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Old 09-27-2008, 10:11 AM
  #11  
sandyda
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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!