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MathGroup Archive 2005

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Re: something like dB

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56645] Re: something like dB
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Sun, 1 May 2005 00:46:48 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 4/30/05 at 4:56 PM, djmp at earthlink.net (David Park) wrote:

>I know that it is commonly used, but just because something is
>commonly used doesn't mean that it is not sloppy, or that it
>doesn't cause headaches to many people. 

I can't really agree with your statement above. I do agree people often use useful things in a sloppy manner. And I agree sloppyness does cause problems (headaches) for others.

>The original poster claimed dB was a Unit, and it certainly isn't. 

This is clearly debatable. It makes a lot of sense to measure gain and attenuation in dB since gain and attenuation are ratios of input to output. If I tell you the gain of an amplifier is 30 dB, I given you some useful information. But simply telling you either the input power or output power of an amplifier doesn't say much at all.

And from the standpoint of computing losses or gains in a system, dB behaves like any other unit.

>It is a function or mapping.

You could make the same claim of radian.

>You can't get the Units package to convert 30 dBm to Watts because
>dBm isn't a Unit that has a conversion factor to Watts.

Simply because there isn't a linear relationship between dBm and watts doesn't mean a package could not be constructed to do the conversion.

<snip>

>But we need the // and and expression like 30 dBm will never work
>usefully in Mathematica and that's why I say the original notation
>is sloppy.

Even if I agree an expression like 30 dBm cannot be made to work usefully in Mathematica does, it doesn't follow the notation is sloppy. In fact, calling a notation sloppy doesn't make sense. If a notation has well defined meaning and is useful (as is the case with dB), the notation isn't sloppy. But a given usage of the notation might well be sloppy.
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