Radio interference control
Carleton F. Maylott · Transactions of the American Institute of Electrical Engineers Part I Communication and Electronics · 1953
RADIO receivers respond to radio transmitters by virtue of antennas which couple them both to free space. As compared with wires, free space is an inefficient coupling medium, and it has erratic efficiency changes. These changes are well known as fading, skip, and sporadic effects, which vary with distance, direction, frequency, and time.