FM broadcasting

src: www.ronpaleybroadcast.com

FM broadcasting is a radio broadcasting method using frequency modulation (FM) technology. Created in 1933 by American engineer, Edwin Armstrong, a wide-band FM is used worldwide to deliver high-quality sound through radio broadcasts. FM broadcasting is capable of producing better sound quality than AM broadcasting, the head of competing radio broadcasting technology, so it is used for most music broadcasts. FM radio stations use VHF frequencies. The term "FM band" describes the frequency band in a particular country dedicated to FM broadcasting.

Video FM broadcasting

Broadcast bands

Around the world, FM broadcast bands fall in the VHF portion of the radio spectrum. Usually 87.5 to 108.0 MHz is used, or some portion thereof, with some exceptions:

• In the former Soviet republic, and some former East Block countries, older 65.8-74Ã, MHz bands are also used. The specified frequency is at a 30 kHz interval. The band, sometimes referred to as the OIRT band, is slowly being wiped out in many countries. In such countries, the band 87.5-108.0 MHz is referred to as the CCIR band.
• In Japan, 76-95 MHz bands are used.

Frequency of FM broadcast stations (more precisely the nominal center frequency assigned) is usually a precise multiple of 100 kHz. In most of South Korea, America, Philippines, and the Caribbean, only odd odds are used. In parts of Europe, Greenland and Africa, only a few are used. In the UK weird or even used. In Italy, a 50 kHz multiple is used. In most countries, the maximum allowed permissible frequency error is specified, the operator must be within 2000 Hz of the specified frequency.

There are unusual and outdated FM broadcasting standards in several countries, including 1, 10, 30, 74, 500, and 300 kHz. However, to minimize inter-channel interference, stations operating from similar or near-geographic transmitter sites tend to maintain at least 500 kHz frequency spacing even when closer frequency ranges are technically permitted, with a closer barrel provided for remote transmitters, as a signal potentially disturbing is already more attenuated and so has less effect on neighboring frequencies.

Maps FM broadcasting

Modulation Characteristics

Modulation

Frequency or FM modulation is a modulation form that conveys information by varying the carrier wave frequency; the older amplitude modulation or AM varies the carrier amplitude, with its frequency constant. With FM, the frequency deviation from the specified carrier frequency at any time is directly proportional to the input signal amplitude, determining the instantaneous frequency of the transmitted signal. Because the transmitted FM signal uses more bandwidth than the AM signal, this modulation form is usually used with higher frequencies (VHF or UHF) used by TV, FM broadcasting and ground cellular radio systems.

Pre-emphasis and de-emphasis

The random noise has a spectrum distribution of triangles in the FM system, with the effect that sound occurs mainly at the highest audio frequencies in the baseband. This can be offset, to some extent, by increasing the high frequency before transmission and reducing them to the appropriate number in the receiver. Reducing high-frequency audio on the receiver also reduces high-frequency noise. The processes of increasing and subsequently reducing certain frequencies are known as pre-emphasis and de-emphasis, respectively.

The number of pre-emphasis and de-emphasis used is determined by the time constants of a simple RC filter circuit. In most of the world, 50 Âμs time constants are used. In America and South Korea, 75Ã,Âμs is used. This applies to mono and stereo transmissions. For stereo, pre-emphasis is applied on the left and right channels before multiplexing.

The use of pre-emphasis is a problem due to the fact that many forms of contemporary music contain more high frequency energy than the musical styles prevailing at the birth of FM broadcasting. Pre-suppression of this high-frequency sound will cause excessive deviations from the FM operator. The modulator control device (limiter) is used to prevent this. More modern systems than FM broadcasts tend to use pre-emphasis variables that depend on the program; e.g. dbx in the BTSC TV sound system, or none at all.

Stereo FM

Long before stereo FM transmission is considered, FM multiplexing other types of audio level information is being experimented. Edwin Armstrong who discovered FM was the first to experiment with multiplexing, at his 41 MHz W2XDG experimental station located on the 85th floor of the Empire State Building in New York City.

This FM multiplex transmission started in November 1934 and consisted of a main channel audio program and three subcarriers: fax program, sync signal for fax program and telegraph "order" channel. The original multiplexed FM subcarrier is amplitude modulated.

Two music programs, comprised of the NBC Network Network's Red and Blue Network program, are transmitted simultaneously using the same subcarrier modulation system as part of an inter-studio link system. In April 1935, the subcarrier AM was replaced by the FM subcarrier, with much better results.

The first FM subcarrier transmission originated from the Major Armstrong KE2XCC experimental station in Alpine, New Jersey occurred in 1948. The transmission consisted of a two-channel audio program, a binaural audio program, and a fax program. The original subcarrier frequency used on KE2XCC is 27.5 kHz. IF bandwidth is  ± 5 kHz, because the only purpose at the time was to deliver AM-quality radio audio. This transmission system primarily uses 75 Âμs pre-emphasis audio, a technical innovation that is part of the original Stereo Multiplex Standard FM.

In the late 1950s, some systems for adding stereo to FM radio were considered by the FCC. Includes systems from 14 supporters including Crosby, Halstead, Electrical and Music Industries, Ltd. (EMI), Zenith, and General Electric. Individual systems were evaluated for their strengths and weaknesses during field tests in Uniontown, Pennsylvania using KDKA-FM in Pittsburgh as home stations. The Crosby system was rejected by the FCC because it is not compatible with existing subsidiary communication communication services (SCAs) that use a variety of subcarrier frequencies including 41 and 67 kHz. Many non-revenue-generating stations use SCA for "storecasting" and other non-broadcasting purposes. The Halstead system was rejected due to the lack of high frequency stereo separation and reduction of the main channel signal-to-noise ratio. The GE and Zenith systems, so similar that they are considered theoretically identical, were officially approved by the FCC in April 1961 as standard stereo FM broadcasting methods in the United States and subsequently adopted by most other countries. It is important that stereo broadcasts are compatible with mono receivers. For this reason, the left (L) and right (R) channels are algebraically encoded into the number (L R) and the difference (L-R) signals. The mono receiver will only use the L R signal so that the listener will hear both channels through a single loudspeaker. The stereo receiver will add a difference signal to the addition signal to recover the left channel, and reduce the difference signal from the number to recover the correct channel.

The main channel signal (L R) is transmitted as a limited audio baseband in the range of 30 Hz to 15 kHz. The signal (L-R) is the amplitude modulated to a 38dHz 38DHz double-sideband suppressed-carrier (DSB-SC) signal occupying a baseband range of 23-53 kHz. A 19 kHz pilot tone, right at half the 38 kHz sub-carrier frequency and with the exact phase relationship, as defined by the formula below, is also generated. It is transmitted at 8-10% of the overall modulation rate and is used by the receiver to regenerate the 38 kHz sub-carrier with the correct phase. The final multiplex signal from the stereo generator contains the Main Channel (L R), the pilot tone, and the sub-channel (L-R). This composite signal, together with other sub-operators, modulates the FM transmitter.

Penyimpangan sesaat frekuensi pembawa pemancar karena audio stereo dan nada pilot (pada 10% modulasi)

${\ displaystyle \ left [0.9 \ left [{\ frac {A B} {2}} {\ frac {AB} {2}} \ sin 4 \ pi f_ {p} t \ right] 0.1 \ sin 2 \ pi f_ {p} t \ right] \ kali 75 ~ \ mathrm {kHz}}  ÂÂ$

where A and B are the previously emphasized left and right audio signals and ${\ displaystyle f_ {p}}$ = 19Ã, kHz is the frequency of the pilot tone. Some variations in peak irregularities may occur in the presence of other subcarriers or due to local regulations.

Another way to see the resulting signal is that it alternates between left and right at 38 kHz, with a phase determined by a 19 kHz pilot signal. Convert the multiplex signal back into a left and right audio signal performed by the decoder, built into the stereo receiver.

In addition, for the RF level given at the receiver, the signal-to-sound ratio and the multipath distortion for the stereo signal will be worse than the mono receiver. For this reason many stereo FM receivers include a stereo/mono switch to allow listening in mono when reception conditions are less than ideal, and most car radios are set to reduce the separation because the signal-to-noise ratio worsens, eventually becoming mono while still showing the signal stereo is being received. To maintain stereo separation and signal-to-noise parameters, it is normal practice to apply pre-emphasis on left and right channels before encoding and to apply de-emphasis on the receiver after decoding.

In the US starting around 2010 using a single sideband subwoofer for stereo is proposed. It theorizes to be more power efficient and has less noise on the receiver. A number of radio stations throughout the country broadcast stereos in this way. This is not compatible with very old receivers. The modern receiver can not tell the difference.

FM Quadraphonic

In 1969, Louis Dorren invented the station's single, discrete Quadraplex system, FM broadcast four channels compatible. There are two additional subcarriers in the Quadraplex system, complementing one more used in standard stereo FM. The baseband layout is as follows:

• 50Ã, Hz to 15Ã, kHz Main Channel (number of all 4 channels) (LF RF RR) signal, for mono FM listening compatibility.
• 23 to 53 kHz (subcarrier quadrature sinus) (LF LR) - (RF RR) Left minus Signal difference is correct. This signal modulation in algebraic number and difference with Main channel is used for 2 channel stereo listeners compatibility.
• 23 to 53 kHz (cosine quadrature 38 kHz subcarrier) (LF RR) - (LR RF) Difference diagonal. Modulation of this signal in algebraic number and difference with Main channel and all other subcarrier is used for Quadraphonic listeners.
• 61 to 91Ã, kHz (quadrature 76Ã, kHz subcarrier) sinus (LF RF) - (LR RR) Front-back difference. Modulation of this signal in algebraic quantities and differences with the main channel and all other subcarriers is also used for Quadraphonic listeners.
• SCA subcarrier 105 kHz, phase locked to 19 kHz pilot, for reading service for the blind, background music, etc.

A normal stereo signal can be considered as a transfer between the left and right channels at 38 kHz, the exact band is limited. Quadraphonic signals can be considered as cycling through LF, LR, RF, RR, at 76 kHz.

Initial attempts to transmit quadraphonic four-channel music differently require the use of two FM stations; one transmission front audio channel, another back channel. A breakthrough came in 1970 when KIOI ( K-101 ) in San Francisco successfully delivered the correct quadraphonic sound from one FM station using the Quadraplex system under the FCC's Special Provisional Authority. After this experiment, a proposed long-term test period will allow one FM station in each of the top 25 radio markets to transmit at the Quadraplex. The test results are expected to prove to the FCC that the system is compatible with the existing two-channel stereo transmission and reception and that it does not interfere with adjacent stations.

There are several variations on this system proposed by GE, Zenith, RCA, and Denon for testing and consideration during the National Quadraphonic Radio Committee field trials for the FCC. The original Dorren Quadraplex system outperformed the others and was selected as the national standard for Quadraphonic FM broadcasting in the United States. The first commercial FM station to broadcast quadraphonic program content is WIQB (now called WWWW-FM) in Ann Arbor/Saline, Michigan under the guidance of Chief Engineer Brian Jeffrey Brown.

Noise reduction

Various attempts to add analog noise reduction to FM broadcasts were conducted in the 1970s and 1980s:

The commercially ineffective noise reduction system used with FM radio in some countries during the late 1970s, Dolby FM is similar to Dolby B but uses modified 25-μs pre-emphasis constant constant and selective frequency selective compsition to reduce noise. The pre-emphasis change compensates for the treble overload response which would otherwise make it difficult to listen for those who do not have a Dolby decoder.

Similar systems named High ComÃ, FM were tested in Germany between July 1979 and December 1981 by the IRT. It is based on the Broadband Telefunken High Com broadband system, but has never been commercially introduced in FM broadcasts.

Yet another system was the CX FMX-based noise reduction system that was implemented in several radio stations in the United States in the 1980s.

Other subcarrier services

FM broadcasting includes the capability of a child's communication communication service (SCA) from the outset, as it is considered to be another service that licensees can use to create additional income. The use of SCA is very popular in the US, but much less elsewhere. The use of such subcarriers includes the Radio reading service for the blind, which becomes common and remains, private data transmission services (eg sending stock market information to stockbrokers or credit card number lists stolen to stores, subscription to background music services without any commercial cost for stores, paging ("pager") services, non-native programming languages, and providing program feeds for AM/FM station AM transmitters. SCA subcarrier is usually 67 kHz and 92 kHz. Initially SCA service users are private analogue audio channels that can be used internally or rented, for example Muzak type services. There is an experiment with quadraphonic sound. If the station is not broadcast in stereo, anything from 23 kHz upwards can be used for other services. A guard band of about 19 kHz (Ã, Â ± 4 kHz) should be maintained, so as not to trigger the stereo decoder on the receiver. If there is a stereo, there will usually be a guard band between the upper limit of the DSBSC stereo signal (53 kHz) and the lower limit of the other subcarrier.

Digital services are now available as well. The 57-kHz subcarrier (phase locked into the harmonic of the three stereo tone voices) is used to carry Low-Band Radio Data System bandwidth signals, providing additional features such as station names, Alternative Frequency (AF), traffic data for commercial GPS receivers and Radio text ). This narrowband signal only runs at 1,187.5 bits per second, so it is only suitable for text. Some proprietary systems are used for personal communication. RDS variant is North American RBDS or "smart radio" system. In Germany the analog ARI system is used before RDS to broadcast traffic announcements to riders (without interfering with other listeners). Plans to use ARI for other European countries lead to the development of RDS as a stronger system. RDS is designed to be used with ARI despite using identical subcarrier frequencies.

In the United States and Canada, digital radio services are being used in FM bands rather than using Eureka 147 or ISDB Japanese standards. This in-band on-channel approach, like all digital radio techniques, uses sophisticated compressed audio. The exclusive iBiquity system, labeled as "Radio HD", is currently approved for "hybrid mode" operations, in which both conventional analog FM operators and digital sideband sub-operators are transmitted. Finally, assuming the widespread deployment of HD Radio receivers, analog services can theoretically be terminated and FM bands become all digital.

src: d1o50x50snmhul.cloudfront.net

Reception distance

VHF waves Radio does not travel far beyond the visual horizon, so the reception distance for FM stations is usually limited to 30--40 miles (50â € 65 km). They can also be blocked by hills. This is less than the range of AM radio waves, which due to lower frequencies can travel as ground waves or reflect the ionosphere, so that AM radio stations can be received in hundreds (sometimes thousands) of miles. This is a property of the typical frequency (and power) of the carrier wave, not the modulation of the mode.

The range of FM transmission is related to transmitter RF power, antenna gain, and high antenna. Interference from other stations is also a factor in some places. In the US, the FCC publishes curves that assist in calculating this maximum distance as a function of signal strength at the receiving location. Computer modeling is more commonly used for this worldwide.

Many FM stations, especially those located in severe multipath areas, use extra audio compression/processing to keep sound important above the background sound for listeners, sometimes at the expense of overall perceived sound quality. However, this technique is often very effective in increasing the useful range of stations.

src: i.ytimg.com

FM broadcast adoption

United States

Although FM was patented in 1933, commercial FM broadcasts did not begin until the late 1930s, when initiated by a handful of early pioneering stations including W8HK, Buffalo, New York (now WTSS); W1XOJ/WGTR and W1XTG/WSRS, both emit from Paxton, Massachusetts (now listed as Worcester, Massachusetts); W1XSL/W1XPW/WDRC-FM, Meriden, Connecticut (now WHCN); W2XMN/KE2XCC/WFMN, Alpine, New Jersey (owned by Edwin Armstrong himself, closed after Armstrong's death in 1954); W2XQR/WQXQ/WQXR-FM, New York; W47NV Nashville, Tennessee (signed in 1951); W1XER/W39B/WMNE, whose studio is in Boston but its transmitter is on the highest mountain in the northeastern United States, Mount Washington, New Hampshire (closed in 1948); W9XAO Milwaukee, Wisconsin (later WTMJ-FM, airs in 1950, back in 1959 on another frequency). Also worth noting is the General Electric station W2XDA Schenectady and W2XOY New Scotland, New York - two experimental frequency modulation transmitters at 48.5 MHz - signed in 1939. The two were merged into one station using the W2XOY call letter on November 20, 1940, with the station picking up the WGFM call letter a few years later, and moving to 99.5 MHz when the FM band was moved to the 88-108 MHz section of the radio spectrum. General Electric sold the station in the 1980s, and today the station is called WRVE.

WEFM (in the Chicago area) and WGFM (in Schenectady, New York) reported as the first stereo station.

The first commercial FM broadcasting station was in the United States, but initially they were primarily used to simulate their AM sister stations, to broadcast lush orchestral music for stores and offices, to broadcast classical music to an upscale audience in urban areas, or for educational programs. By the late 1960s, FM had been adopted for stereo broadcasting "A.O.R.-- 'Rock-Oriented Album' Format", but it was not until 1978 that listeners to FM stations exceeded from AM stations in North America. During the 1980s and 1990s, Top 40 music stations and even country music stations have largely left AM for FM. Today AM primarily conserves radio talk, news, sports, religious programs, ethnic broadcasting (minority languages) and some minority musical types. This shift has turned AM into an "alternative band" FM has ever had. (Some AM stations have started to simulcast on, or switch to, FM signals to appeal to younger listeners and help with reception issues in buildings, during thunderstorms, and near high voltage cables Some of these stations now emphasize their presence on the FM dial. )

Europe

The medium wave band (known as the band AM because most stations use it using amplitude modulation) is too full in Western Europe, which causes interference problems and, consequently, many MW frequencies are only suitable for broadcast speech.

Belgium, the Netherlands, Denmark and especially Germany were among the first countries to adopt FM on a wide scale. Among the reasons for this are:

1. The mid-wave band in Western Europe became overcrowded after World War II, largely because the best available medium-wave frequencies were used at high power levels by the Allied Forces Forces, both to broadcast entertainment to their troops and to broadcast war propaganda Cold in the Iron Curtain.
2. After World War II, the frequency of broadcasting was reorganized and reallocated by the delegates of the winning countries in the Copenhagen Frequency Plan. German broadcasters left only two remaining AM frequencies and were forced to look to FM for expansion.

Public service announcers in Ireland and Australia are much slower in adopting FM radio than those in North America or the European continent.

United Kingdom

In the United Kingdom, the BBC began broadcasting FM in 1955, with three national networks: the Light Program, the Third Program and the Home Service. These three networks use sub-band 88.0-94.6 MHz. The sub-band 94.6-97.6 MHz is then used for the BBC and local commercial services.

However, only when commercial broadcasts were introduced to the UK in 1973, the use of FM took in the UK. With gradual clearance from other users (notably the Public Service such as police, fire and ambulance) and the extension of the FM band to 108.0 MHz between 1980 and 1995, FM extends rapidly throughout the British Isles and effectively takes over from LW and MW as the preferred delivery platform for domestic receivers and permanent and portable based vehicles. In addition, Ofcom (formerly the Radio Authority) in the United Kingdom issued a request for a Limited Service Permit on FM as well as on AM (MW) for short-term local broadcast broadcasts open to anyone who does not carry a ban and may place the appropriate license and royalty fees. In 2010, about 450 licenses were issued.

When the BBC radio network was renamed Radio 2, Radio 3 and Radio 4 respectively in 1967 to coincide with the launch of Radio 1, the new station was the only one of the four major to have no FM frequency allocated, which is the case for 21 years. Instead Radio 1 shared time with Radio 2 FM, on Saturday afternoon, Sunday night, night (10 pm to midnight) and Bank Holiday. Finally in 1987 the 97.6-99.8 MHz frequency range was allocated as a police relay transmitter removed from a 100 MHz frequency, beginning in London before being completed extensively in 1989.

Italy

Italy adopted broadcast FM broadly in the early 1970s, but the first experiments made by RAI date back to 1950, when the "movement for free radio", developed by so-called "pirates", forced the recognition of the right to free speech also through the use of from "free radio media such as Broadcast broadcasters", and brought the case to the Italian Constitutional Court. The court finally decided to support Free Radio. Just a few weeks after the final court decision there was an "FM radio explosion" involving small private radio stations across the country. In the mid-1970s, every city in Italy had a solid FM radio spectrum.

Greek

Greece was another European country where the FM radio spectrum was used initially by so-called "pirates" (both in Athens and Thessaloniki, two of Greece's major cities) in the mid-1970s, before any national stations began to broadcast it; there are many AM stations (MW) used for that purpose. By late 1977, the national public service broadcasting company EIRT (later also known as ERT) was placed in its first FM transmitter service in the capital, Athens. In the late 1970s, most of the Greek territory was covered by three National FM programs, and each city had many "pirate" FM as well. The adaptation of the FM band to private commercial radio stations came much later, in 1987.

Australia

FM broadcasting began in the Australian capital in 1947 on an "experimental" basis, using ABC's national network feed, comprised mostly of classical music and Parliament, as the source of the program. It has a very small audience and closed in 1961 as if to clear the television band: 5 TV channels (102,250 video carriers) if allocated will fall in the FM VHF band (98-108 MHz). The official policy on FM at the time was to eventually introduce it to other bands, which would require an FM tuner tailor-made for Australia. The policy was eventually canceled and FM broadcast reopened in 1975 using VHF tape, after several disturbing TV stations were moved. Furthermore, it continued until the 1980s many AM stations were transferred to FM due to superior sound quality and lower operating costs. Today, as elsewhere in the developed world, most of Australia's urban broadcasts are in FM, although the AM talk station is still very popular. Regional broadcasters still often operate the AM station because of the additional range offered by the broadcasting method. Several stations in major regional centers perform simulcast on AM and FM bands. Digital radio using DAB standards has been launched into major cities.

New Zealand

Like Australia, New Zealand adopts a relatively late FM format. As with privately owned AM radios in the late 1960s, it is necessary to broadcast 'pirates' to persuade control-oriented governments, technology to allow FM to be introduced after at least five years of consumer campaigns beginning in the mid-1970s, Auckland. An experimental FM station, FM 90.7, was broadcasted in Whakatane in early 1982. Later that year, Victoria University of Wellington Active Radio initiated a full-time FM transmission. The commercial FM license was finally approved in 1983, with 91FM based in Auckland and 89FM being the first to accept the offer. [1]. Broadcasting was deregulated in 1989.

Trinidad and Tobago

Trinidad and Tobago's first FM Radio Station is 95.1FM, now renamed 951 Remix, launched in March 1976 by TBC Radio Network.

Turkish

In Turkey, FM broadcasts began in the late 1960s, carrying several shows from One's television network that were transferred from AM frequencies (also known as MW in Turkey). In subsequent years, more MW stations were slowly transferred to FM, and by the late 1970s, most of the earlier MW stations had been moved to FM, despite much talk, news and sports, but most religious stations, still remain on MW.

Other countries

Most other countries implemented FM broadcasts until the 1960s and expanded the use of FM through the 1990s. Since a large number of FM transmitter stations are required to cover large geographically, especially where there are field difficulties, FM is more suitable for local broadcasting than for national networks. In such countries, especially where there are economic or infrastructure issues, "launching" the national FM broadcast network to reach the majority of the population can be a slow and costly process. Nonetheless, mostly in eastern European countries, the national FM broadcast network was established in the late 1960s and 1970s. In all Soviet-dependent countries but the GDR, OIRT tape is used. First limited to 68-73 MHz with 100 kHz channel spacing, then in 1970 finally expanded to 65,84-74,00 MHz with 30 kHz channel distance.

ITU Conference on FM

The frequencies available for FM are decided by several important ITU conferences. The milestone of the conference was the Stockholm agreement of 1961 among 38 countries. A 1984 conference in Geneva made some modifications to the original Stockholm agreement especially in the frequency range above 100 MHz.

src: www.liveradio.ie

FM broadcast switch

or

src: i.ytimg.com

Small-scale use of FM broadcast band

Consumer use FM transmitter

In some countries, small-scale transmitters (Section 15 in the United States) are available that can transmit signals from audio devices (usually MP3 players or similar) to a standard FM radio receiver; these devices range from small units built to carry audio to car radios without audio-in capability (often previously provided by a special adapter for audio cassette decks, which are less common in car radio designs) to full-sized, near-professional grade broadcasting systems which can be used to send audio to the entire property. Most of these units transmit in full stereo, although some models designed for novice fans may not. Similar transmitters are often included in satellite radio receivers and some toys.

The legality of this device varies by country. The Federal Communications Commission of the US and Canada Industries permitted it. Starting October 1, 2006, this device becomes legal in most countries in the European Union. Devices made for European specifications are harmonized to be valid in the UK on December 8, 2006.

FM broadcast bands are also used by some cheap wireless microphones that are sold as toys for karaoke or similar purposes, allowing users to use FM radio as output rather than amplifiers and special speakers. Professional grade wireless microphones generally use bands in the UHF area so they can run on special equipment without any broadcast interruptions.

Some wireless headphones transmit in FM broadcast bands, with melodious headphones only a subset of broadcast bands. High quality wireless headphones use infrared transmissions or ISM UHF bands such as 315 MHz, 863 MHz, 915 MHz, or 2.4 GHz rather than FM broadcasting.

Microbroadcasting

Low-power transmitters as mentioned above are also sometimes used for campus environments or stations, although campus radio stations often run above the carrier stream. This is generally regarded as a form of microbroadcasting. As a general rule, enforcement of low-power FM stations is tighter than AM stations, due to problems such as capture effects, and as a result, FM microbroadcasters generally do not reach as far as their AM competitors.

Use of FM transmitter silently

FM transmitters have been used to build miniature wireless microphones for espionage and surveillance purposes (secret listening devices or so-called "bugs"); The advantage of using an FM broadcast tape for such an operation is that the receiving equipment is not considered a suspect. A common practice is to set the bug transmitter from the ends of the broadcast band, into what in the United States will be a TV channel 6 (& lt; 87.9 MHz) or flight navigation frequency (& gt; 107.9 MHz); most FM radio with analog tuners have the advantage of being adequate to pick up frequencies that are a little too far away, although many of the radios are tuned digitally yet.

Building "bugs" is a common start project for electronics enthusiasts, and project kits to do so are available from multiple sources. Devices that are built, however, are often too large and not well protected for use in underground activities.

In addition, many pirate radio activities are broadcast within the FM range, due to greater clarity and listener, smaller size and lower equipment costs.

src: img.wonderhowto.com

See also

FM broadcast by country

• FM broadcast in Australia
• FM broadcast in Canada
• FM broadcast in Egypt
• FM broadcast in India
• FM broadcast in Japan
• FM broadcasting in New Zealand
• FM broadcasting in Pakistan
• FM broadcast in UK
• FM broadcasts in the United States

FM broadcasting (technical)

• AM broadcasting
• AM stereo (related technology)
• FM broadcast band
• stereo FM
• Frequency modulation
• Remote FM reception (FM DX)
• Rip music from FM broadcast
• RDS (Radio Data System)

List

• List of broadcast stations
• List of radio stations in North America

History

• Radio history
• The oldest radio station

src: i.ytimg.com

See also

• Band I
• Band II
• Band III

src: banner2.kisspng.com

References

src: www.engineeringradio.us

External links

Relevant technical content

• AS. Patent 1,941,066
• AS. Patent 3,708,623 FM System Four Compatible Channels
• Introduction to MPX FM
• Frequency Modulation (FM) Tutorial
• Stereo Multiplexing for Dummies Graphs that show waveforms at different points in the Multiplex FM process
• Station fact-book list worldwide
• History of Discovery - Mr FM
• Audio Engineering Society
• FM Aural Subcarrier TV Broadcasts - Clifton Laboratories

Source of the article : Wikipedia