12 



OCEAN ELECTRONIC NAVIGATIONAL AIDS 



After the "slave" transmits its pulse, the entire cycle is repeated again 

 and again. 



Thus the "master" station "sets the pace" and the "slave", by following, 

 completes the Loran transmitting cycle. This is shown diagramatically in 

 Figure 1-9). 



By this simple process, a pair of Loran stations send out their guiding sig- 

 nals to the hundreds or thousands of navigators who may be within the area 

 of their service which, in most cases, is well over 1 million square miles! 



TRANSMITTING STATION EQUIPMENT 



In order to send out a succession of reliable Loran signals to aid navigators 

 at sea in determining their position, the transmitting station has two funda- 

 mental responsibilities. The first of these is the generation of radio pulses 

 of the proper frequency, power, and duration. The second is the timing of 

 these radio pulses at the correct intervals and with the required degree of 

 precision. The three major units of transmitting station equipment are the 



Figure 1-10. — View of latest type Loran transmitting equipment. 



Loran transmitter, the Loran timer, and the electronic switching equipment. 



The Loran transmitter is a "pulse" type of equipment of a special design 

 developed specifically for Loran application. The radio frequency pulses 

 generated by the equipment, while of short duration, contain a great deal of 

 electrical energy and are as powerful as the largest commercial broadcasting 

 stations' transmissions. The Loran transmitter functions in such a manner 

 that a single pulse of radio energy is sent out each time the transmitter receives 

 an electrical timing impulse. The timing impulse is a "trigger" pulse and 

 serves to "turn on" the transmitter for the duration of the pulse. These 

 "trigger" pulses are generated by Loran timing equipment. 



The Loran timer is the fundamental unit of equipment on which the accu- 

 racy of the Loran system depends. The timer is made up of the following 

 basic components which serve the purposes indicated: 



(a) Radio receiver. — The receiver permits the reception of Loran signals 

 from the distant station and also those transmitted by the local station. 



(&) Indicator. — Based upon the function of the cathode ray tube which 

 permits the operator to "see" electrical impulses, the indicator permits visual 

 inspection of the signals themselves and other basic functions of the equip- 

 ment. 



(c) Oscillator and timing circuits. — The complex and precise timing func- 

 tions stem from a crystal-controlled oscillator of the highest laboratory 

 standards. The timing circuits permit the measurement of the time interval 

 between the signals received and furnish the necessary "trigger" pulses for 



