Broadcast range

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A broadcast range (also listening range or listening area for

receivers to decode it. However, this also depends on interference
from other stations.

The "primary service area" is the area served by a station's strongest signal. The "city-grade contour" is 70 dBμ (

non-commercial educational and low-power
stations.

The legally protected range of a station extends beyond this range, out to the point where signal strength is expected to be 1mV/m for most stations in North America, though for class B1 stations it is 0.7mV/m, and as low as 0.5mV/m for full class B stations (the maximum allowed in densely populated areas of both Canada and the U.S.).

Practical application

In reality,

atmospheric phenomena like sunspots and even meteor showers. Thus, while a broadcasting authority might fix the range to an area with exact boundaries (defined as a series of vectors), this is rarely if ever true. When a broadcast reaches well outside of its intended range due to unusual conditions, DXing
is possible.

The local terrain can also play a major role in limiting broadcast range.

COFDM
.

US/Mexico border
and across most of the United States.

Various

Distributed transmission has also undergone tests in the U.S., but to preserve stations' market share in their home media markets, 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.

Edge-of-range issues

Those at the edge of a station's broadcast range will typically notice

digital signal clear until it hits the cliff effect and suddenly disappears completely. FM stations may flip back and forth (sometimes annoyingly rapidly when moving) due to the capture effect, while AM
stations (including TV video) may overlay or fade with each other.

manufacturer's product design
, manually disabling this when at the edge of the broadcast range prevents the annoying noisy-stereo/quiet-mono switching.

The same is true of

analog TV stereo and second audio programs, and even for color TV, all of which use subcarriers. Radio reading services
and other subcarrier services will also tend to suffer from dropouts sooner than the main station.

Technologies are available that allow for switching to a different signal carrying the same radio program when leaving the broadcast range of a station.

broadcast engineer
has synchronized the two.

Digital versus analog

Digital transmissions require less power to be received clearly than analog ones. The exact figure for various modes depends on how robust the signal is made to begin with, such as modulation,

definition
signal, in exchange for an increase in the usable range of the lower-definition part of the video.

Digital stations in North America usually are operated by the same groups as the analog side, and thus operate their own independent facilities. Because of this, the FCC requires U.S. TV stations to replicate their analog coverage with their digital signal as well. However, ATSC digital TV only requires about one-fifth the amount of power to reach the same area on the same channel as analog does. For HD Radio, the figure is only one percent of the station's analog

sensitivity and/or selectivity
.

References

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