significannce of 20LOg

[deepa]

20log

Can anyone tell me why we always use 20log(something) to represent a signal in db,why not 30 log() or 5log() .What is so special about this number

 

[Kral]

20 log db

deepa,
The "bel" is the logarithm of a power ratio. Since 1 bel represents a large power ratio (10), the decibel was introduced as a matter of convenience. One bel = 10 decibels, so 10 decibels (10 log(10)) also represents a power ratio. of 1. Gain is often specified as a voltage ratio. Power is proprtional to V^2. 10 log(V^2) = 20 log(V). Remember this from algebra?
Regards,
Kral

 

[mark123]

www.edaboard.com ftopic239264

I use to always think of power dbs as 3 db is twice the power and voltage dbs as 6 db is twice the voltage until a college pointed out that dbs were dbs there. Asking if the db figure is a power or voltage is meaningless
If the voltage increases X2 ie 6 db the associated power into a constant load goes up by 2 squared
so twice the voltage is 6 db which gives 2 X 2 times the power - 3 + 3 = 6 hence 6 db is twice the voltage that exuates to 4 times the power - which is a power increase of 6 db

I hope this is clear - it was when I initially understood it !