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#1
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I am going to be installing a 23' whip antenna for a new SSB radio installation on my boat. My vessel is all-aluminum construction with a center pilot house. How would you suggest mounting this antenna on this vessel? I understand that it is important to keep the whip from coming too close to any metal. This is an obvious problem, since this boat is all aluminum. Any suggestions or references would be appreciated.
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#2
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You didn't mention how large the vessel is or whether she is power or
sail. I assume she is power the pilot house is on the order of seven feet above deck. If you are able to keep the antenna at least two feet from the pilot house, you shouldn't experience too much signal loss. The proximity of the pilot house is likely to cause some directivity in the antenna's radiation pattern, but with two-thirds of the antenna above the pilot house, it will probably be ok. I have seen cases where the antenna is insulated to just above the height where it is supported so the antenna actually starts seven feet above the deck. It is only 16 feet long in that case but the entire 16 feet would radiate efficiently. Most auto tuners should handle that on all but the lowest frequencies, and there are workarounds available. Your alternatives to the above are to mount the antenna farther from the pilot house (e.g., at the stern), giving up the support attachment, or mounting it atop the pilot house (ugh) and guying it. Of course, depending upon your frequencies of interest, a much shorter whip could be the solution, maybe obviating the need for guys. On a calm day, you should be able to do some experimentation before actually installing the antenna. Good luck, Chuck bradleyj wrote: I am going to be installing a 23' whip antenna for a new SSB radio installation on my boat. My vessel is all-aluminum construction with a center pilot house. How would you suggest mounting this antenna on this vessel? I understand that it is important to keep the whip from coming too close to any metal. This is an obvious problem, since this boat is all aluminum. Any suggestions or references would be appreciated. |
#3
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I am going to be installing a 23' whip antenna for a new SSB radio
installation on my boat. My vessel is all-aluminum construction with a center pilot house. How would you suggest mounting this antenna on this vessel? I understand that it is important to keep the whip from coming too close to any metal. This is an obvious problem, since this boat is all aluminum. Any suggestions or references would be appreciated. Well, I don't know if you are talking about something like a metal Morad WH-23 or a fiberglass 23' Shakespeare or equivalent, but both need a two piece mount. Probably some swivel bottom mount so it can be laid down at times, and an upper support mount at least two feet up from the bottom. Placing these two mounts as high as possible on the metal side of the pilot house is fairly common. If you really want to gain all that length above the pilot house, a fabricated aluminum tripod or sturdy welded post about three feet high is cool. The lead-in from the antenna to the tuner should be almost all outside the aluminum pilothouse. Lots of boats (and ships) put the tuner outside the pilothouse, near the antenna base to avoid any lead-in inside the pilothouse. If you do the latter, very careful attention to sealing of the coupler, and if you elect to vent it (Usually a plus), be sure the vent hole is where the manufacturer recommends (at the very bottom, of course). It would make suggestions a lot easier if you could post a picture or drawing of your boat. Tell us when you test so we can listen and report! Old Chief Lynn |
#4
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bradleyj wrote in
: I understand that it is important to keep the whip from coming too close to any metal. This is an obvious problem, since this boat is all aluminum. Any suggestions or references would be appreciated. You're very lucky, as HF operators go. The metal boat will make an excellent "ground plane", the counterpoise plastic boat owners dream of. What kills HF is any PARALLEL metal which the RF waves intercept on their way out of the boat. This actually creates a capacitor, its two plates being the mast at boat ground and the whip, with the air as its insulator, thus shunting the RF energy off to ground. Two feet is not enough, infinity is. The further you can get the whip away from any metal rising over it, the better. The best place is atop the mast with the whip sticking way up above it, but this isn't very practical as you'll be going under overhead obstructions. So, let's mount the whip as far away from the mast as we can get, including its guy wires and other metal/wire/conductive things going aloft. Let's put the base for the whip on TOP of the nice metal pilot house ground plane (which ends up perpendicular to the whip). This makes USE of the excellent ground plane effect of the horizontal pilot house roof, while keeping the E-field from intersecting it. PLEASE DO NOT MOUNT THE WHIP ON THE SIDE OF ANY METAL HOUSE if you can at all help it. The shunt capacitance of the whip near the wall of the pilot house exterior mounted for convenience on the side somewhere is just awful...sucking your signal off to that metal along side the whip. Signals suck like that. You didn't mention a flybridge atop the pilot house so I'll assume you don't have one. So, let's mount the whip dead centerline of the pilot house roof, about a foot from the forward edge of it, with the weatherproof tuner right next to it. The tuner's output wire to the whip should be as short as you can possibly make it as that becomes part of the antenna (and part of the shunt signal off to metal problem). The ideal mount would be a hole in the pilot house roof with an insulator mounted THROUGH the roof with the tuner mounted safely INSIDE the pilot house right next to where the feed-thru mount's "hot" bolt protrudes inside. Of course, though I'd be proud as hell of it, myself, the yachties would scowl, seeing the tuner overhead of the pilothouse...(c; Be sure, wherever you mount the whip/tuner to put a heavy metal stainless strap from the tuner's ground bolt to the BARE METAL under the closest leg of the tuner where it's bolted to the pilot house roof, a fantastic ground. I'm green with envy. Lionheart has a long strap ground to the engine block...the only metal mass of any consequence in the plastic ketch.... (sigh). Larry W4CSC Lionheart WDB-6254 Icom M802, Icom AT-130, 55' long insulated backstay....poorly grounded...dammit. |
#5
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On Sun, 29 Jan 2006 22:41:06 -0500, Larry wrote:
bradleyj wrote in : I understand that it is important to keep the whip from coming too close to any metal. This is an obvious problem, since this boat is all aluminum. Any suggestions or references would be appreciated. You're very lucky, as HF operators go. The metal boat will make an excellent "ground plane", the counterpoise plastic boat owners dream of. What kills HF is any PARALLEL metal which the RF waves intercept on their way out of the boat. This actually creates a capacitor, its two plates being the mast at boat ground and the whip, with the air as its insulator, thus shunting the RF energy off to ground. Two feet is not enough, infinity is. The further you can get the whip away from any metal rising over it, the better. The best place is atop the mast with the whip sticking way up above it, but this isn't very practical as you'll be going under overhead obstructions. So, let's mount the whip as far away from the mast as we can get, including its guy wires and other metal/wire/conductive things going aloft. Let's put the base for the whip on TOP of the nice metal pilot house ground plane (which ends up perpendicular to the whip). This makes USE of the excellent ground plane effect of the horizontal pilot house roof, while keeping the E-field from intersecting it. PLEASE DO NOT MOUNT THE WHIP ON THE SIDE OF ANY METAL HOUSE if you can at all help it. The shunt capacitance of the whip near the wall of the pilot house exterior mounted for convenience on the side somewhere is just awful...sucking your signal off to that metal along side the whip. Signals suck like that. You didn't mention a flybridge atop the pilot house so I'll assume you don't have one. So, let's mount the whip dead centerline of the pilot house roof, about a foot from the forward edge of it, with the weatherproof tuner right next to it. The tuner's output wire to the whip should be as short as you can possibly make it as that becomes part of the antenna (and part of the shunt signal off to metal problem). The ideal mount would be a hole in the pilot house roof with an insulator mounted THROUGH the roof with the tuner mounted safely INSIDE the pilot house right next to where the feed-thru mount's "hot" bolt protrudes inside. Of course, though I'd be proud as hell of it, myself, the yachties would scowl, seeing the tuner overhead of the pilothouse...(c; Be sure, wherever you mount the whip/tuner to put a heavy metal stainless strap from the tuner's ground bolt to the BARE METAL under the closest leg of the tuner where it's bolted to the pilot house roof, a fantastic ground. I'm green with envy. Lionheart has a long strap ground to the engine block...the only metal mass of any consequence in the plastic ketch.... (sigh). Larry W4CSC Lionheart WDB-6254 Icom M802, Icom AT-130, 55' long insulated backstay....poorly grounded...dammit. And just how would you recommend supporting that 23 foot whip mounted on top of the pilot house? regards Gary |
#6
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Gary Schafer wrote in
: And just how would you recommend supporting that 23 foot whip mounted on top of the pilot house? regards Gary Shrouds?....(c; The discussion was about where to mount the antenna for best radiation. There are many antennas and mounts that require no cheap little plastic support like Shakespeare uses on their antennas. What I'd like to see mounted on top of his pilot house is an antenna like the Moonraker 18B, with a proper, supportive deck mounting: http://www.moonraker.com.au/marine.htm#MFHF Click on 18B for the PDF file. Get the untuned version. I'd mount this antenna THROUGH the cabin roof so it comes out in the overhead panel or a cabinet with the tuner mounted out of the weather inside the pilot house inside the panel. We have no pictures of his pilot house so we can't see where that might happen. With the tuner inside the boat, it'd take a direct lightning hit to destroy it, not seawater. No cables, connectors, wires only the whip would be in the weather, solving the big corrosion problems completely. This antenna mount is designed to do just that, feeding the RF through the roof into the dry tuner inside. No extra "support" for the bassboat swingdown is necessary.... All this depends on other data we don't have. Where does he go boating?....Is he going to be going to sea, or is he going up and down the ditch with all the drawbridges? (If he's not going to sea, there's no point in HF comms, anyway, so I assume he's going to sea.)....How high is his mast over the pilothouse?....Does he need a swingdown mount, really, or are we doing this just because that's the way it's always been done? We don't have all the data. I was just responding to where the antenna would be best mounted for best radiation. That's not necessarily the best for his situation.... |
#7
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Boy, I never expected to get so much great advice so fast!! I'm digesting it all now. I've known since I started looking in to this that I'd have an awesome ground plane, but I never gave much thought to problems I'd have mounting the antenna. I'll let you know how I decide to go. By the way, I tried to post photos of the boat, but this server kept giving me errors. Here's a web site with a pictu
http://www.specmar.com/boatpics/boatpic55.jpg |
#8
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Larry makes some good points, although they are couched a little too
heavily in absolutes. I don't agree that the losses with a two-foot separation would necessarily be unacceptable. Leaving aside whether the near-field losses will arise from electric (displacement currents as Larry suggests) or magnetic fields, almost all metal structures above the deck will alter the near-field properties of a deck-mounted antenna. Regarding the sufficiency of a two-foot separation, I would point out that most HF mobile antennas are mounted well within two feet of the vehicle's vertical metal components for something like two feet of vertical rise. There is ample evidence that these installations "work", or if they do not, it is usually not because of proximity to the vehicle's vertical surfaces. HF antennas on aircraft have been run entirely along the metal fuselage with separations on the order of two feet. These "work" also. So before rejecting the customary deck-mounting of a 23-foot whip with a horizontal support, it would be useful to provide the OP with some concrete indication of how well the antenna is likely to perform compared to the next best alternative. While I can't do that quantitatively, (I did suggest an experiment, which a competent tech could do fairly quickly) it is my experience that such an installation could be satisfactory. With only the top 16 feet as a radiator, near-field losses become negligible but tuner losses predominate. At higher frequencies (above 8 MHz, for example) 16 feet in the clear will probably outperform 23 feet mounted next to the pilothouse. At lower frequencies it is more difficult to say which would be better. Lacking further information from the OP, that is probably the best we can offer. The antenna, tuner, and SSB manufacturers should be contacted to mine their experience. For the strong of heart, center- and/or top-loading could even be employed in some circumstances to shape the current distribution on the whip in such a way as to reduce losses near the pilothouse. Out of curiosity, did the boat's designer/naval architect not address this design detail? Surely it is not an out-of-the-ordinary design question. Chuck Larry wrote: bradleyj wrote in : I understand that it is important to keep the whip from coming too close to any metal. This is an obvious problem, since this boat is all aluminum. Any suggestions or references would be appreciated. You're very lucky, as HF operators go. The metal boat will make an excellent "ground plane", the counterpoise plastic boat owners dream of. What kills HF is any PARALLEL metal which the RF waves intercept on their way out of the boat. This actually creates a capacitor, its two plates being the mast at boat ground and the whip, with the air as its insulator, thus shunting the RF energy off to ground. Two feet is not enough, infinity is. The further you can get the whip away from any metal rising over it, the better. The best place is atop the mast with the whip sticking way up above it, but this isn't very practical as you'll be going under overhead obstructions. So, let's mount the whip as far away from the mast as we can get, including its guy wires and other metal/wire/conductive things going aloft. Let's put the base for the whip on TOP of the nice metal pilot house ground plane (which ends up perpendicular to the whip). This makes USE of the excellent ground plane effect of the horizontal pilot house roof, while keeping the E-field from intersecting it. PLEASE DO NOT MOUNT THE WHIP ON THE SIDE OF ANY METAL HOUSE if you can at all help it. The shunt capacitance of the whip near the wall of the pilot house exterior mounted for convenience on the side somewhere is just awful...sucking your signal off to that metal along side the whip. Signals suck like that. You didn't mention a flybridge atop the pilot house so I'll assume you don't have one. So, let's mount the whip dead centerline of the pilot house roof, about a foot from the forward edge of it, with the weatherproof tuner right next to it. The tuner's output wire to the whip should be as short as you can possibly make it as that becomes part of the antenna (and part of the shunt signal off to metal problem). The ideal mount would be a hole in the pilot house roof with an insulator mounted THROUGH the roof with the tuner mounted safely INSIDE the pilot house right next to where the feed-thru mount's "hot" bolt protrudes inside. Of course, though I'd be proud as hell of it, myself, the yachties would scowl, seeing the tuner overhead of the pilothouse...(c; Be sure, wherever you mount the whip/tuner to put a heavy metal stainless strap from the tuner's ground bolt to the BARE METAL under the closest leg of the tuner where it's bolted to the pilot house roof, a fantastic ground. I'm green with envy. Lionheart has a long strap ground to the engine block...the only metal mass of any consequence in the plastic ketch.... (sigh). Larry W4CSC Lionheart WDB-6254 Icom M802, Icom AT-130, 55' long insulated backstay....poorly grounded...dammit. |
#9
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bradleyj wrote:
Boy, I never expected to get so much great advice so fast!! I'm digesting it all now. I've known since I started looking in to this that I'd have an awesome ground plane, but I never gave much thought to problems I'd have mounting the antenna. I'll let you know how I decide to go. By the way, I tried to post photos of the boat, but this server kept giving me errors. Here's a web site with a pictu http://www.specmar.com/boatpics/boatpic55.jpg Nice boat, but I would not use a deck-mounted whip since it would be surrounded by metal: not only by the pilothouse, but by the sides as well! Instead, consider a 16-foot whip mounted on an insulated support at the level of the gunwhales and supported at the pilothouse roof. With all the windows in the pilothouse, I wouldn't give losses a second thought. Good luck. Chuck |
#10
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In article ,
"Lynn Coffelt" wrote: I am going to be installing a 23' whip antenna for a new SSB radio installation on my boat. My vessel is all-aluminum construction with a center pilot house. How would you suggest mounting this antenna on this vessel? I understand that it is important to keep the whip from coming too close to any metal. This is an obvious problem, since this boat is all aluminum. Any suggestions or references would be appreciated. Well, I don't know if you are talking about something like a metal Morad WH-23 or a fiberglass 23' Shakespeare or equivalent, but both need a two piece mount. Probably some swivel bottom mount so it can be laid down at times, and an upper support mount at least two feet up from the bottom. Placing these two mounts as high as possible on the metal side of the pilot house is fairly common. If you really want to gain all that length above the pilot house, a fabricated aluminum tripod or sturdy welded post about three feet high is cool. The lead-in from the antenna to the tuner should be almost all outside the aluminum pilothouse. Lots of boats (and ships) put the tuner outside the pilothouse, near the antenna base to avoid any lead-in inside the pilothouse. If you do the latter, very careful attention to sealing of the coupler, and if you elect to vent it (Usually a plus), be sure the vent hole is where the manufacturer recommends (at the very bottom, of course). It would make suggestions a lot easier if you could post a picture or drawing of your boat. Tell us when you test so we can listen and report! Old Chief Lynn After looking at the Jpeg of the boat in question, I would like to ask only one question. What would be the purpose of a MF/HF Marine Radio Installation aboard this vessel? It hardly looks big enough to do any High Seas operations, but if one could come up with a reasonable answer, then Old Chief Lynn, makes a good case for the best MF/HF Antenna installation for this vessel. All the above not withstanding, understand that any 23Ft unloaded antenna isn't really long enough to provide quality communications below about 6 Mhz. Also understand that in order to fit a MF/HF Marine Radio System, you MUST apply for, and be granted, a Vessel Radio Station License, by the FCC, as this type of radio is NOT covered by the Blanket Station License granted to all non-commercial vessels of US flag. All Radio Operators who use this radio, MUST also apply for, and be Granted, a Restricted Marine Radiotelephone Operators Permit. (unless you are operating the vessel in alaska) Bruce in alaska -- add a 2 before @ |
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