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Thanks for the comments, Roger.
While I don't disagree with what you have said (except that antennae are magic), I don't believe your remarks touch on the issues here. The typical marine VHF antenna, for example, does not depend upon the sea for its operation. I am assuming the usual quarter-wave ground plane vertical atop a mast. Do you believe that because VHF and HF antennas involve different frequencies the underlying theory is different? A backstay "vertical" antenna may or may not depend on the sea for its return path. Me has unequivocally asserted that it always depends on the sea and thus its ground must be coupled to the sea. (400 sq. ft. of copper is no better than nothing at all he believes) Conventional antenna theory suggests that a backstay "vertical" could utilize a counterpoise or other return path element (like a horizontal dipole half) with no coupling to the sea at all. Me asserts this is false: that such an antenna will not work. I attempted to present a "reductio ad absurdum" argument showing that if Me is correct, his reasoning leads to absurd results. There is no magic here. I would be pleased to reconsider any of my comments if they appear incorrect or incomprehensible. Regards, Chuck Roger Derby wrote: When you talk of capacitive coupling, frequency does matter. (Xc = 1/[2*pi*F]) There's two orders of magnitude difference between HF at 1.8 MHz and VHF at 180 MHz. "Ground" is one of those elusive concepts that get more magic/conundrum (aka BS) than it deserves. A full dipole needs no ground. The whip or backstay needs a ground plane so that its "virtual image" creates a full dipole. Note that aircraft use HF communications with a half dipole antenna (trailing wire) with no ground plane. Of course they do have an excellent antenna height. (Don't hold the end in your fingers to test on the surface. When your boss hits the transmit key, it hurts, for weeks.) Antennae are magic. Roger http://home.earthlink.net/~derbyrm "chuck" wrote in message ink.net... You seem to be saying that sea water (which is one heck of a lot less conductive than copper -- I mean orders of magnitude less conductive) is the only rf ground (return path) that works? And that the only way to utilize it in a fiberglass hull is with capacitive coupling? By your reasoning, radio communication from a vessel on fresh water is impossible. Or, as a corollary, radio communication from a vessel on the hard is impossible because the capacitive coupling to the sea is over a distance of more than 12". And of course, for VHF, we all use the equivalent of copper that is not capacitively coupled to the sea. Since we all agree that VHF works fine that way, can you tell us at what frequency the laws of electromagnetic radiation "jump ship" and no longer work the same as at VHF? A reference would be most welcome. The issue here is radiation, not propagation. Can you also provide a reference to the published and repeatable testing of 400 sq. ft. of copper ground that didn't work any better than having nothing at all? Radio stations thousands of miles from the sea would be amazed to learn that their ground systems don't work better than nothing at all. Why not post your theory on rec.radio.amateur.antenna and see how it is received there? Suggest you reef those sails a tad, Me. Chuck Me wrote: In article .com, "Skip Gundlach" wrote: As further background, we have full rails, with the gates combined electrically with brass straps belowdecks, attached to the arch, the pushpit and pulpit. We have about 110 lineal feet of 1" SS tube rail, unless you count the inner rails, plus the arch. In addition we have the standard 4" copper strapping leading to a sintered bronze Guest plane below the boat, and also connected to a 3x5' plate under the workbench top. I think we have a reasonably good ground. You will never know if you have a "reasonably good ground", unless you get yourself an Impedance Bridge, and check it at the frequencies that you commonly work. Anything that is more than 12" away from the water, isn't going to add "diddley-squat" toward building a Low Impedance Wideband RF Ground System, and anyone who tells you otherwise, is just as uneducated about MF/HF Marine Radio Antenna Systems, as you seem to be. I have seen all kinds of Systems that looked very impresive, untill they were evaluated with real insurmentation. 400 Sq Ft of Copper Screen in the Cabin Overhead was proffered, as a really good RF Ground, by a well known Boat Builder, 20 years ago. It didn't work any better than having nothing at all, when tested, in a real radio enviorment. If you got a Plastic Hull, you are NEVER going to get a Real RF Ground, UNLESS the hull builder was smart, (they never are) and put 200+ Sq Ft of screen under the gellcoat down by the keel. Cellulose hulls are just as bad, and harder to retrofit that Plastic ones. Like I said in my first reply, Autotuners were invented to allow any "Dufus" to think he install an MF/HF Marine Radio System, and save himself all that money he would have paid a Compitant Radioman. SGC Autotuners are some of the worst of the lot, even if they did steal the design from the real inventers. SGC couldn't even copy the design correctly, and "Old PeeAir" couldn't design his way out of a "Wet Paper Bag". Me |
#2
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We're not discussing theory, we're discussing implementation. VHF and HF
differ significantly due to near-field considerations as well as physical dimensions. A ground plane for a VHF whip can live on the same pole. For HF, you'd need a MUCH bigger boat. We once asked the lab to do a finite element analysis of a hunk of beef being roasted. They came back later and said there wasn't enough computer power in the world to do the job due to the various elements (water, fat, protein, bone, etc.) By the same token, HF antenna theory is useless because so many things on the boat are part of the "near field." One can't ignore the rails, the other antennae, the people walking about, ... In general, I tend to agree with "me" that the sea is the significant ground plane if we're talking small boats (under 65'). 400 sq.ft. of copper is 20' x 20' or so. The wavelength of 4215 KHz is 75 meters = 277 feet. The magic comes in when the various elements interact. Even small dish antenna are tested for their radiation pattern before going into production. Theory, hah. Google antenna "near field" and you'll get sufficient theory, mostly applicable to small dishes, to convince you. As Arthur C. Clarke stated, "Any technology which is sufficiently advanced (or complex) is indistinguishable from magic." Roger http://home.earthlink.net/~derbyrm "chuck" wrote in message ink.net... Thanks for the comments, Roger. While I don't disagree with what you have said (except that antennae are magic), I don't believe your remarks touch on the issues here. The typical marine VHF antenna, for example, does not depend upon the sea for its operation. I am assuming the usual quarter-wave ground plane vertical atop a mast. Do you believe that because VHF and HF antennas involve different frequencies the underlying theory is different? A backstay "vertical" antenna may or may not depend on the sea for its return path. Me has unequivocally asserted that it always depends on the sea and thus its ground must be coupled to the sea. (400 sq. ft. of copper is no better than nothing at all he believes) Conventional antenna theory suggests that a backstay "vertical" could utilize a counterpoise or other return path element (like a horizontal dipole half) with no coupling to the sea at all. Me asserts this is false: that such an antenna will not work. I attempted to present a "reductio ad absurdum" argument showing that if Me is correct, his reasoning leads to absurd results. There is no magic here. I would be pleased to reconsider any of my comments if they appear incorrect or incomprehensible. Regards, Chuck Roger Derby wrote: When you talk of capacitive coupling, frequency does matter. (Xc = 1/[2*pi*F]) There's two orders of magnitude difference between HF at 1.8 MHz and VHF at 180 MHz. "Ground" is one of those elusive concepts that get more magic/conundrum (aka BS) than it deserves. A full dipole needs no ground. The whip or backstay needs a ground plane so that its "virtual image" creates a full dipole. Note that aircraft use HF communications with a half dipole antenna (trailing wire) with no ground plane. Of course they do have an excellent antenna height. (Don't hold the end in your fingers to test on the surface. When your boss hits the transmit key, it hurts, for weeks.) Antennae are magic. Roger http://home.earthlink.net/~derbyrm "chuck" wrote in message ink.net... You seem to be saying that sea water (which is one heck of a lot less conductive than copper -- I mean orders of magnitude less conductive) is the only rf ground (return path) that works? And that the only way to utilize it in a fiberglass hull is with capacitive coupling? By your reasoning, radio communication from a vessel on fresh water is impossible. Or, as a corollary, radio communication from a vessel on the hard is impossible because the capacitive coupling to the sea is over a distance of more than 12". And of course, for VHF, we all use the equivalent of copper that is not capacitively coupled to the sea. Since we all agree that VHF works fine that way, can you tell us at what frequency the laws of electromagnetic radiation "jump ship" and no longer work the same as at VHF? A reference would be most welcome. The issue here is radiation, not propagation. Can you also provide a reference to the published and repeatable testing of 400 sq. ft. of copper ground that didn't work any better than having nothing at all? Radio stations thousands of miles from the sea would be amazed to learn that their ground systems don't work better than nothing at all. Why not post your theory on rec.radio.amateur.antenna and see how it is received there? Suggest you reef those sails a tad, Me. Chuck Me wrote: In article .com, "Skip Gundlach" wrote: As further background, we have full rails, with the gates combined electrically with brass straps belowdecks, attached to the arch, the pushpit and pulpit. We have about 110 lineal feet of 1" SS tube rail, unless you count the inner rails, plus the arch. In addition we have the standard 4" copper strapping leading to a sintered bronze Guest plane below the boat, and also connected to a 3x5' plate under the workbench top. I think we have a reasonably good ground. You will never know if you have a "reasonably good ground", unless you get yourself an Impedance Bridge, and check it at the frequencies that you commonly work. Anything that is more than 12" away from the water, isn't going to add "diddley-squat" toward building a Low Impedance Wideband RF Ground System, and anyone who tells you otherwise, is just as uneducated about MF/HF Marine Radio Antenna Systems, as you seem to be. I have seen all kinds of Systems that looked very impresive, untill they were evaluated with real insurmentation. 400 Sq Ft of Copper Screen in the Cabin Overhead was proffered, as a really good RF Ground, by a well known Boat Builder, 20 years ago. It didn't work any better than having nothing at all, when tested, in a real radio enviorment. If you got a Plastic Hull, you are NEVER going to get a Real RF Ground, UNLESS the hull builder was smart, (they never are) and put 200+ Sq Ft of screen under the gellcoat down by the keel. Cellulose hulls are just as bad, and harder to retrofit that Plastic ones. Like I said in my first reply, Autotuners were invented to allow any "Dufus" to think he install an MF/HF Marine Radio System, and save himself all that money he would have paid a Compitant Radioman. SGC Autotuners are some of the worst of the lot, even if they did steal the design from the real inventers. SGC couldn't even copy the design correctly, and "Old PeeAir" couldn't design his way out of a "Wet Paper Bag". Me |
#3
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In article et,
"Roger Derby" wrote: We're not discussing theory, we're discussing implementation. VHF and HF differ significantly due to near-field considerations as well as physical dimensions. A ground plane for a VHF whip can live on the same pole. For HF, you'd need a MUCH bigger boat. We once asked the lab to do a finite element analysis of a hunk of beef being roasted. They came back later and said there wasn't enough computer power in the world to do the job due to the various elements (water, fat, protein, bone, etc.) By the same token, HF antenna theory is useless because so many things on the boat are part of the "near field." One can't ignore the rails, the other antennae, the people walking about, ... In general, I tend to agree with "me" that the sea is the significant ground plane if we're talking small boats (under 65'). 400 sq.ft. of copper is 20' x 20' or so. The wavelength of 4215 KHz is 75 meters = 277 feet. The magic comes in when the various elements interact. Even small dish antenna are tested for their radiation pattern before going into production. Theory, hah. Google antenna "near field" and you'll get sufficient theory, mostly applicable to small dishes, to convince you. As Arthur C. Clarke stated, "Any technology which is sufficiently advanced (or complex) is indistinguishable from magic." Roger Roger has it right on....Not much Moss growing under hs feet..... Me |
#4
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On Sat, 30 Jul 2005 19:41:03 GMT, Me wrote:
In article et, "Roger Derby" wrote: In general, I tend to agree with "me" that the sea is the significant ground plane if we're talking small boats (under 65'). 400 sq.ft. of copper is 20' x 20' or so. The wavelength of 4215 KHz is 75 meters = 277 feet. Roger Roger has it right on....Not much Moss growing under hs feet..... Me I just had a wild guess that if Roger was agreeing with anonymous poster 'me' and me was agreeing with Roger, then Roger was probably going to be in error too. So I checked a Roger fact: that 4215 kHz = 75 meters = 277 ft. Here's the scoop: 4215 kHz = 71.2 meters = 233.5 ft Waddaya know! :-) Brian Whatcott |
#5
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In article . net,
chuck wrote: Thanks for the comments, Roger. While I don't disagree with what you have said (except that antennae are magic), I don't believe your remarks touch on the issues here. The typical marine VHF antenna, for example, does not depend upon the sea for its operation. I am assuming the usual quarter-wave ground plane vertical atop a mast. Do you believe that because VHF and HF antennas involve different frequencies the underlying theory is different? A backstay "vertical" antenna may or may not depend on the sea for its return path. Me has unequivocally asserted that it always depends on the sea and thus its ground must be coupled to the sea. (400 sq. ft. of copper is no better than nothing at all he believes) Conventional antenna theory suggests that a backstay "vertical" could utilize a counterpoise or other return path element (like a horizontal dipole half) with no coupling to the sea at all. Me asserts this is false: that such an antenna will not work. I attempted to present a "reductio ad absurdum" argument showing that if Me is correct, his reasoning leads to absurd results. There is no magic here. I would be pleased to reconsider any of my comments if they appear incorrect or incomprehensible. Regards, Chuck Best you go back to Elementary Physics, and relearn everything that you didn't get the first time, on Antenna Theory, Frquency vs Impedance, and Smith Charting of basic Marconi Style Antennas..... Me |
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