Also known as: path loss

Path loss is the attenuation a signal experiences travelling from transmitter to receiver.¹ It is dominated by the spreading of energy over distance, plus losses from terrain, buildings, and foliage.

Path loss grows with distance (and frequency); it can exceed 100 dB over a few kilometres.

How it works

In free space, power falls with the square of distance, and loss rises with frequency; real environments add much more. Path loss can total 100+ dB over a few kilometres, which is why link budgets are done in decibels.

Relevance to SDR

Path loss explains why a distant or obstructed system arrives near the noise floor, and why antenna height and a clear path (propagation) matter so much.

Sources

1. Path loss — Wikipedia, for the definition and distance/frequency dependence of propagation loss. ↩

See also

• Attenuation
• Radio propagation
• Decibel (dB)
• Signal-to-noise ratio (SNR)

Learn it step by step

• How signals travel
• Decibels & signal power