What is the difference between db and dbm?
dB is used for expressing the ratio between two power values.
dbm is used for expressing an absolute value of power.
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examples:
If P1=1,000,000,000,000 and P2=1 then
P1/P2=1,000,000,000,000 /1
This result looks very long. In short this can be written as : 10 * log(1,000,000,000,000 /1) = 10* 9=90db
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dbm:
dBm denotes absolute power level measured in decibels and referenced to 1 milliwatt (mW).
To convert from absolute power "P" (in watts) to dBm, the formula is dBm = 10*log (P/1 mW).
0dbm = 1 milliwatt
20 dbm=100 milli watt
-20dbm=0.01 milli watt
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