Question

What exactly is a dBm and how would you measure it?

Asked by: Steve Drake

 Answer

It is often convenient to express power or voltage ratios, (or any ratio for that matter), using a logarithmic scale. For example the definition of a power ratio in terms of decibels is:

Power ratio in dB = 10*Log(P2/P1)

for example if the output power of a device is found to be half of the input power then we could express this as -3dB (plug in some numbers to see this).

Now to answer your question concerning dBm. We use dBm to express absolute values of power relative to a milliwatt. The definition is

Measure of power in dBm = 10*Log(power in milliwatts / 1 milliwatt)

So if you wanted to express your power in terms of dBm instead of milliwatts you would use the above equation.

For example if your power level were 1 milliwatt, you could also call this power level 0 dBm. Or if your power level were 100 milliwatts you could instead say 20 dBm.

Answered by: Bryan Benson, B.S., Physics Grad Student, CSUF

Search

Loading



Sponsors

USC University of Southern California Dornsife College Physics and Astronomy Department McMaster University Physics and Astronomy Department

Science Quote

'A scientist is happy, not in resting on his attainments but in the steady acquisition of fresh knowledge.'

Max Planck
(1858-1947)

Deal of the Day

Image of Shark Tooth Fossil in Matrix. Click on this image for more info. Shark Tooth Fossil in Matrix
Regular Price: $39.95
Today's Price: $15.00
Superb shark fossil specimen for the science classroom! Buy it now! Deal ends at midnight!

Top Selling

Here are our physics & astronomy bestsellers:
Mini Plasma Ball
Slide Making Kit
Top Secret - Spinning Top
Wood Grain Newtons Cradle
Deluxe 3D Mirascope
Solar Radiometer
Periscope
Solar Science 4M Kit
Ultimate Chemistry Set CHEM C3000
3D Magnetic Field Tube