Page 615 radio acoustic ranging 6562 



of live rubber clamped between two circular brass plates by means of six ^^-20 brass bolts that pass 

 through the rubber. A central hole passes through the brass and rubber for the passage of an electric 

 cable. When the plug is inserted in the end cf the cylindrical section and the six brass nuts are 

 tightened, the rubber is compressed by the plates and expands normal to the direction of compression 

 to seal the opening. 



By means of an adapter an electromagnetic unit is screwed into the loose threads of a hole that 

 connects the cavity behind the diaphragm with the cavity of the cylindrical section, the electro- • 

 magnetic unit being in the cylindrical section. The outside diaphragm and the diaphragm of the 

 electromagnetic unit are coupled by means of the air in the cavity between the diaphragms. The 

 electromagnetic unit used in the Dorsey hydrophone is No. //-56741-1, made by the Automatic 

 Electric Company of Chicago, Illinois. It consists of a balanced armature suspended between the 

 pole pieces of a permanent electromagnet, the armature being connected to a small aluminum-alloy 

 diaphragm by means of a pin. The impedance of this unit is 900 ohms. The calculated natural 

 frequency of the hydrophone diaphragm in water is 141 cycles. There are additional resonant points 

 because of the air cavity and the resonance of the electroacoustic unit. 



The Dorsey hydrophone was formerly used with ship stations and is now used 

 ahnost exclusively with sono-radio buoys on the Atlantic and Gulf Coasts of the 

 United States. 



6562. Suspension of the Dorsey Hydrophone 



Where the sono-radio buoy is connected to a relieving buoy that is anchored, the 

 hydrophone should be suspended by a cable from the sono-radio buoy. It should be 

 suspended about 7 fathoms below the water surface. This depth is not at all critical, 

 but it is essential that once a depth is selected it should be used for all sono-radio buoys 

 of one control scheme. \^Qiere there are strong water currents the diaphragm of the 

 hydrophone should be horizontal. It is suspended thus by a yoke attached to the three 

 eyebolts on the back of the base plate of the hydrophone. The upper end of the yoke 

 is attached to the suspension cable which in turn is attached to the sono-radio buoy. 

 Where the water currents are weak there is some advantage in keeping the diaphragm 

 of the hydrophone vertical. It is suspended thus by a yoke attached to only two of 

 the three eyebolts on the back plate of the hydrophone. 



The suspension cable should be suitable %-inch flexible cable. The electric cable 

 from the buoy to the hydrophone should be Tyrex Simplex, type SJ, No. 16, two- 

 conductor, with )^2-inch insulation, or equal. The electric cable is lashed to the sus- 

 pension cable at 2-foot intervals, leaving slack in the electric cable between lashings 

 to avoid any strain on it. Other details of this hydrophone suspension are described in 

 2841(A). 



Wliere the sono-radio buoy is anchored without an intermediate relieving buoy,, 

 the hydrophone should be suspended from the anchor cable in such a way as to avoid 

 fouling. The hydrophone may be suspended in the center of a triangular frame of 

 angle iron by means of six rubber straps, two straps to each side of the triangle. The 

 frame may be made of angle iron Iji inches wide by ^4 inch thick, the length of each 

 side being 35 inches. For suspension, one side of the triangle is clamped to the anchor 

 cable at a distance of about 45 feet from where the cable joins the buoy. The electric 

 cable is fastened to the anchor cable at 2-foot intervals. The electric cable should be 

 parceled to protect it from chafing against the anchor cable or any part of the buoy. 



6563. Vincent Hydrophones 



There are several models of Vincent hydrophones, whoge principles of operation 

 are very similar, although they differ in size, material, and construction. 



