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MathGroup Archive 2005

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Re: Re: something like dB

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56631] Re: [mg56629] Re: something like dB
  • From: Chris Chiasson <chris.chiasson at gmail.com>
  • Date: Sun, 1 May 2005 00:46:27 -0400 (EDT)
  • References: <200504300528.BAA23976@smc.vnet.net>
  • Reply-to: Chris Chiasson <chris.chiasson at gmail.com>
  • Sender: owner-wri-mathgroup at wolfram.com

The dB measurement, as you are most likely aware, comes from the
logarithm of a ratio. One of the terms in the ratio might be a
standard (20 micro Pascal, or whatever). You could try keeping that
definition in your calculations.

Try using the Notation package.

Maybe something like (pseudo code .. don't forget to use the palette):

Notation[x_ dB <==> dB[x_]]

then, assuming you're not working with equations... just expressions
(again, pseudo code):

FromdBRule=dB[x_]->reference*10^(x/20)

FromdBRule=num_->20 Log[10,num/reference] (*be careful with this rule...*)

Regards,

On 4/30/05, Bill Rowe <readnewsciv at earthlink.net> wrote:
> On 4/29/05 at 3:20 AM, djmp at earthlink.net (David Park) wrote:
> 
> >It is only sloppyness to say that something is x dB. (Maybe I'll
> >hear differently from other responders.) In any case, if you use
> >0.0 dB then the 0.0 will be retained, but if you write exact 0
> >anything Mathematica always returns 0.
> 
> No, it isn't just sloppyness to use dB. For example, it is perfectly logical to talk of an attenuation or gain of say 3 dB which would mean for attenuation half of the input power is lost. Linear amplifiers increase power by a fixed ratio for a given setting and attenuators decrease power by a fixed ratio.
> 
> This is made even more useful by measuring power levels in units like dBm. Here the m tells me the power level is referenced to 1 mW. So, 0 dBm would be 1 mW of power. And with an input of 0 dBm and an amplifer with a gain of 30 dB, I can easily determine the output power is 30 dBm or equivalently 1 Watt.
> --
> To reply via email subtract one hundred and four
> 
> 


-- 
Chris Chiasson
http://chrischiasson.com
Kettering University
Mechanical Engineering
Graduate Student
1 810 265 3161


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