Furuno SC-50 User Manual

 

Own ship's heading can be determined by decoding the data in the carrier 
frequency in addition to ordinary GPS parameters. In principle, a pair of two 
antennas A1(ref) and A2(fore), each connected with an associated GPS engine 
and processor, are installed along the ship's fore-and-aft line. GPS systems at 
A1 and A2 calculate the range and azimuth to the satellite. Difference in range 
between A1 and A2 is 

∆λ

 + n

λ

 where 

λ

 is 19 cm. “n” is automatically found 

during the initialization stage by receiving three satellites. A fraction of a carrier 
wavelength, 

∆λ

, is processed by FURUNO’s advanced kinematic technology in 

geographical survey, thus determining a vector (range and orientation) A1 to A2. 
 
In reality, a third antenna is used to reduce the influence of pitch, roll and yaw, 
and five satellites are processed to process 3D data. If the GPS signal is blocked 
by a tall building or the vessel is under a bridge, the 3-axis solid-state angular 
rate gyros in the processor unit take place of the satellite compass, maintaining 
the current heading continuously. 

 

Heading

θ

Antenna A1

Antenna A2

Antenna A3

Difference between the
range from satellite to
antenna 1 and the range
to antenna 2.

n

λ

∆λ

λ

Fo

re-

an

d-aft

line

Ve

ctor

to

decid

e

heading

 

Principle of satellite compass operation