Join Date: Jul 2008
Location: Smithfield, RI
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I'm not sure I follow the logic of not mounting the GPS antenna on the masthead. I agree that it's not the best place, but not for the reasons stated.
Each GPS satellite orbits at an altitude of 20200 kilometers and moves at a speed of about 14000 km/hour. Whether the antenna is at seal level, or 50 feet up, or 100 feet up is of no consequence at all. Yes, the changes in the heel and pitch of the boat are exaggerated at the mast head, but this is still negligible compared to the speed of the sats.
With WAAS and a clear day with 12 birds in view (pretty normal for a sailboat), you can achieve an accuracy maybe as good as 14 feet. If the idea is that having the mast head outside the rail when viewed from the top impacts where the GPS says you are, I would not worry too much.
For these reasons, there is no harm in putting it there, but also there is no benefit for the same reasons.
The only big concern I would have about the mast head mount is the length of the feed wire, which is going to be lossy. If you are mounting an entire receiver up there then this is not an issue as the unit is sending data down the wire. If it is an actual antenna, use a good quality feedline and it should be fine.
Of course, space on the masthead is at a premium. Seems a waste to put a GPS antenna up there. This, and the feedline issue, are why I would not put the GPS antenna on the mast head.