58 



HYDROGRAPHIC MANUAL 



J i 

 Figure 14. — Shoran ship set AN/APN-3, receiver-indicator on left, transmitter on right. 



watts of power as compared to 1600 watts 

 for other ground station equipments. How- 

 ever, these converted systems can serve only 

 4 survey units simultaneously, whereas the 

 AN/CPN-2 or 2A can serve a maximum of 

 20 units. 



Shoran antennas corrode rapidly when the 

 priming coat is scratched. Application of an 

 acrylic plastic will prevent corrosion for a 

 considerable period. It is advisable to spray 

 nuts and bolts and the coaxial connector as 

 well as the scratched areas. The coaxial 

 connector should be packed with Dow-Corn- 

 ing compound-DC 4 and taped. 



3-36 Operation of Shoran. — The position 

 of a survey vessel can be determined at any 

 instant by measuring and plotting the dis- 

 tance to two known points. The ship trans- 

 mits radio waves, or pulses, alternately on 

 frequencies of about 230 and 250 megacycles. 

 The ground station receives the signal, and. 



after a short delay, triggers a transmitter 

 which returns the signal to the ship on a 

 frequency of about 310 megacycles. The ship 

 operator matches the returning pulses with 

 a fixed index, thus automatically converting 

 the elapsed time for the round trip to dis- 

 tances in statute miles. These distances are 

 read from dials to the nearest .001 statute 

 mile. In addition to the operator of the ship 

 equipment, one man must be continuously on 

 duty at each shore station while the equip- 

 ment is in operation. 



3-37 Accuracy and range of Shoran. — 



The radial accuracy of a measured distance 

 from any one ground station is about plus or 

 minus 75 feet. The errors in observed dis- 

 tances vary with distance and signal inten- 

 sity. Some distance errors may be deter- 

 mined and compensated by careful and re- 

 peated calibrations. The correction is not a 

 constant. It starts as a small value near the 



