INTRODUCTION TO SONAR 



of confusion, however, a full call should be 

 used. Example: full call: NJRV DE NILX; abbre- 

 viated call: DE NILX. 



Text 



The call is followed by the text, wliich is 

 the main part of the message. It is the basic 

 idea or information that the originator (station 

 with information to send) desires to commiuiicate 

 to the addressee (station receiving the message). 

 The text may be sent in plain language or it may 

 be sent coded. In addition to regular coded 

 signals. Sonar Technicians use a special 3-letter 

 code with meanings that cover most of the in- 

 formation sent or exchanged in underwater com- 

 munications. This code is contained in FXP 1. 



The 3-letter code sometimes is referred to 

 as the "short signals." Use of short signals 

 shortens the time required to exchange informa- 

 tion. Even so, you will handle many underwater 

 messages with plain language texts. 



The he adin g and text of a message are 

 separated by BT. Li kewi se, the text and ending 

 are also separated by BT. 



Ending 



The ending marks the conclusion of the 

 message. In underwater sound communications, 

 the ending consists of the prosign K or AR, 

 depending on whether a reply is required. 



Challenging 



In some situations the use of CW, rather 

 than voice, is highly desirable. Here is an 

 example: Your ship (or submarine) is on a 

 routine patrol. You have a "probable" sonar 

 contact. The captain wants to know its nation- 

 ality, and orders you to challenge. One method 

 is to use voice transmission: 



UNKNOWN STATION — THIS IS (your ship's 

 international call sign)— IDENTIFY YOUR- 

 SELF— OVER 



You could also tell the unknown station its 

 bearing and range from you. He may not have 

 an underwater telephone installation, however. 

 Even though equipped with a telephone, if he 

 is from a foreign nation he may not understand 

 you. By using CW, you can transmit an inter- 

 national interrogation signal. This signal is 

 AA (two di-dahs sent as a single group: di- 

 dah-di-dah). The challenge is followed by the 



letters DE (from) and the four letters of your 

 ship's call sign, ending with K (over). If the 

 contact is a submarine, and he decides to answer 

 you, he will transmit his call letters. You then 

 can look up his call sign in ACP 113 to obtain 

 his name and coontry. 



Many search sonars can be used to transmit 

 CW signals. This usage puts a power drain on 

 the equipment, however, causing it to heat up. 

 Built-in overloads are provided to reduce power 

 output before damage occurs to the equipment, 

 resulting in reduction of range with the lesser 

 power output. Thus, under normal conditions, 

 CW transmission is not recommended for search 

 sonars. 



SUBMARINE COMMUNICATION METHODS 



The AN/UQC underwater telephone is the 

 submerged submarine's prim^ary means of com- 

 municating with surface ships. For this reason, 

 daring exercise periods ships are required to man 

 the UQC continuously. In addition to its required 

 use for safety purposes, the UQC is used through- 

 out an exercise by ships and submarines for 

 sending attack signals, obtaining range checks, 

 transmitting sonar short signals, and for several 

 other purposes. Subject to equipment limitations, 

 keyed sonar is the secondary means of underwater 

 communications. Many submarine sonars do not 

 have CW capability. 



Emergency communication equipment carried 

 by a subm marine include a radio and a telephone. 

 The radio is battery-powered and floats to the 

 surface upon release through the signal ejector. 

 Once on the surface it automatically transmits 

 on emergency radlofrequencies. 



The emergency telephone, designated AN/ 

 BQC-IA, is also battery-powered, and is portable. 

 It has tlie same voice frequency characteristics 

 as Gertrude, with a range of about 5000 yards. 

 The usual installation provides one set in both 

 the forward and after torpedo rooms. In addition 

 to its voice transmission capability, the AN/ 

 BQC-IA can emit a 24.26 kHz continuous tone 

 for homing purposes. Submarine rescue vessels 

 have equipment capable of detecting and homing 

 on the tone. With all batteries in good condition, 

 72 hours of continuous tone transmission is 

 possible. Range of the homing signal is 2000 to 

 5000 yards. 



Colored flares and smoke signals afford 

 another means of commimication. Black or green 

 signals are used by the submarine to indicate 

 the simulated firing of torpedoes and to mark 



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