What is the meaning of the term "picket fencing"?

The term "picket fencing" refers to the phenomenon of rapid flutter or variation in the quality of mobile signals, primarily caused by multipath propagation. This occurs when signals reflect off various surfaces such as buildings, trees, or hills, creating multiple paths for the radio waves to reach the receiver. As the receiver moves, it can encounter these reflected signals at different times, leading to changes in the signal strength and quality experienced by the user. This effect can result in a noticeable fluctuation in the audio or data quality of the transmission, giving it a "fluttering" appearance, similar to looking through the slats of a picket fence.

The other choices refer to different concepts within radio communications: alternating transmissions during a net operation relate to how operators share frequency time, ground systems with vertical antennas pertain to antenna performance and grounding techniques, and local vs long-distance communication involves typical differences in signal propagation and frequency use. Understanding these distinctions is crucial for comprehending the complete landscape of radio operations and technology.