16 



OCEAN ELECTRONIC NAVIGATIONAL AIDS 

 BASE RATE 25 CYCLES (PULSES) PER SECOND 



BASE RATE 33^ CYCLES (PULSES) PER SECOND 



New Loran transmitting station equipment is capable of operation on a base rate of 20 c. p. s. to provide 

 for future expansion of the system without requiring additional radio frequency allocations. 



traces appear with the first half directly above the second half. Both traces 

 are horizontal in time sweep. 



The controls of the receiving instrument are adjusted until the master 

 signal is viewed near the beginning of the upper, or A, trace. The slave sig- 

 nal will appear in its proper place on the lower trace. Measurement of the 

 Loran time difference is made by evaluating the horizontal displacement of 

 the slave station with respect to the master in terms of time, microseconds. 

 By this physical arrangement of the traces the half recurrence interval delay 

 which was introduced by the slave is effectually canceled from the measure- 

 ment. Loran readings thus obtained may be interpreted in conventional 

 coordinates by the use of Loran charts or tables. A fast speed time base 

 having a duration of roughly from 100 to 300 microseconds is provided to 

 permit visual examination of the pulse envelope itself which is necessary to 

 establish the precise adjustment required in making a Loran reading. 



BUNKER SIGNAL. — The timers at Loran transmitting stations are equipped 

 to perform a function known as blinking. The signal is used to indicate that 

 the transmissions should not be considered reliable during the period of blink- 

 ing. In general, blinking causes the received pulse to rhythmically swing 

 back and forth as viewed on the slow sweep, and to rhythmically appear and 

 disappear on the fast sweep. In the few exceptions to this method, there is 

 a rhythmic appearance and disappearance on both slow and fast sweeps. 



LORAN RECEIVER-INDICATOR FUNCTIONAL SPECIFICATION 



RADIO RECEIVER 



OPERATING RADIO FREQUENCIES. — The radio receiver of a Loran receiver- 

 indicator is provided with four radio-frequency channels and may be set 

 for operation on any of the frequencies tabulated in the system specification. 

 In operation, receiver tuning is fixed and a four-position switch provides sim- 

 ple means of changing channels. Inasmuch as only two transmitting fre- 

 quencies are allocated for standard Loran, the four-position frequency selector 

 switch, if provided, permits future system flexibility. 



RECEIVER SENSITIVITY. — The receiver has a sensitivity sufiBciently high that a 

 signal of approximately 10 microvolts delivered by the antenna to the receiver 

 input will result in full scope deflection of the cathode ray indicator. Receiver 

 and indicator form an integrated unit and are not intended to function 

 separately. 



