TM No. 306 



The Decca Hi-Fix "net" in the Tongue of the Ocean, shown on Figure 3, 

 consists of three land based transmitting stations. (Two slave stations in 

 conjunction with the common master station.) A single pair of stations 

 produces a pattern which, being dependent on the distance AB (Figure 6a) 

 and on the frequency used, can occupy calculable and highly stable 

 positions on the earth's surface. Therefore, from the point of view 

 of an observer carrying a phase comparison device (Receiver), 

 the pattern constitutes a set of navigational position lines taking 

 the form of a family of hyperbolae focussed on the two transmitters. 



To enable the observer to fix his geographical position with 

 reference to the ground stations, two sets of position lines are required. 

 These are provided by a second hyperbolic pattern generated by Station C 

 (Figure 6b) in conjunction with the common Master Station A. The receiving 

 (phase-comparison) apparatus is duplicated to work with the two sets of 

 coordinates, and the observer fixes his position at any instant by trans- 

 ferring the readings of the two phase meters to a map on which numbered 

 lanes of the two patterns are printed. 



Typical operating distances between Hi=Fix transmitters and receivers 

 are between 5 and 35 miles, but the receiver can be used close to the 

 transmitting station without loss of accuracy, or at a maximum, offshore 

 range of about 100 miles, if the radiated power from the stations is 

 increased. The radiated power of the transmitting stations in TOTO is 

 sufficient to ensure a working range normally in excess of 50 miles 

 over seawater. During this program, Hi-Fix was used at a distance of 

 approximately 110 nautical miles (Transect 1, Figure 3) from the farthest 

 slave station with fair reliability. From a nomogram it was calculated 

 that the lane width along Transect 1 was from 1700 to 19OO meters. 

 Since the receivers are capable of reading to l/lOO of a lane, this 

 provides an accuracy in the order of 17 - 19 meters. 



A series of Decca transformation charts were available for the TOTO 

 area to plot the positions of the drogue floats between 23° 50' and 2k 

 50 ' north latitude. Although there was no chart coverage for the transect 

 in the Northeast Providence Channel, the Naval Oceanographic Office has 

 a computer program for converting Decca coordinates to latitude and 

 longitude, and this was used to plot the positions of the floats in 

 these areas. 



In general, the Decca Hi-Fix System, backed up by radar, was quite 

 adequate for tracking the drogues, and the position fixes obtained were 

 satisfactory. 



