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Old 02-09-2008, 07:51   #16
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SSB on arch

good morning, If I tie the leg of the arch to the grounding plate in sea water which is bronze to the ALU. framework with copper strap will I have electrolysis on the tower? Is there any high power rf that will go through the strap which goes past my engine pc that would cause my computer to have problems as when the tuner was near the engine? The frame is over 100 square feet but it is not solid. there are a series of round and square tubes supporting fiberglass sheets, there are long stainless strips over the seams of the glass sheets screwed into the alum. There are 6 solar panels and the panel frames grounded (not electrically) using 12 gauge wire into the Alum tower. my other question is will a 23 foot Shakespeare whip antenna hold up if I don't have a stand off on it? I can move the whip to the top of the frame but it will be supported only from the bottom.
Thank you
Adam
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Old 02-09-2008, 21:31   #17
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Hi Adam,

I don't believe you will have an electrolysis problem. You can block any DC by cutting the copper strap and jumping across it will some small capacitors. These will be transparent to rf, but not allow dc current. See about 3/4 down the page here: Grounding . Our Manta's arch has been connected this way for 10 years without electrolysis issues.

The ground plane for rf is defined by surface area, so those tubes have a lot of surface area to offer. I forgot that Manta switched to a fiberglass top instead of aluminum, so you won't get any help from that. We have a fabric top, so we also don't get rf ground help from it.

I don't know the answer to your question about rf interference on your engine pc through the copper foil. Maybe someone else will help there.

Your current antenna will not stand without support. You would need to change to a different model if you wanted to move it to the top of the arch.

Mark
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Old 02-09-2008, 21:51   #18
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good evening, If possible could you send me a photo of the install including the antenna, My boat was one of the first with the NEW electronic engine start stop and displays. The MDI box sure didn't like my placement of the tuner. Add VIPOWERNET.NET to my screen name and you have my e-mail. Thanks for any help. I was scratching my head with it for 2 hours today. If I tie the rf ground to the arch with out putting it up top side the tuner will be below the the rf ground with 1/3 of the antenna. We have a 42 foot MANTA 2008.
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Old 03-09-2008, 09:43   #19
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Hi Adam,
There is a photo in post #8 above showing the tuner (white box) just below the free-standing antenna. There is ~15" of GTO-15 wire connecting the tuner to the antenna and a 2" piece of copper foil connecting the ground lug to the arch.

Our antenna is this one: Shakespeare Marine Antennas Specifications: Shakespeare 5300 SSB

Another choice would be the 23' free standing antenna: Shakespeare Marine Antennas Specifications: Shakespeare 390-1 SSB

Is there a way to encase the MDI box in a metal screen enclosure connected to ground (the engine)? Just some copper, stainless or aluminum screen from the hardware store with a wire connecting it to a bolt on the engine block. This might provide a faraday cage to block rf from the MDI box.

I also suspect that the tuner wasn't the problem, and the problem was the antenna connection wire connecting the tuner to the antenna. This is an active part of the antenna and would be radiating into the engine compartment. Maybe your solution is to simply mount the tuner above deck and leave your current ground system in place (extending it as needed). Can you mount it in your cockpit locker beside the antenna? That would raise the radiating part of the system 3-4' above the engines. If you pull the closet or the stove, you can get access to run ground strap from the engine compartment back to the cockpit locker without cutting into anything.

Mark
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Old 03-09-2008, 10:25   #20
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Good afternoon, we have the same whip. Ours is mounted on the starboard hull near the aft cleat with a stay on the hard top. What base do you use that it can be mounted with no support? I took the hard top stay off the antenna and the antenna has a lot of movement at the base. I am using a solid stainless mount that can be laid down. I have no problem moving the rig to the top of the arch but don't want the whip or the mount to break. Putting everything up top would solve all of my problems. I have no idea how to secure it. Thank you
Adam
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Old 03-09-2008, 12:33   #21
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Hi Adam,
Do you have the 5300 whip or the 390? The 390 comes with a flange that can be bolted or welded to your arch. The 5300 (ours) needs a mounting socket. Many of Shakespeare's whips look exactly alike, but only two specific models are designed to be free-standing.

Attached is a picture of that socket. It appears to be an aftermarket bracket, but I don't know who makes them. It is a tube inserted halfway through a plate and supported on the plate with gussets. The bracket is mounted on the arch so that half the tube is below the mounting point. The bottom end of the tube is closed (except for a small drain hole). The antenna simply inserts into the tube. There is a bolt hole drilled through both the mounting tube and the antenna bottom. A bolt passed through prevents the antenna from rotating (or falling off when the boat flips upside down as these types are wont to do).

Mark
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Old 03-09-2008, 15:03   #22
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Good evening, ours is the 3 part 23 foot ssb antenna. It has a metal female bottom that can screw down onto something. Is that bracket welded or bolted to the frame? I can have one made and will probably cost $500 or so to make at 80 dollars an hour plus material. I will go and have one made. I think that will work. Any worries with lightening strikes with it? does your manta have a canvas top? Our top is fiberglass. Adam
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Old 03-09-2008, 18:19   #23
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Hi Adam,

It's bolted to the frame - you can see the bolts if you squint hard enough.

You may want to check with Shakespeare - I don't know if the 393 model is meant to be free-standing without an intermediate support.

I don't worry about lightning hitting it. I just assume that it strikes the mast instead. Although it may cause less damage if it hit the arch.

We have the canvas top.

Mark
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Old 04-09-2008, 21:01   #24
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Getting a ssb antenna to St. Thomas will be fun I see the antenna with the base, that may be easier to mount, all i would need is a angular shim to get it level on the arch. I shook our antenna with out the stay and it is fairly bendy. I bet the other flange mount must be stiffer. I hate to throw that new whip away. Our antenna is mounted on the starboard side. The way the 08 Mantas are designed there is no way to get the strap into the crawl space. It looks like i wont need to custom design a base after-all they already have them. Our mast has lightning & ground protection so this antenna will be the path Where is your Manta? I can ground the leg of the frame to the dynaplate as i would only need another foot of strap. Just as long as it wont transmit RF into the bilge that will be great.
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Old 06-09-2008, 17:40   #25
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WOW! The local tackle shop will get the antenna and its only 15 dollars to ship it to St Thomas! I will have it in 2 weeks! Thank you for all of your help and the photo came in handy!! Has anyone heard of the "New" digital SSB antennas? I wonder if they work better. The guy told me about them as a possible option.
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