NorthStar 958 Operator's Manual page 196

is for the sound to travel to the cliff and back; you want the
distance one way only.)
The calculation is: 1,100 x 6 = 6,600/2 = 3,300 feet.
Radio waves transmitted with high power and very high
frequency bounce back from hard objects (called "targets")
exactly the same way your voice is bounced from the cliff. The
speed of radio waves is constant (162,000 nautical miles per
second), so a computer inside the radar receiver acts as a
stop-watch to measure the time. The result is then displayed
on a radar screen. The technical name for a radar screen is
Plan Position Indicator (PPI).
Think of a radar operator as looking down from a helicopter
How does the radar
flying above the boat. The helicopter is always above the boat
screen work?
and in the center of the display. The ship's heading is
indicated by the heading marker, an electronic line that
extends from the center of the screen to the edge of the
display. It points towards the bow of the boat.
Range rings are concentric rings that represent distance from
your vessel. They are changed any time the radar range is
adjusted; therefore, the operator must be careful to note what
range the display is on. An object three rings away on a 0.5 nm
per range ring is 1.5 nm from the boat. However, on a 5 nm per
range ring, the object is 15 nm from the boat.
In standard atmospheric conditions, there are three basic
Detectability of
horizons: geometric, optical, and radar. Geometric is the
radar
straight line between the sighting point and the horizon. The
optical horizon is caused by the normal bending of light waves
and this increases the geometric horizon by about 6 percent.
The radar horizon is created by the even greater curvature of
radio waves and extends the horizon by about 15 percent.
Radio waves generally travel in straight lines. Hence the
detectable range of radar increases in accordance with the
height of the radar antenna and the target. For this reason, and
when set to a long range, a coast line may not be seen yet the
high mountains inland further away may be detected.
Page 188 958 Operator's Manual, Rev. A