Explain the concept of fading and multipath in radio signals, and how diversity improves reception.

• A. Fading causes signal strength variations due to interference of multiple paths; diversity reduces deep fades by combining signals.
• B. Fading only occurs in urban areas and is unaffected by multipath.
• C. Diversity reduces signal-to-noise ratio.
• D. Multipath always improves signal.

Answer: (A)

Fading is the way a radio signal strength changes because the signal travels along several different paths and those multiple copies combine with each other. Each path can have a different length, reflect off objects, or scatter, so the signals arrive at the receiver with different amplitudes, delays, and phases. As the relative phases of these paths shift—due to movement, changing environment, or frequency—their sum can be higher (constructive interference) or lower (destructive interference). This changing sum is fading, and it can cause the signal to dip toward the noise floor at certain times or locations.

Multipath is the existence of those multiple propagation paths. It’s the reason fading happens: instead of a single clean path, the receiver gets several copies of the signal that can either reinforce or cancel each other.

Diversity helps reception by providing multiple independently faded versions of the signal that can be combined to improve reliability. For example, using multiple antennas spaced apart, or different frequencies or polarizations, makes it unlikely that all copies fade at the same moment. When one path is in a deep fade, another is likely not, so combining the signals increases the overall received power and the signal-to-noise ratio. In short, diversity reduces the impact of deep fades and makes the link more robust.

The other statements aren’t correct because fading isn’t limited to urban areas, and multipath doesn’t inherently improve the signal—its effects depend on how the paths interfere. Diversity does not reduce the signal-to-noise ratio; it is used to improve it.