. Basic methods for the calibration of sonar equipment. EQUIPMENT AT MOUNTAIN LAKES 109. -13. View ot liigh lrc([iK'iK\ t; lank, show ini; iiRi cquipinciil Idi hdldiiig ami posilioiiinj^ I he iiisliiiineius. not be coniplclc wiihoui emphasis on imcnialh cloiil)h shielded traiisrormcrs. I'hese make it p(«sil)le to transmit or to leeeive, at will, on baianeed or on unbalanced lines. Under most circmnstances, bal- anced lines are much more effecti\ e in reducing cross talk and the use of the internal shields on the trans- formers results in the lumping of all stray ca
. Basic methods for the calibration of sonar equipment. EQUIPMENT AT MOUNTAIN LAKES 109. -13. View ot liigh lrc([iK'iK\ t; lank, show ini; iiRi cquipinciil Idi hdldiiig ami posilioiiinj^ I he iiisliiiineius. not be coniplclc wiihoui emphasis on imcnialh cloiil)h shielded traiisrormcrs. I'hese make it p(«sil)le to transmit or to leeeive, at will, on baianeed or on unbalanced lines. Under most circmnstances, bal- anced lines are much more effecti\ e in reducing cross talk and the use of the internal shields on the trans- formers results in the lumping of all stray capacities between the shields, reducing cross talk still further. These transformers also allow a better treatment of the ground loop problem and are used for coupling between all circuits and lines. Acoustical System The acoustical system, in general, consists of an indoor calibration tank, mechanical equipment for holding and positioning the instruments, absorbers for reverberation control, transducers, and outdoor test equipment. Calibrations may be made in the tank from 80 to 2,200 kc. The lower limit is determined by the rever- beration, while ihc uppir limit is imposed b\ the response of the stantlaixl transducers. CuUbralioit Tinili oj PasUioniug E<iiiil)titcut. The calibration tank is made of -^s-inch sleel and has an elliptical cross section with approximate dimensions of 7 feet for the major axis and 4 feet for the minor. The depth of the tank is 4 feet. The tank has a capacity of fi.'iO gallons and is equipped with a drain and a water inlet at the bot- tom and an o\erflowpipe at the top. Water is pinnped directl)' from the lake, and as a residt the problem of fungus and slime assumes major proportions. Water from a conununity system, as a rule, will contain the same organisms, biu in nuich smaller niunbcrs. .So many different materials are used in the tank that care must be exercised in the choice of a fimgicide. It must be noncorrosive, nonpoisonous, odorless, an
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