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Appendix A
Antenna Installation
Installing the GPSMAP 178/178C
The GPSMAP 178/178C must be properly installed according to the following instructions to get the
best possible performance. To complete the installation, you’ll need the appropriate fasteners and a 1”
x 14-thread marine antenna mount available at most marine dealers. (If you have a GPSMAP 178/178C
with an internal antenna, skip to the next page.) When in doubt, seek professional assistance.
Mounting the GPS Antenna
The antenna should be mounted in a location that has a clear, unobstructed view of the sky in all
directions to ensure the best reception. Avoid mounting the antenna where it is shaded by the boat’s
superstructure, a radome antenna, or mast. Keep the antenna away from the path of a radar’s beam.
Sailboat users should avoid mounting the antenna high on the mast to prevent inaccurate speed readings
caused by excessive heeling. Most marine VHF and LORAN antennas do not seriously degrade the GPS
antenna’s reception. Never paint the antenna or clean it with harsh solvents.
The Garmin antenna screws directly onto any standard 1” x 14-thread antenna mount. If you need
to raise the antenna to avoid shading, try using a 1” x 14-thread extension mast available at most marine
dealers.
To install the GPS antenna:
1. Screw the antenna directly onto the 1” x 14-thread mount.
2. Route the cable to the mounting location of the display unit. Use appropriate tie-wraps, fasteners, and
sealant to secure the cable along the route and through any bulkhead or deck.
3. Once the GPSMAP 178/178C unit has been installed, connect the cable to the antenna connector on
the back of the display unit. Make sure that you turn the antenna cable connector 1/4 turn clockwise
to lock the cable into place.
It is possible to route the coaxial cable either through or
outside the antenna mount. It is possible to remove the BNC
connector on the coaxial cable and shorten the coaxial cable
to ease installation, however, doing so voids the antenna
warranty. If the BNC connector is removed it must be
replaced with a new solder-on or crimp BNC (RG 58 or 59
compatible) connector.
Suggested locations for mounting the GA 29 antenna.