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Difference between dBm and dB ?

+3 votes
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Difference between dBm and dB ?
posted Apr 6, 2014 by Neeraj Mishra

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1 Answer

+2 votes

dBm and dB both are used to measure power level.
dBm is used to measure power with reference of 1 milliwatt. I mean to say power level is calculated using following formula:

dBm = 10 * log (P2/1milliwatt).

Whereas decibel is used for ratio of two power level using the following formula:
dB = 10 * log (P2/P1).

answer Apr 6, 2014 by Vimal Kumar Mishra
Some comments -
1. dB is used to quantify ratio between two intensity or power values while dBm is used to express an absolute value of power.
2. dB is a dimensionless unit while dBm is an absolute unit.
3. dB is relative often relative to the power of the input signal while dBm is always relative to 1 mW signal.
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