Page 475 



ECHO SOUNDING 



5242 



Power to operate the transceiver is furnished by a 17.5-kc vacuum-tube oscillator 

 and an accompanying vacuum-tube power amplifier. In addition to the 17.5-kc 

 alternating current, there is a d-c polarizing current of about 1.75 amperes flowing 

 continuously through the transceiver. The purpose of this direct current is to prevent 



Figure 105.— Magnetostrictive transceiver mounting. A. Transceiver housing. B. Diaphragm. C. Hull mounting. 

 D. Hull plate. E. Fairwater cement or steel plate. 



double periodicity of the .transceiver and to furnish the magnetomotive force used in 

 the reception of the echo. (See also 5261.) 



5242. Echo Amplifier 



The echo amplifier amplifies- the feeble voltage generated across the terminals of 

 the transceiver when an echo is received; it embodies a superheterodyne circuit capable 

 of high gain, and has a high degree of stability and frequency discrimination. The 

 output voltage of this amplifier operates the grid of a type 884 gas-discharge tube, 

 which in turn flashes the indicator neon tube. This amplifier is similar to that used 

 in the Dorsey Fathometer No. 3, except for mechanical details, and except for the 

 fact that no headphone outlet is provided. 



5243. Indicator 



The visually indicating device of this Fathometer is housed in a black-finished 

 metal cabinet, 10 by 10 by 5 inches in size. The front of the cabinet contains a cu-- 

 cular opening, fitted with a glass on which are the circular depth scales, one divided 

 into foot intervals and the other into fathom intervals, up to 20 fathoms. On the 

 lower left-hand rounded edge of the cabinet are two toggle switches. The front switch 

 is for starting and stopping the motor generator that supplies a-c power to the Fath- 



