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 and/or space:
“But that I love the gentle Desdemona,
I would not my unhousèd free condition
Put into circumscription and confine
For the sea’s worth.”
—William Shakespeare (1564–1616)
“Let the space under the first storey be dark, let the water
lap the stone posts, and vivid green slime glimmer
upon them; let a boat be kept there.”
—Denise Levertov (b. 1923)