Page 465 echo sounding 5232 



Part of the moving mechanism, consisting of the driving motor, governor, gear 

 box, rotating stylus arm, and contactor, is mounted on the inner side of the door of 

 the cabinet. The two motor generators are mounted in the bottom of the cabinet; 

 one supphes 300 volts for part of the plate power of the amplifier; the output tubes, 

 however, being supplied by a 350-volt generator which also actuates the transmitting 

 unit. The driving motor operates a train of gears to rotate the stylus arm and to 

 operate the contactor 11.18 times per second for sounding in feet, and at one-sixth that 

 speed for soundiug in fathoms, or 123 revolutions in 66 seconds. The rotating arm is 4.5 

 inches long and carries at its end a stylus of fine piano wire, which sweeps in an arc 

 across the fathogram paper. A condenser is charged continuously through a resistor by 

 the 350 volts from the motor generator. Once each revolution, contactors are closed 

 by the rotating arm, normally at the instant the steel stylus wire passes a point on 

 the fathogram scale corresponding to the depth of the fish below the water surface. 

 These contactors discharge the condenser into the magnetostrictive transmitter, pro- 

 ducing a short pulse of vibrations at the rate of 20,000 per second, and thus the signal 

 is sent. 



There are two ways by which the position of the contactors in the cycle of rotation 

 may be changed with reference to the zero of the fathogram scale. Small adjustments 

 may be easily and quickly made, by means of a knurled knob, while the machine is 

 running, so that the transmitted signal is made to record at exactly zero, or if desired, 

 at a depth corresponding to the draft of the fish, thereby referring all recorded depths 

 to the water surface. 



The position of the contactors is also changed when the phase is changed. The 

 printed scale of the fathogram reads from to 55 — feet at liigh speed (11.18 soundings 

 per second) or fathoms at slow speed. However, if the contactors are advanced, oppo- 

 site to the direction of rotation, so that the signal is emitted the equivalent of 35 feet 

 (or fathoms) before the stylus reaches the zero of the fathogram scale, the scale will 

 then record depths from 35 to 90 feet (or fathoms). Advancing the contactors in this 

 way is called phasing. It is accomplished simply by lifting a little knob on the face of 

 the recorder and turning an arm to the phase desired. This knob has a plunger which 

 drops into a hole to maintain the contactors at exact position for each phase. 



There are four phases in all, to 55, 35 to 90, 70 to 125, and 105 to 160 feet (or 

 fathoms), each phase overlapping the preceding one by 20 feet (or fathoms) so that no 

 soundings need be missed when changing from one phase to another. The shift in 

 phase can be made quickly, in either direction. The transmitted signal is recorded 

 on the fathogram on the first phase only, the to 55 scale. Even then its recorded 

 intensity may be greatly reduced by turning a switch, so that it will not interfere with 

 the record of extremely shoal depths; for example, depths less than 3 feet under the, fish. 



The magnetostrictive receiver is connected to the echo amplifier, located inside 

 the recorder cabinet. The amplifier is a three-stage, tuned, push-f»ull type, completely 

 shielded, containing six tubes having their 6-volt heaters grouped in three pairs in series 

 on the 12-volt storage battery. With maximum gain the amplifier sensitivity is 0.2 

 microvolt. A graduated gain-control knob is located on the front of the cabinet door. 

 The echo is amplified untU the third pair of tubes develops about 180 volts across an 

 output transformer. This voltage is applied between the stylus and the metal platen 

 under the paper so that a series of sparks of diminishing intensity pass through the 

 paper at the time the signal is sent, and upon reception of the echo. These sparks re- 

 move the gray coating leaving the black paper visible, as though a series of closely spaced 



465382 — 44 31 



