III. POWER REQUIREMENTS 



TODAS was designed to operate on a direct -current power supply which 

 would give experimental capability in remote localities. In previous 

 experiments, either a conventional source or a portable generator (alter- 

 nating current) was used to avoid the problems of handling and charging 

 batteries. During field experiments, a small portable gasoline-powered 

 generator proved adequate for operating the receiver, discriminator, 

 data logger, analog, and digital recorders. The power consumption of 

 the onshore system is about 7 amperes per hour. 



All components onboard the sea sled are powered by four 12-volt 

 rechargeable Gel Cell batteries housed in an aluminum cylinder (0.63 by 

 27.3 centimeters, outside diameter) that rides on the sled (Fig. 14). 

 Each battery is rated at 20 ampere-hours , giving a total of 80 ampere- 

 hours (equivalent to 260 hours) continuous underwater operation without 

 recharging. The battery and instrument package are connected by an eight- 

 conductor neoprene cable with bulkhead connectors (Fig. 15) . 



1. Electronics. 



In an earlier version of the present system, all data were obtained, 

 processed, and recorded as analog signals (voltage) onboard the sled. 

 Since this system precluded real-time observation of the data flow needed 

 for appraising the performance of sensors and for determining whether 

 significant values of ocean parameters are being recorded, modifications 

 were undertaken which separated data acquisition into onboard (on the 

 sled) and onshore components. 



a. Signal Acquisition, Mixing, and Telemetry . Outputs of the current 

 meters are dual overlapping pulses which are converted to an analog signal 

 (± volt, direct current) by the signal-conditioning circuitry, one for 

 each sensor (Fig. 16 and App.). The processed signals are amplified to 

 match the input of the VCO and then mixed before being relayed to the 

 transmitter (Fig. 16). Pulse to analog conversion, amplification, analog 

 to frequency conversion, and mixing take place within the instrument pack- 

 age housed inside an aluminum cylinder (0.61 meter long by 27.3 meters in 

 diameter) which rides on the sled (Fig. 17) . 



Output of the pressure wave gage (0 to 5 volts, direct current) and 

 the direct-current signals from each current meter are converted into 

 frequencies by the VCO's, mixed through a series of operational amplifiers, 

 and transmitted to a shore-based receiver on 27.454 megahertz frequency 

 band. The transmitter, with its antenna mounted at the top of the mast, 

 has a power output of 2.2 watts (Fig. 18). Effective operational limits 

 of the telemetry system is about 8.05 kilometers (5 miles). Radio noise 

 becomes a problem beyond this distance. 



b. Receiving and Demodulation . The modulated signals are usually 

 received onshore (Fig. 19) (although signals can also be received on the 



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