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Old 07-20-2015, 10:23 AM   #1
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GPS in the Box

I looked at a Garmin 741 radar/plotter and the salesperson said that the GPS antenna is in the unit's case rather on an outside antenna. I ask him if it would work in a fiberglass box mounted up under the fiberglass hardtop. He said that it would.

Does anyone have experience with the internal antenna units?
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Old 07-20-2015, 10:31 AM   #2
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I have used the hockey puck GPS units mounted under my fiberglass pilot house roof and it works well.
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Old 07-20-2015, 11:09 AM   #3
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Had a Raymarine with integral antenna and it performed as well as the unit with external antenna.
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Old 07-20-2015, 11:21 AM   #4
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Quote:
Originally Posted by seasalt007 View Post
I looked at a Garmin 741 radar/plotter and the salesperson said that the GPS antenna is in the unit's case rather on an outside antenna. I ask him if it would work in a fiberglass box mounted up under the fiberglass hardtop. He said that it would.

Does anyone have experience with the internal antenna units?
I have a similar unit (7" screen 70s echosounder) . It has a very sensitive 10 channel (glonass) receiver and It works perfectly under all conditions at my lower station with a hardtop and bridge above . Picks up a fix almost instantly upon turn on.
Older, less sensitive units required an external antenna at this location, but not needed with the new stuff. Since updating my plotters I've been able to trim down the antenna farm..
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Old 07-20-2015, 11:22 AM   #5
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I have a couple of Standard Horizon 390i units from a few years ago and the work OK with the internal antenna from both the upper and lower Helm. these are perhaps a little slower getting their first, full fix, but once they have it, no problem.

In theory, it should work fine in the fiberglass box, but the more material you keep adding around the unit, the more you will desensitize the antenna. I would have no problem putting the unit in a fiberglass box, but keep it as thin as possible.

Again, your first full fix after turn-on may take a little longer, but after that I seriously doubt you will notice any difference.
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Old 07-20-2015, 11:22 AM   #6
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I have a Garmin 740 with the internal antenna and it works well on a mount on top of the instrument panel. I do believe the 740 has a connection point for an external antenna.
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Old 07-20-2015, 01:27 PM   #7
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I have two of these units. One on the flybridge with the internal antenna and one at the lower helm with the external antenna. There is no difference in performance at the lower helm with the external antenna disconnected and using the internal.
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Old 07-20-2015, 02:27 PM   #8
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fiberglass is transparent to RF energy. As long as there isn't grounded metal embedded in the fiberglass, you should have no signal loss.

Putting it in a steel vessel wouldn't work though

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Old 07-20-2015, 03:46 PM   #9
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There is an app for the iPhone called "GPS Status" that will tell you the strength of your gps signal. You can put the iPhone where you want to install the Garmin and see if you have a good gps signal at that location.

I have an automatic trim tab controller that requires a gps signal. The controller works fine underneath my fiberglass top.
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