Re: 3 dB bandwidth

Tony Williams wrote:
> In article <pan.2005.06.26.02.55.08.123263@xxxxxxxxxx>,
> keith <krw@xxxxxxxxxx> wrote:
>
>> On Fri, 24 Jun 2005 22:41:12 +0100, Adrian Tuddenham wrote:
>
>>> Decibels are, as you say, dimensionless; but they are
>>> specifically a way of expressing the ratio of two power levels
>>> - only power levels, not voltages or currents or anything else.
>
>> You're as pig-ignorant as Guy! Decibels are a log ratio of
>> *anything*. Crap, what are they teaching engineers these days?
>
> The Decibel is a Unit of Attenuation, defined in
> terms of the ratio of power levels only.> Only the power ratio
> produces legitimate units of dB.

You are mistaken. You are confusing the possible *first* use of the dB
with what it actually means after the fact.

The dB is a totally general term. It simply signifies that a log of a
number was taken. Thats it. End of story.

The db is not even a real unit, that is, it is not a dimension. The term
under the log must be a unitless. You cant take a function of something
with dimensions. e.g.

I=Io.exp(qV/KT)

note, qV/KT is dimensionless.

db's are applied in many fields, the power use is no more than a
historical incidental.

You are trying to claim that, for example, if it is stated that an
amplifier has 25dB gain more than another, that such a statment is
wrong. You will be pretty much alone on that idea.

Kevin Aylward
informationEXTRACT@xxxxxxxxxxxxx
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
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