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RF grounding methods for sailboats: A Summary
This is a distillation of several recent postings and other readily
available information on securing a good RF "ground" for a vertical antenna on a plastic or wood sailboat. The basis for each method was either reported model results or a presumed "organizational authority" on the subject (i.e., ARRL, Icom, and SGC). No ranking or recommendation was intended. If anyone spots any errors of fact or significant omissions, I'd welcome appropriate "recalibration". Thanks in advance. 1) Grounding plates Will not work if submerged as much as four feet, but will work as near-perfect if at the waterline, and may work if attached to hull even when submerged four feet (awaiting clarification from Roy, W7EL). In fresh water or low-conductivity water, a ground plate may not function acceptably. Sometimes used in combination with #4 below. Recommended only "as a last resort" by Icom. 2) Wire in water A one-foot length of wire immersed near water surface is sufficient for near-perfect results based on W7EL's NEC-4 model results. Assumed performance is similar to grounding plate. 3) Radials Even shortened (loaded) radials elevated over seawater work as near-perfect based on N6LF's NEC-4 modeling. Objections to radials are safety (high-voltage insulation notwithstanding), tripping hazard, undesirable RF coupling, and the necessity of either tuning the radial(s) or installing multiple 1/4 wavelength wires. Radials will be useful even over fresh water or when boat is on land. Single radials can provide significant near-vertical radiation which may be useful, but at the cost of reduced radiation from the vertical radiator. Considered a viable alternative by Icom but not recommended by ARRL. 4) Counterpoise (i.e., mast, forestay, shrouds, lifelines, engine, metal tanks, 100 square feet of copper, keel, rudder, etc. bonded together) One of the traditional approaches to marine SSB installations on plastic and wood sailboats. The mast and rigging often provide the equivalent of ~200 lineal feet of counterpoise wire above deck with additional metal structures connected on and below deck. Sometimes used in combination with a grounding plate. If copper is placed inside hull below waterline, useful capacitive coupling to the water may occur. Will work over fresh water and on land. This is the method recommended in the ARRL Antenna Book, where radials, as the only considered alternative, are discouraged in their discussion for the reasons stated in #3. This type of counterpoise is also the approach recommended by both Icom and SGC. 5) OCF dipole w/horizontal component along deck Not commonly used, but obviates the need for multiple resonant radials. Analyzed by W4RNL. Usually requires a current choke in the coax from tuner to rig to reduce undesired RF coupling. Suffers from some of the same objections listed for radials; will also provide some near-vertical radiation. Will work over fresh water and on land. Is that where it stands, folks? 73, Chuck, NT3G ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
RF grounding methods for sailboats: A Summary
chuck writes:
3) Radials 5) OCF dipole w/horizontal component along deck Is that where it stands, folks? Beside the name, is there any difference between an OCF dipole and a single radial? 73 LA4RT Jon |
RF grounding methods for sailboats: A Summary
"Jon Kåre Hellan" wrote:
Beside the name, is there any difference between an OCF dipole and a single radial? By definition, a "radial" would be physically orthogonal to the other element. The elements in an OCF are usually collinear. -- 73, Cecil http://www.qsl.net/w5dxp |
RF grounding methods for sailboats: A Summary
Jon Kåre Hellan wrote:
chuck writes: 3) Radials 5) OCF dipole w/horizontal component along deck Is that where it stands, folks? Beside the name, is there any difference between an OCF dipole and a single radial? 73 LA4RT Jon We don't seem to have widely used, descriptive names for these configurations. Cecil is correct, and perhaps the OCF referred to should be called an OCF "L". The vertical radiator with a single, elevated, horizontal, resonant "radial" perhaps should be called an "L" dipole. On inspection, either antenna, on a boat with a tuner at the feedpoint, could be mistaken for the other. You could tell the difference only by observing how the antenna is operated. If the antenna is operated only on those frequencies for which the horizontal element is an odd multiple of a 1/4 wavelength, we would call the antenna an "L" dipole (or whatever). If that same antenna were operated not only on those frequencies, but on all others (HF spectrum) as well, we would call it an OCF "L". But if, on inspection, the antenna has multiple resonant radials, that would unambiguously differentiate it from the OCF. Whenever the two antennas are physically identical, they will obviously operate identically. Make sense, Jon? Sorry for the confusion. 73, Chuck NT3G ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
RF grounding methods for sailboats: A Summary
Cecil is correct,
==================================== He usually is! |
RF grounding methods for sailboats: A Summary
On Tue, 30 May 2006 09:21:56 -0400, chuck wrote:
If anyone spots any errors of fact or significant omissions, I'd welcome appropriate "recalibration". Thanks in advance. 1) Grounding plates Will not work if submerged as much as four feet Hi Chuck, Don't know how you got this miss-impression. 2) Wire in water A one-foot length of wire immersed near water surface is sufficient for near-perfect results based on W7EL's NEC-4 model results. Assumed performance is similar to grounding plate. This conclusion is conflict with the first, making it a mystery how you came to either in summary. The focus on "water surface" is as though you are trying to force it work like a pool of mercury. Water is NOT a ground plane in the sense of conductivity. Water is a terrible conductor. It is only its huge mismatch with air that gives it such superb propagation, not match, characteristics. Distinguish between the two. 3) Radials Even shortened (loaded) radials elevated over seawater work as near-perfect based on N6LF's NEC-4 modeling. Objections to radials are The objections are they are wholly unnecessary when ground is so easily achieved by conventional means. You would need 120 radials to shield against the loss you perceive, and that loss doesn't matter when you stand to gain so much in propagation. You couldn't even field a tenth of these radials. At HF, and maintaining their tune and symmetry, you would be lucky to fit in 2. At that stage of the game, there is absolutely no match advantage over conventional techniques aboard a small craft (and at HF you don't qualify for any thing other). 4) Counterpoise (i.e., mast, forestay, shrouds, lifelines, engine, metal tanks, 100 square feet of copper, keel, rudder, etc. bonded together) This type of counterpoise is also the approach recommended by both Icom and SGC. Only because it is already available and doesn't ask you to go any further for no obvious advantage. 5) OCF dipole w/horizontal component along deck Not commonly used, Who would choose a complicated design over so many simple ones? Is that where it stands, folks? If you want a dipole, make a VERTICAL dipole, even a lousy one. Finally, and to repeat, learn the distinction between matching and propagation. Your focus on matching issues is like seeing your glass 3/4ths empty. Looking at the propagation advantages in comparison is like seeing a pitcher of water nearby that will fill that glass a dozen times. 73's Richard Clark, KB7QHC |
RF grounding methods for sailboats: A Summary
Richard, there you go again, overcomplicating quite simple matters
with your Shakespearian, Queen Elizabeth the 1st English. Anything you toss into sea water makes a good ground. You can consider the connecting lead to be a part of the ground sytem or a part of the antenna. Take your pick. You will get precisely the same answers, on analysis, whatever you do. ========================================== |
RF grounding methods for sailboats: A Summary
"Reg Edwards" wrote:
Cecil is correct, He usually is! Especially about California wines, a subject upon which I am a guru. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
RF grounding methods for sailboats: A Summary
Richard Clark wrote:
On Tue, 30 May 2006 09:21:56 -0400, chuck wrote: If anyone spots any errors of fact or significant omissions, I'd welcome appropriate "recalibration". Thanks in advance. 1) Grounding plates Will not work if submerged as much as four feet Hi Chuck, Hello Richard, Perhaps the context for the summary was unclear. My objective was simply to identify several existing recommendations for obtaining RF grounds on plastic and wood vessels over sal****er. Regrettably, I lack knowledge of any published theoretical or empirical comparison of these proposals that provides an objective, quantifiable measure of performance. Don't know how you got this miss-impression. That it will not work if submerged as much as four feet? From Roy's report on his NEC-4 modeling. It is presumably based on the known skin depth of RF at 14 MHz. 2) Wire in water A one-foot length of wire immersed near water surface is sufficient for near-perfect results based on W7EL's NEC-4 model results. Assumed performance is similar to grounding plate. This conclusion is conflict with the first, making it a mystery how you came to either in summary. The focus on "water surface" is as though you are trying to force it work like a pool of mercury. Water is NOT a ground plane in the sense of conductivity. Water is a terrible conductor. It is only its huge mismatch with air that gives it such superb propagation, not match, characteristics. Distinguish between the two. Well, some of what you are saying is pretty much what I had thought. If you read my posts on the other thread, you'll see where I was heading. We agree that seawater's conductivity is lower than copper's but greater than earth's. We agree that a single ground rod driven into the earth will perform poorly as the only return path for a vertical antenna over land, but at least in some cases will perform better than if it were not there. Will a wire dipped into the sea perform better than the ground rod driven into the earth? I doubt there is much disagreement on that, even though water might be characterized in relative terms as a "terrible conductor". The only relevant question, then, is "how much better?" and so far, the only numerical answer that I am aware of has come from NEC modeling. The characterization I reported of a wire dipped into the sea is based on Roy's modeling, assuming I have not misunderstood of course. Others have made the same point, but now we have model results to support it. BTW, I have just discovered a response from Roy to one of my posts on the other thread that is available on Google, but has never shown up on either of the two newsgroup subscriptions I have. Roy addressed some of my concerns in that post so if you have not seen it you might do a search for it on Google. 3) Radials Even shortened (loaded) radials elevated over seawater work as near-perfect based on N6LF's NEC-4 modeling. Objections to radials are The objections are they are wholly unnecessary when ground is so easily achieved by conventional means. You would need 120 radials to shield against the loss you perceive, and that loss doesn't matter What loss is it that I perceive? N6LF's results show near lossless results with only four shortened radials over seawater. when you stand to gain so much in propagation. You couldn't even field a tenth of these radials. At HF, and maintaining their tune and symmetry, you would be lucky to fit in 2. Other studies have shown a single elevated radial over land to lose less than one dB over a perfect ground plane. At that stage of the game, there is absolutely no match advantage over conventional techniques aboard a small craft (and at HF you don't qualify for any thing other). 4) Counterpoise (i.e., mast, forestay, shrouds, lifelines, engine, metal tanks, 100 square feet of copper, keel, rudder, etc. bonded together) This type of counterpoise is also the approach recommended by both Icom and SGC. Only because it is already available and doesn't ask you to go any further for no obvious advantage. Well, what makes life interesting is that to advocates of the other approaches, there are obvious advantages. 5) OCF dipole w/horizontal component along deck Not commonly used, Who would choose a complicated design over so many simple ones? Multiple resonant radials that cover the popular marine and ham bands on a small boat are not seen by all as simple. One might ask the same question of those who advocate the counterpoise approach, since the wire in the water is simpler. I think choosing the best system (broadly defined to also consider operation over fresh water and near-vertical radiation when important) will be easy if we can only get some objective, reproducible data and/or analysis. Is that where it stands, folks? If you want a dipole, make a VERTICAL dipole, even a lousy one. Certainly worthy of consideration. Many backstay antennas are probably operated as half-wave vertical dipoles (end-fed, of course) above 10 MHz or so. Finally, and to repeat, learn the distinction between matching and propagation. Your focus on matching issues is like seeing your glass 3/4ths empty. Looking at the propagation advantages in comparison is like seeing a pitcher of water nearby that will fill that glass a dozen times. I didn't address any matching issues at all that I can see, Richard. Sorry if I misled you. All of the alternatives utilize the same seawater for propagation and the same vertical radiator. They differ in whether there is any high-angle radiation from a horizontal radiator, and possibly in the magnitude of their "ground return losses." Appreciate your comments. 73, Chuck 73's Richard Clark, KB7QHC ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
RF grounding methods for sailboats: A Summary
On Wed, 31 May 2006 16:44:40 -0400, chuck wrote:
That it will not work if submerged as much as four feet? From Roy's report on his NEC-4 modeling. It is presumably based on the known skin depth of RF at 14 MHz. Hi Chuck, You are drawing conclusions from different facts. These plates are successfully put to this very purpose every day. There is no model that says that a dynaplate submerged 4 feet "will not work." The object lesson is that it will merely be a tie point to the length of wire that is working every inch to it, and that the current in the last inch will, in all likelihood, not see any benefit of that plate, IF AND ONLY IF that wire travels through the water, or in very close proximity to the water. The plate is not ineffective, it is merely redundant. If the wire travels through the interior of the boat, where most transmitters reside, that dynaplate will conduct just as well, and at as high a current as is necessary for a modestly efficient connection. This is, after all, the whole point of installing these plates. Other's have commented you can as easily wire to the engine (if you have one) to create one great big gobstopper of a capacitor to the water. Capacitors work quite effectively too, they are called counterpoises. No engine? The same surface area in metal will substitute. Too much surface area to equal effectively? Move the capacitor plate closer to the hull, and reduce the area by proportion. Does it matter your hull is fiberglass? None whatever. What loss is it that I perceive? N6LF's results show near lossless results with only four shortened radials over seawater. You still don't know how much loss there is through conventional means, then, do you? "Near" lossless is not quantitative data. Other studies have shown a single elevated radial over land to lose less than one dB over a perfect ground plane. You have terrible sources for "other studies," then. That elevated radial must be up a wavelength. How does this relate to "RF grounding methods for sailboats?" Well, what makes life interesting is that to advocates of the other approaches, there are obvious advantages. You still don't have anything that amounts to more than testimonials. Multiple resonant radials that cover the popular marine and ham bands on a small boat are not seen by all as simple. Exactly. Why would you want to do it? If you want a dipole, make a VERTICAL dipole, even a lousy one. Certainly worthy of consideration. Many backstay antennas are probably operated as half-wave vertical dipoles (end-fed, of course) Then it ceases to be a dipole. I didn't address any matching issues at all that I can see, Richard. Sorry if I misled you. Every comment of yours that contains counterpoise, radial, loss, skin depth, length of wire, or connection is a matching issue. All of the alternatives utilize the same seawater for propagation and the same vertical radiator. They differ in whether there is any high-angle radiation from a horizontal radiator, and possibly in the magnitude of their "ground return losses." If they all utilize the same seawater for propagation and the same vertical radiator, they all suffer equally - it stands to reason there is no difference given all the "sameness." It also stands to reason by your assertion that they differ, that they do not all use the same seawater or vertical.... Which is it? Let's skip that and cut to the heart of the matter. How MUCH different? Start with a conventional untuned vertical using a dynaplate and tell me, in dB, how much better any other scheme is. Let's confine this to a practical situation where the rig is under cover and inside the boat and that you need two leads, one from the tuner antenna connection, and another from the tuner ground connection. 73's Richard Clark, KB7QHC |
RF grounding methods for sailboats: A Summary
chuck writes:
Jon KÃ¥re Hellan wrote: We don't seem to have widely used, descriptive names for these configurations. Cecil is correct, and perhaps the OCF referred to should be called an OCF "L". The vertical radiator with a single, elevated, horizontal, resonant "radial" perhaps should be called an "L" dipole. On inspection, either antenna, on a boat with a tuner at the feedpoint, could be mistaken for the other. You could tell the difference only by observing how the antenna is operated. If the antenna is operated only on those frequencies for which the horizontal element is an odd multiple of a 1/4 wavelength, we would call the antenna an "L" dipole (or whatever). If that same antenna were operated not only on those frequencies, but on all others (HF spectrum) as well, we would call it an OCF "L". But if, on inspection, the antenna has multiple resonant radials, that would unambiguously differentiate it from the OCF. Whenever the two antennas are physically identical, they will obviously operate identically. Make sense, Jon? Sorry for the confusion. Sure. Thanks. |
RF grounding methods for sailboats: A Summary
chuck wrote:
Richard Clark wrote: On Tue, 30 May 2006 09:21:56 -0400, chuck wrote: If anyone spots any errors of fact or significant omissions, I'd welcome appropriate "recalibration". Thanks in advance. 1) Grounding plates Will not work if submerged as much as four feet Hi Chuck, Hello Richard, Perhaps the context for the summary was unclear. My objective was simply to identify several existing recommendations for obtaining RF grounds on plastic and wood vessels over sal****er. Regrettably, I lack knowledge of any published theoretical or empirical comparison of these proposals that provides an objective, quantifiable measure of performance. Don't know how you got this miss-impression. That it will not work if submerged as much as four feet? From Roy's report on his NEC-4 modeling. It is presumably based on the known skin depth of RF at 14 MHz. 2) Wire in water A one-foot length of wire immersed near water surface is sufficient for near-perfect results based on W7EL's NEC-4 model results. Assumed performance is similar to grounding plate. This conclusion is conflict with the first, making it a mystery how you came to either in summary. The focus on "water surface" is as though you are trying to force it work like a pool of mercury. Water is NOT a ground plane in the sense of conductivity. Water is a terrible conductor. It is only its huge mismatch with air that gives it such superb propagation, not match, characteristics. Distinguish between the two. Well, some of what you are saying is pretty much what I had thought. If you read my posts on the other thread, you'll see where I was heading. We agree that seawater's conductivity is lower than copper's but greater than earth's. We agree that a single ground rod driven into the earth will perform poorly as the only return path for a vertical antenna over land, but at least in some cases will perform better than if it were not there. Will a wire dipped into the sea perform better than the ground rod driven into the earth? I doubt there is much disagreement on that, even though water might be characterized in relative terms as a "terrible conductor". The only relevant question, then, is "how much better?" and so far, the only numerical answer that I am aware of has come from NEC modeling. The characterization I reported of a wire dipped into the sea is based on Roy's modeling, assuming I have not misunderstood of course. Others have made the same point, but now we have model results to support it. BTW, I have just discovered a response from Roy to one of my posts on the other thread that is available on Google, but has never shown up on either of the two newsgroup subscriptions I have. Roy addressed some of my concerns in that post so if you have not seen it you might do a search for it on Google. 3) Radials Even shortened (loaded) radials elevated over seawater work as near-perfect based on N6LF's NEC-4 modeling. Objections to radials are The objections are they are wholly unnecessary when ground is so easily achieved by conventional means. You would need 120 radials to shield against the loss you perceive, and that loss doesn't matter What loss is it that I perceive? N6LF's results show near lossless results with only four shortened radials over seawater. when you stand to gain so much in propagation. You couldn't even field a tenth of these radials. At HF, and maintaining their tune and symmetry, you would be lucky to fit in 2. Other studies have shown a single elevated radial over land to lose less than one dB over a perfect ground plane. At that stage of the game, there is absolutely no match advantage over conventional techniques aboard a small craft (and at HF you don't qualify for any thing other). 4) Counterpoise (i.e., mast, forestay, shrouds, lifelines, engine, metal tanks, 100 square feet of copper, keel, rudder, etc. bonded together) This type of counterpoise is also the approach recommended by both Icom and SGC. Only because it is already available and doesn't ask you to go any further for no obvious advantage. Well, what makes life interesting is that to advocates of the other approaches, there are obvious advantages. 5) OCF dipole w/horizontal component along deck Not commonly used, Who would choose a complicated design over so many simple ones? Multiple resonant radials that cover the popular marine and ham bands on a small boat are not seen by all as simple. One might ask the same question of those who advocate the counterpoise approach, since the wire in the water is simpler. I think choosing the best system (broadly defined to also consider operation over fresh water and near-vertical radiation when important) will be easy if we can only get some objective, reproducible data and/or analysis. Is that where it stands, folks? If you want a dipole, make a VERTICAL dipole, even a lousy one. Certainly worthy of consideration. Many backstay antennas are probably operated as half-wave vertical dipoles (end-fed, of course) above 10 MHz or so. Finally, and to repeat, learn the distinction between matching and propagation. Your focus on matching issues is like seeing your glass 3/4ths empty. Looking at the propagation advantages in comparison is like seeing a pitcher of water nearby that will fill that glass a dozen times. I didn't address any matching issues at all that I can see, Richard. Sorry if I misled you. All of the alternatives utilize the same seawater for propagation and the same vertical radiator. They differ in whether there is any high-angle radiation from a horizontal radiator, and possibly in the magnitude of their "ground return losses." Appreciate your comments. 73, Chuck 73's Richard Clark, KB7QHC ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- I would also add that sea waters conductivity is not a consistent as some seem to think. The salinity of salt water varies with temperature. NASA has surveyed most of the world oceans using microwave radar and salinity if far from consistent. This fact combined with tidal flows, man made pollution from storm water drains and other factors makes "connecting" to sea water seem dubious. If we assume you can connect to sea water, do you want to place most of your current in such a small area? I doubt someone could keep this connection clean enough in seawater to be efficient. This fact combined with electrolysis will lay waste to any connection very quickly. Maybe a gold plated conductor might be able to survive in a salt water environment. The way most people install radials in yacht would make them elevated, rather than buried below skin depth. N6LF has indicated in his modeling that short radials as long as .1 wavelength work just as effectively as 0.5 wavelength radials over sea water. Since you not trying to combat ground loss whats the point of trying to build a radial field when 2 or 4 .1 wavelength radials will do the job? Besides building a elevated radial system will have some capacitance to ground. A single radial should over sea water capture most of not all of the antenna return currents Besides from all the posts i have read burying something like a Dynaplate below skin depths is akin to burying your rf current below a copper plate. I also believe there is a rule of thumb that 5 skins depths is the maximum return on investment in using the available conductive depth of any material. Its probably that its only ever the piece of wire to the dynaplate thats working as a short radial. I dont see how anyone can say a dynaplate could ever work when below skin depth? One thing i am curious about is that if you suspend a radiator or conductor well below skin depth in air whats the radiation efficiency like of that conductor? To me on a yacht it looks like a conductor suspended in a U channel suspended in air with the top open and exposed. Maybe it will operate like a waveguide with some cut off frequency, this is a wild guess.Maybe someone who can model conductors below ground can model this. Most yachts have at least 3ft of freeboard above water to play with. But who knows there seems to conflicting advice on several points. Maybe Roy can clarify all these issues with his models. Bob |
RF grounding methods for sailboats: A Summary
Reg, G4FGQ wrote:
"Anything you toss into the sea water makes a good ground." Certainly correct if "anything" is a low-impedance RF path. If "skin effect" prevents penetration to a copper plate on the hull, fine. RF has then made the transfer to the sea at a shallow depth. That`s the goal. Best regards, Richard Harrison, KB5WZI |
RF grounding methods for sailboats: A Summary
In article ,
Richard Clark wrote: If they all utilize the same seawater for propagation and the same vertical radiator, they all suffer equally - it stands to reason there is no difference given all the "sameness." It also stands to reason by your assertion that they differ, that they do not all use the same seawater or vertical.... Which is it? Let's skip that and cut to the heart of the matter. How MUCH different? Start with a conventional untuned vertical using a dynaplate and tell me, in dB, how much better any other scheme is. Let's confine this to a practical situation where the rig is under cover and inside the boat and that you need two leads, one from the tuner antenna connection, and another from the tuner ground connection. 73's Richard Clark, KB7QHC This is exactly right. If they all use the same water for RF Ground, and vertical, for the antenna, then the only difference is, "How much coupling from the ground stud on the antenna tuner does each system give to the water?" And that is the Thousdan Dollar question. DynaPlate, Bonded RF Ground System, wires, radials, whatever, all, just make up one side of the capacitor, with the water as the otherside and the distance between is the dielectric. More effective coupling equals lower impedance RF Ground. All this talk of Modelling is just so much FuFurrR, for anyone who has installed MF/HF Marine Antenna Systems on these type, wood or plastic vessels. Anyone with much experience in the field will tell you, simply, get as much surface area as possible, bonded with low impedance connections, (Copper Strap) and get it as close to the water as possible. The Physics of building a bigger capacitor is: Have as much surface area as possible, with the least space between the plates. This isn't Rocket Science, it is just basic physics, and all the crap about tuned counterpoises, and copper screens in the overhead, and the like is just that...... crap...woun't work, never has, and never will. It doesn't take a NEC Modelling Software Package to figure this out, it just takes some common sense and a bit of OJT Experience.... Bruce in alaska -- add a 2 before @ |
RF grounding methods for sailboats: A Summary
|
RF grounding methods for sailboats: A Summary
You wrote: In article , (Richard Harrison) wrote: If "skin effect" prevents penetration to a copper plate on the hull, fine. RF has then made the transfer to the sea at a shallow depth. That`s the goal. Bull****, where do you guys come up with this stuff....Skin Effect is a a Boundry Thing, and the hull of the vessel is the "Boundry of the Sea Water" even if it is 10 feet below the sea surface. Finally someone gets it! This is what Roy said way back in his first report of his modeling, that the ground plate if fastened to the hull will be on the surface of the water even if it happens to be several feet below. The other side of the ground plate is air. In other words the hull is displacing the water. Unless of course the boat has sunk. For the guys that are referencing the N6?? Article about very short elevated radials over sea water; please note that he is saying those short elevated radials are tuned with loading coils. Elevated radials will not work unless they are 1/4 wave resonant or tuned with a loading coil. 73 Gary K4FMX |
RF grounding methods for sailboats: A Summary
chuck wrote:
As Roy pointed out, one reason seawater "works" despite its low conductivity relative to copper is that a high percentage of the "ground" return current is concentrated very close to the antenna where path conductance is high. If the water path from the surface to the Dynaplate is vertical (four feet) does that mean return currents must travel along four additional feet of seawater (at the hull-water interface) and thus will encounter greater losses than if the Dynaplate were at the surface? OOPS! "pass through" should be changed to "travel along" and the parenthetical expression (at the hull-water interface) should be added for clarification. Text above has been so edited. Sorry about that. Chuck ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
RF grounding methods for sailboats: A Summary
Chuck wrote:
"If thee water parh from the surface to the Dynaplate is vertical (four feet) does that mean return currents must pass through four additional feet of seawater and thus encounter greater losses than if the Dynaplate were at the surface?" Well, the Dynaplate is at the surface of the water in contact with the hull. That surface makes a turn to the horizontal at the sea surface. The Dynaplate could also be connected by copper strap(s) on the extertior of the insulated hull so as to contact the sea at a shallower depth depending on the list (tilt) and trim of the boat. Capacitive coupling through an insulated hull is usually comparatively easy at RF. Best regards, Richard Harrison, KB5WZI |
RF grounding methods for sailboats: A Summary
bob wrote:
. . . One thing i am curious about is that if you suspend a radiator or conductor well below skin depth in air whats the radiation efficiency like of that conductor? To me on a yacht it looks like a conductor suspended in a U channel suspended in air with the top open and exposed. Maybe it will operate like a waveguide with some cut off frequency, this is a wild guess.Maybe someone who can model conductors below ground can model this. Most yachts have at least 3ft of freeboard above water to play with. But who knows there seems to conflicting advice on several points. Maybe Roy can clarify all these issues with his models. There's no good way to model this situation with the tools I have. Conceptually, though, you can get a fair idea by imagining the sea to be made of metal. The boat makes a depression in the surface, and you can connect to the metal at the bottom of the depression just as you can anywhere else on its surface. Imagine that the depression is perfectly round and symmetrical, with a grounded vertical extending up from its center. The current flowing into the "ground" connection at the bottom of the depression will flow along the conductor's surface, up the sides of the "dish" to the flat water surface. The total current flowing from the center of the dish upward to the flat surface will equal the current flowing up the vertical wire near its base. The fields from the two will nearly cancel, so there'll be little radiation from the vertical in the region below the flat surface of the water. The vertical above that point should radiate normally. This simplification will of course be modified by the reality of a non-symmetrical hull, but it helps in getting a general idea of what will happen. Another way to look at the situation is to view the depression as the outer conductor of a shorted coaxial cable, with the "ground wire" extending down to its center as its center conductor, and the shorted end the bottom of the depression. This shows you'd get some inductive reactance in your connection to the surface of the water. A rough calculation would probably get you in the ballpark of the actual value. This doesn't represent loss, however. The main thing, though, is that connection to the water requires a conductor either in contact with or capacitively coupled to the water's surface or only a very short distance below it (assuming salt water), whether the surface is below the boat's hull in a depression or on the flat surface of the ocean. Roy Lewallen, W7EL |
RF grounding methods for sailboats: A Summary
Chuck wrote:
"If the water path from the surface of the Dynaplate is vertical (four feet) does that mean return currents must travel along four additional feet of seawater (at the hull-water interface)---? Maybe, but there is a lot of area in that path. The hull-water interface includes the entire submerged surface of the hull. It has been assumed in this thread that the sail-boat hull is fiberglass, an insulator. The impedance of fiberglass is vastly different from that of seawater. The great mismatch between fiberglass and seawater means a radio wave traveling along one of the surfaces won`t be readily absorbed into the other. Dynaplate is a name given copperfoil on a roll. Dynaplate is also a name given a copper plate which has been etched to increase surface area thereby increasing its contact area with water. The surface of seawater contacting a boat hull is continuous with the horizontal surface of the sea. Vertical polarization is effective over seawater. Horizontal polarization is ineffective. The sea short-circuits the voltage wave. A horizontal wire can produce vertically polarized radiation. The Beverage antenna works over poor soil. On page 720 of Kraus` 3rd edition of "Antennas" is the "Flush Disc" antenna which produces vertically polarized radiation over a highly conductive surface. It`s a radiator in a pit and should be useful in a vessel. Best regards, Richard Harrison, KB5WZI |
RF grounding methods for sailboats: A Summary
Roy Lewallen wrote:
bob wrote: . . . One thing i am curious about is that if you suspend a radiator or conductor well below skin depth in air whats the radiation efficiency like of that conductor? To me on a yacht it looks like a conductor suspended in a U channel suspended in air with the top open and exposed. Maybe it will operate like a waveguide with some cut off frequency, this is a wild guess.Maybe someone who can model conductors below ground can model this. Most yachts have at least 3ft of freeboard above water to play with. But who knows there seems to conflicting advice on several points. Maybe Roy can clarify all these issues with his models. There's no good way to model this situation with the tools I have. Conceptually, though, you can get a fair idea by imagining the sea to be made of metal. The boat makes a depression in the surface, and you can connect to the metal at the bottom of the depression just as you can anywhere else on its surface. Imagine that the depression is perfectly round and symmetrical, with a grounded vertical extending up from its center. The current flowing into the "ground" connection at the bottom of the depression will flow along the conductor's surface, up the sides of the "dish" to the flat water surface. The total current flowing from the center of the dish upward to the flat surface will equal the current flowing up the vertical wire near its base. The fields from the two will nearly cancel, so there'll be little radiation from the vertical in the region below the flat surface of the water. The vertical above that point should radiate normally. This simplification will of course be modified by the reality of a non-symmetrical hull, but it helps in getting a general idea of what will happen. Another way to look at the situation is to view the depression as the outer conductor of a shorted coaxial cable, with the "ground wire" extending down to its center as its center conductor, and the shorted end the bottom of the depression. This shows you'd get some inductive reactance in your connection to the surface of the water. A rough calculation would probably get you in the ballpark of the actual value. This doesn't represent loss, however. The main thing, though, is that connection to the water requires a conductor either in contact with or capacitively coupled to the water's surface or only a very short distance below it (assuming salt water), whether the surface is below the boat's hull in a depression or on the flat surface of the ocean. Back around the beginning of this thread a thought occurred to me, and I'm surprised that no one else mentioned it. Unless we are planning on putting out ship on the great Salt lake, of one of the few other salt water inland lakes or seas, we're going to be putting the thing in the ocean. Immediately, one sees that if a ground is at the surface of the water, at many points it will be 4 or more feet under the water. Dem boats rock! There are moments that it will be quite a distance under water, depending on the sea state. Depending on the load, the water line is going to be different, and will be changing constantly as fuel and food is used. Certainly any capacitive coupling through the hull makes for a variable capacitor? Does this have an effect? Will we eventually come to the conclusion that we can't put radios on ships?? ;^) - 73 de Mike KB3EIA - |
RF grounding methods for sailboats: A Summary
Michael Coslo wrote:
Back around the beginning of this thread a thought occurred to me, and I'm surprised that no one else mentioned it. Unless we are planning on putting out ship on the great Salt lake, of one of the few other salt water inland lakes or seas, we're going to be putting the thing in the ocean. Immediately, one sees that if a ground is at the surface of the water, at many points it will be 4 or more feet under the water. Dem boats rock! There are moments that it will be quite a distance under water, depending on the sea state. Use a bare wire, and the top few inches will do the job regardless of how much additional wire goes below the water. As I've said before, there's no harm in having additional wire below the water; it simply doesn't do anything useful. The problem is that as the boat rocks, the length of the wire to the ocean surface will vary in length, which will change the antenna's impedance. So a plate just inside or outside the bottom of the hull (or someplace that's always below the water line) would seem to me a better idea from a practical standpoint. Surely some boater who understood basic electromagnetics has thought about this and devised a method that's both practical and effective. Depending on the load, the water line is going to be different, and will be changing constantly as fuel and food is used. Certainly any capacitive coupling through the hull makes for a variable capacitor? Does this have an effect? What will cause it to vary? In any case, just make the capacitance large enough so the reactance is always small compared to the ground impedance, then it won't matter. Will we eventually come to the conclusion that we can't put radios on ships?? ;^) It wouldn't surprise me if some folks reach that conclusion. Millions firmly believe much more ridiculous things. Roy Lewallen, W7EL |
RF grounding methods for sailboats: A Summary
"Roy Lewallen" wrote:
Michael Coslo wrote: Will we eventually come to the conclusion that we can't put radios on ships?? ;^) It wouldn't surprise me if some folks reach that conclusion. Millions firmly believe much more ridiculous things. Since the feedpoint impedance of a dipole changes as it blows in the wind, guess we also can't use them on windy days. -- 73, Cecil http://www.qsl.net/w5dxp |
RF grounding methods for sailboats: A Summary
Roy Lewallen wrote:
Michael Coslo wrote: Back around the beginning of this thread a thought occurred to me, and I'm surprised that no one else mentioned it. Unless we are planning on putting out ship on the great Salt lake, of one of the few other salt water inland lakes or seas, we're going to be putting the thing in the ocean. Immediately, one sees that if a ground is at the surface of the water, at many points it will be 4 or more feet under the water. Dem boats rock! There are moments that it will be quite a distance under water, depending on the sea state. Use a bare wire, and the top few inches will do the job regardless of how much additional wire goes below the water. As I've said before, there's no harm in having additional wire below the water; it simply doesn't do anything useful. The problem is that as the boat rocks, the length of the wire to the ocean surface will vary in length, which will change the antenna's impedance. So a plate just inside or outside the bottom of the hull (or someplace that's always below the water line) would seem to me a better idea from a practical standpoint. Surely some boater who understood basic electromagnetics has thought about this and devised a method that's both practical and effective. Depending on the load, the water line is going to be different, and will be changing constantly as fuel and food is used. Certainly any capacitive coupling through the hull makes for a variable capacitor? Does this have an effect? What will cause it to vary? In any case, just make the capacitance large enough so the reactance is always small compared to the ground impedance, then it won't matter. Well, I could be wrong, but if one side of the capacitor is on the inside of the hull, and the other side is the sea water, is not the motion of the ship going to affect that? ships move up and down quite a bit, and low draft ones can have a *lot* of that hull out of the water, and then a few seconds later have water coming over the bow. Will we eventually come to the conclusion that we can't put radios on ships?? ;^) It wouldn't surprise me if some folks reach that conclusion. Millions firmly believe much more ridiculous things. Hehe, I've seen that actually happen.... - 73 de Mike KB3EIA - |
RF grounding methods for sailboats: A Summary
Mike Coslo wrote:
Roy Lewallen wrote: . . . What will cause it to vary? In any case, just make the capacitance large enough so the reactance is always small compared to the ground impedance, then it won't matter. Well, I could be wrong, but if one side of the capacitor is on the inside of the hull, and the other side is the sea water, is not the motion of the ship going to affect that? ships move up and down quite a bit, and low draft ones can have a *lot* of that hull out of the water, and then a few seconds later have water coming over the bow. Well, I was envisioning a plate on some part of the hull which always had water on the other side. If the hull on the other side of the plate comes out of the water, you'll of course effectively lose coupling to the water from that part of the plate. But again, if you make the plate large enough so that enough of the plate always has water on the other side of the hull to make a low impedance, the variation won't matter. Sounds like you might have to make the plate cover a fair portion of the hull to insure that there's always water on the other side of some of it. If the entire hull comes out of the water, just remember to say "mayday" really quick every time the hull hits the water. Other than that, seems to me you'll probably be too busy to be playing with the radio anyway. Roy Lewallen, W7EL |
RF grounding methods for sailboats: A Summary
In article ,
Mike Coslo wrote: Well, I could be wrong, but if one side of the capacitor is on the inside of the hull, and the other side is the sea water, is not the motion of the ship going to affect that? ships move up and down quite a bit, and low draft ones can have a *lot* of that hull out of the water, and then a few seconds later have water coming over the bow. We are not talking about 16 foot dingys here, we are talking about vessels mostly over 30 feet in length, and usually with over 3 or 4 feet of draft. Just how much coupling to the seawater you have is a function of area of the inside capacitive plate, and the distance between it and the seawater. If the dielectric distance is a few inches, and the inside plate is below the waterline, then coupling will not change apperciably, just because the water is sloshing around a bit on the hull. Even if a bit of the surface area of the inside plate did come above the waterline for a little while, say on a hard tack in a sail rig, the coupling still wouldn't be appreciably reduced by loosing 5% of the surface area. These are not really valid problems that one sees, when operating MF/HF Marine Radios that have a decent, Low Impedance RF Ground System installed in the first place. doing it right the first time solves a lot of ills down the road, and skimping on the RF Ground, is a presciption for disaster. Bruce in alaska long time Marine RadioMan....... -- add a 2 before @ |
RF grounding methods for sailboats: A Summary
Bruce in Alaska wrote:
In article , Mike Coslo wrote: Well, I could be wrong, but if one side of the capacitor is on the inside of the hull, and the other side is the sea water, is not the motion of the ship going to affect that? ships move up and down quite a bit, and low draft ones can have a *lot* of that hull out of the water, and then a few seconds later have water coming over the bow. We are not talking about 16 foot dingys here, we are talking about vessels mostly over 30 feet in length, and usually with over 3 or 4 feet of draft. I'm not so sure the exact size ship we speak of. But if you recall back a long time ago when the original poster spoke of a hypothetical wire not working at 4 feet underwater. I even suspect that a 30 foot vessel might take greater than a 4 foot excursion, especially in your neck of the woods! Just how much coupling to the seawater you have is a function of area of the inside capacitive plate, and the distance between it and the seawater. If the dielectric distance is a few inches, and the inside plate is below the waterline, then coupling will not change apperciably, just because the water is sloshing around a bit on the hull. Even if a bit of the surface area of the inside plate did come above the waterline for a little while, say on a hard tack in a sail rig, the coupling still wouldn't be appreciably reduced by loosing 5% of the surface area. These are not really valid problems that one sees, when operating MF/HF Marine Radios that have a decent, Low Impedance RF Ground System installed in the first place. doing it right the first time solves a lot of ills down the road, and skimping on the RF Ground, is a presciption for disaster. I don't doubt that the problem has been solved (if it exists in the first place). - 73 de Mike KB3EIA - |
RF grounding methods for sailboats: A Summary
On Sun, 11 Jun 2006 21:33:51 -0400, Mike Coslo
wrote: the original poster spoke of a hypothetical wire not working at 4 feet underwater. Hi Mike, This hypothesis was a home-grown and hand rolled fantasy. I don't doubt that the problem has been solved (if it exists in the first place). Oh, there is a problem alright: Making the lesson penetrate a quarter inch of skull with more success than RF struggling through an imaginary 4 foot skin depth of water problem. 73's Richard Clark, KB7QHC |
RF grounding methods for sailboats: A Summary
Richard Clark wrote:
On Sun, 11 Jun 2006 21:33:51 -0400, Mike Coslo wrote: the original poster spoke of a hypothetical wire not working at 4 feet underwater. Hi Mike, This hypothesis was a home-grown and hand rolled fantasy. I don't doubt that the problem has been solved (if it exists in the first place). Oh, there is a problem alright: Making the lesson penetrate a quarter inch of skull with more success than RF struggling through an imaginary 4 foot skin depth of water problem. Which won't happen until we discuss this into showing how it is impossible to put a radio on a ship! hehehe 8^) - 73 de Mike KB3EIA - |
RF grounding methods for sailboats: A Summary
In article ,
Mike Coslo wrote: I'm not so sure the exact size ship we speak of. But if you recall back a long time ago when the original poster spoke of a hypothetical wire not working at 4 feet underwater. I even suspect that a 30 foot vessel might take greater than a 4 foot excursion, especially in your neck of the woods! It really doesn't matter if the vessel has a draft of 4 feet or 24 feet,as the coupling to the seawater is to the hull/water boundry which is the same as the surface of the water from the RF point of view. Skin Effect, or Skin Depth @ any frequency is a Surface Effect and that surface is the hull/water boundry, for any hull material. Bruce in alaska -- add a 2 before @ |
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