Chapter 16 where other antennas are dis-
cussed. Compared to many other electronic
systems on board, GPS is generallynot sensi-
tive to outside interference (although there are
some specific instances discussed below). This,
at least, makes installation relatively easy.
A GPS receiver is a line-of-sight device. But
unlike VHF radios where the line is horizontal,
the GPS line of sight is vertical. Its small, typi-
cally hockey puck–shaped antenna must have a
clear view of the sky to receive signals from the
GPS satellites. Anything blocking the sky view
also blocks signals, so careful attention must be
given to the location of the antenna “puck.”
Think about ergonomics here as well. I’ve
recently noticed an alarming trend of mount-
ing GPS antennas on the cockpit coamings of
sailboats. Recently, I was on board a test boat
with just such an antenna mounting. While
beating down Chesapeake Bay, I noticed that
the GPS unit was no longer displaying posi-
tion or speed over ground. I looked around
the cockpit and, sure enough, a crewmember
was sitting on the little hockey puck, blocking
its reception of satellite signals!Installation guidelines:- Match the brand and model number of
your GPS antenna with the receiver and
the cable harness connecting them. - Position the GPS antenna as follows:
out of the way of people and normal
on-deck traffic areas
with a clear view of the sky above
as close as possible to the boat’s centerline
not too far aloft; the boat’s rolling and
pitching motion, amplified by
increased height abovedeck, will tend
to send the GPS a bit crazy trying to
figure out where it is - Because the cable is a proprietary one, do
not alter its length. - Flake excess cable in large elliptically
shaped loops. Do not coil tightly. (Vendors
GPS antennaA cockpit coaming is a really poor mounting location for a GPS antenna——right where
crew can sit on it and block satellite reception. Not only is it vulnerable to being
stepped on and kicked, it may also snag jibsheets, and it even interferes with the
coaming’s otherwise comfy function as a seat or armrest.installing communicationsand position-finding systems 149