430 



MECHANICAL AND ACOUSTICAL SENSES 



arrival time (re: interrogate signal departure time) permits the desired dis- 

 tance determination. A capability of this type is being developed for addi- 

 tion to the standard CSULB Mark V transmitters. In addition to the boat- 

 based receiver /interrogate unit, a diver-held underwater unit will be used 

 to allow easy interception of the shark for the purpose of making visual 

 observations. 



A transponding transmitter intended primarily for long-term use with 

 home-ranging species of reef sharks is also under development at CSULB 

 (Figure 6). The shark unit will be normally silent (listening mode) until it 

 receives the proper interrogation signal. Then it will switch to the transmit- 

 listening mode, remaining there for about 1 h past its last interrogation. 

 This facilitates unbroken transmission without having repeatedly to inter- 

 rogate the unit to keep it on. In this mode, the shark unit will respond to 

 interrogation with its special reply pulse (frequency shifted) from which 

 distance is obtained. If no interrogation is received for 1 h, the shark unit 

 switches back to the listening mode, thus conserving power during the 

 times the trackers are not present. 



Battery conservation can be an important advantage of transponding as 

 listening (receiving) circuitry can be made to draw relatively little power. For 

 long-term studies where only intermittent checks on the telemetered subject 

 are planned, useful transmitter lives of several months or more can be ob- 

 tained while still retaining high acoustic power during on-times. 



The degree of battery savings possible with transponding, however, de- 

 pends on the normal power drain of the basic transmitter. As pointed out by 

 Pincock and Luke (1975), for some small, low-power USTs, addition of 

 transponding can actually increase the battery drain, even though the output 



; MULTIPLEXER ; 

 ! AND SENSORS ' 

 ! -IF DESIRED ! 



L 



40-kHz 



TRANSMITTER 



LOGIC 



POWER 

 AMP 



P2T 

 TRANSDUCER 



TRANSM IT-RECEIVE 



ISOLATION 



NETWORK 



BATTERY 

 SWITCH 



BATTERY 



-~S- 



RECEIVER 

 BROAOBAND 

 AMP -I- CLIPPER 



l OTHER FREQ FILTERS a I 



•HRECOG CRCUITS FOR I 



'OTHER FUNCTIONS -IF I 



[ DESIRED l 



12.8-kHz 

 NARROW BAND 

 FILTER 



RECOGNITION 



CIRCUIT 



(5mt) 



ONE -SHOT 38 -kHz 



OSCILLATOR 



(25mt) 



ON -OFF TIMER 

 (RESETTABLE) 

 (l-h ON) 



Figure 6 Functional diagram for a transponding transmitter. Interrogate frequency, 1 2.8 

 kHz; reply frequency, 38 kHz; data-transmit frequency, 40 kHz. In the listening mode, 

 power is connected only to the receiver and timer sections. 



