Advanced Marine Electrics and Electronics Troubleshooting A Manual for Boatowners and Marine Technicians

where D distance in nautical miles,
H 1 height in feet of the antenna, and
H 2 height of the distant object
Increase this distance by 15% for the
absolute maximum radar range.
While the height of the radome has an
obvious effect on maximum range, it affects
minimum range as well. The radiated beam
from the radar transmitter extends in a vertical
arc 12.5 degrees above and below the horizon-
tal centerline. The area below the lower half of
the beam is a radar blind spot, or blind zone,
and the higher the antenna is mounted, the

farther out this blind spot will extend (see

Table 16-8). The near distance can be calcu-

lated from:

N 1 H 1 tangent 20°2.75(H 1 H 0 )

For example, a 40-foot-high antenna can-

not see surface objects closer than 110 feet.

Reducing the antenna height to 20 feet

reduces the blind zone radius to 55 feet. On

most boats, practical mounting locations are

fairly limited, however, so the near blind spot

may be relatively fixed. That said, I feel that

radomes mounted on purpose-built articulat-

ing pole mounts, like the one shown in the

coaxial cable and antennas 187

Radar Height Target Height (H 2 , ft.)

(H 1 , ft.) 5 10 20 40 60 80 100 200 400

5 5 6 8 10 12 13 14 19 26

10 679111314152027

15 7 8 10 12 14 15 16 21 2 8

20 8 9 11 13 14 16 17 22 29

25 9 10 11 13 15 16 18 22 29

30 9 10 12 14 16 17 18 23 30

40 10 11 13 15 17 18 19 24 31

50 11 12 14 16 17 19 20 25 32

Reprinted with permission from Boatowner’s Illustrated Electrical Handbook, second edition, by Charlie Wing

Radar Line-of-Sight Range in Nautical Miles

TABLE

16-7

D 1

H^1

N^1 H^0

± 20 °

D 2

H 2

Radar range and blind zone versus heights of the antenna and the target. (Reprinted with permission from Boatowner’s Illustrated

Electrical Handbook,second edition, by Charlie Wing)