Editing Broadcast range (section)

==Practical application==
In reality, [[radio propagation]] changes along with the [[weather]] and [[tropospheric ducting]], and occasionally along with other upper-[[atmospheric]] phenomena like [[sunspot]]s and even [[meteor shower]]s.  Thus, while a [[broadcasting authority]] might fix the range to an area with exact [[Boundary (topology)|boundaries]] (defined as a series of [[Euclidean vector|vector]]s), this is rarely if ever true.  When a broadcast reaches well outside of its intended range due to [[anomalous propagation|unusual conditions]], [[DXing]] is possible.

The local terrain can also play a major role in limiting broadcast range.  [[Mountain range]]s block [[FM broadcast]]s, [[AM broadcast]]s, and TV broadcasts, and other signals in the [[VHF]] and especially [[UHF]] ranges, respectively.  This [[terrain shielding]] occurs when the line of sight is blocked by something through which the [[radio wave]]s cannot pass, particularly stone.  At times this may be [[wikt:Moot|moot]] due to weather, such as when the tall [[cumulonimbus]] clouds of a [[squall line]] of [[thunderstorm]]s reflect the signal over the top, like an extremely tall [[radio tower]].  Conversely, heavy rain may [[attenuate]] the range of even local stations.  [[ATSC]] [[digital television]] is affected by wind and trees (even if not surrounding the transmitter or receiver locations), apparently related to its use of [[8VSB]] [[modulation]] instead of [[COFDM]].

[[AM broadcasting]] stations have different issues, due to using the [[mediumwave]] band.  Broadcast range in these stations is determined by [[ground conductivity]], and the proper use and [[Preventive maintenance|maintenance]] of [[grounding radial]]s which act as a [[ground plane]] for the [[mast radiator]]s used.  [[Skywaves]] reflect off the [[ionosphere]] at a much greater distance above [[Earth's surface]] at night.  This in turn causes mediumwave, most [[shortwave]], and even [[longwave]] stations to travel much further at night, which is the side of the Earth where the [[solar wind]] pulls the ionosphere (and [[magnetosphere]]) away from the [[planet]], instead of pushing toward it as on the day side.  Because of this, many AM stations must cut power or go off-air at night, except for the very earliest stations still [[grandfathered]] on [[clear-channel station|clear channel]]s.  [[Border blaster]] stations in northern [[Mexico]] also used this effect, along with very high-[[electrical power|power]] [[transmitter]]s, to extend their nighttime broadcast ranges well over the [[US/Mexico border]] and across most of the United States.

Various [[broadcast relay station]]s can help to extend a station's area by retransmitting them on the same or another [[channel (broadcasting)|channel]].  What is usually called a [[repeater]] in [[amateur radio]] is called a [[broadcast translator]] (different channel) or booster (same channel) in [[American broadcasting]], or the much broader category or [[rebroadcaster]]s in [[Canadian broadcasting]] (which includes more than just the [[low-power broadcasting]] used in the U.S.)  Boosters are used only within the broadcast range of the parent station, and serve the same function locally as regional and national [[single-frequency network]]s do in [[Europe]]. [[Distributed transmission]] has also undergone tests in the U.S., but to preserve stations' [[market share]] in their home [[media market]]s, these will be limited to the broadcast area of a single large station.  [[Satellite radio]], which is designed for use without a dish, also uses ground repeaters in large cities due to the many obstructions their high-rise buildings cause to the many current and potential customers that are concentrated there.