h. LORAC Type "B" System 



Tlie type "B" (Beta) system transmitters T^, T2, and T^ establish 

 one-half of the positioning grid and are called green lanes. The transmitters 

 T2, T3, and T4 establish the red lanes, as shown in Figure V-8. Transmitters 

 T^, T2, and T3 occupy precisely surveyed positions, while the receiver and 

 transmitter of T4 are placed at a convenient position within the grid system. 



Figure V-8 indicates the frequency relationships of the complete Beta 

 system. Mobile receiver No. 1 produces both the green position signal (f2 - fj^) 

 and the red position signal (f^ - f3). Receiver No. 2 receives both the red and 

 green reference signals transmitted as amplitude modulation on carrier f^. 



The Beta system is less complex than the basic system. Beta requires 

 four transmitters, one receiver, and four frequencies to establish a hyperbolic 

 grid. Time sharing is not required. In addition, the Beta system has a some- 

 what greater area of coverage than Alpha. 



Calibration 



The LORAC equipment is a differential-distance-measuring system 

 and for this reason must be calibrated for the particular grid system in which 

 it is to operate. A hyperbolic position grid is drawn^^ when the location of 

 transmitters Tp T2, and To is precisely known. 



The calibration is generally carried out by locating the mobile re- 

 ceiver at an accurately known geographic position within the grid system. The 

 phase counters are then adjusted to the calculated lane settings and the phase 

 meters set to the proper phase position within the lane. As the mobile receiver 

 moves from this position, the phase meters and counters track and continuously 

 indicate the ship's position on the grid system. 



d. Transmitting and Receiving Equipment 



LORAC transmitting and receiving equipment is of unitized construc- 

 tion, providing good portability and interchangeability. The transmitters are of 

 two types, depending upon their function within the LORAC system used. They 

 are adjustable over the frequency range of 1.7 to 2.5 mc and use a temperature- 

 stabilized crystal master oscillator for close frequency control. 



121 



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