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# DB to DBm conversion

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Posts misa
Guest

hi all

how can to convert from DB to DBm
is the formula that DBm=DB+30
and DB=DBm-30 pix
Guest

misa,

no, that is very very wrong.
dB cannot be converted in dBm ! those are not counting the same thing.

dBm is an absolute power. It can be converted in Watts.
2W = 33dBm

dB is a difference of dBm, and it has no physical existence other than this. It is a mathematical tool.

For example, from 39dBm to 42dBm, there is a difference of +3 dB.
You cannot convert 3dB to watts. But you can convert dBm into watts.
39dBm = 8W
42dBm = 16W

but 3dB is not equal to 8W !!!

Regards
pix misa
Guest

thanks pix for explanation , what is the mathematic formula to convert from DBm to Watt and vice versa pix
Guest

misa,

pix Somaliland
Guest

x = 10 log_{10}(1000P)
where P is the power in W and x is the power ratio in dBm lakhindar murmu
Guest

hi all
can anybody help me how to visualize group delay response of a microstrip filter in IE3D software? Dhananchezhiya Parasuram
Guest

I am using Selective Level Meter(SLM) to measure power line carrier communication gain in this meter its showing only the unit of dBm but I need to measure inform of dB Its there any formula to convert dBm to dB, any one can explain details please. pix
Guest

hi,

dB is not a “measurement” unit, it is a “comparison” unit. Your “dBm” measurement can be converted into mW, W or whatever power unit you want.

1dB does not mean anything by itself. You can only use “dB” to compare two values. For example: value A is 1dB higher than value B, whatever the values A and B.

If someone asks you to provide a measurement in “dB”, it means they made a common mistake. They actually want “dBm”.

Cheers
pix paraHO
Guest

As Pix has already stated, but put more simply:

dBm = an “absolute” measurement of power

dB = is a “relative” measurement often used to illustrate a value between e.g. two absolute measurements e.g.

87dbm\
……\
…….> = 3dB relative/difference
……/
85dBm/ Optimustron
Guest

When you are using a Selective Level Meter your are making measurements in a physical circuit, right?, then all the time you are measuring dBm, as the previous answers dB is a relative measure used frequently because you can’t have power directly from that measurements and is more easy to get dB, but in circuits you have power in all parts, then for example to obtain dBs you only need to set a reference.
For example you measure the input to an specific circuit then you measure the output in both cases you get dBm but you need to say about the gain or loss of your circuit then you make the simple math:
dB= dBm at output – dBm at input
From that specific equation if you have a positive dB then you surely have an amplifier and if you have negative dB you have a loss like a network of resistors, if you do the subtraction in opposite way then the signs and interpretations change. I hope this can help you, best regards, soe min aung
Guest

How to calculate Microwave linkbuget for a hop? charlie
Guest

30dbm to db pix
Guest

hi, you cannot convert db to dbm, those are not the same kind of unit at all (like converting WATT to KILOGRAM) ali
Guest

Perform the following conversions plz:
i). -15dB to dBm
ii). -25dBm to mW.
iii). 1W to dB
iv). 1W to dBm. Bhavi
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