Electrical Engineering/A simple Question
Expert: Dave Nyce - 7/1/2002
QuestionSir ,
I am a 22 boy , an assistant Engineer of Audio Engg... Would you mind answering my simple questions ?
Q : 1 dBm = ? Watt
and what is " dBm , dBu , dBV , dBr , dBg " ?
Please answer me ASAP , THANKS !!!!!!!!
Regards
AnswerWhen the range of measurements is too wide to use a linear scale, a logarithmic scale based on the decibel can be used. The decibel is a ratio between two levels.
When the two levels are powers, the formula is:
gain or loss in dB = 10 log10 P1/P2
When the two levels are voltage or current, the formula is:
gain or loss in dB = 20 log10 V1/V2
So, if a power ratio is 3 dB, that means a power ratio of 2 times.
If a voltage ratio is 6 dB, that means a voltage ratio of 2 times.
Often, one of the values in the ratio is a standard value, the other being compared to it. For dBm, the m stands for 1 milliwatt, so the value is compared to 1 milliwatt. So, 0 dBm is 1 milliwatt.
dBu is relative to .775V, because it is the voltage developed by 1 mW when appled to 600 ohms.
dbV is relative to 1 Volt
dBr (relative) is used to specify various levels in a circuit relative to a specified zero level point.
I don't think I've heard of dBg.
Hope this helps!
Dave