tag was attached, the deployment vehicle was released from the tag and could be 

 recovered. If the dart was poorly located, deployment could be aborted by releasing the 

 line attached to the crossbow. 



1990 



Because miniaturization had occurred since the 1989 season, we reappraised the 

 available PTT packages including those by Roger Hill (Wildlife Computers) and Telonics. 

 We decided to use the most compact transmitter, the new Telonics ST-6, which could 

 also operate at a reduced power level. An evaluation of the 1987 pilot whale signal 

 strength data determined that a 60% power reduction (from 1 watt to 400 milliwatts) 

 would result in only a 10% loss in the number of messages received. This was fortunate 

 as the Altus batteries we had previously used for higher power were no longer available. 

 After testing an array of batteries, we settled on the Duracell 2/3A manganese dioxide 

 battery which is small, reasonably priced and readily available because it is commonly 

 used for photographic strobes. 



We incorporated a small Telonics VHF radio transmitter into one end of the 1990 

 transmitter to relocate tagged whales and evaluate the accuracy of satellite-acquired 

 locations (Task J). The VHF transmitters used different repetition rates on individual 

 frequencies, and had an anticipated life of four months. The VHF tags were used to 

 identify tagged whales at a range of several kilometers after satellite-acquired locations 

 brought us into the general area. Thus, we knew which tagged whale we were observing 

 without close approach. 



Housing 



The 1990 transmitter tit into a cylinder that was 5.6 cm in diameter and 12.5 cm 

 long. It weighed 0.57 kg with attachments (Figure 5). This was a 66% reduction in 

 volume and a 91% reduction in weight over the 1989 tag and allowed the entire 

 transmitter to be applied as a projectile without the intermediate steps required in 1989. 

 Drag was reduced by more than 80% because of both the tag size change and the 

 significant loss of the attachment spring, stops and base-plate structure. At each end of 

 the tag was a Delrin plastic endcap. Delrin was chosen to reduce weight, save machining 

 time and function as an insulator for the antennae and saltwater switch. 

 The VHF and Argos antennae were mounted on opposite endcaps. The saltwater switch 

 was located next to the Argos antenna. 



Software 



In 1990, the smaller Telonics ST-6 transmitters did not have software to precisely 

 coordinate PTT transmissions with satellite passes. We decided to transmit two hours 

 out of every six hours, and timed this transmission period to maximize satellite coverage. 

 Because satellites have an orbit of 101 minutes, we knew at least one orbit would occur 

 during each two hour transmission cycle. Figure 6 shows the four transmission periods 



14 



