistance—Ground Systems ... Ground losses arise from the fact that the current charging the capacity between the antenna and ground ?ows through the capacity from the antenna to the earth and then back through the earth to the grounding point at the transmitter. The earth is a relatively poor conductor, so special provision must be made for returning these currents to the grounding point on the transmitter with a minimum of loss. One way of accomplishing this is to bury wires near the surface of the earth for the purpose of providing a low resistance path through the ground back to the transmitter. In order to be effective, these buried wires must be so arranged that the charging currents entering the earth have only a small or moderate distance to travel through the earth to reach a wire. // From E. Laport, Radio Antenna Engineering, McGraw-Hill (1952), pages 115-118: \\ 2.5. Ground Systems for Broadcast Antennas Antenna performance is standardized with reference to the ground being a perfectly conducting flat plane. Such an assumption serves a very useful purpose in revealing the ultimate possibilities of a certain radiator in terms of its dimensions and longitudinal and sectional geometry at a given frequency. All practical deviations from this norm are due to a number of empirical circumstances, of which one is the earth itself. A line of electric force (displacement current) extends from the top of the antenna through surrounding space to the earth. Upon entering a perfectly conducting earth it becomes a conduction current which returns to the base of the antenna and becomes a portion of the antenna current. The electric lines of force of the antenna field are thus seen to be the continuation current of a closed circuit through surrounding space. With a perfectly conducting earth, the electric line of force is always normal to the surface. When the earth is imperfectly conducting, the line of force tilts forward in the
Re: Topband: Modeling Ground and losses
The source of the r-f current flowing on buried radials is the r-f current flowing in the earth as a result of radiation from the vertical monopole. Current is not lost to the earth from the buried radials. Instead, current _ enters_ the radials from the earth around them, because the radial wires provide a lower resistance path back to the 2nd terminal of the antenna system than does the earth. It seems to me that answer ignores other effects. 1.) If we remove the earth, the radials still have current. 2.) If we place a conductor almost anywhere near any antenna, connected or not, it has current. If the wire is long and at 45 degrees or less, it can have very high current. 3.) With the same applied power, a single radial in earth, despite being in the same dirt, has more current than the same radial with just one opposing radial. It's collecting from the same dirt. 4.) Groundplanes still have current in radials 3.) _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Richard, You have just upset the apple cart for me. For the sake of argument, assume a monopole with a single radial in free space. I would assume that this would be a somewhat efficient antenna with a skewed pattern. If I add an imperfect ground with the radial buried just below the ground, I would expect that the efficiency of the antenna would drop. NEC4 shows it loses about 10 dB vs. free space, with about 6 dB of directivity in the direction of the radial wire using average ground. If I use dry sandy ground, then we gain back about 3 dB with a very similar pattern. I'm not claiming accuracy with NEC4 and ground, but the effect is as I would expect. Therefore, if as you indicate that ground currents flow into the radial wire then the efficiency should increase with a buried radial due to additional currents flowing into the radial. If you are correct, then we should all be using uninsulated wires for radials. ?? Jim - KR9U -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Richard Fry Sent: Saturday, February 28, 2015 8:34 AM To: topband@contesting.com Subject: Re: Topband: Modeling Ground and losses Comments to two earlier posts by separate posters (clips below): But if indeed a less lossy ground means that fewer radials are needed to be placed in the field, then the coupling to the less lossy ground is greater which I would expect to mean more loss in the radial field which would then require more radials to reduce the effect. I agree that radials shield the field from the earth; however it seems that it is not quite as simple as it first seems. I agree with Tom's analysis -- a good radial system SHIELDS the field from the earth, returning the field and the IN PLACE OF the lossy earth. Studying N6LF's excellent work lit up the light bulb for me in several ways. First, by noting that current in a radial inductively couples to the lossy earth underneath it, which dissipates power. _ The source of the r-f current flowing on buried radials is the r-f current flowing in the earth as a result of radiation from the vertical monopole. Current is not lost to the earth from the buried radials. Instead, current _ enters_ the radials from the earth around them, because the radial wires provide a lower resistance path back to the 2nd terminal of the antenna system than does the earth. The r-f resistance of a set of buried radials is a circuit element in series with the r-f current flowing on a monopole. That is why it is important to system radiation efficiency for that r-f resistance to be as low as possible. The concepts in my statements above are not original to me. They are based on the publications of Dr. George H. Brown, Dr. Frederick E. Terman, Edmund Laport, and other authors of antenna engineering textbooks and papers. Below are some supporting clips from the textbooks of G. Brown, F. Terman and E. Laport. Please note that none of these authors writes that the function of buried radial wires is to act as a shield. From G. Brown et al, Ground Systems as a Factor in Antenna Efficiency, Proceedings of the Institute of Radio Engineers, Volume 25, Number 6 -- June 1937, page 757: \\ The earth currents are set up in the following manner. Displacement currents leave the antenna, flow through space, and finally flow into the earth where they become conduction currents. If the earth is homogeneous, the skin effect phenomena keep the current concentrated near the surface of the earth as it flows back to the antenna along radial lines. Where there are radial ground wires present, the earth current consists of two components, part of which flows in the earth itself and the remainder of which flows in the buried wires. As the current flows in toward the antenna, it is continually added to by more displacement currents flowing into the earth. It is not necessarily true that the earth currents will increase because of this additional displacement current, since all the various components differ in phase. // From F. Terman, Radio Engineers' Handbook, First Edition (1943), page 842: \\ Loss Resistance-Ground Systems ... Ground losses arise from the fact that the current charging the capacity between the antenna and ground ?ows through the capacity from the antenna to the earth and then back through the earth to the grounding point at the transmitter. The earth is a relatively poor conductor, so special provision must be made for returning these currents to the grounding point on the transmitter with a minimum of loss. One way of accomplishing this is to bury wires near the surface of the earth for the purpose of providing a low resistance path through the ground back to the transmitter. In order to be effective, these buried wires must be so arranged that the charging currents entering the earth have only a small or moderate distance to travel through the earth to reach
Re: Topband: Modeling Ground and losses
Jim, This brings up something I have been wondering about. You make several good points that I agree with. However, on one hand we have a very lossy earth (for instance sand) which would mean less coupling to the ground from the radials - acting more *like* a raised radial field. But if indeed a less lossy ground means that fewer radials are needed to be placed in the field, then the coupling to the less lossy ground is greater which I would expect to mean more loss in the radial field which would then require more radials to reduce the effect. I agree that radials shield the field from the earth; however it seems that it is not quite as simple as it first seems. Jim - KR9U _ I agree with Tom's analysis -- a good radial system SHIELDS the field from the earth, returning the field and the IN PLACE OF the lossy earth. Studying N6LF's excellent work lit up the light bulb for me in several ways. First, by noting that current in a radial inductively couples to the lossy earth underneath it, which dissipates power. He also emphasized the importance of current in elevated radials dividing as equally as possible between them to minimize loss. The logic is simple -- since power is I squared R, uneven division causes a greater increase in the loss of a radial with more current than the decrease in the loss in the radial with less current. That led me to this very simple, but very fundamental concept. Each time we double the number of radials, the current in each is divided by 2, but the power in each divides by four. This beautifully and simply corresponds to what we know about the power lost in radials. Now, that simple analysis assumes a homogeneous earth, which we know is not real, so current division, and power lost in the earth, will vary as a result of that irregularity. But the fundamental concept remains the same. it also explains why we don't need as many radials to hit diminishing returns when the earth is less lossy. 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
On Fri,2/27/2015 7:14 AM, Tom W8JI wrote: I don't think a description like that paints an accurate picture of what actually goes on. I agree with Tom's analysis -- a good radial system SHIELDS the field from the earth, returning the field and the IN PLACE OF the lossy earth. Studying N6LF's excellent work lit up the light bulb for me in several ways. First, by noting that current in a radial inductively couples to the lossy earth underneath it, which dissipates power. He also emphasized the importance of current in elevated radials dividing as equally as possible between them to minimize loss. The logic is simple -- since power is I squared R, uneven division causes a greater increase in the loss of a radial with more current than the decrease in the loss in the radial with less current. That led me to this very simple, but very fundamental concept. Each time we double the number of radials, the current in each is divided by 2, but the power in each divides by four. This beautifully and simply corresponds to what we know about the power lost in radials. Now, that simple analysis assumes a homogeneous earth, which we know is not real, so current division, and power lost in the earth, will vary as a result of that irregularity. But the fundamental concept remains the same. it also explains why we don't need as many radials to hit diminishing returns when the earth is less lossy. 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
... As I understand, the primary loss mechanism for ground mounted vertical systems is EM field penetrating the lossy material below. To lower this loss, one needs to prevent this ground penetration. ... A monopole will not radiate without a return path for the r-f current flowing into/on it. In the case of a ground-mounted vertical monopole, the first part of that return path is provided by the capacitive coupling of the monopole to the earth around its base. Currents are generated in that region of the earth by radiation from the monopole. For greatest radiation efficiency those currents need to be collected and returned to the antenna/transmit system. *That* is the function of the buried radials. Consider that even if a vertical monopole is installed over a perfect, infinite ground plane providing NO penetration of EM fields below it, that monopole will not radiate if there is no path for the current in the ground plane to return to the transmit system. The link below shows a simple block diagram and pictorial of these systems. To clarify my earlier statements in this thread - My posts on this topic are based on the classic 1937 BLE paper on ground systems. That paper includes a considerable amount of measured data along with a detailed discussion about the performance of monopole antennas using buried radials. It is well worth serious study, and comprehension. The BLE paper shows that the currents flowing along buried radials used with a monopole are *not* distributed along their lengths in the same manner as if the only current source for those radials was placed at its common point with other radials, at the base of the monopole. The source for the current flowing on buried radials is the current in the earth produced by radiation from the monopole. That earth current varies in amplitude and phase at different physical locations along the length of the radial, which causes variations in the net amplitude and phase of the current flowing on that radial at various physical locations along its length. For these reasons the current variation on a buried radial wire used with a vertical monopole is not the same as the variation along an end-fed wire in free space, for a given physical/electrical length of conductor (and other things equal). http://s20.postimg.org/lgq8fdkz1/Part_15_AM_Block_Diagram.jpg R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Regarding the quotes below: 2.) We see any radial or counterpoise system, close to the radial or counterpoise, has to have external fields. Those fields must extend out of the counterpoise, and always cause loss when a counterpoise is near a lossy media. 3.) We see we only mitigate the loss by making current density in the lossy media as low as possible, which generally means spreading the current out as evenly as possible in the lossy media or moving the antenna and a counterpoise away from the lossy media to reduce current. Please note that vertical monopoles driven against a set of four- or six-wire counterpoises are in daily use by several AM broadcast stations in the U.S. These stations provide * measured * fields very close to the maximum theoretical field possible from that monopole and applied power when driven against a PERFECT ground plane -- even though these counterpoises are elevated only some 10 or 15 feet above earth of rather poor earth conductivity. Here is a quote about one of the early cases, from the NAB paper titled NEW AM BROADCAST ANTENNA DESIGNS HAVING FIELD VALIDATED PERFORMANCE by Clarence M. Beverage Communications Technologies, Inc. Marlton, NJ \\ In November of 1988, our firm supervised the construction of a temporary antenna system in Newburgh, New York under FCC Special Field Test Authority using call sign KPI-204. The antenna system consisted of a lightweight, 15 inch face tower, 120 feet in height, with a base insulator at the 15 foot elevation and six elevated radials, a quarter wave in length, spaced evenly around the tower and elevated 15 feet above the ground. The radials were fully insulated from ground and supported at the ends by wooden tripods. Approximately ten feet above ground, a T network for matching the antenna was mounted on a piece of marine plywood to isolate the components from contact with the lower section of the \ tower which was grounded. Power was fed to the system through a 200 foot length of coaxial cable with the cable shield connected to the shunt element of the T network and to the elevated radials. A balun or RF choke on the feedline was not employed and the feedline was isolated from the lower section of the tower. The system operated on 1580 kHz at a power of 750 watts. The efficiency of the antenna was determined by radial field intensity measure- ments along 12 radials extending out to a distance of up to 85 kilometers. The measured RMS efficiency was 287 mV/m for 1 kW, at one kilometer, which is the same measured value as would be expected for a 0.17 wave tower above 120 buried radials. // Clearly there is little effect on the radiation efficiency of these systems due to the proximity* of their counterpoise to the lossy media of nearby earth. *about 8.7 degrees, in this case R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
A monopole will not radiate without a return path for the r-f current flowing into/on it. In the case of a ground-mounted vertical monopole, the first part of that return path is provided by the capacitive coupling of the monopole to the earth around its base. Currents are generated in that region of the earth by radiation from the monopole. For greatest radiation efficiency those currents need to be collected and returned to the antenna/transmit system. *That* is the function of the buried radials. I don't think a description like that paints an accurate picture of what actually goes on. There are two things happening at the antenna base: 1.) Any system with a conventional two conductor transmission line, either balanced or unbalanced, needs at least TWO terminals to apply power to the antenna. A monopole antenna requires something for the feedline to push against. This is an unbendable rule. 2.) If the antenna is near earth, or near any other conductive media, it induces currents in that media. This always happens, this is another unbendable rule. If the media is lossy, we have to either shield the media from the antenna to reduce current density in the lossy media, or make the media more conductive (less lossy). If we follow those two rules, we see how all antennas work. 1.) We see an end-fed antenna of any type, even a half wave or Zepp, without counterpoise, cannot possibly work without some feeder radiation. We either provide it a controlled counterpoise, or it just makes its own counterpoise out of the feedline or things around the feedpoint. 2.) We see any radial or counterpoise system, close to the radial or counterpoise, has to have external fields. Those fields must extend out of the counterpoise, and always cause loss when a counterpoise is near a lossy media. 3.) We see we only mitigate the loss by making current density in the lossy media as low as possible, which generally means spreading the current out as evenly as possible in the lossy media or moving the antenna and a counterpoise away from the lossy media to reduce current. The picture of something pouring off the antenna that has to be collected and returned certainly has merit when we consider the electric field and displacement currents, but it also paints an incomplete and somewhat misleading picture. It is like using an etch-a-sketch drawing to describe a complex landscape. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Having lived in the Newburgh area, I have to object again to this report that I have tried to debunk before. I have earlier communicated this objection to Mr. Fry which he chooses to ignore. Given the topography of the area, this report is simply incomplete and unproven unless the GPS coordinates are provided and it is firmly known whether the antenna was at the Hudson river plain level or on one of the 500-1000 foot HAAT hills in the area. Then one would need to know the GPS coordinates of all the data points to evaluate terrain influences along the path. As every ham can tell you, with 80 accumulated years of worldwide irrefutable data only improved upon by transmission over salt water, high hilltop to high hilltop has exceptional overall propagation advantages. I continue to wonder about this report as a possible con job absent sufficient data, or why a reputable firm would even think to advance this study without those qualifications supplied with the report. Simply put, the Newburgh area is at least a difficult area and at worst an entirely inappropriate area to test this thesis. At other sites, it would need to be known whether the site is a conversion site, that is, over old radials. And then it would be necessary to evaluate this concept over pristine ground vs. over conversion site ground. The problem with the Newburgh, NY geography is easily seen by anyone with Google Earth using the slanted view which displays vertical topography as if viewed from a low flying plane or helicopter, and will clearly show the area's characteristic sharp transitions between the river plain and hilltops. As is irrefutably known to any ham, the propagation from the hilltop sites is immensely better than inland sites at locally lower ground, especially for receptors that are themselves at ground. All-in-all the study is a shame to have been published in this missing data format. Otherwise it might have been a demonstration of how much loss can be avoided by elevating the feedpoint. A far better site for the purpose would have been the New Jersey farming area flatlands. If THAT delivers the same readings, then you have something. If it takes hilltops to make hay, there simply is nothing new. 73, Guy. On Fri, Feb 27, 2015 at 1:35 PM, Richard Fry r...@adams.net wrote: Regarding the quotes below: 2.) We see any radial or counterpoise system, close to the radial or counterpoise, has to have external fields. Those fields must extend out of the counterpoise, and always cause loss when a counterpoise is near a lossy media. 3.) We see we only mitigate the loss by making current density in the lossy media as low as possible, which generally means spreading the current out as evenly as possible in the lossy media or moving the antenna and a counterpoise away from the lossy media to reduce current. Please note that vertical monopoles driven against a set of four- or six-wire counterpoises are in daily use by several AM broadcast stations in the U.S. These stations provide * measured * fields very close to the maximum theoretical field possible from that monopole and applied power when driven against a PERFECT ground plane -- even though these counterpoises are elevated only some 10 or 15 feet above earth of rather poor earth conductivity. Here is a quote about one of the early cases, from the NAB paper titled NEW AM BROADCAST ANTENNA DESIGNS HAVING FIELD VALIDATED PERFORMANCE by Clarence M. Beverage Communications Technologies, Inc. Marlton, NJ \\ In November of 1988, our firm supervised the construction of a temporary antenna system in Newburgh, New York under FCC Special Field Test Authority using call sign KPI-204. The antenna system consisted of a lightweight, 15 inch face tower, 120 feet in height, with a base insulator at the 15 foot elevation and six elevated radials, a quarter wave in length, spaced evenly around the tower and elevated 15 feet above the ground. The radials were fully insulated from ground and supported at the ends by wooden tripods. Approximately ten feet above ground, a T network for matching the antenna was mounted on a piece of marine plywood to isolate the components from contact with the lower section of the \ tower which was grounded. Power was fed to the system through a 200 foot length of coaxial cable with the cable shield connected to the shunt element of the T network and to the elevated radials. A balun or RF choke on the feedline was not employed and the feedline was isolated from the lower section of the tower. The system operated on 1580 kHz at a power of 750 watts. The efficiency of the antenna was determined by radial field intensity measure- ments along 12 radials extending out to a distance of up to 85 kilometers. The measured RMS efficiency was 287 mV/m for 1 kW, at one kilometer, which is the same measured value as would be expected for a 0.17 wave tower above 120 buried radials. // Clearly there is
Re: Topband: Modeling Ground and losses
... Simply put, the Newburgh area is at least a difficult area and at worst an entirely inappropriate area to test this thesis. ... Some may not be aware of the methodology used to determine the FCC efficiency of an AM broadcast radiator (see http://www.gpo.gov/fdsys/pkg/CFR-2012-title47-vol4/xml/CFR-2012-title47-vol4-sec73-186.xml ) . Here is another case from that same engineering paper by Clarence Beverage. I believe this system is still in operation. \\ The first permanent use of an elevated radial ground system appears to be at WPCI, 1490 kHz in Greenville, South Carolina. This installation, designed by William A. Culpepper, involved replacing a standard buried system with a four wire elevated system consisting of #10 solid copper wire, one quarter wave in length, and supported on treated wooden posts which keep the radials 4.9 meters above ground. The antenna radiation efficiency, based on field strength readings on the eight cardinal radials, was 302 mV/m at 1 kilometer versus the predicted FCC value of 307 mV/m. The WPCI installation was unique in that the tower was base insulated but the radials came right up to the tower, 4.9 meters above ground and terminated in insulators. The tower was fed from the tuning unit, through a piece of coax to the 5 meter point on the tower where the center conductor of the coax was attached to the tower and the shield to the elevated radials. This feed system resulted in a higher feed resistance than would normally be expected. Data on this facility was taken from the FCC files. // Note that the elevated radials replaced a buried radial ground system. The tower was/is 1/4-wave in height, which with a conventional set of 120 x 1/4-wave buried radials would have an FCC 'efficiency of about 307 mV/m at 1 km for 1 kW of applied power. This system produced 302 mV/m for those conditions, using four elevated wires as a counterpoise. R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
All As far as I can understand, wires / radials just under the surface of the ground are simply conductors embedded in a lossy dielectric (with an interface to air near it), similar to carbon filled plastic or other such material. If the loss and the dielectric constant is low, the wire acts more like free space antenna conductor with standing waves made possible by actually having energy that can be reflected back from the open end. If the loss is high, nothing remains to form a standing wave as the energy in the wire dissipates such that only (mostly) a forward wave is present and no standing wave can be observed. The reason why this might be difficult to understand is that there are some three factors can be different: The dielectric constant, the conductivity and the spatial variations of these both in depth and along the surface of the ground and then the geometry of the multiple wires in this medium and the corresponding coupling(s) between the wires. The detailed predictions for current profile would seem most beneficial if a symmetric field very large number of very long radials is not possible for space or cost reasons. As I understand, the primary loss mechanism for ground mounted vertical systems is EM field penetrating the lossy material below. To lower this loss, one needs to prevent this ground penetration. Building a shield, a large, dense radial field is a way to do this. However, this doesn't change the fact that loss associated with one radial wire changes with current and current profile on it! I guess this is at the core of the debate here. I find it remarkable that we have now free tools to solve EM-problems that took computing center size efforts when I got started with this hobby at late 70's. MarkkuOH2RA/OG2A/WW1C _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
On 26 Feb 2015, at 06:31, Richard Fry wrote: Quote from page 757 of the BLE paper: For those who'd like to read the whole paper, you can access it here http://bit.ly/1LLdtCI Jeremy _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Tom W8JI w...@w8ji.com wrote: Of interest here is that the benchmark Brown, Lewis and Epstein I.R.E paper on ground systems does not show such standing waves along buried radials (clip below). Of interest down here is surface-buried radials down here show definite standing waves in actual measurements, so it doesn't care what BL and E measured. Their Fig. 7 shows results of simplified (manual) calculations, not measurement results. 73, Sinisa YT1NT, VE3EA _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Richard Fry r...@adams.net wrote: Quoting from page 771 of the BLE paper on ground systems: The current in the buried wires was measured in each case. That quote does not apply to Fig. 7, which is 10 pages earlier. This quote from p. 760 applies to Fig. 7: ...the following calculations are made on this basis. The current in the wires is shown... : Fig. 7 ... Fig. 8 ... Fig. 9 ... Fig. 10 ... 73, Sinisa _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Of interest here is that the benchmark Brown, Lewis and Epstein I.R.E paper on ground systems does not show such standing waves along buried radials (clip below). Of interest down here is surface-buried radials down here show definite standing waves in actual measurements, so it doesn't care what BL and E measured. What they measured in different dirt on a different frequency won't change how the radials acted here. This is the problem with radials and models. The dirt isn't the same and the radials are never the same effective depth all over the world. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Radials do have standing waves, and so the minimum impedance at the base will appear when the radial is somewhat less than 1/4 wave long. Of interest here is that the benchmark Brown, Lewis and Epstein I.R.E paper on ground systems does not show such standing waves along buried radials (clip below). The clip also shows that the r-f current flowing on the buried wires at and beyond 0.25 lambda (of their physical length in free space) are considerably less for 15 and 30 radials than for 113 radials. http://s20.postimg.org/oxj3qv59p/BL_E_Fig_7.jpg R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Their Fig. 7 shows results of simplified (manual) calculations, not measurement results. Quoting from page 771 of the BLE paper on ground systems: The current in the buried wires was measured in each case. This was accomplished by placing a coil next to the ground wire at a point where the wire was exposed. The coil was resonated by means of a small shunt condenser. The voltage across this combination was de- termined with a vacuum tube voltmeter. The combination was cali- brated in the laboratory. Fig. 24 shows the procedure in question. This measurement yielded the current in a single wire. To obtain the current flowing in all the buried wires at distance, x, the measured value was multiplied by the number of wires. R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Additional from the BLE paper on the subject of standing waves on buried radial wires... Figure 11 linked below is based on the r-f currents measured along the radial lengths shown in Figure 7. http://s20.postimg.org/k05j5r3al/BL_E_Fig_11.jpg R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
There is a bit of explanation and clarity in BLE regarding standing waves on radials that does not show up until page 781 and figure 42. ** Emphasis added. The current in the buried wires **for an antenna height of 88 degrees** and radials wires 135 feet long is shown in Fig. 42. We see that the current persists in 113 wires much further from the antenna than it does for a smaller number of wires Fig. 43 whows similar results for the same ground system and a **22-degree antenna.** Figure 42 clearly shows standing waves for 113 radials, the hint of standing waves for 60 and 30 radials, while figure 43 shows only the slightest hint of that. Height of the antenna is clearly involved in the production of standing waves. We also must remember these tests were done at 3 MHz, with an assumption that there were not any paradigm shifts going from the lower broadcast band to 3 Mhz. All of us are aware these days of many differences between low BC band and eighty meters, and indeed of differences between 160 and 80. . For all practical purposes, BLE was a series of tests run at 80 meters. Extrapolate to 160 with caution. 73, Guy On Wed, Feb 25, 2015 at 9:58 AM, Richard Fry r...@adams.net wrote: Additional from the BLE paper on the subject of standing waves on buried radial wires... Figure 11 linked below is based on the r-f currents measured along the radial lengths shown in Figure 7. http://s20.postimg.org/k05j5r3al/BL_E_Fig_11.jpg R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
On Wed,2/25/2015 5:27 AM, Tom W8JI wrote: Of interest down here is surface-buried radials down here show definite standing waves in actual measurements, so it doesn't care what BL and E measured. Not only that, but it defies logic that radials would NOT exhibit the same current and voltage distribution of any other conductor carrying RF current. The boundary condition is near zero at the end ( near because of capacitance at the end). Rudy Severns, N6LF, has explored this in his studies of radial systems. Rudy's work includes extensive modeling to understand and document what he was seeing in measurements of carefully constructed experimental systems. I recall seeing at least one study of current distribution in radial systems published in QST -- something like 20-30 years ago. I found it as a pdf on the ARRL website about 10 years ago. I remember that it documented exactly what Tom has observed -- that current varies along the radial and depending on the soil under the radial. 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Not only that, but it defies logic that radials would NOT exhibit the same current and voltage distribution of any other conductor carrying RF current. The boundary condition is near zero at the end ( near because of capacitance at the end). Rudy Severns, N6LF, has explored this in his studies of radial systems. Rudy's work includes extensive modeling to understand and document what he was seeing in measurements of carefully constructed experimental systems. There are only three ways a radial would not exhibit standing waves (waves that increase and decrease in level with distance): 1.) The radial is too short to have enough space for a part of the wavelength to stand. An example of this would be trying to measure the current difference along a 60-foot wire on 160 meters. It would just smoothly taper. 2.) The radial is terminated in the surge impedance of the radial. This would be like a transmission line terminated with the correct resistance. 3.) The ground sucks up the current at such a rate that there is not enough current left to increase. All the radials I have measured that are long enough to be over 1/4 wave electrical have shown standing waves. The current is less at the base than some distance out from the base, and it never seems to have anything noticeable to do with radiator height. I can take a 40M 1/4 wave vertical, surface bury 15-20 radials, and find long lengths (beyond 1/4 wave) that make base impedance go to 50 ohms or more, and the FS measures the same as other systems that have 35-38 ohm base impedance. Feed impedance doesn't even have to track the efficiency. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Previously, from two different posters... ... it defies logic that radials would NOT exhibit the same current and voltage distribution of any other conductor carrying RF current. The ground sucks up the current at such a rate that there is not enough current left to increase. Quote from page 757 of the BLE paper: Where there are radial ground wires present, the earth consists of two components, part of which flows in the earth itself and the remainder of which flows in the buried wires. As the current flows in toward the antenna, it is continually added to by more displacement currents flowing into the earth. It is not necessarily true that the earth currents will increase because of this additional displacement current, since all the various components differ in phase. Note the last sentence in the quote above, in particular. The physical conditions that determine the r-f current distribution along buried radial wires used with a monopole are different than those for wires in free space. The current distribution along a buried radial wire is a function of the current amplitudes and phases present in the earth adjacent to the entire physical length of that radial wire. Those earth currents are produced by the EM fields radiated into the earth by the monopole, within a 1/2-wavelength radius of the base of the monopole. The current on elevated radial wires used as a counterpoise is produced mainly by a direct, metallic (low-loss) connection to the transmitter. Current distribution along such wires is based mostly on their electrical lengths, and the physical configuration of the counterpoise. R. Fry _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
That of course will tell you the antenna is fairly Low Z, in order to get the efficiency back to as high as possible I laid 130 x 0.4 wave radials. With this I know that the effective series ground resistance in my case is about a couple of ohms, and the overall result is good. So the unfortunate reality for amateurs is the shorter the vertical is from a quarter wave, Ideally the longer the radials need to be. That may not be as cut and dry as it appears. Radials do have standing waves, and so the minimum impedance at the base will appear when the radial is somewhat less than 1/4 wave long. Lowest base impedance caused by the radial system does not always translate into lowest loss, however, since there are standing waves on the wires. I've seen this a few times, in the most recent case on 40 meters where 15 ohms more base feedpoint resistance did not cause a decrease in field strength compared to a 35 ohm base impedance. Ham radio has a multitude of wisdoms about antennas and radials, many or most conflict with other views. My feeling on this is most disagreements come from meaningless measurements or comparisons that have built up over the years. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
On Tue, Feb 24, 2015 at 12:16 PM, Clive GM3POI gm3p...@btinternet.com wrote: So the unfortunate reality for amateurs is the shorter the vertical is from a quarter wave, Ideally the longer the radials need to be. Indeed. But if the longer radials put your wire in your neighbor's back yard, or run out into the street, or into your basement, then radials need to be abandoned as your counterpoise solution. That in turn begets the dire need for something counterpoise and efficient that is not radials. That in turn begat the FCP, designed specifically to minimize ground losses in far less space than radials. 73, Guy _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Yes Guy, I agree. Another area that is overlooked perhaps through a lack of room is the need with short verticals to have longer radials to get back the system efficiency. Take my own as an example I only use a 51ft vertical which is top loaded. That of course will tell you the antenna is fairly Low Z, in order to get the efficiency back to as high as possible I laid 130 x 0.4 wave radials. With this I know that the effective series ground resistance in my case is about a couple of ohms, and the overall result is good. So the unfortunate reality for amateurs is the shorter the vertical is from a quarter wave, Ideally the longer the radials need to be. 73 Clive GM3POI -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Guy Olinger K2AV Sent: 24 February 2015 16:07 To: Richard Fry Cc: TopBand List Subject: Re: Topband: Modeling Ground On Tue, Feb 24, 2015 at 7:36 AM, Richard Fry r...@adams.net wrote: NEC4 produces accurate answers for monopole radiators _not_ using overkill radial systems, as long as the NEC model describes the real world conditions for that system. You wish. You're not considering the situation that everyone is complaining about. NEC x.x does not provide accurate answers for UNDERkill radial systems either. I've never heard of a skilled ham getting trounced on 160 who has a 1/4 wave radiator over an overkill radial system. While it might be argued that the ham really didn't have to put down that much copper, at worst he only wasted money. He's still doing right fine getting out on his highly efficient, if over-coppered antenna, and enjoying it. On the other hand, UNDERkill radial systems, too short, not enough, irregular lengths, non-uniform around the compass, especially over poorer ground, are what NEC x.x also significantly overestimates. Advice had by many, including myself, has really been off. I still am waiting for an apology for some glib advice given, resulting in a couple S units worth of unnecessary loss. I was told some number of times regarding my complaining of really poor results that I must be doing something wrong, as the advice had been verified by professionals and the FCC. I'm still hearing that selfsame blanket unqualified advice. Wrong then. Wrong now. Conversions from underkill radials to something efficient designed for limited space opportunities have generated conversion improvements anywhere from five to twelve dB, based on before and after strings of RBN reports. 7-8 dB is very common in these conversion exercises, raising suspicions of some singular issue not treated correctly or at all in NEC. Underkill radials are proven amplifier neutralizers. NEC does NOT directly calculate ground losses after the fashion of its highly accurate wire and tubing calculations. Sommerfeld and all the rest are tuned APPROXIMATION algorithms that seem well-calibrated only in the commercial BC paradigm. The NEC ground APPROXIMATION tuning misses by wide margins in small lots that are not lucky enough to be in 30 mS superdirt. You can say all you want, but there is now (past tense, already happened) a massive experience among hams who are using new methods to get a decent signal on 160, and they just won't believe the old line any more. They have their own experience in their backyard, and RBN reports, and new signal reports from longtime ham acquaintances well situated to report general changes in signal strength. And they simply don't care if NEC is accurate for commercial grade radial systems. It's a completely useless piece of information for them. Most hams do not have the land and circumstances to put down anything remotely resembling a commercially sized radial system. You're really only talking to property-rich hams, and leaving the vast majority to learn the hard way that what you are preaching does not apply to them. 73, Guy. _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Modeling Ground and losses
Radials into neighbors back yard? Yep. At least on contest nights! Radials across basement ceiling and out other side of the house? Yep. Radials across garage floor, out garage windows, through bushes, and across driveway? Yep. I am not abandoning radials as my counterpoise solution!!! But of course Guy, if any US contest stations want to abandon their radial systems in the DX contests, for any reason I'm all for it!!! On Tue, Feb 24, 2015 at 12:33 PM, Guy Olinger K2AV k2av@gmail.com wrote: On Tue, Feb 24, 2015 at 12:16 PM, Clive GM3POI gm3p...@btinternet.com wrote: So the unfortunate reality for amateurs is the shorter the vertical is from a quarter wave, Ideally the longer the radials need to be. Indeed. But if the longer radials put your wire in your neighbor's back yard, or run out into the street, or into your basement, then radials need to be abandoned as your counterpoise solution. That in turn begets the dire need for something counterpoise and efficient that is not radials. That in turn begat the FCP, designed specifically to minimize ground losses in far less space than radials. 73, Guy _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
