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#1
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Boy, I hate web-based posting. I replied to this and the computer ate
it, of course, not saving it anywhere for me... Thanks for the info on non-HF, whip, antenna placement. Our nav VHF is mast top, our cockpit VHF is on the arch, as are other antennas. We'll not be using the backstay for an antenna for a variety of reasons, time, money and security in the potential dismasting among them. 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. We have an SGC-230 tuner within 2 cable-feet of the whip antenna. We expect to have an Icom I-802 HF for our HF comms. Given that we'll have a whip antenna, is centerline, next to the chain plate, as good as, better or worse than, or something else when compared to near the side as it was before (but before the arch was installed)? Thanks. L8R Skip, refitting as fast as I can Morgan 461 #2 SV Flying Pig http://tinyurl.com/384p2 - The vessel as Tehamana, as we bought her "Twenty years from now you will be more disappointed by the things you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Mark Twain |
#2
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Skip
Don't forget, the Icom 802 is also going to want an additional receive-only antenna for the DSC receiver portion. It can't use the main antenna for this. I'm using the backstay for the 802 HF transceiver, a 23 foot whip on one side for the DSC receiver in the 802, and another 23 foot whip on the other side for a separate HF receiver (R-71A). The antenna for the R-71 is also shared with the stereo radio. The backstay uses an AT-140 tuner. The receive-only antennas don't have tuners. Rusty "Skip Gundlach" wrote in message oups.com... Boy, I hate web-based posting. I replied to this and the computer ate it, of course, not saving it anywhere for me... Thanks for the info on non-HF, whip, antenna placement. Our nav VHF is mast top, our cockpit VHF is on the arch, as are other antennas. We'll not be using the backstay for an antenna for a variety of reasons, time, money and security in the potential dismasting among them. 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. We have an SGC-230 tuner within 2 cable-feet of the whip antenna. We expect to have an Icom I-802 HF for our HF comms. Given that we'll have a whip antenna, is centerline, next to the chain plate, as good as, better or worse than, or something else when compared to near the side as it was before (but before the arch was installed)? Thanks. L8R Skip, refitting as fast as I can Morgan 461 #2 SV Flying Pig http://tinyurl.com/384p2 - The vessel as Tehamana, as we bought her "Twenty years from now you will be more disappointed by the things you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Mark Twain |
#3
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"Rusty" wrote in message
... Skip Don't forget, the Icom 802 is also going to want an additional receive-only antenna for the DSC receiver portion. It can't use the main antenna for this. I'm using the backstay for the 802 HF transceiver, a 23 foot whip on one side for the DSC receiver in the 802, and another 23 foot whip on the other side for a separate HF receiver (R-71A). The antenna for the R-71 is also shared with the stereo radio. The backstay uses an AT-140 tuner. The receive-only antennas don't have tuners. Rusty Sorry, I missed this one on the boat, relying on the web-based info and the digest versions sent to me. I'm not familiar with the 802 at all, yet, so didn't know of the separate DSC antenna receive function. The inference is, then, that my similarly equipped VHFs will need some separate antenna? I'd thought they'd connect to a GPS... Thanks for any insights - and the renaming will try to recapture the thread to placement rather than esoteric discussions of antenna frequencies and unrelated theory. Not that I'm not enjoying them - but it's not what I asked, and I have very limited time to sort, witness missing this post. L8R Skip, cleaning up in prep for surgery and being off-line for several weeks -- Morgan 461 #2 SV Flying Pig http://tinyurl.com/384p2 - The vessel as Tehamana, as we bought her "Twenty years from now you will be more disappointed by the things you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Mark Twain |
#4
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"Skip Gundlach on wifi"
skipgundlach.sez.remove.this.part@earthlink.(fish catcher)net wrote in : I'm not familiar with the 802 at all, yet, so didn't know of the separate DSC antenna receive function. I've got Lionheart's DSC antenna hooked to the handrail right over the transceiver's location at the chart table. Seems to work fine. -- Larry |
#5
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In article ,
"Skip Gundlach on wifi" skipgundlach.sez.remove.this.part@earthlink.(fish catcher)net wrote: The inference is, then, that my similarly equipped VHFs will need some separate antenna? I'd thought they'd connect to a GPS... Skip, You inference is likely wrong as most Vhf Radio's with DSC either use a receive scan function, or a internal, but seperate, Vhf Receiver to monitor the DSC Vhf Frequency. (Marine Ch 70) While it is impractical to use that kind of scheme at MF/HF Frequencies because the autotuner would be set for the last band segment transmitted on, and attenuate the DSC signals for all the bands except the autotuned band. It is therefor prefered, that any MF/HF Marine Radio Installation, have a seperate Receive Only antenna for the DSC Watch Receiver. Thus the 802's Watch Receiver Antenna requirment. Bruce in alaska -- add a 2 before @ |
#6
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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 |
#7
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On Sat, 30 Jul 2005 06:12:33 GMT, 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, /// 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.//// Me Hehe...why don't you tell us what you really think, anonymous poster? If it takes 200 sq ft of screen under a gel coat to make a good RF ground, then folks who attempt a similar feat through a hull would need about 0.5 / 0.05 X 200 sq ft of material - That's 2000 sq ft of foil or metal mesh (for a 0.05 in gelcoat, and a mere 0.5 inch hull thickness) Now THAT would be quite a trick - a square about 100 ft by 20 ft. Better not tell the folks who use an antenna coupled through a 1/4 inch glass shield - a coupler that can measure 1.5 inch square. Admitted, this is often for FM radio (say 90 MHz) as opposed to 3MHz (?) on hf. Using these numbers for comparison, 90/3 X 0.5/0.25 X 2.25 sq in = 135 sq in of ground plane, hmmmm that's 1 sq foot in round numbers. Now that *does* look small to me. I expect the truth lies somewhere between 1 sq ft and 2000 sq ft. through a half inch hull section. There! How mealy-mouthed is THAT! :-) OK, let's get serious: how about locating a bronze through hull, and connecting a copper foil externally in contact with it. a square foot THERE, connected internally with good Litz wire might make a serviceable ground.... Brian Whatcott Altus p.s A hint for you: talking about "compitant radiomen" makes prospective customers nervous! :-) |
#8
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In article ,
Brian Whatcott wrote: Hehe...why don't you tell us what you really think, anonymous poster? If it takes 200 sq ft of screen under a gel coat to make a good RF ground, then folks who attempt a similar feat through a hull would need about 0.5 / 0.05 X 200 sq ft of material - That's 2000 sq ft of foil or metal mesh (for a 0.05 in gelcoat, and a mere 0.5 inch hull thickness) Now THAT would be quite a trick - a square about 100 ft by 20 ft. Better not tell the folks who use an antenna coupled through a 1/4 inch glass shield - a coupler that can measure 1.5 inch square. Admitted, this is often for FM radio (say 90 MHz) as opposed to 3MHz (?) on hf. Using these numbers for comparison, 90/3 X 0.5/0.25 X 2.25 sq in = 135 sq in of ground plane, hmmmm that's 1 sq foot in round numbers. Now that *does* look small to me. I expect the truth lies somewhere between 1 sq ft and 2000 sq ft. through a half inch hull section. There! How mealy-mouthed is THAT! :-) OK, let's get serious: how about locating a bronze through hull, and connecting a copper foil externally in contact with it. a square foot THERE, connected internally with good Litz wire might make a serviceable ground.... Brian Whatcott Altus p.s A hint for you: talking about "compitant radiomen" makes prospective customers nervous! :-) Nice thought Brian.... However what you seem to forget is that capacative couping at RF Frequencies, is determined by three things. 1. Area of the Inside the hull Plate. 2. Distance between the two Plates. 3. Conductivity of the Sea Water Plate. A 200 Sq Ft Screen in the cabin overhead isn't near (Orders of magnitude) big enough to be an RF Ground for a MF/HF Antenna System, by itself. Being located far (relative in capactive terms) from the other plate (Salt water) means that the Rf couping into the water is what, can you guess? Less than a few Picofarads. Now calculate the RF Impedance for such a system at ANY, and All MF/HF Marine Frequencies that you like to use, if you have enough computer power in your supercomputer. then come back and explain it all to the rest of the world. Me |
#9
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On Sat, 30 Jul 2005 19:58:46 GMT, Me wrote:
In article , Brian Whatcott wrote: Hehe...why don't you tell us what you really think, anonymous poster? If it takes 200 sq ft of screen under a gel coat to make a good RF ground, then folks who attempt a similar feat through a hull would need about 0.5 / 0.05 X 200 sq ft of material - That's 2000 sq ft of foil or metal mesh (for a 0.05 in gelcoat, and a mere 0.5 inch hull thickness) Now THAT would be quite a trick - a square about 100 ft by 20 ft. Better not tell the folks who use an antenna coupled through a 1/4 inch glass shield - a coupler that can measure 1.5 inch square. Admitted, this is often for FM radio (say 90 MHz) as opposed to 3MHz (?) on hf. Using these numbers for comparison, 90/3 X 0.5/0.25 X 2.25 sq in = 135 sq in of ground plane, hmmmm that's 1 sq foot in round numbers. Now that *does* look small to me. I expect the truth lies somewhere between 1 sq ft and 2000 sq ft. through a half inch hull section. There! How mealy-mouthed is THAT! :-) OK, let's get serious: how about locating a bronze through hull, and connecting a copper foil externally in contact with it. a square foot THERE, connected internally with good Litz wire might make a serviceable ground.... Brian Whatcott Altus p.s A hint for you: talking about "compitant radiomen" makes prospective customers nervous! :-) Nice thought Brian.... However what you seem to forget is that capacative couping at RF Frequencies, is determined by three things. 1. Area of the Inside the hull Plate. 2. Distance between the two Plates. 3. Conductivity of the Sea Water Plate. A 200 Sq Ft Screen in the cabin overhead isn't near (Orders of magnitude) big enough to be an RF Ground for a MF/HF Antenna System, by itself. Being located far (relative in capactive terms) from the other plate (Salt water) means that the Rf couping into the water is what, can you guess? Less than a few Picofarads. Now calculate the RF Impedance for such a system at ANY, and All MF/HF Marine Frequencies that you like to use, if you have enough computer power in your supercomputer. then come back and explain it all to the rest of the world. Me Oh my! Anonymous poster, it was *YOUR* suggestion that an RF ground of 200 sq ft of mesh under the (external hull) gel-coat was required for a satisfactory RF ground at HF. It was the original poster's suggestion of an elevated mesh that caught your interest, not mine. As you asked about antenna testing, I should mention that a supercomputer is not really necessary: there is a handy dandy gadget ( from MFJ ) which combines several RF test functions like antenna bridge, SW ratio etc. It ran about $200 as I recall. I satisfy myself with an LC meter these days - which gets one into the ball park at $100. eBay has an MFJ noise bridge at $25 currently. Hmmm...the capacitance to ground of a few objects in my vicinity runs about 45 pF per sq ft. Like me, standing on carpet It is just possible a hi level ground screen of 200 sq ft might get you 200 X 45 pF = 9000 pF At 3 MHz that would put the capacitive reactance at 1/2pi.f.C ohms = 6 ohms. Not that great. The actual value might well be quite a bit higher than that. But that's just me measuring with an instrument, rather than you guessing how poor it is. Another thing: the conductivity of sea water does not vary all that much - it doesn't have much impact on capacitance. But there I go again, actually measuring things! Regards Brian Whatcott p.s. I have an FCC GROL+rdr. You? |
#10
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In article ,
Brian Whatcott wrote: Oh my! Anonymous poster, it was *YOUR* suggestion that an RF ground of 200 sq ft of mesh under the (external hull) gel-coat was required for a satisfactory RF ground at HF. It was the original poster's suggestion of an elevated mesh that caught your interest, not mine. As you asked about antenna testing, I should mention that a supercomputer is not really necessary: there is a handy dandy gadget ( from MFJ ) which combines several RF test functions like antenna bridge, SW ratio etc. It ran about $200 as I recall. I satisfy myself with an LC meter these days - which gets one into the ball park at $100. eBay has an MFJ noise bridge at $25 currently. Hmmm...the capacitance to ground of a few objects in my vicinity runs about 45 pF per sq ft. Like me, standing on carpet It is just possible a hi level ground screen of 200 sq ft might get you 200 X 45 pF = 9000 pF At 3 MHz that would put the capacitive reactance at 1/2pi.f.C ohms = 6 ohms. Not that great. The actual value might well be quite a bit higher than that. But that's just me measuring with an instrument, rather than you guessing how poor it is. Another thing: the conductivity of sea water does not vary all that much - it doesn't have much impact on capacitance. But there I go again, actually measuring things! Regards Brian Whatcott p.s. I have an FCC GROL+rdr. You? I am not so "Anonymous" as you would think. There are, certainly, folks who know who "Me" really is. Some even post here. I didn't "Say or State" that the above WAS required. I stated that "200 sq ft" would certainly provide a "Low Impedance Wideband RF Ground, on plastic hulled vessles floating in Salt Water." I also introduced the discreditied concept of "copper screen in the overhead" into the thread, if you would go back and actually read the whole thread. Your testing tools seem to be of the consumer variety. Some one should teach you a bit about modern RF Antenna Design & Testing Tools, one of these days. Most compitant folks use both RF Network Analysers, and, or an Antenna Impedance Bridge feeding a Spectrum Analyser with a Tracking Sweep Generator. Best you come back after you learn to use the tools, that "the Big Boys" use. It is just possible that you don't have much of a clue about MF/HF Marine Antenna Systems and RF Grounds aboard Vessles. The above statement about some mythical capacitive reactance at 3 Mhz really shows that your way out of your league in this dicussion. There are few 3 Mhz Marine Frequencies, (Mostly in alaskan waters) and most non-commercial MF/HF Marine Radio Users rarely use any below the Maritime Mobile 4 Mhz Band. There are many 1.6Mhz, 2.0 - 3.3 Mhz, Marine Frequnecies used in alaska, by commerical users, and a daily basis, and have been for many years. When was the last time you actually operated, or for that matter installed, a Private Coast Station, using any frequency at all, or for that matter any Maritime Mobile Station of any kind. I operate a Private Coast/ Alaska Public Fixed Station, on a daily basis, that I designed and installed 20 years ago, and communicate with vessels all over the North Pacific. Tell us all, about your great experience in Marine Communications. The conductivity of Seawater isn't in dispute in this thread on it's own, what is in dispute seems to be how it compares to fresh water, RF Grounds used in MF Commercial Radio Stations, and other mediums. What you fail to understand is that capacative coupling to SeaWater is extremely Frequency Sensitive, and to design an effective Low Impedance, "Wideband" RF Ground on a plastic, or cellulose hulled vessel, requires a very effective coupling to the Seawater over a Wide Frequency Range. That is the crucks of the problem. Again, "It is the RF Ground, sonny, the RF Ground"... Me 1st Class RadioTelegraph, with Seatime Endorsement, Radar Endorsement, and, wait for it.... Aircraft Endorsement... |
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