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   Convert dBW (decibels-Watts) to nanowatts.
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   Form:
   power = DPWToNW( powerDB )
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   ------
   Inputs
   ------
   powerDB       (1,:)  Power (dB)
                        
   -------
   Outputs
   -------
   power         (1,:)  Power (nW)
                        
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