In a long-distance RF link, what statement about Fade Margin is true?

Fade Margin is an additional pad of signal strength designed into the RF system to compensate for unpredictable signal fading.

The Fade Margin of a long-distance radio link should be equivalent to the receiver’s antenna gain.

A Fade Margin is unnecessary on a long-distance RF link if more than 80% of the first Fresnel zone is clear of obstructions.

The Fade Margin is a measurement of signal loss through free space, and is a function of frequency and distance.