Boat Install question
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BigTex1136
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Boat Install question
OK I am wanting to install a VHF radio on my boat. I have a Fiberglass bayliner. I do not want to do a big marine ant. I would like to install a VHF no gain ant. but don't I need to ground the ant. some how?
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Tom in D.C.
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Re: Boat Install question
No. What you need to do is provide a ground plane underneath the antenna, either as part of the antenna or something like a large, round pie plate or aluminum disk under the surface on which the antenna is mounted. The center conductor of the coax cable connects to the antenna and the coax shield connects to the ground plane. You can probably find something to do the job in the marine catalogs, but it they're all too long then you can fab one out of commercial mobile antenna parts.
Tom in D.C.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
Re: Boat Install question
That's why the marine antennas are so long. They are half wave which don't require a ground plane. They really would be your best choice. There are a number of mounting options including cleats that let you fold the antenna down for towing and storage.
Re: Boat Install question
The other option is to find an antenna that is designed to work without a groundplane such as the Sinclabs 1482 antenna.
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SteveC0625
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Re: Boat Install question
Installers are having the same problem with fiberglass trunk lids for mobile installs.
At VHF frequencies, you need a unity gain antenna approximately 18" tall. The ground plane needs to be as large a circle as possible up to about the height of the spike in diameter. Ideally, you could get a piece of copper screen material, and fasten it up under the bow deck of the boat. Then mount the antenna in the center of it, making sure the ground side of the coax and antenna base is securely bonded to the screen. (Copper screening is the same stuff used in RF cages.) Aluminum screening will work, but oxidizes rapidly in the salty marine environment.
There are also copper foils available that will work just as well. Even thin copper sheeting if you can find it.
All this presumes you have a flat surface on the boat that you can utilize to place the ground plane material on the underside. If there is no flat surface available, then I think you'll want to take a much closer look at the various antennas available for the marine environment that have built in ground planes.
My little 16' fiberglass runabout has a nice flat bow deck that would work perfectly for this type of install, but not all boats do.
At VHF frequencies, you need a unity gain antenna approximately 18" tall. The ground plane needs to be as large a circle as possible up to about the height of the spike in diameter. Ideally, you could get a piece of copper screen material, and fasten it up under the bow deck of the boat. Then mount the antenna in the center of it, making sure the ground side of the coax and antenna base is securely bonded to the screen. (Copper screening is the same stuff used in RF cages.) Aluminum screening will work, but oxidizes rapidly in the salty marine environment.
There are also copper foils available that will work just as well. Even thin copper sheeting if you can find it.
All this presumes you have a flat surface on the boat that you can utilize to place the ground plane material on the underside. If there is no flat surface available, then I think you'll want to take a much closer look at the various antennas available for the marine environment that have built in ground planes.
My little 16' fiberglass runabout has a nice flat bow deck that would work perfectly for this type of install, but not all boats do.
Re: Boat Install question
Considering the weather exposure the antenna will have, you need to look at the purpose built marine antennas, rather than trying to fabricate a ground plane.
Re: Boat Install question
Shakespear makes some nice small antennas around 4 to 5 feet that do not require ground planes.
Search for the 396 series which is a nice sized antenna that's perfect for fiberglass boats.
Mike
Search for the 396 series which is a nice sized antenna that's perfect for fiberglass boats.
Mike