INTRODUCTION TO SONAR 



The AN/UQN-IC fathometer employs the hot 

 stylus and sensitized paper method of recording 

 depths. It also has a visual scope presentation 

 for shallow depths. This fathometer is a compact 

 unit, capable of giving accurate readings at a 

 wide range of depths — from about 5 feet to 

 6000 fathoms. Three recorder ranges are pro- 

 vided on the AN/UQN-IC, They are to 600 

 feet, to 600 fathoms, and to 6000 fathoms. 

 The CRT ranges are to 100 feet and to 

 100 fathoms. The equipment may be keyed man- 

 ually or automatically. (NOTE: All depths are 

 measured from the ship's keel, not the water's 

 surface.) 



Two styluses are used, but they are spaced 

 so that only one stylus records at a time. When 

 the fathometer records, a stylus starts down 

 the recorder chart simultaneously with the trans- 

 mission pulse. The stylus moves at a constant 

 velocity and marks the paper twice — once at 

 the top of the chart when the pulse is trans- 

 mitted, and again on the depth indication when 

 the echo returns. A depth recording made by 

 a fathometer of this type is seen in figure 6-13. 

 The recording illustrated was made from 

 a ship sailing over a sea with steadily de- 

 creasing depth. The first part of the trace was 

 recorded on the 6000-fathom scale. Inasmuch 

 as the paper moves from right to left, you 

 can see in the section of the paper shown that 

 the depth decreased from 4000 to 600 fathoms, 

 (Later depth information is to the right of 

 the paper.) When depth was about 600 fathoms, 

 the scale was shifted to the 600-fathom setting. 

 (See how shifting makes use again of the entire 

 width of the paper.) Because depth decreased 

 still further, the scale was shifted to the 600- 

 foot setting when a depth of about 100 fathoms 

 was recorded. 



The marking on the paper is downward (stylus 

 motion is downward) in alternate rows printed 

 from to 600 and to 6000. Marking the chart 

 paper in this manner allows the same paper 

 to be used for all recorder settings. You must 

 check which scale the equipment is recording 

 on to make sure whether the marking is in 

 thousands of fathoms, hundreds of fathoms, or 

 hundreds of feet. 



Be sure the range scale in use is greater 

 than the water depth. Otherwise, a false depth 

 indication (or no indication) will result, depend- 

 ing on the position of the styluses at the time 

 of echo return. If water depth actually is 120 

 feet, for instance, and you have selected the 

 100-foot range scale, a depth of 20 feet will 

 be indicated. 



Other false indications are multiple echoes 

 and reverberations, both of which usually are 

 caused by too high a gain setting. Multiple 

 echoes are the result of the transmitted pulse 

 being reflected back and forth several times 

 between the bottom and the ship's keel. In 

 shallow water a solid line may be recorded, 

 maiking it impossible to read the depth. Both 

 multiple echoes and reverberation effects can 

 be reduced by decreasing the gain. 



Visual indication is supplied by a circular 

 sweep on the face of a CRT. Transmitted pulse 

 and returning echo mark the sweep trace radially. 

 The visual indicator, pointing to a depth of 82 

 (feet or fathoms, depending on the scale setting) 

 is shown in figure 6-14, 



OPERATIONAL PROCEDURE 



Following is a brief discussion on normal 

 operation, security operation, and shutdown pro- 

 cedures. Refer to figure 6-15 while reading 

 this description, 



'Normal Operation 



For simplicity, it may be assumed that 

 there is only one normal way of operating the 



Figure 6-14. — Visual depth 



71.57 

 indicator. 



102 



