Flush Mount (Option); Antenna - Furuno FM-4721 Operator's Manual

8. INSTALLATION
8.1.2

Flush mount (option)

Requires the MMB-84 flush mount bracket.
1. Make a rectangular template for the flush mount measuring 65×161 mm.
2. Use the template to mark the location where the rectangular hole is to be cut. Con-
firm that the space behind the dash or panel is deep enough to accommodate the
transceiver (at least 177 mm deep). There must be at least 150 mm between the
transceiver's heatsink and any wiring, cables or structures.
3. Cut out the rectangular hole and insert the transceiver.
4. Fasten the brackets to the sides of the transceiver with the lock-washer screw
combination.
5. Turn the adjusting screws to adjust the tension so that the transceiver is tight
against the mounting surface.
Bracket
8.2

Antenna

Marine antennas are made to radiate signals equally in all horizontal directions, but
not straight up. The objective of a marine antenna is to enhance the signal toward the
horizon. The degree to which this is accomplished is called the antenna's gain. It is
measured in decibels (dB) and is one of the major factors in choosing an antenna. In
terms of effective radiated power (ERP), antennas are rated on the basis of how much
gain they have over a theoretical antenna with zero gain. A 1 m, 3 dB gain antenna
represents twice as much gain over the imaginary antenna.
Typically a 1 m 3 dB gain stainless steel whip is used on a sailboat mast. The longer
2.5 m 6 dB fiberglass whip is primarily used on power boats that require the additional
gain.
8-2
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Adjusting Screw
Lock-washer screw combination