Checking dB and dBm Calculations by Hand

Question I started with

I write the reference and unit first to avoid mixing a dB ratio with absolute dBm power.

Checking dB and dBm Calculations by Hand — concept flow — I redrew the relationships before returning to the equations.

Connecting the concepts

dB is a ratio; dBm is a power level referenced to 1 mW. Adding gains and losses in dB to an input dBm gives an output level, while available power and compression remain separate checks.

dB
dBm
mW
gain
loss

Equations and assumptions

I write the reference impedance, units, and linear-versus-decibel domain before substituting numbers.

P_dBm = 10 log10(P_mW)P_mW = 10^(P_dBm / 10)

Worked example

−10 dBm is 0.1 mW, 20 dBm is 100 mW, and 30 dBm is 1 W. A 10 dBm signal through 2 dB loss and 12 dB gain becomes 20 dBm under a linear assumption.

Checking dB and dBm Calculations by Hand — calculation relationship — This is my explanatory redraw, not an imported RFDH figure or a measurement result.

Connecting it to my coursework and projects

A −3 dB S-parameter split is not an absolute output power; input power and the reference conditions are needed before converting to watts or dBm.

High-frequency engineering course hub

What I will check next

I do not use 10 log for voltage ratios or 20 log for power ratios, and I do not equate voltage and power dB without the equal-impedance condition.

Pages I read

Official references I checked

Analog Devices: Understand Wireless Data Sheet Specifications, Part 1