Primary service area
Encyclopedia
A broadcast range is the service area that a broadcast station
or other transmission covers via radio wave
s (or possibly infrared
light
, which is closely related). It is generally the area in which a station's signal strength
is sufficient for most receiver
s to decode it, however this also depends on interference
from other stations.
s relative to one microvolt per meter of signal strength) or 3.16mV/m (millivolts per meter) for FM stations in the United States
, according to Federal Communications Commission
(FCC) regulations. This is also significant in broadcast law
, in that a station must cover its city of license
within this area, except for 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-populate
d areas of both Canada
and the U.S.).
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 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. Mountain range
s block FM broadcasts, AM broadcasts, 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 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 maintenance
of grounding radials which act as a ground plane
for the mast radiator
s used. skywave
reflects 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 channels. Border blaster
stations in northern Mexico
also used this effect, along with very high-power transmitter
s, to extend their nighttine 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
. 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 rebroadcasters 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.
in an analog
broadcast, while error correction will keep a 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.
FM stereo will tend to get static more quickly than the monophonic
sound due to its use of subcarrier
s, so stations may choose to extend the usable part of their range by disabling the stereo generator. Listeners can also choose to disable stereo decoding on the receiver, though loss of the stereo pilot tone causes this to happen automatically. Because this tends to turn on and off when at the threshold of reception, and the threshold is often set too low by the 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 program
s, and even for color TV, all of which use subcarriers. Radio reading service
s 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. Radio Data System
allows for switching to a different FM or station with the same identifier
, or even to (but not necessarily from) an AM station. Satellite radio also is designed to switch seamlessly between repeaters and/or satellite when moving outside the range of one or the other. HD Radio
switches back to the analog signal as a fallback when the edge of the digital range is encountered, but the success of this from the listener's perspective depends on how well the station's broadcast engineer has synchronized the two.
, and forward error correction
. In each of these three factors, the caveat
is that a higher data signaling rate
means a tradeoff with reduced broadcast range. The hierarchical modulation
used on DVB is a unique case, which reduces the range of the full-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 watt
age, in part because it is an in-band on-channel
method, which uses sideband
s that must prevent interference to adjacent channel
s, especially for older or cheaper receivers which have insufficient sensitivity and/or selectivity.
Broadcasting
Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
or other transmission covers via radio wave
Radio Wave
Radio Wave may refer to:*Radio frequency*Radio Wave 96.5, a radio station in Blackpool, UK...
s (or possibly infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
, which is closely related). It is generally the area in which a station's signal strength
Signal strength
In telecommunications, particularly in radio, signal strength refers to the magnitude of the electric field at a reference point that is a significant distance from the transmitting antenna. It may also be referred to as received signal level or field strength. Typically, it is expressed in...
is sufficient for most receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
s to decode it, however this also depends on interference
Electromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
from other stations.
Legal definitions
The "primary service area" is the area served by a station's strongest signal. The "city-grade contour" is 70 dBµ (decibelDecibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
s relative to one microvolt per meter of signal strength) or 3.16mV/m (millivolts per meter) for FM stations in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, according to Federal Communications Commission
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
(FCC) regulations. This is also significant in broadcast law
Broadcast law
Broadcast law is the field of law which pertains to broadcasting. These laws and regulations pertain to radio stations and TV stations, and are also considered to include closely related services like cable TV and cable radio, as well as satellite TV and satellite radio...
, in that a station must cover its city of license
City of license
A city of license or community of license, in American and Canadian broadcasting, is the community that a radio station or television station is officially licensed to serve by that country's broadcast regulator....
within this area, except for non-commercial educational
Non-commercial educational
The term non-commercial educational applies to a radio station or TV station that does not accept on air advertisements , as defined in the United States by the Federal Communications Commission . NCE stations do not pay broadcast license fees for their non-profit uses of the radio spectrum...
and low-power
Low-power broadcasting
Low-power broadcasting is electronic broadcasting at very low power and low cost, to a small community area.The terms "low-power broadcasting" and "micropower broadcasting" should not be used interchangeably, because the markets are not the same...
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
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, 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-populate
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
d areas of both Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
and the U.S.).
Practical application
In reality, radio propagationRadio propagation
Radio propagation is the behavior of radio waves when they are transmitted, or propagated from one point on the Earth to another, or into various parts of the atmosphere...
changes along with the weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
and tropospheric ducting, and occasionally along with other upper-atmospheric phenomena like sunspot
Sunspot
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....
s and even meteor shower
Meteor shower
A meteor shower is a celestial event in which a number of meteors are observed to radiate from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller...
s. Thus, while a broadcasting authority might fix the range to an area with exact boundaries
Boundary (topology)
In topology and mathematics in general, the boundary of a subset S of a topological space X is the set of points which can be approached both from S and from the outside of S. More precisely, it is the set of points in the closure of S, not belonging to the interior of S. An element of the boundary...
(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
Anomalous propagation
Anomalous propagation includes different forms of electromagnetic wave propagation that are not encountered in a standard atmosphere. While technically the term includes propagation with larger losses than in standard atmosphere, in practical applications it is most often meant to refer to cases...
, DXing
DXing
DXing is the hobby of tuning in and identifying distant radio or television signals, or making two way radio contact with distant stations in amateur radio, citizens' band radio or other two way radio communications. Many DXers also attempt to receive written verifications of reception from the...
is possible.
The local terrain can also play a major role in limiting broadcast range. Mountain range
Mountain range
A mountain range is a single, large mass consisting of a succession of mountains or narrowly spaced mountain ridges, with or without peaks, closely related in position, direction, formation, and age; a component part of a mountain system or of a mountain chain...
s block FM broadcasts, AM broadcasts, 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
Radio Wave
Radio Wave may refer to:*Radio frequency*Radio Wave 96.5, a radio station in Blackpool, UK...
s cannot pass, particularly stone. At times this may be moot due to weather, such as when the tall cumulonimbus clouds of a squall line
Squall line
A squall line is a line of severe thunderstorms that can form along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front. It contains heavy precipitation, hail, frequent lightning, strong straight-line winds, and possibly tornadoes and waterspouts....
of thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
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
ATSC
ATSC standards are a set of standards developed by the Advanced Television Systems Committee for digital television transmission over terrestrial, cable, and satellite networks....
digital television
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
is affected by wind and trees (even if not surrounding the transmitter or receiver locations), apparently related to its use of 8VSB
8VSB
8VSB is the modulation method used for broadcast in the ATSC digital television standard. ATSC and 8VSB modulation is used primarily in North America; in contrast, the DVB-T standard uses COFDM....
modulation
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
instead of COFDM.
AM broadcasting
AM broadcasting
AM broadcasting is the process of radio broadcasting using amplitude modulation. AM was the first method of impressing sound on a radio signal and is still widely used today. Commercial and public AM broadcasting is carried out in the medium wave band world wide, and on long wave and short wave...
stations have different issues, due to using the mediumwave
Mediumwave
Medium wave is the part of the medium frequency radio band used mainly for AM radio broadcasting. For Europe the MW band ranges from 526.5 kHz to 1606.5 kHz...
band. Broadcast range in these stations is determined by ground conductivity
Ground conductivity
Ground conductivity refers to the electrical conductivity of the subsurface of the earth.-Radio propagation:Ground conductivity is an extremely important factor in determining the field strength and propagation of surface wave radio transmissions...
, and the proper use and maintenance
Preventive maintenance
Preventive maintenance has the following meanings:#The care and servicing by personnel for the purpose of maintaining equipment and facilities in satisfactory operating condition by providing for systematic inspection, detection, and correction of incipient failures either before they occur or...
of grounding radials which act as a ground plane
Ground plane
In electrical engineering, a ground plane is an electrically conductive surface.-Radio antenna theory :In telecommunication, a ground plane structure or relationship exists between the antenna and another object, where the only structure of the object is a structure which permits the antenna to...
for the mast radiator
Mast radiator
A mast radiator is a radio mast or tower in which the whole structure itself functions as an antenna. This design is commonly used for transmitting antennas operating at low frequencies, in the VLF, LF and MF ranges, in particular those used for AM broadcasting. The metal mast is electrically...
s used. skywave
Skywave
Skywave is the propagation of electromagnetic waves bent back to the Earth's surface by the ionosphere. As a result of skywave propagation, a broadcast signal from a distant AM broadcasting station at night, or from a shortwave radio station can sometimes be heard as clearly as local...
reflects off the ionosphere
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
at a much greater distance above Earth's surface at night. This in turn causes mediumwave, most shortwave
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
, and even longwave
Longwave
In radio, longwave refers to parts of radio spectrum with relatively long wavelengths. The term is a historic one dating from the early 20th century, when the radio spectrum was considered to consist of long, medium and short wavelengths...
stations to travel much further at night, which is the side of the Earth where the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
pulls the ionosphere (and magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
) away from the planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
, 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 channels. Border blaster
Border blaster
A border blaster is a licensed commercial radio station that transmits at very high power from one nation to another. Border blasters should not be confused with international broadcast stations...
stations in northern Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
also used this effect, along with very high-power transmitter
Transmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
s, to extend their nighttine broadcast ranges well over the US/Mexico border and across most of the United States.
Various broadcast relay station
Broadcast relay station
A broadcast relay station, relay transmitter, broadcast translator , rebroadcaster , or repeater is a broadcast transmitter which relays, repeats, or reflects the signal of another radio station or television station, usually to an area not covered by the signal of the originating station...
s can help to extend a station's area by retransmitting them on the same or another channel
Channel (communications)
In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel...
. What is usually called a repeater
Repeater
A repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
in amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
is called a broadcast translator (different channel) or booster (same channel) in American broadcasting, or the much broader category or rebroadcasters in Canadian broadcasting (which includes more than just the low-power broadcasting
Low-power broadcasting
Low-power broadcasting is electronic broadcasting at very low power and low cost, to a small community area.The terms "low-power broadcasting" and "micropower broadcasting" should not be used interchangeably, because the markets are not the same...
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
Single-frequency network
A single-frequency network or SFN is a broadcast network where several transmitters simultaneously send the same signal over the same frequency channel.-Overview:...
s do in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
. Distributed transmission has also undergone tests in the U.S., but to preserve stations' market share
Market share
Market share is the percentage of a market accounted for by a specific entity. In a survey of nearly 200 senior marketing managers, 67 percent responded that they found the "dollar market share" metric very useful, while 61% found "unit market share" very useful.Marketers need to be able to...
in their home media market
Media market
A media market, broadcast market, media region, designated market area , Television Market Area , or simply market is a region where the population can receive the same television and radio station offerings, and may also include other types of media including newspapers and Internet content...
s, these will be limited to the broadcast area of a single large station. Satellite radio
Satellite radio
Satellite radio is an analogue or digital radio signal that is relayed through one or more satellites and thus can be received in a much wider geographical area than terrestrial FM radio stations...
, 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 staticWhite noise
White noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...
in an analog
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
broadcast, while error correction will keep a digital signal
Digital signal
A digital signal is a physical signal that is a representation of a sequence of discrete values , for example of an arbitrary bit stream, or of a digitized analog signal...
clear until it hits the cliff effect
Cliff effect
In telecommunications, the cliff effect or brickwall effect describes the sudden loss of digital signal reception. Unlike analog signals, which gradually fade when signal strength decreases or electromagnetic interference or multipath increases, a digital signal provides data which is either...
and suddenly disappears completely. FM
FM broadcasting
FM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
stations may flip back and forth (sometimes annoyingly rapidly when moving) due to the capture effect
Capture effect
In telecommunication, the capture effect, or FM capture effect, is a phenomenon associated with FM reception in which only the stronger of two signals at, or near, the same frequency will be demodulated....
, while AM
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
stations (including TV video) may overlay or fade with each other.
FM stereo will tend to get static more quickly than the monophonic
Monaural
Monaural or monophonic sound reproduction is single-channel. Typically there is only one microphone, one loudspeaker, or channels are fed from a common signal path...
sound due to its use of subcarrier
Subcarrier
A subcarrier is a separate analog or digital signal carried on a main radio transmission, which carries extra information such as voice or data. More technically, it is an already-modulated signal, which is then modulated into another signal of higher frequency and bandwidth...
s, so stations may choose to extend the usable part of their range by disabling the stereo generator. Listeners can also choose to disable stereo decoding on the receiver, though loss of the stereo pilot tone causes this to happen automatically. Because this tends to turn on and off when at the threshold of reception, and the threshold is often set too low by the manufacturer's product design
Product design
-Introduction:Product design is the process of creating a new product to be sold by a business or enterprise to its customers. It is concerned with the efficient and effective generation and development of ideas through a process that leads to new products.Product designers conceptualize and...
, 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 program
Second audio program
Second audio program , also known as secondary audio programming, is an auxiliary audio channel for analog television that can be broadcast or transmitted both over the air and by cable TV.-Usage:...
s, and even for color TV, all of which use subcarriers. Radio reading service
Radio reading service
A radio reading service or reading service for the blind is a service of many universities, community groups and public radio stations, where a narrator reads books, newspapers and magazines aloud for the benefit of the blind and vision-impaired. It is most often carried on a subcarrier, with...
s 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. Radio Data System
Radio Data System
Radio Data System, or RDS, is a communications protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts. RDS standardises several types of information transmitted, including time, station identification and programme information.Radio Broadcast Data...
allows for switching to a different FM or station with the same identifier
Identifier
An identifier is a name that identifies either a unique object or a unique class of objects, where the "object" or class may be an idea, physical [countable] object , or physical [noncountable] substance...
, or even to (but not necessarily from) an AM station. Satellite radio also is designed to switch seamlessly between repeaters and/or satellite when moving outside the range of one or the other. HD Radio
HD Radio
HD Radio, which originally stood for "Hybrid Digital", is the trademark for iBiquity's in-band on-channel digital radio technology used by AM and FM radio stations to transmit audio and data via a digital signal in conjunction with their analog signals...
switches back to the analog signal as a fallback when the edge of the digital range is encountered, but the success of this from the listener's perspective depends on how well the station's 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, guard intervalGuard interval
In telecommunications, guard intervals are used to ensure that distinct transmissions do not interfere with one another. These transmissions may belong to different users or to the same user ....
, and forward error correction
Forward error correction
In telecommunication, information theory, and coding theory, forward error correction or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels....
. In each of these three factors, the caveat
Caveat emptor
Caveat emptor is Latin for "Let the buyer beware". Generally, caveat emptor is the property law doctrine that controls the sale of real property after the date of closing.- Explanation :...
is that a higher data signaling rate
Data signaling rate
In telecommunication, data signaling rate , also known as gross bit rate, is the aggregate rate at which data pass a point in the transmission path of a data transmission system.Notes:#The DSR is usually expressed in bits per second....
means a tradeoff with reduced broadcast range. The hierarchical modulation
Hierarchical modulation
Hierarchical modulation, also called layered modulation, is one of the signal processing techniques for multiplexing and modulating multiple data streams into one single symbol stream, where base-layer symbols and enhancement-layer symbols are synchronously overplayed before...
used on DVB is a unique case, which reduces the range of the full-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 watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
age, in part because it is an in-band on-channel
In-band on-channel
In-band on-channel is a hybrid method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency....
method, which uses sideband
Sideband
In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, containing power as a result of the modulation process. The sidebands consist of all the Fourier components of the modulated signal except the carrier...
s that must prevent interference to adjacent channel
Adjacent channel
In broadcasting an adjacent channel is an AM, FM, or TV channel that is next to another channel. First-adjacent is immediately next to another channel, second-adjacent is two channels away, and so forth. Information on adjacent channels is used in keeping stations from interfering with one...
s, especially for older or cheaper receivers which have insufficient sensitivity and/or selectivity.