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   Signal conversion to decibels. dB = 10 log10(s).
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   Form:
   dB = DBSignal( s )
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   ------
   Inputs
   ------
   s			  (:)     Signal
                        
   -------
   Outputs
   -------
   dB            (:)     decibels
                         
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	References:	Lambert, S. G. and W. L. Casey (1995.) Laser Communications in
               Space. Artech, Boston.
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