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What is difference between dB and dBm?

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Question ajoutée par awais hafeez , Hardware Developer , powersoft19
Date de publication: 2013/10/24
Muhammad Jahanzaib
par Muhammad Jahanzaib , Associate Engineer , Pakistan Air Force

When a physical quantity, such as power or intensity, is measured relative to a reference level it is expressed in decibels (dB), which is a logarithmic unit.dB =10 log (P1/P2)

dBm is used to express an absolute value of power and dBm is always relative to1 mW signal.dBm =10 * log (P/1mW)

Ayodele  Hazeley
par Ayodele Hazeley , IT Technician , Phazel Solutions

Decibel (dB) is the ratio of two values whiles dBm is relative to milliwat and the reference for absolute power

Mohammad Bilbeisi
par Mohammad Bilbeisi , Project Director , Modern Technology Company Ltd

dBm is a power unit in the logarithmic scale

dB is a ratio that represents gain or loss

Sulaimon Olubanji Agbabiaka
par Sulaimon Olubanji Agbabiaka , RF/RNO ENGINEER , ERICSSON

dB is used to quantify ratio between two intensity or power values while dBm is used to express an absolute value of power.

Badreddine Ben Mohamed
par Badreddine Ben Mohamed , Stream Lead Manufacturing domain and DMC Expert , Delaware

Le dBm est unité de puissance absolue (0 dBm=1mW), alors que le dB exprime un rapport entre deux puissances : on peut par exemple dire que la puissance d'un amplificateur est de 47dBm (soit 50W), ce qui est une valeur absolue, alors que si l'on parle de son gain qui est de 20 dB par exemple, cela correspond à un rapport entre la puissance d'entrée et la puissance de sortie de 100.

Hasan Syed
par Hasan Syed , Hub Engineer , Azyan Telecom

Decibel (dB) and dB relative to a milliwatt (dBm) represent two different but related concepts. A dB is a shorthand way to express the ratio of two values. As a unit for the strength of a signal, dB expresses the ratio between two power levels. To be exact, dB = 10log (P1/P2).

Fadi Ezzeddin
par Fadi Ezzeddin , Engineering Manager , Syrian radio and TV organization

In general dB =10*log10(X) where X is unitless.

Power in (dB) is a logarithmic ratio of powers

 

PdB=10* log10(P1/P2)

Since dB is a ratio of powers, dBm is defined by forming the ratio of the power you want to express relative to a reference power, which is 1 mW

Formally speaking,

PTdBm=10* log10(PT/1mW)

Rostom El Baz
par Rostom El Baz , ICT-Project Engineer , Alghanim International

power or intensity, is measured relative to a reference level it is expressed in decibels 

dB =10 log (P1/P2)

dBm is used to express an absolute value of power  relative to1 mWdBm =10 * log (P/1mW) this is usual more simple for small quantity

more info 

http://www.differencebetween.net/science/difference-between-db-and-dbm/

 

 

Salman Qamar
par Salman Qamar , Instrumentation Engineer Internee , Fauji Fertilizer Company Limited

As per your question "is dB relative to watts and dBm to miliwatts". dB is used in comparing two powers (supppse P1 and P2, dB =10.log(P1/P2)) and the answer is expressed in "watts" or is in "watts". dB is not relative to watts but dB is meausred in watts 

dBm is relative to1 milliwatt :

dBm =10.log(P1/*P2)

*P2 =1mWfor the equation above P1 is always measured and substituted in milliwatts and P2 is always substituted as1mWdBm is used in comparing powers relative to1 milliwatt

awais hafeez
par awais hafeez , Hardware Developer , powersoft19

is dB is relative to watts and dBm to miliwatts

saira kanwal
par saira kanwal , Hospital Pharmacist , Eshaal Surgical Hospital

in terms of power it is20logp2/p1 and in terms of signal it is10logv2/v1

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