Also known as: dBm

dBm is power expressed in decibels relative to one milliwatt, making it an absolute measure of signal strength rather than a mere ratio.¹ 0 dBm equals 1 mW; +30 dBm is 1 watt.

dBm is absolute power referenced to 1 mW. Received signals are negative; closer to zero is stronger.

How it works

Because received radio signals are tiny fractions of a milliwatt, they are negative dBm values — and the one closer to zero is stronger (−70 dBm beats −90 dBm by 100×).

Relevance to SDR

Receiver meters report signal and noise-floor levels in dBm; their difference is the SNR that determines whether a signal decodes.

Sources

1. dBm — Wikipedia, power referenced to one milliwatt. ↩

See also

• Decibel (dB)
• dBFS
• Noise floor
• Signal-to-noise ratio (SNR)

Learn it step by step

• Decibels & signal power