In quiet fresh water the sound waves 

 transmitted by the transducer can be detected 

 at distances up to 2, 000 feet. In turbulent 

 and aerated water, such as is found close to 

 and immediately upstream of a fishway weir, 

 the distance is reduced to 65 feet. The dis- 

 tances in sea water are reduced by approx- 

 imately one -third. The length of time during 

 which the sound waves can be detected vary 

 from 10 to 100 hours depending upon the size 

 battery used. 



The transducer operates on a carrier 

 frequency of 132 kilocycles per second with 

 a repetition rate of 450 cycles per second. 

 This carrier frequency is slightly higher than 

 the frequency of the ambient water noises and 

 therefore gives the best detection under a 

 variety of hydraulic conditions . An increase 

 in carrier frequency reduces the range at 

 which the soundwaves can be detected, espec- 

 ially in turbulent water . A lower frequency 

 would require a crystal of a greater diameter 

 which would necessitate a larger tag. In 

 order to use several sonic tags at the same 

 time, in the same area, the repetition rates 

 of the transducers are adjustable. By using 

 receiving equipment which can be tuned to a 

 desired frequency, the position of up to ten 

 tags can be pin-pointed and identified. 



The capsule within which the component 

 parts are fitted is spun in two halves from 

 soft aluminum sheeting .007 inches thick. Be- 

 fore the sonic tag is assembled, the device 

 for attaching the unit to a fish is soldered onto 

 one -half of the capsule. After the component 

 parts have been assembled and secured in 

 place, the two halves are joined and the joint 

 is sealed with an elastic tape. The entire 

 unit is dipped in a clear liquid plastic to make 

 it completely waterproof. 



Assembled tags can be stored for a maxi- 

 mum of one year with no serious effect on their 

 -operation. When used within a year for track- 

 ing a fish, the tag can be made operational by 



simply twisting together two wires which 

 closes the electrical circuit. These wires 

 protrude through the capsule and through 

 the plastic covering. If it becomes neces- 

 sary to change the battery, the tag can be 

 easily disassembled and reassembled after 

 the battery has been replaced. 



Automatic -Tracking Receiver 



An automatic -tracking device was de- 

 signed and incorporated with an echo- 

 ranging system to produce an automatic - 

 tracking receiver. The automatic -tracking 

 device seeks out and "homes" on the sonic 

 tag attached to a fish, aiming the echo- 

 ranging system in that direction. The 

 echo-ranging system supplies the informa- 

 tion on the movements of the sonic tag at- 

 tached to the fish up to a distance of 800 

 feet (this is the maximum radius within 

 which the fish can be "tracked", even 

 though, as stated above, they can be de- 

 tected at distances up to 2, 000 feet). 

 Ultrasonic impulses are sent into the water 

 by the system in the form of a narrow beam; 

 returning echoes from the fish supply the 

 information of its position through an in- 

 dicator unit. The frequency of this beam of 

 sound impulses differs from the frequency 

 of the sonic tag thus creating no interfer- 

 ence . 



The indicator unit contains a viewing 

 screen, a tilt -angle meter, a loudspeaker 

 and a signal -level indicator plus the operat- 

 ing controls The viewing screen is a 

 calibrated cathode-ray tube on which return- 

 ing echoes are observed visually as a 

 bright spot of light after conversion into 

 electrical energy. The bearing and dis 

 tance of the fish can be read directly. The 

 tilt-angle meter shows the angle at which 

 the beam of sound impulses is projected 

 into the water when aimed at the fish. With 

 this information (distance and angle) the 

 depth of the fish can be calculated. The 



