Free Space Propagation
In free space, all electromagnetic waves (radio, light, X-rays, etc.) obey the inverse-square law which states that the power density of an electromagnetic wave is proportional to the inverse of the square of the distance from a point source or:
Doubling the distance from a transmitter means that the power density of the radiated wave at that new location is reduced to one-quarter of its previous value.
The power density per surface unit is proportional to the product of the electric and magnetic field strengths. Thus, doubling the propagation path distance from the transmitter reduces each of their received field strengths over a free-space path by one-half.
Read more about this topic: Radio Propagation
Famous quotes containing the words free space, free and/or space:
“In New York—whose subway trains in particular have been “tattooed” with a brio and an energy to put our own rude practitioners to shame—not an inch of free space is spared except that of advertisements.... Even the most chronically dispossessed appear prepared to endorse the legitimacy of the “haves.””
—Gilbert Adair, British author, critic. “Cleaning and Cleansing,” Myths and Memories (1986)
“A country where every citizen is free to suppress liberty.”
—George Bernard Shaw (1856–1950)
“Even the most subjected person has moments of rage and resentment so intense that they respond, they act against. There is an inner uprising that leads to rebellion, however short- lived. It may be only momentary but it takes place. That space within oneself where resistance is possible remains.”
—bell hooks (b. c. 1955)