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88-814: WEPS (88.9 FM ) is a radio station licensed to serve Elgin, Illinois , United States. The station is owned by the Elgin Area School District U46 and licensed to Board of Education School District U-46. Founded in 1950, WEPS is the oldest non-commercial educational radio station in the state of Illinois. WEPS broadcasts a classical music format as a member of Wisconsin Public Radio 's WPR Music network. WEPS broadcasts student programming aside WPR Music. Student programming broadcasts weekdays at 7 AM and PM and on 8AM and PM on Fridays Originally licensed in 1950 to broadcast at 88.1 MHz , WEPS originally broadcast instructional programs to

176-419: A transition band the gain is not specified. In this case, the filter bandwidth corresponds to the passband width, which in this example is the 1 dB-bandwidth. If the filter shows amplitude ripple within the passband, the x  dB point refers to the point where the gain is x  dB below the nominal passband gain rather than x  dB below the maximum gain. In signal processing and control theory

264-402: A fax program. The original subcarrier frequency used at KE2XCC was 27.5 kHz. The IF bandwidth was ±5 kHz, as the only goal at the time was to relay AM radio-quality audio. This transmission system used 75 μs audio pre-emphasis like the main monaural audio and subsequently the multiplexed stereo audio. In the late 1950s, several systems to add stereo to FM radio were considered by

352-557: A program feed for AM transmitters of AM/FM stations. SCA subcarriers are typically 67 kHz and 92 kHz. Initially the users of SCA services were private analog audio channels which could be used internally or leased, for example Muzak -type services. There were experiments with quadraphonic sound. If a station does not broadcast in stereo, everything from 23 kHz on up can be used for other services. The guard band around 19 kHz (±4 kHz) must still be maintained, so as not to trigger stereo decoders on receivers. If there

440-417: A stereo/mono switch to allow listening in mono when reception conditions are less than ideal, and most car radios are arranged to reduce the separation as the signal-to-noise ratio worsens, eventually going to mono while still indicating a stereo signal is received. As with monaural transmission, it is normal practice to apply pre-emphasis to the left and right channels before encoding and to apply de-emphasis at

528-435: A system of frequency response H ( f ) {\displaystyle H(f)} is the bandwidth of an ideal filter with rectangular frequency response centered on the system's central frequency that produces the same average power outgoing H ( f ) {\displaystyle H(f)} when both systems are excited with a white noise source. The value of the noise equivalent bandwidth depends on

616-631: Is a less meaningful measure in wideband applications. A percent bandwidth of 100% corresponds to a ratio bandwidth of 3:1. All higher ratios up to infinity are compressed into the range 100–200%. Ratio bandwidth is often expressed in octaves (i.e., as a frequency level ) for wideband applications. An octave is a frequency ratio of 2:1 leading to this expression for the number of octaves, log 2 ⁡ ( B R ) . {\displaystyle \log _{2}\left(B_{\mathrm {R} }\right).} The noise equivalent bandwidth (or equivalent noise bandwidth (enbw) ) of

704-525: Is added. VHF radio waves usually do not travel far beyond the visual horizon , so reception distances for FM stations are typically limited to 30–40 miles (50–60 km). They can also be blocked by hills and to a lesser extent by buildings. Individuals with more-sensitive receivers or specialized antenna systems, or who are located in areas with more favorable topography, may be able to receive useful FM broadcast signals at considerably greater distances. The knife edge effect can permit reception where there

792-440: Is also used in spectral width , and more generally for the extent of functions as full width at half maximum (FWHM). In electronic filter design, a filter specification may require that within the filter passband , the gain is nominally 0 dB with a small variation, for example within the ±1 dB interval. In the stopband (s), the required attenuation in decibels is above a certain level, for example >100 dB. In

880-458: Is also used to denote system bandwidth , for example in filter or communication channel systems. To say that a system has a certain bandwidth means that the system can process signals with that range of frequencies, or that the system reduces the bandwidth of a white noise input to that bandwidth. The 3 dB bandwidth of an electronic filter or communication channel is the part of the system's frequency response that lies within 3 dB of

968-401: Is as follows: The normal stereo signal can be considered as switching between left and right channels at 38 kHz, appropriately band-limited. The quadraphonic signal can be considered as cycling through LF, LR, RF, RR, at 76 kHz. Early efforts to transmit discrete four-channel quadraphonic music required the use of two FM stations; one transmitting the front audio channels, the other

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1056-422: Is authorized for "hybrid" mode operation, wherein both the conventional analog FM carrier and digital sideband subcarriers are transmitted. The output power of an FM broadcasting transmitter is one of the parameters that governs how far a transmission will cover. The other important parameters are the height of the transmitting antenna and the antenna gain . Transmitter powers should be carefully chosen so that

1144-515: Is claimed that no difference can be heard with most newer receivers. At present, the FCC rules do not allow this mode of stereo operation. In 1969, Louis Dorren invented the Quadraplex system of single station, discrete, compatible four-channel FM broadcasting. There are two additional subcarriers in the Quadraplex system, supplementing the single one used in standard stereo FM. The baseband layout

1232-449: Is defined as the ratio of the upper and lower limits of the band, B R = f H f L . {\displaystyle B_{\mathrm {R} }={\frac {f_{\mathrm {H} }}{f_{\mathrm {L} }}}\,.} Ratio bandwidth may be notated as B R : 1 {\displaystyle B_{\mathrm {R} }:1} . The relationship between ratio bandwidth and fractional bandwidth

1320-508: Is defined by the time constant of a simple RC filter circuit. In most of the world a 50  μs time constant is used. In the Americas and South Korea , 75 μs is used. This applies to both mono and stereo transmissions. For stereo, pre-emphasis is applied to the left and right channels before multiplexing . The use of pre-emphasis becomes a problem because many forms of contemporary music contain more high-frequency energy than

1408-596: Is designed to be capable of use alongside ARI despite using identical subcarrier frequencies. In the United States and Canada , digital radio services are deployed within the FM band rather than using Eureka 147 or the Japanese standard ISDB . This in-band on-channel approach, as do all digital radio techniques, makes use of advanced compressed audio . The proprietary iBiquity system, branded as HD Radio ,

1496-462: Is given by the Carson bandwidth rule which is the sum of twice the maximum deviation and twice the maximum modulating frequency. For a transmission that includes RDS this would be 2 × 75 kHz + 2 × 60 kHz  = 270 kHz . This is also known as the necessary bandwidth . Random noise has a triangular spectral distribution in an FM system, with the effect that noise occurs predominantly at

1584-490: Is given by, B F = 2 B R − 1 B R + 1 {\displaystyle B_{\mathrm {F} }=2{\frac {B_{\mathrm {R} }-1}{B_{\mathrm {R} }+1}}} and B R = 2 + B F 2 − B F . {\displaystyle B_{\mathrm {R} }={\frac {2+B_{\mathrm {F} }}{2-B_{\mathrm {F} }}}\,.} Percent bandwidth

1672-408: Is half its maximum value (or the spectral amplitude, in V {\displaystyle \mathrm {V} } or V / H z {\displaystyle \mathrm {V/{\sqrt {Hz}}} } , is 70.7% of its maximum). This figure, with a lower threshold value, can be used in calculations of the lowest sampling rate that will satisfy the sampling theorem . The bandwidth

1760-592: Is inconsequentially larger. For wideband applications they diverge substantially with the arithmetic mean version approaching 2 in the limit and the geometric mean version approaching infinity. Fractional bandwidth is sometimes expressed as a percentage of the center frequency ( percent bandwidth , % B {\displaystyle \%B} ), % B F = 100 Δ f f C . {\displaystyle \%B_{\mathrm {F} }=100{\frac {\Delta f}{f_{\mathrm {C} }}}\,.} Ratio bandwidth

1848-429: Is limited to 30 Hz to 15 kHz to protect a 19 kHz pilot signal. The (L−R) signal, which is also limited to 15 kHz, is amplitude modulated onto a 38 kHz double-sideband suppressed-carrier (DSB-SC) signal, thus occupying 23 kHz to 53 kHz. A 19 kHz ± 2 Hz pilot tone , at exactly half the 38 kHz sub-carrier frequency and with a precise phase relationship to it, as defined by

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1936-480: Is mainly the preserve of talk radio, news, sports, religious programming, ethnic (minority language) broadcasting and some types of minority interest music. This shift has transformed AM into the "alternative band" that FM once was. (Some AM stations have begun to simulcast on, or switch to, FM signals to attract younger listeners and aid reception problems in buildings, during thunderstorms, and near high-voltage wires. Some of these stations now emphasize their presence on

2024-671: Is no direct line of sight between broadcaster and receiver. The reception can vary considerably depending on the position. One example is the Učka mountain range, which makes constant reception of Italian signals from Veneto and Marche possible in a good portion of Rijeka , Croatia, despite the distance being over 200 km (125 miles). Other radio propagation effects such as tropospheric ducting and Sporadic E can occasionally allow distant stations to be intermittently received over very large distances (hundreds of miles), but cannot be relied on for commercial broadcast purposes. Good reception across

2112-459: Is often quoted relative to the frequency of operation which gives a better indication of the structure and sophistication needed for the circuit or device under consideration. There are two different measures of relative bandwidth in common use: fractional bandwidth ( B F {\displaystyle B_{\mathrm {F} }} ) and ratio bandwidth ( B R {\displaystyle B_{\mathrm {R} }} ). In

2200-526: Is one of the determinants of the capacity of a given communication channel . A key characteristic of bandwidth is that any band of a given width can carry the same amount of information , regardless of where that band is located in the frequency spectrum . For example, a 3 kHz band can carry a telephone conversation whether that band is at baseband (as in a POTS telephone line) or modulated to some higher frequency. However, wide bandwidths are easier to obtain and process at higher frequencies because

2288-496: Is only suitable for text. A few proprietary systems are used for private communications. A variant of RDS is the North American RBDS or "smart radio" system. In Germany the analog ARI system was used prior to RDS to alert motorists that traffic announcements were broadcast (without disturbing other listeners). Plans to use ARI for other European countries led to the development of RDS as a more powerful system. RDS

2376-444: Is open to anyone who does not carry a prohibition and can put up the appropriate licensing and royalty fees. In 2010 around 450 such licences were issued. Bandwidth (signal processing) Bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies . It is typically measured in unit of hertz (symbol Hz). It may refer more specifically to two subcategories: Passband bandwidth

2464-508: Is related to the transmitter 's RF power, the antenna gain , and antenna height . Interference from other stations is also a factor in some places. In the U.S, the FCC publishes curves that aid in calculation of this maximum distance as a function of signal strength at the receiving location. Computer modelling is more commonly used for this around the world. Many FM stations, especially those located in severe multipath areas, use extra audio compression /processing to keep essential sound above

2552-630: Is stereo, there will typically be a guard band between the upper limit of the DSBSC stereo signal (53 kHz) and the lower limit of any other subcarrier. Digital data services are also available. A 57 kHz subcarrier ( phase locked to the third harmonic of the stereo pilot tone) is used to carry a low-bandwidth digital Radio Data System signal, providing extra features such as station name, alternative frequency (AF), traffic data for satellite navigation systems and radio text (RT). This narrowband signal runs at only 1,187.5 bits per second , thus

2640-493: Is the difference between the upper and lower cutoff frequencies of, for example, a band-pass filter , a communication channel , or a signal spectrum . Baseband bandwidth is equal to the upper cutoff frequency of a low-pass filter or baseband signal, which includes a zero frequency. Bandwidth in hertz is a central concept in many fields, including electronics , information theory , digital communications , radio communications , signal processing , and spectroscopy and

2728-480: Is the total bandwidth (i.e. the maximum passband bandwidth of the carrier-modulated RF signal and the minimum passband bandwidth of the physical passband channel), and W {\displaystyle W} is the positive bandwidth (the baseband bandwidth of the equivalent channel model). For instance, the baseband model of the signal would require a low-pass filter with cutoff frequency of at least W {\displaystyle W} to stay intact, and

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2816-727: Is used, or some portion of it, with few exceptions: The frequency of an FM broadcast station (more strictly its assigned nominal center frequency) is usually a multiple of 100 kHz. In most of South Korea , the Americas , the Philippines , and the Caribbean , only odd multiples are used. Some other countries follow this plan because of the import of vehicles, principally from the United States, with radios that can only tune to these frequencies. In some parts of Europe , Greenland , and Africa , only even multiples are used. In

2904-620: Is usually defined as the arithmetic mean of the upper and lower frequencies so that, f C = f H + f L 2   {\displaystyle f_{\mathrm {C} }={\frac {f_{\mathrm {H} }+f_{\mathrm {L} }}{2}}\ } and B F = 2 ( f H − f L ) f H + f L . {\displaystyle B_{\mathrm {F} }={\frac {2(f_{\mathrm {H} }-f_{\mathrm {L} })}{f_{\mathrm {H} }+f_{\mathrm {L} }}}\,.} However,

2992-831: The FCC . Included were systems from 14 proponents including Crosby, Halstead, Electrical and Musical Industries, Ltd ( EMI ), Zenith, and General Electric. The individual systems were evaluated for their strengths and weaknesses during field tests in Uniontown, Pennsylvania , using KDKA-FM in Pittsburgh as the originating station. The Crosby system was rejected by the FCC because it was incompatible with existing subsidiary communications authorization (SCA) services which used various subcarrier frequencies including 41 and 67 kHz. Many revenue-starved FM stations used SCAs for "storecasting" and other non-broadcast purposes. The Halstead system

3080-595: The Light Programme , Third Programme and Home Service . These three networks used the sub-band 88.0–94.6 MHz. The sub-band 94.6–97.6 MHz was later used for BBC and local commercial services. However, only when commercial broadcasting was introduced to the UK in 1973 did the use of FM pick up in Britain. With the gradual clearance of other users (notably Public Services such as police, fire and ambulance) and

3168-543: The United Kingdom , both odd and even are used. In Italy , multiples of 50 kHz are used. In most countries the maximum permitted frequency error of the unmodulated carrier is specified, which typically should be within 2 kHz of the assigned frequency. There are other unusual and obsolete FM broadcasting standards in some countries, with non-standard spacings of 1, 10, 30, 74, 500, and 300 kHz. To minimise inter-channel interference, stations operating from

3256-560: The § Fractional bandwidth is smaller. Bandwidth is a key concept in many telecommunications applications. In radio communications, for example, bandwidth is the frequency range occupied by a modulated carrier signal . An FM radio receiver's tuner spans a limited range of frequencies. A government agency (such as the Federal Communications Commission in the United States) may apportion

3344-467: The (audio) input signal, determining the instantaneous frequency of the transmitted signal. Because transmitted FM signals use significantly more bandwidth than AM signals, this form of modulation is commonly used with the higher ( VHF or UHF ) frequencies used by TV , the FM broadcast band , and land mobile radio systems . The maximum frequency deviation of the carrier is usually specified and regulated by

3432-679: The 85th floor of the Empire State Building in New York City . These FM multiplex transmissions started in November 1934 and consisted of the main channel audio program and three subcarriers : a fax program, a synchronizing signal for the fax program and a telegraph order channel. These original FM multiplex subcarriers were amplitude modulated. Two musical programs, consisting of both the Red and Blue Network program feeds of

3520-487: The Elgin Public Schools, local high school sporting events, and was partially staffed by students to give them experience in high school radio station operation. The effort to bring WEPS on the air was led by Ernest C. Waggoner, director of audio-visual education for the school district. The station originally had an ERP of 10 watts. In 1960, the station's frequency was changed to 90.9 MHz, and its ERP

3608-665: The FCC announced the reassignment of the FM band to 90 channels from 88–106 MHz (which was soon expanded to 100 channels from 88–108 MHz). This shift, which the AM-broadcaster RCA had pushed for, made all the Armstrong-era FM receivers useless and delayed the expansion of FM. In 1961 WEFM (in the Chicago area) and WGFM (in Schenectady, New York ) were reported as the first stereo stations. By

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3696-496: The FCC that the system was compatible with existing two-channel stereo transmission and reception and that it did not interfere with adjacent stations. There were several variations on this system submitted 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 all

3784-520: The FM band.) The medium wave band (known as the AM band because most stations using it employ amplitude modulation) was overcrowded in western Europe, leading to interference problems and, as a result, many MW frequencies are suitable only for speech broadcasting. Belgium , the Netherlands , Denmark and particularly Germany were among the first countries to adopt FM on a widespread scale. Among

3872-979: The FM radio band from 87.5-108.0 MHz to 76.1-108.0 MHz to enable the migration of AM radio stations in Brazilian capitals and large cities. FM broadcasting began in the late 1930s, when it was initiated by a handful of early pioneer experimental stations, including W1XOJ/W43B/WGTR (shut down in 1953) and W1XTG/ WSRS , both transmitting from Paxton, Massachusetts (now listed as Worcester, Massachusetts ); W1XSL/W1XPW/W65H/WDRC-FM/WFMQ/WHCN , Meriden, Connecticut; and W2XMN , KE2XCC , and WFMN , Alpine, New Jersey (owned by Edwin Armstrong himself, closed down upon Armstrong's death in 1954). Also of note were General Electric stations W2XDA Schenectady and W2XOY New Scotland, New York—two experimental FM transmitters on 48.5 MHz—which signed on in 1939. The two began regular programming, as W2XOY, on November 20, 1940. Over

3960-399: The FM transmitter. The terms composite , multiplex and even MPX are used interchangeably to describe this signal. The instantaneous deviation of the transmitter carrier frequency due to the stereo audio and pilot tone (at 10% modulation) is where A and B are the pre-emphasized left and right audio signals and f p {\displaystyle f_{p}} =19 kHz is

4048-590: The NBC Radio Network, were simultaneously transmitted using the same system of subcarrier modulation as part of a studio-to-transmitter link system. In April 1935, the AM subcarriers were replaced by FM subcarriers, with much improved results. The first FM subcarrier transmissions emanating from Major Armstrong's experimental station KE2XCC at Alpine, New Jersey occurred in 1948. These transmissions consisted of two-channel audio programs, binaural audio programs and

4136-518: The background noise for listeners, often at the expense of overall perceived sound quality. In such instances, however, this technique is often surprisingly effective in increasing the station's useful range. The first radio station to broadcast in FM in Brazil was Rádio Imprensa, which began broadcasting in Rio de Janeiro in 1955, on the 102.1 MHz frequency, founded by businesswoman Anna Khoury. Due to

4224-583: The bandwidth is the frequency at which the closed-loop system gain drops 3 dB below peak. In communication systems, in calculations of the Shannon–Hartley channel capacity , bandwidth refers to the 3 dB-bandwidth. In calculations of the maximum symbol rate , the Nyquist sampling rate , and maximum bit rate according to the Hartley's law , the bandwidth refers to the frequency range within which

4312-585: The center frequency is sometimes defined as the geometric mean of the upper and lower frequencies, f C = f H f L {\displaystyle f_{\mathrm {C} }={\sqrt {f_{\mathrm {H} }f_{\mathrm {L} }}}} and B F = f H − f L f H f L . {\displaystyle B_{\mathrm {F} }={\frac {f_{\mathrm {H} }-f_{\mathrm {L} }}{\sqrt {f_{\mathrm {H} }f_{\mathrm {L} }}}}\,.} While

4400-402: The context of Nyquist symbol rate or Shannon-Hartley channel capacity for communication systems it refers to passband bandwidth. The Rayleigh bandwidth of a simple radar pulse is defined as the inverse of its duration. For example, a one-microsecond pulse has a Rayleigh bandwidth of one megahertz. The essential bandwidth is defined as the portion of a signal spectrum in

4488-431: The country is one of the main advantages over DAB/+ radio . This is still less than the range of AM radio waves, which because of their lower frequencies can travel as ground waves or reflect off the ionosphere , so AM radio stations can be received at hundreds (sometimes thousands) of miles. This is a property of the carrier wave's typical frequency (and power), not its mode of modulation. The range of FM transmission

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4576-567: The extension of the FM band to 108.0 MHz between 1980 and 1995, FM expanded rapidly throughout the British Isles and effectively took over from LW and MW as the delivery platform of choice for fixed and portable domestic and vehicle-based receivers. In addition, Ofcom (previously the Radio Authority) in the UK issues on demand Restricted Service Licences on FM and also on AM (MW) for short-term local-coverage broadcasting which

4664-404: The following, the absolute bandwidth is defined as follows, B = Δ f = f H − f L {\displaystyle B=\Delta f=f_{\mathrm {H} }-f_{\mathrm {L} }} where f H {\displaystyle f_{\mathrm {H} }} and f L {\displaystyle f_{\mathrm {L} }} are

4752-481: The formula below, is also generated. The pilot is transmitted at 8–10% of overall modulation level and used by the receiver to identify a stereo transmission and to regenerate the 38 kHz sub-carrier with the correct phase. The composite stereo multiplex signal contains the Main Channel (L+R), the pilot tone, and the (L−R) difference signal. This composite signal, along with any other sub-carriers, modulates

4840-470: The frequencies beyond which performance is degraded. In the case of frequency response , degradation could, for example, mean more than 3  dB below the maximum value or it could mean below a certain absolute value. As with any definition of the width of a function, many definitions are suitable for different purposes. In the context of, for example, the sampling theorem and Nyquist sampling rate , bandwidth typically refers to baseband bandwidth. In

4928-1279: The frequency domain using H ( f ) {\displaystyle H(f)} or in the time domain by exploiting the Parseval's theorem with the system impulse response h ( t ) {\displaystyle h(t)} . If H ( f ) {\displaystyle H(f)} is a lowpass system with zero central frequency and the filter reference gain is referred to this frequency, then: B n = ∫ − ∞ ∞ | H ( f ) | 2 d f 2 | H ( 0 ) | 2 = ∫ − ∞ ∞ | h ( t ) | 2 d t 2 | ∫ − ∞ ∞ h ( t ) d t | 2 . {\displaystyle B_{n}={\frac {\int _{-\infty }^{\infty }|H(f)|^{2}df}{2|H(0)|^{2}}}={\frac {\int _{-\infty }^{\infty }|h(t)|^{2}dt}{2\left|\int _{-\infty }^{\infty }h(t)dt\right|^{2}}}\,.} The same expression can be applied to bandpass systems by substituting

5016-463: The frequency domain which contains most of the energy of the signal. In some contexts, the signal bandwidth in hertz refers to the frequency range in which the signal's spectral density (in W/Hz or V /Hz) is nonzero or above a small threshold value. The threshold value is often defined relative to the maximum value, and is most commonly the 3 dB point , that is the point where the spectral density

5104-482: The frequency of the pilot tone. Slight variations in the peak deviation may occur in the presence of other subcarriers or because of local regulations. Another way to look at the resulting signal is that it alternates between left and right at 38 kHz, with the phase determined by the 19 kHz pilot signal. Most stereo encoders use this switching technique to generate the 38 kHz subcarrier, but practical encoder designs need to incorporate circuitry to deal with

5192-428: The gain is non-zero. The fact that in equivalent baseband models of communication systems, the signal spectrum consists of both negative and positive frequencies, can lead to confusion about bandwidth since they are sometimes referred to only by the positive half, and one will occasionally see expressions such as B = 2 W {\displaystyle B=2W} , where B {\displaystyle B}

5280-406: The geometric mean is more rarely used than the arithmetic mean (and the latter can be assumed if not stated explicitly) the former is considered more mathematically rigorous. It more properly reflects the logarithmic relationship of fractional bandwidth with increasing frequency. For narrowband applications, there is only marginal difference between the two definitions. The geometric mean version

5368-513: The high import costs of FM radio receivers, transmissions were carried out in circuit closed to businesses and stores, which played ambient music offered by radio. Until 1976, Rádio Imprensa was the only station operating in FM in Brazil. From the second half of the 1970s onwards, FM radio stations began to become popular in Brazil, causing AM radio to gradually lose popularity. In 2021, the Brazilian Ministry of Communications expanded

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5456-478: The higher audio frequencies within the baseband . This can be offset, to a limited extent, by boosting the high frequencies before transmission and reducing them by a corresponding amount in the receiver. Reducing the high audio frequencies in the receiver also reduces the high-frequency noise. These processes of boosting and then reducing certain frequencies are known as pre-emphasis and de-emphasis , respectively. The amount of pre-emphasis and de-emphasis used

5544-418: The ideal filter reference gain used. Typically, this gain equals | H ( f ) | {\displaystyle |H(f)|} at its center frequency, but it can also equal the peak value of | H ( f ) | {\displaystyle |H(f)|} . The noise equivalent bandwidth B n {\displaystyle B_{n}} can be calculated in

5632-524: The late 1960s, FM had been adopted for broadcast of stereo "A.O.R.—' Album Oriented Rock ' Format", but it was not until 1978 that listenership to FM stations exceeded that of AM stations in North America. In most of the 70s FM was seen as highbrow radio associated with educational programming and classical music, which changed during the 1980s and 1990s when Top 40 music stations and later even country music stations largely abandoned AM for FM. Today AM

5720-501: The late 1970s, Dolby FM was similar to Dolby B but used a modified 25 μs pre-emphasis time constant and a frequency selective companding arrangement to reduce noise. The pre-emphasis change compensates for the excess treble response that otherwise would make listening difficult for those without Dolby decoders. A similar system named High Com FM was tested in Germany between July 1979 and December 1981 by IRT . It

5808-465: The left (L) and right (R) channels are algebraically encoded into sum (L+R) and difference (L−R) signals. A mono receiver will use just the L+R signal so the listener will hear both channels through the single loudspeaker. A stereo receiver will add the difference signal to the sum signal to recover the left channel, and subtract the difference signal from the sum to recover the right channel. The (L+R) signal

5896-449: The licensing authorities in each country. For a stereo broadcast, the maximum permitted carrier deviation is invariably ±75 kHz, although a little higher is permitted in the United States when SCA systems are used. For a monophonic broadcast, again the most common permitted maximum deviation is ±75 kHz. However, some countries specify a lower value for monophonic broadcasts, such as ±50 kHz. The bandwidth of an FM transmission

5984-474: The musical styles which prevailed at the birth of FM broadcasting. Pre-emphasizing these high-frequency sounds would cause excessive deviation of the FM carrier . Modulation control (limiter) devices are used to prevent this. Systems more modern than FM broadcasting tend to use either programme-dependent variable pre-emphasis; e.g., dbx in the BTSC TV sound system, or none at all. Pre-emphasis and de-emphasis

6072-540: The next few years this station operated under the call signs W57A, W87A and WGFM, and moved to 99.5 MHz when the FM band was relocated to the 88–108 MHz portion of the radio spectrum. General Electric sold the station in the 1980s. Today this station is WRVE . Other pioneers included W2XQR/W59NY/WQXQ/WQXR-FM , New York; W47NV/WSM-FM Nashville, Tennessee (signed off in 1951); W1XER/W39B/WMNE , with studios in Boston and later Portland, Maine, but whose transmitter

6160-570: The others and was chosen as the national standard for Quadraphonic FM broadcasting in the United States. The first commercial FM station to broadcast quadraphonic program content was WIQB (now called WWWW-FM ) in Ann Arbor / Saline, Michigan under the guidance of Chief Engineer Brian Jeffrey Brown. Various attempts to add analog noise reduction to FM broadcasting were carried out in the 1970s and 1980s: A commercially unsuccessful noise reduction system used with FM radio in some countries during

6248-437: The physical passband channel would require a passband filter of at least B {\displaystyle B} to stay intact. The absolute bandwidth is not always the most appropriate or useful measure of bandwidth. For instance, in the field of antennas the difficulty of constructing an antenna to meet a specified absolute bandwidth is easier at a higher frequency than at a lower frequency. For this reason, bandwidth

6336-507: The rear channels. A breakthrough came in 1970 when KIOI ( K-101 ) in San Francisco successfully transmitted true quadraphonic sound from a single FM station using the Quadraplex system under Special Temporary Authority from the FCC . Following this experiment, a long-term test period was proposed that would permit one FM station in each of the top 25 U.S. radio markets to transmit in Quadraplex. The test results hopefully would prove to

6424-559: The reasons for this were: Public service broadcasters in Ireland and Australia were far slower at adopting FM radio than those in either North America or continental Europe . Hans Idzerda operated a broadcasting station, PCGG , at The Hague from 1919 to 1924, which employed narrow-band FM transmissions. In the United Kingdom the BBC conducted tests during the 1940s, then began FM broadcasting in 1955, with three national networks:

6512-478: The receiver after decoding. In the U.S. around 2010, using single-sideband modulation for the stereo subcarrier was proposed. It was theorized to be more spectrum-efficient and to produce a 4 dB s/n improvement at the receiver, and it was claimed that multipath distortion would be reduced as well. A handful of radio stations around the country broadcast stereo in this way, under FCC experimental authority. It may not be compatible with very old receivers, but it

6600-444: The regionally available bandwidth to broadcast license holders so that their signals do not mutually interfere. In this context, bandwidth is also known as channel spacing . For other applications, there are other definitions. One definition of bandwidth, for a system, could be the range of frequencies over which the system produces a specified level of performance. A less strict and more practically useful definition will refer to

6688-570: The required area is covered without causing interference to other stations further away. Practical transmitter powers range from a few milliwatts to 80 kW. As transmitter powers increase above a few kilowatts, the operating costs become high and only viable for large stations. The efficiency of larger transmitters is now better than 70% (AC power in to RF power out) for FM-only transmission. This compares to 50% before high efficiency switch-mode power supplies and LDMOS amplifiers were used. Efficiency drops dramatically if any digital HD Radio service

6776-399: The response at its peak, which, in the passband filter case, is typically at or near its center frequency , and in the low-pass filter is at or near its cutoff frequency . If the maximum gain is 0 dB, the 3 dB bandwidth is the frequency range where attenuation is less than 3 dB. 3 dB attenuation is also where power is half its maximum. This same half-power gain convention

6864-401: The same or close frequencies. Frequency modulation or FM is a form of modulation which conveys information by varying the frequency of a carrier wave ; the older amplitude modulation or AM varies the amplitude of the carrier, with its frequency remaining constant. With FM, frequency deviation from the assigned carrier frequency at any instant is directly proportional to the amplitude of

6952-399: The same or nearby transmitter sites tend to keep to at least a 500 kHz frequency separation even when closer frequency spacing is technically permitted. The ITU publishes Protection Ratio graphs, which give the minimum spacing between frequencies based on their relative strengths. Only broadcast stations with large enough geographic separations between their coverage areas can operate on

7040-462: The switching harmonics. Converting the multiplex signal back into left and right audio signals is performed by a decoder, built into stereo receivers. Again, the decoder can use a switching technique to recover the left and right channels. In addition, for a given RF level at the receiver, the signal-to-noise ratio and multipath distortion for the stereo signal will be worse than for the mono receiver. For this reason many stereo FM receivers include

7128-451: The upper and lower frequency limits respectively of the band in question. Fractional bandwidth is defined as the absolute bandwidth divided by the center frequency ( f C {\displaystyle f_{\mathrm {C} }} ), B F = Δ f f C . {\displaystyle B_{\mathrm {F} }={\frac {\Delta f}{f_{\mathrm {C} }}}\,.} The center frequency

7216-616: Was atop the highest mountain in the northeast United States, Mount Washington , New Hampshire (shut down in 1948); and W9XAO/W55M/WTMJ-FM Milwaukee, Wisconsin (went off air in 1950). A commercial FM broadcasting band was formally established in the United States as of January 1, 1941, with the first fifteen construction permits announced on October 31, 1940. These stations primarily simulcast their AM sister stations, in addition to broadcasting lush orchestral music for stores and offices, classical music to an upmarket listenership in urban areas, and educational programming. On June 27, 1945

7304-530: Was based on the Telefunken High ;Com broadband compander system, but was never introduced commercially in FM broadcasting. Yet another system was the CX -based noise reduction system FMX implemented in some radio broadcasting stations in the United States in the 1980s. FM broadcasting has included subsidiary communications authorization (SCA) services capability since its inception, as it

7392-450: Was effectively a full-time feed of the network due to the closure of U-46 facilities. In 2024. U-46 resumed programming on the station. In May 20th, 2024, the station rebranded as WPR Music specializing in classical, jazz, world, and folk music. FM broadcasting Throughout the world, the FM broadcast band falls within the VHF part of the radio spectrum . Usually 87.5 to 108.0 MHz

7480-465: Was increased to 380 watts. In 1977, the station began sharing time on the frequency with WDCB . WEPS moved to its current 88.9 MHz frequency in 1987, after reaching an agreement with WDCB, which allowed WDCB to begin full-time operations. The station became an affiliate of Wisconsin Public Radio's Ideas Network on September 28, 2005. During the COVID-19 pandemic throughout 2020 and early 2021, it

7568-509: Was rejected due to lack of high frequency stereo separation and reduction in the main channel signal-to-noise ratio. The GE and Zenith systems, so similar that they were considered theoretically identical, were formally approved by the FCC in April 1961 as the standard stereo FM broadcasting method in the United States and later adopted by most other countries. It is important that stereo broadcasts be compatible with mono receivers. For this reason,

7656-613: Was seen as another service which licensees could use to create additional income. Use of SCAs was particularly popular in the US, but much less so elsewhere. Uses for such subcarriers include radio reading services for the blind , which became common and remain so, private data transmission services (for example sending stock market information to stockbrokers or stolen credit card number denial lists to stores, ) subscription commercial-free background music services for shops, paging ("beeper") services, alternative-language programming, and providing

7744-446: Was used in the earliest days of FM broadcasting. According to a BBC report from 1946, 100 μs was originally considered in the US, but 75 μs subsequently adopted. Long before FM stereo transmission was considered, FM multiplexing of other types of audio-level information was experimented with. Edwin Armstrong, who invented FM, was the first to experiment with multiplexing, at his experimental 41 MHz station W2XDG located on

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