Re: 3 dB bandwidth

In article <11boa5cre5q1e7f@xxxxxxxxxxxxxxxxxx>, Guy Macon
<http://www.guymacon.com/> says...
>
>
>
> Keith Williams wrote:
>
> >>> That forms a potential divider with a value of 0.5.
> >>
> >> The 0.5 appears to be correct, but the -6dB he pulled out of his arse.
> >
> >Appears to be? Do you have a problem with *voltage* dividers?
>
> Given the repeated basic errors that the poster in question has made,
> I was not sure whether he meant voltage when he wrote "potential"
> Thus my usage of "appears to be." One can't be too careful when dealing
> with the ineducable; sometimes they appear to make sense when actually
> they are simply lacking the vocabulary to express their ignorance.

What does "impedance matching" or "maximum power transfer" mean to you?
Hint: It's a R/R+R voltage divider.
>
> >Do you have a problem calculating 20log(.5)?
>
> Nope. Do *you* have a problem calculating 10log(.5)?

Well, a *voltage* divider divides, um, voltage. Thus 20log(.5) or 6dB.

> Do you have a problem with the established fact that decibels are,
> by definition, a ratio of *power* levels?

....and an R/R+R voltage divider does what to the power level. Another
hint: It drops it by 6db. P=V^2/r sorta thing, dontcha know.

> "bel (B): A unit of measure of ratios of power levels, i.e., relative
> power levels. Note 1: The number of bels for a given ratio of power
> levels is calculated by taking the logarithm, to the base 10, of
> the ratio. Mathematically, the number of bels is calculated as
> B = log10(P 1/P 2) where P 1 and P 2 are power levels. Note 2: The
> dB, equal to 0.1 B, is a more commonly used unit."
> Source: http://www.atis.org/tg2k/_bel.html

Wow, you know how to use Google. Now try learning something about
electronics.

> >> If he had bothered to read the references I provided, or even done a
> >> basic web search, he would have found out that half the voltage equals
> >> -6dB but half the power equals -3dB. Alas, he is ineducable and thinks
> >> that aserting "0.5 equals -6dB" over and over again does not change the
> >> reality of 0.5 equaling -3dB when measuring power.
> >
> >Umm, isn't 1/2 voltage = 1/4 power? ...thus 6bB, either way (funny how
> >the arithmetic works out).
>
> If you had bothered to read the references I provided, or even done a
> basic web search, you would have found out that half the voltage equals
> -6dB but half the power equals -3dB.

Man you are dense. If you drop the voltage to half, the power is
quartered; 6db. The arithmetic works again.

> Do A Google web search on [ decibels dB power -3db half voltage -6db ]
> ( http://www.google.com/search?&q=decibels+dB+power+-3db+half+voltage+-6db ).
>
> Key quotes from the first ten pages returned by the above search:

You are amazing!

> "The -3 dB point is often referred to as a "half-power point"

That's well known in these parts. Now what happens to the power when
the voltage is halved (we are talking about a R/R+R voltage divider
here). Is it really your position that it is cut in half?

<snipped obvious C&P stuff from Google and just as obviously not
understood by GM>

> Half the voltage equals -6dB. Half the power equals -3dB.
> Double the voltage equals +6dB. Double the power equals +3dB.
> Anyone who disagrees with this basic fact after having the
> references proving it provided to him is willfully ignorant.

Let me try translating into idioteese; YOU DON'T HAVE HALF THE POWER.
YOU HAVE ONE QUARTER THE POWER. ONE QUARTER POWER = 6dB, AND AGAIN,
THE MATH WORKS).

Amazing. Simply amazing.

--
Keith
.

Relevant Pages

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