Standard Horizon CPV350 - Manual (Page 15)

Page 15 CPV350
Figure 2.5 CPV350 Rear Panel
2.3.1 VHF Antenna
ABOUT VHF RADIO
The radio frequencies used in the VHF marine band lie between 156 and 158 MHz with some
shore stations available between 161 and 163 MHz. The marine VHF band provides
communications over distances that are essentially “line of sight” (VHF signals do not travel
well through objects such as buildings, hills or trees). Actual transmission range depends
much more on antenna type, gain and height than on the power output of the transmitter.
On a fixed mount 25W radio transmission expected distances could be greater than 15
miles.
2.3.2 Selecting a Marine VHF 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 3-foot, 3dB gain antenna represents twice as much
gain over the imaginary antenna. Typically a 3-foot 3dB gain stainless steel whip is used on
a sailboat mast. The longer 8-foot 6dB fiberglass whip is primarily used on powerboats that
require the additional gain.
1
5
2
3
4
6
7