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ext antenna or no under t top....

Old 09-22-2008, 04:10 PM
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Default ext antenna or no under t top....

will i need one with the newer 5 series of garmin? its a basic t top with blue sumbrella material on top....thanks....
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Old 09-22-2008, 04:12 PM
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Default Re: ext antenna or no under t top....

supposedly they can be mounted under certain items on a boat. mine has about 70% exposed to the sky and the rest is blocked by the rod holders on the roof. works fine full service. play with different locations before you stick it on. but should work.
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Old 09-22-2008, 06:20 PM
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Default Re: ext antenna or no under t top....

anybody else ??
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Old 09-23-2008, 05:49 AM
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Default Re: ext antenna or no under t top....

The sunbrella top is transparent to radio signals. Your GPS should work fine with the antenna under a t-top.

Metal is what blocks radio signals. So as long as you are not under a hard steel top - you are fine. Fiberglass is also transparent to radio signals - mostly.

By the way, I have a little touch screen GPS that works fine in my truck - which is not a convertible. I get enough of a signal through the front windshield I guess.

If you have a GPS that uses an external antenna, go ahead and mount it on the t-top. Get it out of your way! Put it up there and forget it. If your GPS uses an internal antenna then you will be ok - just remember that flush mounting it *MAY* result in a poor signal.
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Old 09-23-2008, 06:56 AM
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Default Re: ext antenna or no under t top....

The 500 series from Garmin do have an option for an external antenna
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Old 09-23-2008, 04:54 PM
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Default Re: ext antenna or no under t top....

tculin - 9/23/2008 6:56 AM

The 500 series from Garmin do have an option for an external antenna
.......yeah i know ..........just didnt want to bother with the install or extra cost if i could help it......
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Old 09-23-2008, 04:56 PM
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Default Re: ext antenna or no under t top....

Lazy_Iguana - 9/23/2008 5:49 AM

The sunbrella top is transparent to radio signals. Your GPS should work fine with the antenna under a t-top.

Metal is what blocks radio signals. So as long as you are not under a hard steel top - you are fine. Fiberglass is also transparent to radio signals - mostly.

By the way, I have a little touch screen GPS that works fine in my truck - which is not a convertible. I get enough of a signal through the front windshield I guess.

If you have a GPS that uses an external antenna, go ahead and mount it on the t-top. Get it out of your way! Put it up there and forget it. If your GPS uses an internal antenna then you will be ok - just remember that flush mounting it *MAY* result in a poor signal.
.....tx lazy....sounds good enough........
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Old 09-23-2008, 06:22 PM
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Default Re: ext antenna or no under t top....

If you mount it on top of your helm (not flush mounted) then you will be fine. Flush mounting it may result in poor performance caused by changing the orientation (polarization) of the antenna (which could result in anything from a 0 - 40 db signal loss) AND could also expose the antenna to electromagnetic interference from other wires under the console.

I mounted my GPS on top of the helm, by the magnetic compass. Theft prevention is accomplished by simply removing the whole unit from the boat. My GPS uses an external antenna - which resides in the back of the boat near the engine. GPS antennas do not have to be mounted high, they just need a "clear" view of the sky. And by "clear" I do not mean clear by human eye standards, but clear to a radio receiver.
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Old 09-24-2008, 04:36 PM
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Default Re: ext antenna or no under t top....

Lazy_Iguana - 9/23/2008 6:22 PM

If you mount it on top of your helm (not flush mounted) then you will be fine. Flush mounting it may result in poor performance caused by changing the orientation (polarization) of the antenna (which could result in anything from a 0 - 40 db signal loss) AND could also expose the antenna to electromagnetic interference from other wires under the console.

I mounted my GPS on top of the helm, by the magnetic compass. Theft prevention is accomplished by simply removing the whole unit from the boat. My GPS uses an external antenna - which resides in the back of the boat near the engine. GPS antennas do not have to be mounted high, they just need a "clear" view of the sky. And by "clear" I do not mean clear by human eye standards, but clear to a radio receiver.
my old garmin 180 gps mount is still on the helm.....thats where i had it mounted with an ext ant.....on the t top.....be nice not to have to fool with that ant again....thanks...
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Old 09-24-2008, 05:17 PM
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Default Re: ext antenna or no under t top....

bradv - 9/23/2008 8:12 AM

can be mounted under certain items on a boat. mine has about 70% exposed to the sky and the rest is blocked by the rod holders on the roof. works fine full service.....
Yes they can be mounted under certain things, they will work to an extent but one has to accept the compromises in doing so.

However "70% exposed" and "works fine full service" comments do not go together as if 70% then you certainly wil not have "full service" as such.
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Old 09-27-2008, 10:11 AM
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Default Re: ext antenna or no under t top....

The 400 an 500 series Garmins' internal antennas are very sensitive, and will perform perfectly well under soft-tops and lighter fiberglass structures, with no [yes Kerry, I said no] practical loss of performance. Metal tube frames block radio transmissions exactly as they block sunlight. As the boat rocks, and the 1.5" shadow of a particular satellite passes over the 3" wide antenna, the signal from that particular satellite will be partially obscured (never a total eclipse) and the GPS could decide to rely, for a few seconds, on information that's a minute older. With 5 birds in sight, that loss is utterly meaningless.

p.s. The most ridiculous thing I've seen on a boat was a Garmin 182 with internal antenna mounted on a small boat, connected to an eternal antenna on a 12" extension, tucked right up under the windshield arch!
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Old 09-29-2008, 09:46 PM
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Default Re: ext antenna or no under t top....

sandyda - 9/27/2008 10:11 AM

The 400 an 500 series Garmins' internal antennas are very sensitive, and will perform perfectly well under soft-tops and lighter fiberglass structures, with no [yes Kerry, I said no] practical loss of performance. Metal tube frames block radio transmissions exactly as they block sunlight. As the boat rocks, and the 1.5" shadow of a particular satellite passes over the 3" wide antenna, the signal from that particular satellite will be partially obscured (never a total eclipse) and the GPS could decide to rely, for a few seconds, on information that's a minute older. With 5 birds in sight, that loss is utterly meaningless.

p.s. The most ridiculous thing I've seen on a boat was a Garmin 182 with internal antenna mounted on a small boat, connected to an eternal antenna on a 12" extension, tucked right up under the windshield arch!
....thanks san......
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