What can cause multipath interference in radio communications?

Multipath interference in radio communications is primarily caused by reflections of the radio signal off various surfaces such as buildings, mountains, or other structures. When a radio signal is transmitted, it can reach the receiving antenna via multiple paths due to these reflections. This phenomenon creates multiple versions of the same signal arriving at slightly different times, which can lead to constructive or destructive interference. The result is variations in signal strength and quality, often causing distortion or fading of the received signal.

Static electricity does not contribute directly to multipath interference; instead, it primarily affects the signal integrity by introducing noise. Excessive modulation depth can lead to distortion in the transmitted audio or information but does not cause multipath. Lastly, improper antenna alignment can lead to poor signal reception but is not a direct cause of the multipath effect itself. Therefore, the correct answer focuses on the actual mechanism that leads to the undesired interference in radio communication.