FM broadcasting

AM and FM modulated signals for radio. AM (amplitude modulation) and FM (frequency modulation) are types of modulation (coding). The sound of the program material, usually coming from a radio studio, is used to modulate (vary) a carrier wave of a specific frequency, then broadcast.<BR>
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In AM broadcasting, the amplitude of the carrier wave is modulated to encode the original sound. In FM broadcasting, the frequency of the carrier wave is modulated to encode the sound. A radio receiver extracts the original program sound from the modulated radio signal and reproduces the sound in a loudspeaker.
Position of FM radio in the electromagnetic spectrum
A commercial 35 kW FM radio transmitter built in the late 1980s. It belongs to FM radio station KWNR in Henderson, Nevada and broadcasts over a frequency of 95.5 MHz.
FM has better rejection of static (RFI) than AM. This was shown in a dramatic demonstration by General Electric at its New York lab in 1940. The radio had both AM and FM receivers. With a million-volt arc as a source of interference behind it, the AM receiver produced a roar of static, while the FM receiver clearly reproduced a music program from Armstrong's experimental FM transmitter in New Jersey.
Crossed dipole antenna of station KENZ's 94.9 MHz, 48 kW transmitter on Lake Mountain, Utah. It radiates circularly polarized radio waves.
Armstrong's first prototype FM broadcast transmitter, located in the Empire State Building, New York City, which he used for secret tests of his system between 1934 and 1935. Licensed as experimental station W2XDG, it transmitted on 41 MHz at a power of 2 kW.
Instantaneous spectrum and waterfall plot in the FM broadcast band showing three strong local stations; speech and music show different patterns of frequency vs. time. When the transmitted audio is quiet, the 19 kHz stereo pilot tones can be resolved in the spectrum.
Typical spectrum of composite baseband signal, including DirectBand and a subcarrier on 92 kHz
One of the first FM radio stations, Edwin Armstrong's experimental station W2XMN in Alpine, New Jersey, USA. The insets show a part of the transmitter, and a map of FM stations in 1940. The tower still stands today.
Belkin ''TuneCast II FM microtransmitter

Method of radio broadcasting using frequency modulation .

- FM broadcasting
AM and FM modulated signals for radio. AM (amplitude modulation) and FM (frequency modulation) are types of modulation (coding). The sound of the program material, usually coming from a radio studio, is used to modulate (vary) a carrier wave of a specific frequency, then broadcast.<BR>
<BR>
In AM broadcasting, the amplitude of the carrier wave is modulated to encode the original sound. In FM broadcasting, the frequency of the carrier wave is modulated to encode the sound. A radio receiver extracts the original program sound from the modulated radio signal and reproduces the sound in a loudspeaker.

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Graphical depiction of FM broadcasting allotments.

FM broadcast band

Graphical depiction of FM broadcasting allotments.

The FM broadcast band is a range of radio frequencies used for FM broadcasting by radio stations.

Baseband bandwidth. Here the bandwidth equals the upper frequency.

Bandwidth (signal processing)

Difference between the upper and lower frequencies in a continuous band of frequencies.

Difference between the upper and lower frequencies in a continuous band of frequencies.

Baseband bandwidth. Here the bandwidth equals the upper frequency.
The magnitude response of a band-pass filter illustrating the concept of −3 dB bandwidth at a gain of approximately 0.707.

An FM radio receiver's tuner spans a limited range of frequencies.

Hi-fi speakers are a key component of quality audio reproduction.

High fidelity

High-quality reproduction of sound.

High-quality reproduction of sound.

Hi-fi speakers are a key component of quality audio reproduction.
Modular components made by Samsung and Harman Kardon
A Sony "midi" hifi from the late 1980s. Despite its appearance mimicking separate components, this is an all-in-one unit featuring a record player, dual cassette decks, a digital tuner and an amplifier. Other midi systems integrating a CD player were also increasingly common by this point.

FM radio, with wider audio bandwidth and less susceptibility to signal interference and fading than AM radio.

A diagram of monaural sound

Monaural

Sound intended to be heard as if it were emanating from one position.

Sound intended to be heard as if it were emanating from one position.

A diagram of monaural sound

FM radio stations broadcast in stereo, while most AM radio stations broadcast in mono.

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AM broadcasting

Radio broadcasting using amplitude modulation transmissions.

Radio broadcasting using amplitude modulation transmissions.

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One of the earliest radio broadcasts, French soprano Mariette Mazarin singing into Lee de Forest's arc transmitter in New York City on February 24, 1910
Lee de Forest used an early vacuum-tube transmitter to broadcast returns for the Hughes-Wilson presidential election returns on November 7, 1916, over 2XG in New York City. Pictured is engineer Charles Logwood.
Nellie Melba making a broadcast over the Marconi Chelmsford Works radio station in England on 15 June 1920
Farmer listening to U.S. government weather and crop reports using a crystal radio in 1923. Public service government time, weather, and farm broadcasts were the first radio "broadcasts".
A family listening to an early broadcast using a crystal radio receiver in 1922. Crystal sets, used before the advent of vacuum tube radios in the 1920s, could not drive loudspeakers, so the family had to listen on earphones.
1938 Zenith Model 12-S vacuum-tube console radio, capable of picking up mediumwave and shortwave AM transmissions. "All Wave" receivers could also pick up the third AM band, longwave stations.
In July 1912, Charles "Doc" Herrold began weekly broadcasts in San Jose, California, using an arc transmitter.
Broadcasting in Germany began 1922 as a Post Office monopoly on a subscription basis, using sealed receivers which could only receive one station.
A live radio play being broadcast at NBC studios in New York. Most 1920s through 1940s network programs were broadcast live.
A BBC receiver licence from 1922. The British government required listeners to purchase yearly licences, which financed the stations.
When broadcasting began in 1920, music was played on air without regard to its copyright status. Music publishers challenged this practice as being copyright infringement, which for a time kept many popular tunes off the air, and this 1925 U.S. editorial cartoon shows a rich publisher muzzling two radio performers. The radio industry eventually agreed to make royalty payments.
Radios meeting the AMAX standards could display a certification logo, with the "stereo" notation reserved for those capable of AM stereo reception
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Many U.S. AM stations no longer publicize their AM signals, instead promoting simulcasts by FM band translators and Internet streams.

Subsequently, AM radio's audiences have also greatly shrunk due to competition from FM (frequency modulation) radio, Digital Audio Broadcasting (DAB), satellite radio, HD (digital) radio, Internet radio, music streaming services, and podcasting.

Long wave radio broadcasting station, Motala, Sweden

Radio broadcasting

Transmission of audio , sometimes with related metadata, by radio waves to radio receivers belonging to a public audience.

Transmission of audio , sometimes with related metadata, by radio waves to radio receivers belonging to a public audience.

Long wave radio broadcasting station, Motala, Sweden
Slovak Radio Building, Bratislava, Slovakia (architects: Štefan Svetko, Štefan Ďurkovič and Barnabáš Kissling, 1967–1983)
Broadcasting tower in Trondheim, Norway
Advertisement placed in the November 5, 1919 Nieuwe Rotterdamsche Courant announcing PCGG's debut broadcast scheduled for the next evening.
Use of a sound broadcasting station
Transmission diagram of sound broadcasting (AM and FM)
AM broadcasting stations in 2006
FM radio broadcast stations in 2006
Worldwide presence of Radio Maria broadcasters.

Radio stations broadcast with several different types of modulation: AM radio stations transmit in AM (amplitude modulation), FM radio stations transmit in FM (frequency modulation), which are older analog audio standards, while newer digital radio stations transmit in several digital audio standards: DAB (digital audio broadcasting), HD radio, DRM (Digital Radio Mondiale).

A signal may be carried by an AM or FM radio wave.

Frequency modulation

Encoding of information in a carrier wave by varying the instantaneous frequency of the wave.

Encoding of information in a carrier wave by varying the instantaneous frequency of the wave.

A signal may be carried by an AM or FM radio wave.
FM has better noise (RFI) rejection than AM, as shown in this dramatic New York publicity demonstration by General Electric in 1940. The radio has both AM and FM receivers. With a million-volt electric arc as a source of interference behind it, the AM receiver produced only a roar of static, while the FM receiver clearly reproduced a music program from Armstrong's experimental FM transmitter W2XMN in New Jersey.
Frequency spectrum and waterfall plot of a 146.52MHz carrier, frequency modulated by a 1,000Hz sinusoid. The modulation index has been adjusted to around 2.4, so the carrier frequency has small amplitude. Several strong sidebands are apparent; in principle an infinite number are produced in FM but the higher-order sidebands are of negligible magnitude.
FM modulation
An American FM radio transmitter in Buffalo, NY at WEDG

Frequency modulation is widely used for FM radio broadcasting.

Electromagnetic interference in analog TV signal

Electromagnetic interference

Disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction.

Disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction.

Electromagnetic interference in analog TV signal
Interference by 5 GHz Wi-Fi seen on Doppler weather radar

It can also affect mobile phones, FM radios, and televisions, as well as observations for radio astronomy and atmospheric science.

VHF television antennas used for broadcast television reception. These six antennas are a type known as a Yagi antenna, which is widely used at VHF

Very high frequency

ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter.

ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter.

VHF television antennas used for broadcast television reception. These six antennas are a type known as a Yagi antenna, which is widely used at VHF
"Rabbit-ears" VHF television antenna (the small loop is a separate UHF antenna).
A VHF television broadcasting antenna. This is a common type called a super turnstile or batwing antenna.
A plan showing VHF use in television, FM radio, amateur radio, marine radio and aviation.

Common uses for radio waves in the VHF band are Digital Audio Broadcasting (DAB) and FM radio broadcasting, television broadcasting, two-way land mobile radio systems (emergency, business, private use and military), long range data communication up to several tens of kilometers with radio modems, amateur radio, and marine communications.

Subcarries in the OFDMA scheme

Subcarrier

Sideband of a radio frequency carrier wave, which is modulated to send additional information.

Sideband of a radio frequency carrier wave, which is modulated to send additional information.

Subcarries in the OFDMA scheme

Stereo broadcasting is made possible by using a subcarrier on FM radio stations, which takes the left channel and "subtracts" the right channel from it — essentially by hooking up the right-channel wires backward (reversing polarity) and then joining left and reversed-right.