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85-458: WLFM (103.9 FM , "K-LOVE") is a broadcast radio station licensed to Lawrenceburg, Tennessee , serving Lawrenceburg and Lawrence County, Tennessee . WLFM is owned and operated by Educational Media Foundation , and broadcasts EMF's contemporary Christian K-LOVE format. 35°15′24.8″N 87°18′24.1″W  /  35.256889°N 87.306694°W  / 35.256889; -87.306694 This Tennessee radio station–related article

170-421: A liquid-crystal display capable of showing images such as weather maps, accompanied by "a light pen with which the radio can be programmed from barcodes", these barcodes encoding programme information, and supported detachable modules, of which a cassette player module and a printer module were developed. Despite reluctance to develop screen-based functionality that might bring RDS into competition with television,

255-422: A "group" of 104 bits (64 data bits + 40 check bits). There are slightly over 11.4 groups transmitted per second. There is no gap between blocks. The receiver synchronizes to groups and blocks by checking CRCs on each 26 bits until synchronization is achieved. Once synchronized (the offset word is predictable), the code is capable of correcting up to 5-bit burst errors . This basic modulation and block structure

340-399: 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 the same or close frequencies. Frequency modulation or FM

425-448: A 57  kHz subcarrier , so there are exactly 48 cycles of subcarrier during every data bit. The RBDS/RDS subcarrier was set to the third harmonic of the 19 kHz FM stereo pilot tone to minimize interference and intermodulation between the data signal, the stereo pilot and the 38 kHz DSB-SC stereo difference signal. (The stereo difference signal extends up 38 kHz + 15 kHz = 53 kHz, leaving 4 kHz for

510-402: 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

595-424: A growing number of RDS implementations in portable audio and navigation devices thanks to lower-priced, small-footprint solutions. The RDS sub-carrier at 57 kHz occupies ±2 kHz of the composite spectrum which in theory keeps it above the upper cutoff of the stereo subcarrier at 53 kHz. However the 53 kHz cutoff is entirely dependent on the performance of the 15 kHz low pass filters used before

680-512: A problem for people taking portable radios into or out of North America. The RDS standard as specified in EN 50067:1998 is separated into these sections according to the OSI model . (The network and transport layers are excluded, as this is a unidirectional broadcast standard.) The physical layer in the standard describes how the bitstream is retrieved from the radio signal. The RDS hardware first demodulates

765-557: 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

850-641: A project of the European Broadcasting Union (EBU), but has since become an international standard of the International Electrotechnical Commission (IEC). Radio Broadcast Data System ( RBDS ) is the official name used for the U.S. version of RDS. The two standards are only slightly different, with receivers able to work with either system with only minor inconsistencies in the displayed data. Both versions carry data at 1,187.5 bits per second (about 1.2   kbit/s ) on

935-429: A receiver can quickly search for a station which includes traffic reports. Another bit, traffic announcement (TA), is sent in block types 0A, 0B and 15B to indicate that such a report is in progress. It is common for otherwise- simulcast transmitters to have periodic local traffic reports which are customized to the individual transmitter. The traffic announcement bit tells a receiver that a transmitter-specific broadcast

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1020-417: 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

1105-515: Is a stub . You can help Misplaced Pages by expanding it . 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 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 ,

1190-408: 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 the (audio) input signal, determining the instantaneous frequency of

1275-525: 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

1360-401: 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

1445-464: Is assigned to France , Norway , Belarus and Egypt . Neighbouring countries never have the same country code which means it is not necessary for PI codes to be coordinated with adjacent countries. This is a short list of the full group type. Each group type may have a secondary version available This can be considered an additional program type bit, and indicates that the station broadcasts periodic traffic reports . By including it in every group,

1530-422: 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

1615-506: 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

1700-503: 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

1785-536: 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 ,

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1870-504: Is in progress, and it should avoid switching frequencies while they are in progress. (There is a different form of traffic announcement bit in block type 14B, which indicates the presence of a traffic announcement on a different frequency, so that radio receivers can automatically switch.) These are non-comprehensive examples that cover just the simple messages likes station name, radio text, and date/time. As we have already described previous fields above, these dot points below show just

1955-429: 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

2040-480: 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

2125-671: 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

2210-487: 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

2295-498: 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. Radio Data System Radio Data System ( RDS ) is a communications protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts . RDS standardizes several types of information transmitted, including time , station identification and program information. The standard began as

2380-508: 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

2465-626: 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

2550-402: 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 the higher audio frequencies within

2635-817: 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

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2720-580: 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

2805-440: 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

2890-415: The "offset", or block number within a 4-block group. The error correction is done using a 10-bit cyclic redundancy check , with polynomial x +x +x +x +x +x +1 . (Neither a preset nor post-invert is used, as they are not necessary with a fixed-size data field.) The CRC is also summed with one of five "offset" words which identify the block: A, B, C, C′, or D. Four consecutive blocks (ABCD or ABC′D) make up

2975-486: The 57 kHz RDS subcarrier signal to extract a differential Manchester encoded signal which contains both the bit clock and the differentially encoded bitstream. This allows the RDS decoder to tolerate phase inversion of its input. At the data link layer, 26 consecutive bits form a "block", consisting of 16 data bits followed by 10 error correction bits. Four blocks make a 104-bit "group". The error correction bits also encode

3060-655: 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

3145-663: 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 the United Kingdom , both odd and even are used. In Italy , multiples of 50 kHz are used. In most countries

3230-638: 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

3315-481: 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

3400-511: 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

3485-969: 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

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3570-399: 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

3655-579: 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

3740-480: The PI code; offset C is used when the third block contains something else. Block 1 always contains the 16-bit program identifier. The first 11 bits (bits 15–5) of block 2 are also the same in all groups. The first 4 bits (bits 15–11) of block 2 are the "group type code", which describe the interpretation of the remaining data. Each group type comes "A" and "B" variants, distinguished by the fifth "B" bit (bit 10): If B=0, then

3825-459: The RBS offset words are chosen to appear as uncorrectable errors to MBS receivers.) Data within each block (and group) is transmitted most significant bit first , and thus are numbered from bit 15 (transmitted first) to bit 0 (transmitted last). The most frequently information transmitted is a 16-bit "program identification" code, identifying the transmitting radio station. Blocks A and C′ always include

3910-424: The RDS and RBDS (North American) program type (PTY) codes and their meanings: The PTY codes have undergone several expansions. The first RDS standard only defined 0–15 and 31. The later RBDS standard implemented in the U.S. assigned the same meanings to codes 0, 1 and 31, but made no attempt to match the rest of the original RDS plan and created its own list for codes 2–22 and 30, including commercially important (in

3995-399: The RDS sub-carrier because of the harmonics created by the clipping. More modern composite clippers include filtering to protect the RDS subcarrier. The RDS subcarrier typically uses 2–4 kHz of carrier deviation. Therefore, the deviation available for the program material is reduced by this amount, assuming the usual 75 kHz deviation limit is not exceeded. The following table lists

4080-618: The U.S. National Radio Systems Committee issued the North American version of the RDS standard, called the Radio Broadcast Data System. The CENELEC standard was updated in 1992 with the addition of Traffic Message Channel and in 1998 with Open Data Applications and, in 2000, RDS was published worldwide as IEC standard 62106. The RDS-Forum (Geneva/CH) decided at its annual meeting (8–9 June 2015) in Glion/Montreux to bring

4165-532: The U.S.) radio formats such as top 40, religious, country, jazz and R&B which were not in the RDS list. This included mismatched codes for information. sport, and rock. Later RBDS standards added types 23 (College) and 29 (Weather), while the RDS type code list grew to its current size, importing some types (e.g. jazz and country) from the RDBS list. RDBS types 24–26 were added in April 2011. The code mismatches are mainly

4250-498: The application specific fields. The station name and decoder identification code is sent progressively over 4 groups, where the offset is defined by bit C1 and C0. As we have already described previous fields above, these dot points below show just the application specific fields. The station name and decoder identification code is sent progressively over 4 groups, where the offset is defined by bit C1 and C0. That This Field Is For Program Identification Code When group type 4A

4335-511: 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

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4420-431: 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

4505-553: 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

4590-516: The first 4 bits for Application/Group Type. Meaning of Block 2 Bits Block 3 is used for repeating program identification code. This allows for quick identification of radio program type, based on country, coverage area, and program reference number. While the country code is specified by the standard, bit 11 to bit 0 is specified by each country local authorities. Country codes are re-used, but only in geographically distant regions beyond FM broadcast range from each other. For example, country code F

4675-475: 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

4760-482: 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

4845-499: The group is 0A through 15A, and contains 5+16+16 = 37 bits of data. If B=1, block 2 contains a PI code (and is encoded with offset word C′), the group is one of 0B through 15B, and contains 21 bits of data. Within Block 1 and Block 2 are structures that will always be present in both group versions, for fast and responsive identifications. The first block of every group, will always be the program identification code. The second block dedicates

4930-505: 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

5015-517: 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

5100-496: 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

5185-462: 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

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5270-410: The lower sideband of the RDS signal.) The data is sent with an error correction code , but receivers may choose to use it only for error detection without correction. RDS defines many features including how private (in-house) or other undefined features can be "packaged" in unused program groups. RDS is only used on analog stations. The HD Radio equivalent is Program-associated data (PAD). RDS

5355-476: 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 is given by the Carson bandwidth rule which

5440-427: 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 the same or nearby transmitter sites tend to keep to at least

5525-469: 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

5610-415: The new standard RDS2 on the way. The standard will be created in close collaboration with U.S. colleagues from NRSC RBDS-Subcommittee and should offer a unified platform for FM broadcasting and data services worldwide. The following information fields are normally contained in the RDS data: As far as implementation is concerned, most car stereos will support at least AF, EON, REG, PS and TA/TP. There are

5695-536: 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

5780-565: 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

5865-500: 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

5950-551: 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:

6035-478: 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

6120-570: 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

6205-420: The stereo encoder. In older equipment, these filters were only designed to protect the 19 kHz pilot and sometimes did not provide sufficient protection to the RDS subcarrier when a significant amount of stereo information was present. In this situation, stereo enhancement devices combined with aggressive audio processing could render the RDS subcarrier unreceivable. Composite clipping systems may also degrade

6290-462: 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

6375-528: The three broadcasting partners of the EBU, the BBC were reportedly pursuing the application of RDS technology most enthusiastically and sought to attract bids from manufacturers to make a "BBC-accredited radio" supporting RDS features. Having received no manufacturer interest, however, the corporation engaged designers at Kinneir Dufort to produce a prototype showcasing these features. This prototype, unveiled in 1989, incorporated

6460-462: 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 the licensing authorities in each country. For a stereo broadcast,

6545-405: The utility of being able to print out information such as weather maps or even advertising was regarded as potentially interesting to both radio and television manufacturers alike. Enhancements to the alternative frequencies functionality were added to the standard and it was subsequently published as a European Committee for Electrotechnical Standardization (CENELEC) standard in 1990. In 1992

6630-616: 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

6715-518: 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

6800-556: Was inspired by the development of the Autofahrer-Rundfunk-Informationssystem (ARI) in Germany by the Institut für Rundfunktechnik (IRT) and the radio manufacturer Blaupunkt . ARI used a 57-kHz subcarrier to indicate the presence of traffic information in an FM radio broadcast. The EBU Technical Committee launched a project at its 1974 Paris meeting to develop a technology with similar purposes to ARI, but which

6885-544: Was more flexible and which would enable automated retuning of a receiver where a broadcast network transmitted the same radio programme on a number of different frequencies. The modulation system was based on that used in a Swedish paging system and the baseband coding was a new design, mainly developed by the British Broadcasting Corporation (BBC) and the IRT. The EBU issued the first RDS specification in 1984. Of

6970-598: Was originally developed for the MBS (radio paging)  [ fr ] "mobile search" protocol, with the difference that MBS (or the North American equivalent MMBS "modified MBS") does not use an offset word. To allow the two systems to interoperate (and to allow FM radio stations to transmit RBDS data while maintaining their pager contracts), the RBDS standard defines a sixth all-zero offset word E. Groups of four E blocks may be mixed with RBDS groups, and ignored by RBDS receivers. (Likewise,

7055-457: 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,

7140-610: 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

7225-446: 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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