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decibel and logarithmic scales

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PG1995

Active Member
Hi

Could you please help me with these queries? Thanks.

Regards
PG
 

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Q1
I hesitate to call the decibel a "unit" in the same way that a Volt or a Farad is a "unit".
A decibel is a ratio. It only becomes a unit when given a modifier such as dBm.
dBm is a power relative to 1 milli-watt, so 1 Watt can be expressed as +30dBm.

Which leads on to the concept of larger or smaller.

10dB = 1Bel

So the dB is less than the B.
I think you have blown your own mind on this one!;)

Q2
I cannot see where the 0.5 comes from.
I think that the author has had a moment of confusion, possibly he was thinking about V being the peak voltage as you may measure with an oscilloscope.

JimB
 
hi PG,

Consider the prefix's used for length measurement units.

1metre= 100centi-metres= 1000milli-metres

1Bel =10 deci-Bel

The conventions used are the same throughout most of the engineering values

E

Thanks Jim for the heads up on my typo.:eek:
 
Last edited:
Thank you, Eric.

I do know that what those prefixes mean. But the way that text puts it is not very clear and that was the reason I reached this wrong conclusion which I mentioned in my previous post.

Regards
PG
 
Consider this: 10 pennies equal a dime, but (number of dimes)x10 = number of pennies needed to equal that amount in value.

It is all in how the question is asked.
John
 
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