140 marine electronics installation and troubleshooting
estimating 1 statute mile per watt of transmit-
ting power is a fairly reliable rule of thumb for
the expected range of a VHF radio. For example,
a 5-watt handheld VHF would have a 5-mile
range, and so forth.
With transmitting power limited by law,
one of the only practical methods of increas-
ing a VHF radio’s effective range is to locate
the antenna higher. Since VHF operates on a
line-of-sight basis, raising the antenna extends
its range by extending the effective horizon
(see Table 14-1).
We will look further at issues relating to
the antenna and the coaxial cable that con-
nects it to the radio in Chapter 16.Wiring
Since low voltage to the radio will dramatically
affect its performance, proper wiring using the
correct gauge to ensure minimum voltage
drop, and high-quality termination points, are
critical to the installation.
Installation guidelines:- Use the wire gauge as specified by the
manufacturer for the DC power feed and
negative return. - Install wiring to keep voltage drop to
the maximum of 3% based on ABYC
standards.
Transmitter Height (ft.)
Receiver Height (ft.) 5 1020406080100200400
5 5 6 8 10 12 13 14 19 26
10 6 7 9 11 13 14 15 20 27
20 8 9 10 13 14 16 17 22 29
40 10 11 13 15 17 18 19 24 31
60 12 13 14 17 18 20 21 26 33
80 13 14 16 18 20 21 22 27 34
100 14 15 17 19 21 22 23 28 35- The distances in the table are based on the formulas D = 1.17 H and D 1 + D 2 = 1.17(H 1 + H 2 ) where
D = distance in nautical miles, H 1 = height in feet of the receiver, and H 2 = height in feet of the transmitter.
Reprinted with permission from Boatowner’s Illustrated Electrical Handbook, second edition, by Charlie
Wing
TABLE Line-of-Sight Distance, D 1 + D 2 , for VHF Radios 1
14-1Line-of-sight transmit/receive distances for VHF radio. (Reprinted with permission from Boatowner’s Illustrated
Electrical Handbook,second edition, by Charlie Wing)D^1 D^2H^1 H 2