What is the relation between dB AND dBm

HELLO,ALL

WHAT IS THE RELATION BETWEEN dB AND dBm,GIVE THE RELATION EQUATION.


THANKYOU,ALL.

I don't think such a formula exists ..

Read this:
http://www.isa.org/Content/ContentGr...dB_vs__dBm.htm

Regards,
IanP

0dB=30dBm
Power in dB=10log(power in watt)
Power in dBm=10log(Power in milliwatt).

Dear friend,
dB has no units ..
I think you should read that stuff too ..

Regards,
IanP

BTW:
30dBm = 0dBW

Hi...

I agree with IanP. dB is dimensionless. The different is that dB is 10 log(value/value) and dBm is 10 log (value/1miliwatt). I think it's clear enough.

CMIIW

yes friends dB has no unit.
Sorry I've expressed in wrong manner.

But 0dBW=30dBm not 1dBW=30dBm

you're all right. dbm is used as reference,

Of course it is ..
:D

XdBm = XdBW + 30

you just add 30 :)

......

x = 10log10(P)

P = 10(x / 10)

where P is the power and x is the dBm

dBm is just the power referenced to one milliwatt (mW)

thanks to all

IF U SUBTRACT DBM WITH DBM the answer is in DB.

DBM does not exist.....it is dBm....also
it is not DBm nore dbm nore dbM....

it is dBm

Hello All,



dB or not dB?
Everything you ever wanted to know
about decibels but were afraid to ask?

True or false: 30 dBm + 30 dBm = 60 dBm? Why does 1% work out to be -40 dB one time but
then 0.1 dB or 0.05 dB the next time? These questions sometimes leave even experienced
engineers scratching their heads. Decibels are found everywhere, including power levels,
voltages, reflection coefficients, noise figures, field strengths and more.
What is a decibel and how should we use it in our calculations?
A. Winter
Rohde & Schwarz

This Application Note is intended as a refresher on the subject of decibels.

http://www.techonline.com/learning/techpaper/202802480

I hope this helps...


---manju---

dBm= 10log10(P/1mW)
dB= 10log10(p/1W)

hello friends,
this attachment might be useful for you.

thanks
vivek

Mod Aya2002: Attachement deleted because it is already on the net. Next time use the link only
link is: http://www.google.com/url?sa=t&sourc...ZDfsww&cad=rja

First of all there are a series of mistakes in the various posts above so be careful with all of the comments (this one too).

dB is a relative measurement and dBm is a specific value referenced to milliwatts so therre is no equation to relate the two terms. One often sees a variety of letters after dB indication various reference values.

Again, beware of the comments in this thread. Much of it is in error and will just add to the confusion.

I agree with Azulykit; this thread is full of errors.

The dB is unitless, like saying some thing is twice (or 2x) as large as something else. Absolute numbers in logarithmic format are expressed as dB[x], where [x] is an abbreviation for the reference. For instance, dBm is a power level referenced to 1 mW. Mathmatically, 10*log10(P/1mW).

Threre's a great reference on the decibel, dB, dBm, etc. on this site:
http://www.bitweenie.com/listings/the-decibel/

That link also mentions when to use 20*log10 or 10*log10, which is a source of confusion sometimes.

in simple words

dB value can be taken as signal to noise ratio (Better the signal as compared to noise, more the dB value)
and
dBm is power output. (actual power output in miliwatt or watts is known if dBm is known)

dB is a particularly useful unit and one of the best ways to use it is to confound your peers. The above thread is a perfect example. It continues for years ......

This book has a chapter devoted to the subject if any of you re serious about really understanding the subject:

Introduction to Airborne Radar (Aerospace & Radar Systems) [George W. Stimson]



Stimson does a fine job of taking all the confusion and some of the fun out of the subject.

Azulykit