Also known as: signal-to-noise ratio, SNR

Signal-to-noise ratio (SNR) is the gap, in decibels, between a signal’s power and the noise floor.¹ It is the single best predictor of whether a signal will decode.

SNR is how far a signal rises above the noise floor; digital modes need a minimum SNR to decode.

How it works

SNR = signal level − noise-floor level (both in dBm). A signal at −85 dBm over a −105 dBm floor has 20 dB of SNR. Each digital mode has a minimum SNR below which demodulation starts dropping symbols.

Relevance to SDR

Improving SNR — better antenna, placement, correct gain — is usually what moves a marginal signal from un-decodable to clean.

Sources

1. Signal-to-noise ratio — Wikipedia, definition and significance of SNR. ↩

See also

• Noise floor
• Decibel (dB)
• dBm
• Demodulation

Learn it step by step

• Decibels & signal power