Also known as: multipath, multipath propagation

Multipath propagation occurs when a signal reaches the receiver by several paths at once — directly and via reflections off buildings, terrain, and vehicles.¹ The copies arrive slightly out of step and add or cancel.

Multipath: copies arrive by direct and reflected paths and interfere, causing fading and decode errors.

How it works

The interference makes signal strength fade and smears digital symbols into one another (intersymbol interference), degrading decoding. Moving the antenna a short distance can change multipath markedly.

Relevance to SDR

Multipath is a common reason a strong signal still won’t decode; an equalizer and good clock recovery help combat it.

Sources

1. Multipath propagation — Wikipedia, on multiple-path arrival, fading, and intersymbol interference. ↩

See also

• Radio propagation
• CMA equalizer
• Clock recovery
• Radio horizon

Learn it step by step

• How signals travel