decibels are (very nearly) always power.
?? 100% natural
Antenna question
Jan 21, 2011
49 Replies
Again, wrong. Decibels are useful in all sorts of contexts, which is confusing at times.
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I've never used the dBV is that the log of a voltage ratio?
George H.
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Yes, it's 20log(V/1V). The point being that decibels are *not* only a measure of power (ratio). "dB" is unitless.
Just to clarify: dB is relative _power_ measurement (10logP1/P2). The dB scale can also be use for absolute measurements if you agree on P2. For instance, if P2=1mW, you get dBm=10logP1/1mW. If power is delivered to the same impedances, then dB may relate voltages by dB=20logV1/V2. An absolute voltage measurement is possible if you specify V2, for instance if V2=1uV, you get dBuV. So, dBV is 20logV1/1V, i.e. an absolute measure.
So, on the same impedance, voltage x2 means power x4 .
Pere Pere
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OK, I don't want to get all 'cranky' about it. But you can move the 2 inside the log and write it as,
10log(V^2/1V^2), and that looks a bit like a power. That dBV's are independent of the impedance is kinda weird.George H.
But they're not.
Check this out:
news:647rj6ls8va2aokl52hg4nu649uffmh2k5@4ax.com
"John Fields"
** Fraid they are.** The link is dead.
.... Phil
What you say is true but dB is also used for strictly voltage specifications (either relative or absolute, referenced to an agreed V2) without regard to impedances.
Phil Allison:
If you really have to use OutOfLuck, why don't you install Quotefix?
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