E. SHORAN 



1. GENERAL 



Shoran, a navigation and positioning system developed by RCA, uses 

 radar principles for establishing an accurate fix. The original equipment was 

 designed with the intent of controlling aircraft during a bombing mission. 



TTie inherently high accuracy of the Shoran fix has made the system 

 very useful as a control in hydrographic surveys at distances of 50 miles or 

 more from shore. It has been used at minimum ranges of the order of 1 mile. 



The accuracy of the system has been measured by assuming a con- 

 stant velocity of signal propagation with a mean value of the refraction coeffi- 

 cient. Corrections in propagation velocity may be made by measuring the re- 

 fractive index and computing a corrected velocity of propagation. 



The Shoran system utilizes radar transponders placed at known shore 

 sites at either end of a base line. Each transponder returns an amplified and 

 reshaped signal to the ship's radar receiver. An accurate and stable time 

 base converts the signal travel time to distance, which is read on a digital dial. 

 Returns from two or more transponders on the base line establishes a fix. 



2. DESCRIPTION 



A shipborne transmitter transmits precisely timed pulses toward the 

 shore stations. The signal is received at the shore stations, amplified, re- 

 shaped, and retransmitted. A shipboard receiver operating from the same 

 directional antenna as the transmitter demodulates and amplifies the return 

 signal. It is further processed in the indicator, and the elapsed time between 

 transmit and receive pulses is measured and converted to a one-way distance. 

 If the positions of the two ground stations are accurately known, then the posi- 

 tion of the ship can be determined. Arcs are drawn whose radii are equal to 

 the measured distances to the shore stations. 



A single pair of intersecting arcs can give rise to ambiguity, as the 

 fix can fall on either side of a line bisecting the base line between the shore 

 stations. This ambiguity is resolved by following a known course and taking 

 additional fixes . 



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