hi dear all
can you plz tell me what is difference between db and dbm.
what is the relationship between both and how difference also.

 

Try the Wikipedia article - http://en.wikipedia.org/wiki/Decibel.

 

Hello,

A lot of information on decibels can be found here:
http://www.educypedia.be/electronics/decibels.htm

Greetings,
Bertus

 

DB is a dimensionless value, just a ratio between two values, where as DBM is a ratio of a value referenced to 1 milliwatt. At least that's how I recall the difference.

Lefty

 

DB is a dimensionless value, just a ratio between two values, where as DBM is a ratio of a value referenced to 1 milliwatt. At least that's how I recall the difference.

Lefty

That is correct.

Eric

 

+3DBs doubles the power -3DBs cuts it in half. +10 DBs its a 100 fold increase, -10DBs is 1/100th the signal strength.

 

sorry, i meant a 10DB change is equal to 10 times not 100

 

DB is a dimensionless value, just a ratio between two values, where as DBM is a ratio of a value referenced to 1 milliwatt. At least that's how I recall the difference.

Lefty

Roger that.
The origin of the Decibel is interesting unto itself because it was based on how the human ear perceives changes in audio amplitude. A.G.B determined that our ears are not linear. I've often wondered how many human test subjects A.G.B used for his experiments.

 

... what is difference between db and dbm.

dB on its own means that the figure which precedes it is so much greater than some other, unstated, figure. It is therefore a (logarithmic) multiplier, but without knowing the unstated figure there is no way of knowing just how large either of them is.

e.g. 3dB means a power which is twice as large as another one, or, another way of saying the same thing, a voltage which is 1.41 times as large as another one. In neither case we can't deduce the actual value of the smaller or larger voltage or power.

dBm means that the figure which precedes it is so much greater than 1mW.
e.g. 6dBm means a power which is 4 times greater than 1mW, or 4mW.

 

dB on its own means that the figure which precedes it is so much greater than some other, unstated, figure. It is therefore a (logarithmic) multiplier, but without knowing the unstated figure there is no way of knowing just how large either of them is.

e.g. 3dB means a power which is twice as large as another one, or, another way of saying the same thing, a voltage which is 1.41 times as large as another one. In neither case we can't deduce the actual value of the smaller or larger voltage or power.

dBm means that the figure which precedes it is so much greater than 1mW.
e.g. 6dBm means a power which is 4 times greater than 1mW, or 4mW.

LeftyRetro (Post4) gave the correct and textbook answer.

 

LeftyRetro (Post4) gave the correct and textbook answer.

Yes, I noticed that too - except that textbooks usually get the conventions right. dB, not DB, and dBm not DBM.

And by the way, it's decibel, not Decibel.

 

Yes, I noticed that too - except that textbooks usually get the conventions right. dB, not DB, and dBm not DBM.

And by the way, it's decibel, not Decibel.

Since we're going to get anal over this I might as well point out that the decibel translates to 1/10th of a Bel but I've never seen a Bel.
Oops, I capitalized again! I guess I just like those caps.