Page 479 echo sounding 5261 



ceiver, are nearly identical with those in the Dorsey No. 1. The major differences are 

 in the indicating mechanism, and the addition of certain features of the 312 Fathometer. 

 The several parts of this Fathometer are the transceiver, filter junction box, echo 

 amplifier, indicator, power supply, and certain parts of the 312 Fathometer system 

 (see 521). The latter are the 525-cycle motor generator, 1050-cycle oscillator, hydro- 



FiGURE 106.— Sounding with the Dorsey Fathometer No. 3. The indicator cabinet with its three scales may be seen above the open 



record book, with the amplifier below it. 



phone, echo amplifier, and all the necessary operating controls. A circuit diagram of 

 this instrument is shown in figure 107. 



5261. Transceiver 



The transceiver (fig. 105) is a-magnetostrictive diaphragm-type unit which is fitted into an 

 opening cut in the bottom of the vessel in such a way that the entire diaphragm is in contact with 

 sea water. The steel diaphragm is 14^ inches in diameter, back of which are 19 short nickel tubes 

 that press against the inner side of the diaphragm. A coil is wound around each nickel tube so that 

 when energized by a 17.5-kc current and a steady polarizing direct current, these tubes contract and 

 expand in unison 17,500 times per second, causing the diaphragm to vibrate at this frequency. 

 Conversely, the vibration of the diaphragm, caused by the variation in pressure of received sound of 

 this frequency, expands and contracts the nickel tubes, inducing an electric current in the coils wound 

 around them, which in turn produces a voltage across the coil terminals. The rectified polarizing cur- 

 rent required to operate the transceiver is introduced through a filter which serves the dual purpose 

 of preventing the 17.5-kc current from getting back to the rectifier circuit, and of eliminating strays 



