# dBm vs dBc – What’s the Difference?

dBm and dBc are both units of measurement used in the field of electrical and RF (radio frequency) engineering to express signal levels, but they have different meanings and applications.

dBm measures the absolute power level of a signal with reference to one milliwatt, while dBc measures the relative strength of a signal component (e.g., harmonics, spurious emissions) with respect to the carrier signal.

## What is dBm?

dBm (Decibels relative to one milliwatt):

• dBm is a unit used to measure power levels in a signal, particularly in terms of absolute power. It quantifies the ratio of a power level to one milliwatt (1 mW) on a logarithmic scale.
• The formula for calculating dBm is: PdBm = 10*log10(PmW) where PmW is the power in milliwatts.

Convert Watt to dBm

• dBm is commonly used to represent the absolute power level of a signal, such as the output power of a transmitter, the received power at an antenna, or the power dissipated by a component.
• Examples of dBm values include +30 dBm (1 Watt), 0 dBm (1 mW), -10 dBm (0.1 mW), and so on.

## What is dBc?

dBc (Decibels relative to the carrier):

• dBc is a unit used to express the relative level of a signal component (e.g., a harmonic, spurious emission, or sideband) with respect to the carrier signal’s power level.
• The formula for calculating dBc is: dBc = 10 * Log10(Ps / Pc), where Ps is the power of the signal component, and Pc is the power of the carrier signal.

Calculate dBc from dBm

• dBc is often used in frequency domain analysis and spectral measurements to quantify the strength of unwanted or interfering components relative to the main carrier signal.
• A positive dBc value indicates that the signal component is stronger than the carrier, while a negative dBc value indicates that the signal component is weaker than the carrier.

## Summary

dBm measures the absolute power level of a signal with reference to one milliwatt, while dBc measures the relative strength of a signal component (e.g., harmonics, spurious emissions) with respect to the carrier signal.

Both units are essential in RF engineering for characterizing and analyzing signals and ensuring proper performance and compliance with specifications.