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84-689: Narrow band Frequency Modulation was developed and demonstrated by Hanso Idzerda in 1919. Wide band Frequency modulation radio originated in the United States during the 1930s; the system was developed by the American electrical engineer Edwin Howard Armstrong . However, FM broadcasting did not become widespread, even in North America , until the 1960s. Frequency-modulated radio waves can be generated at any frequency. All

168-418: A carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications , radio broadcasting , signal processing , and computing . In analog frequency modulation, such as radio broadcasting, of an audio signal representing voice or music, the instantaneous frequency deviation , i.e. the difference between the frequency of the carrier and its center frequency, has

252-456: A "converter" to down-convert the 87.5 to 107.9 MHz band to the frequencies that the radio can accept. In addition to showing an incorrect frequency, there are two other disadvantages that can result in undesired performance; the converter cannot down-convert in full the regular international FM band (up to 20.5 MHz wide) to the only 14 MHz-wide Japanese band (unless the converter incorporates two user-switchable down-convert modes), and

336-432: A 2.2 kHz audio tone produces a modulation index of 1.36. Suppose that we limit ourselves to only those sidebands that have a relative amplitude of at least 0.01. Then, examining the chart shows this modulation index will produce three sidebands. These three sidebands, when doubled, gives us (6 × 2.2 kHz) or a 13.2 kHz required bandwidth. A rule of thumb , Carson's rule states that nearly all (≈98 percent) of

420-443: A baseband modulating signal may be approximated by a sinusoidal continuous wave signal with a frequency f m . This method is also named as single-tone modulation. The integral of such a signal x m ( t ) = c o s ( 2 π f m t ) {\displaystyle x_{m}(t)=cos(2\pi f_{m}t)} is: In this case, the expression for y(t) above simplifies to: where

504-435: A binary signal modulates the carrier, the modulation index is given by: where T s {\displaystyle T_{s}\,} is the symbol period, and f m = 1 2 T s {\displaystyle f_{m}={\frac {1}{2T_{s}}}\,} is used as the highest frequency of the modulating binary waveform by convention, even though it would be more accurate to say it

588-695: A decree was issued that required all new radios produced in the Free Economic Zone of Manaus beginning on January 1, 2019, to support tuning the extended band. By 2019, some makers of new automobiles, including Ford and Hyundai , and stereo manufacturer Pioneer Corporation were producing radios that supported the new band. Necessary regulatory changes by the National Telecommunications Agency (ANATEL) came into effect on November 3, 2020. The new frequencies will support AM–FM migration in parts of Brazil where there

672-541: A functional relation to the modulating signal amplitude. Digital data can be encoded and transmitted with a type of frequency modulation known as frequency-shift keying (FSK), in which the instantaneous frequency of the carrier is shifted among a set of frequencies. The frequencies may represent digits, such as '0' and '1'. FSK is widely used in computer modems such as fax modems , telephone caller ID systems, garage door openers, and other low-frequency transmissions. Radioteletype also uses FSK. Frequency modulation

756-456: A lack of selectivity may cause one station to be overtaken by another on an adjacent channel . Frequency drift was a problem in early (or inexpensive) receivers; inadequate selectivity may affect any tuner. A wideband FM signal can also be used to carry a stereo signal; this is done with multiplexing and demultiplexing before and after the FM process. The FM modulation and demodulation process

840-475: A limit of three kilowatts of effective radiated power (ERP) and an antenna height limit for the center of radiation of 300 feet (91.4 m) height above average terrain ( HAAT ). These frequencies were 92.1, 92.7, 93.5, 94.3, 95.3, 95.9, 96.7, 97.7, 98.3, 99.3, 100.1, 100.9, 101.7, 102.3, 103.1, 103.9, 104.9, 105.5, 106.3 and 107.1. On other frequencies, a station could be Class B (50 kW, 500 feet) or Class C (100 kW, 2,000 feet), depending on which zone it

924-644: A method to support AM stations by migrating them to FM; that year, President Dilma Rousseff signed a law that started the AM–FM migration process in Brazil. Since then, 1,720 of the country's 1,781 AM outlets have requested migration, including in areas where no further FM stations could be added. Jovem Pan News in São Paulo was allowed by the Ministry of Communications to conduct tests on 84.7 MHz in 2014. In 2017,

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1008-632: A mirror of normal FM broadcasts. The main purpose of those stations is compatibility with older equipment. In 2014, Russia began replacing OIRT-banded transmitter with CCIR-banded (the "western") FM transmitters. The main reason for the change to CCIR FM is to reach more listeners. Unlike Western practice, OIRT FM frequencies are based on 30 kHz rather than 50, 100 or 200 kHz multiples. This may have been to reduce co-channel interference caused by Sporadic E propagation and other atmospheric effects, which occur more often at these frequencies. However, multipath distortion effects are less annoying than on

1092-717: A reservation of 106.1–107.9 MHz for community and indigenous stations in 2014, though dozens of stations are grandfathered due to lack of space to relocate them.) Originally, the American Federal Communications Commission (FCC) devised a bandplan in which FM radio stations would be assigned at intervals of four channels (800 kHz separation) for any one geographic area. Thus, in one area, stations might be at 88.1, 88.9, 89.7, etc., while in an adjacent area, stations might be at 88.3, 89.1, 89.9, 90.7 etc. Certain frequencies were designated for Class A only (see FM broadcasting ), which had

1176-489: A scientific and technical conversation in the Nizhny Novgorod Radio Laboratory , reported about his new method of telephony, based on a change in the period of oscillations. Demonstration of frequency modulation was carried out on the laboratory model. Frequency modulated systems are a widespread and commercially available assistive technology that make speech more understandable by improving

1260-472: A special audio carrier on their ATSC 3.0 signals to continue the status quo. With the gradual adoption of digital radio broadcasting (e.g. HD Radio , DAB+ ) radio, some countries have planned and started an FM radio switch-off . Norway , in January 2018, was the first country to discontinue FM as a result. Frequency Modulation Frequency modulation ( FM ) is the encoding of information in

1344-465: A target, its outgoing sounds return as echoes, which are Doppler-shifted upward in frequency. In certain species of bats, which produce constant frequency (CF) echolocation calls, the bats compensate for the Doppler shift by lowering their call frequency as they approach a target. This keeps the returning echo in the same frequency range of the normal echolocation call. This dynamic frequency modulation

1428-470: A tone-modulated FM wave, if the modulation frequency is held constant and the modulation index is increased, the (non-negligible) bandwidth of the FM signal increases but the spacing between spectra remains the same; some spectral components decrease in strength as others increase. If the frequency deviation is held constant and the modulation frequency increased, the spacing between spectra increases. Frequency modulation can be classified as narrowband if

1512-414: A wider signal bandwidth than amplitude modulation by an equivalent modulating signal; this also makes the signal more robust against noise and interference . Frequency modulation is also more robust against signal-amplitude-fading phenomena. As a result, FM was chosen as the modulation standard for high frequency, high fidelity radio transmission, hence the term " FM radio " (although for many years

1596-748: Is 6 MHz wide). The narrowness of the Japanese band (19 MHz compared to slightly more than 20 MHz for the CCIR band) limits the number of FM stations that can be accommodated on the dial with the result that many commercial radio stations are forced to use AM . Many Japanese radios are capable of receiving both the Japanese FM band and the CCIR FM band, so that the same model can be sold within Japan or exported. The radio may cover 76 to 108 MHz,

1680-434: Is broadcast over FM radio . However, under severe enough multipath conditions it performs much more poorly than AM, with distinct high frequency noise artifacts that are audible with lower volumes and less complex tones. With high enough volume and carrier deviation audio distortion starts to occur that otherwise wouldn't be present without multipath or with an AM signal. Frequency modulation and phase modulation are

1764-512: Is called the Doppler Shift Compensation (DSC), and was discovered by Hans Schnitzler in 1968. FM is also used at intermediate frequencies by analog VCR systems (including VHS ) to record the luminance (black and white) portions of the video signal. Commonly, the chrominance component is recorded as a conventional AM signal, using the higher-frequency FM signal as bias . FM is the only feasible method of recording

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1848-454: Is entirely within the OIRT FM band. Operators on this band and the 6-meter band (50–54 MHz) use the presence of broadcast stations as an indication that there is an "opening" into Eastern Europe or Russia. This can be a mixed blessing because the 4 meter amateur allocation is only 0.5 MHz or less, and a single broadcast station causes considerable interference to a large part of

1932-418: Is identical in stereo and monaural processes. FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech . In broadcast services, where audio fidelity is important, wideband FM is generally used. Analog TV sound is also broadcast using FM. Narrowband FM is used for voice communications in commercial and amateur radio settings. In two-way radio , narrowband FM (NBFM)

2016-493: Is insufficient room to migrate stations on the standard band alone, which is the case in 14 states. However, they will not be accessible on all radio receivers, including smartphones, if these cannot be updated or replaced. On May 7, 2021, the first ten stations began broadcasting on the extended band. Five, all on 87.1 MHz, are owned by the public broadcaster Brazil Communication Company (EBC). Four of those five are being used to rebroadcast Rádio Nacional 's AM service, while

2100-875: Is largely no longer possible due to the 2009 digital television transition , though in 2023 the FCC authorized fourteen low-powered Channel 6 television stations to continue to operate radio services indefinitely. In the United States, the twenty-one channels with center frequencies of 87.9–91.9 MHz (channels 200 through 220) constitute the reserved band , exclusively for non-commercial educational ( NCE ) stations. The other channels (92.1 MHz through 107.9 MHz (Channels 221–300) may be used by both commercial and non-commercial stations. (Note that in Canada and in Mexico this reservation does not apply; Mexico introduced

2184-420: Is reduced to an acceptable level. FM is also used at audio frequencies to synthesize sound. This technique, known as FM synthesis , was popularized by early digital synthesizers and became a standard feature in several generations of personal computer sound cards . Edwin Howard Armstrong (1890–1954) was an American electrical engineer who invented wideband frequency modulation (FM) radio. He patented

2268-405: Is the frequency deviation , which represents the maximum shift away from f c in one direction, assuming x m ( t ) is limited to the range ±1. It is important to realize that this process of integrating the instantaneous frequency to create an instantaneous phase is quite different from what the term "frequency modulation" naively implies, namely directly adding the modulating signal to

2352-466: Is the Deviation ratio which is the ratio of frequency deviation to highest frequency of modulating non-sinusoidal signal. FM provides improved signal-to-noise ratio (SNR), as compared for example with AM . Compared with an optimum AM scheme, FM typically has poorer SNR below a certain signal level called the noise threshold, but above a higher level – the full improvement or full quieting threshold –

2436-486: Is the Modulation index which is the ratio of frequency deviation to highest frequency in the modulating signal and f m {\displaystyle f_{m}\,} is the highest frequency in the modulating signal. Condition for application of Carson's rule is only sinusoidal signals. For non-sinusoidal signals: where W is the highest frequency in the modulating signal but non-sinusoidal in nature and D

2520-468: Is the highest fundamental of the modulating binary waveform. In the case of digital modulation, the carrier f c {\displaystyle f_{c}\,} is never transmitted. Rather, one of two frequencies is transmitted, either f c + Δ f {\displaystyle f_{c}+\Delta f} or f c − Δ f {\displaystyle f_{c}-\Delta f} , depending on

2604-416: Is used for FM broadcasting , in which music and speech are transmitted with up to 75 kHz deviation from the center frequency and carry audio with up to a 20 kHz bandwidth and subcarriers up to 92 kHz. For the case of a carrier modulated by a single sine wave, the resulting frequency spectrum can be calculated using Bessel functions of the first kind, as a function of the sideband number and

FM broadcast band - Misplaced Pages Continue

2688-513: Is used for AM broadcasting. A better solution is to replace the radio and antenna with ones designed for the country where the car will be used. Australia had a similar situation with Australian TV channels 3, 4 and 5 that are between 88 and 108 MHz, and was intending to follow Japan, but in the end opted for the western bandplan, due to CCIR radios that entered the country. There were some radios sold in Australia for 76 to 90 MHz. In

2772-586: Is used to conserve bandwidth for land mobile, marine mobile and other radio services. A high-efficiency radio-frequency switching amplifier can be used to transmit FM signals (and other constant-amplitude signals ). For a given signal strength (measured at the receiver antenna), switching amplifiers use less battery power and typically cost less than a linear amplifier . This gives FM another advantage over other modulation methods requiring linear amplifiers, such as AM and QAM . There are reports that on October 5, 1924, Professor Mikhail A. Bonch-Bruevich , during

2856-523: Is widely used for FM radio broadcasting . It is also used in telemetry , radar , seismic prospecting, and monitoring newborns for seizures via EEG , two-way radio systems, sound synthesis , magnetic tape-recording systems and some video-transmission systems. In radio transmission, an advantage of frequency modulation is that it has a larger signal-to-noise ratio and therefore rejects radio frequency interference better than an equal power amplitude modulation (AM) signal. For this reason, most music

2940-634: The BBC called it "VHF radio" because commercial FM broadcasting uses part of the VHF band – the FM broadcast band ). FM receivers employ a special detector for FM signals and exhibit a phenomenon known as the capture effect , in which the tuner "captures" the stronger of two stations on the same frequency while rejecting the other (compare this with a similar situation on an AM receiver, where both stations can be heard simultaneously). Frequency drift or

3024-614: The Czech Republic and Slovakia . The first transmitter was put into operation on 102.5 MHz near Prague in November 1984. Three years later, there were eleven transmitters in service across the country, including three in the Prague neighborhood of Žižkov. In 1988, the plan was to set up 270 transmitters in 45 locations eventually. The transition was finished in 1993. In Poland all OIRT broadcast transmitters were closed down at

3108-405: The FM capture effect removes print-through and pre-echo . A continuous pilot-tone, if added to the signal – as was done on V2000 and many Hi-band formats – can keep mechanical jitter under control and assist timebase correction . These FM systems are unusual, in that they have a ratio of carrier to maximum modulation frequency of less than two; contrast this with FM audio broadcasting, where

3192-625: The sinusoidal carrier is x c ( t ) = A c cos ⁡ ( 2 π f c t ) {\displaystyle x_{c}(t)=A_{c}\cos(2\pi f_{c}t)\,} , where f c is the carrier's base frequency, and A c is the carrier's amplitude, the modulator combines the carrier with the baseband data signal to get the transmitted signal: where f Δ = K f A m {\displaystyle f_{\Delta }=K_{f}A_{m}} , K f {\displaystyle K_{f}} being

3276-553: The 1930s investigations were begun into establishing radio stations transmitting on "Very High Frequency" (VHF) assignments above 30 MHz. In October 1937, the Federal Communications Commission (FCC) announced new frequency allocations, which included a band of experimental and educational " Apex " stations, that consisted of 75 channels spanning from 41.02 to 43.98 MHz. Like the existing AM band these stations employed amplitude modulation, however

3360-536: The 40 kHz spacing between adjacent frequencies was four times as much as the 10 kHz spacing on the standard AM broadcast band, which reduced adjacent-frequency interference, and provided more bandwidth for high-fidelity programming. Also during the 1930s Edwin Howard Armstrong developed a competing transmission technology, "wide-band frequency modulation", which was promoted as being superior to AM transmissions, in particular due to its high-fidelity and near immunity to static interference. In May 1940, largely as

3444-428: The 88–108 section band as normal FM. The compatibility of "TV sound" with conventional FM radio ended with the U.S. digital TV transition in 2009, with the exception of the limited number of low-power stations on channel 6 that still use analog; these low-power stations will switch to digital in 2021. Second-hand automobiles imported from Japan contain a radio designed for the Japanese FM band, and importers often fit

FM broadcast band - Misplaced Pages Continue

3528-421: The CCIR band. Stereo is generally achieved by sending the stereo difference signal, using a process called polar modulation . Polar modulation uses a reduced subcarrier on 31.25 kHz with the audio on both side-bands. This gives the following signal structure: L + R --> 31.25 kHz reduced subcarrier L - R. The 4-meter band (70–70.5 MHz) amateur radio allocation used in many European countries

3612-632: The OIRT band are Russia (including Kaliningrad ), Belarus , Moldova , Ukraine , and Turkmenistan . In Czechoslovakia , the decision to use the 87.5 to 108 MHz band instead of 65.9 to 74 MHz band was made in the beginning of the eighties. The frequency plan was created, which was internationally coordinated at Regional Administrative Conference for FM Sound Broadcasting in the VHF band in Geneva, 1984. Allocated frequencies are still valid and are used in

3696-755: The SNR is much improved over AM. The improvement depends on modulation level and deviation. For typical voice communications channels, improvements are typically 5–15 dB. FM broadcasting using wider deviation can achieve even greater improvements. Additional techniques, such as pre-emphasis of higher audio frequencies with corresponding de-emphasis in the receiver, are generally used to improve overall SNR in FM circuits. Since FM signals have constant amplitude, FM receivers normally have limiters that remove AM noise, further improving SNR. FM signals can be generated using either direct or indirect frequency modulation: Many FM detector circuits exist. A common method for recovering

3780-457: The amplitude A m {\displaystyle A_{m}\,} of the modulating sinusoid is represented in the peak deviation f Δ = K f A m {\displaystyle f_{\Delta }=K_{f}A_{m}} (see frequency deviation ). The harmonic distribution of a sine wave carrier modulated by such a sinusoidal signal can be represented with Bessel functions ; this provides

3864-463: The band. The System D television channels R4 and R5 lie wholly or partly within the 87.5–108 MHz FM audio broadcast band. Countries which still use System D therefore have to consider the re-organisation of TV broadcasting in order to make full use of this band for audio broadcasting. The FM band in Japan is 76–95 MHz (previously 76–90). The 90–108 MHz section was used for analog VHF TV Channels 1, 2 and 3 (each NTSC television channel

3948-484: The band. Stations in the U.S. may go up to 10% over this limit if they use non-stereo subcarriers , increasing total modulation by 0.5% for each 1% used by the subcarriers. Some stations may limited to (±50 kHz) deviation in order to reduce transmitted bandwidth so that additional stations can be squeezed in. The OIRT FM broadcast band covers 65.8 to 74 MHz. It was used in the Soviet Union and most of

4032-559: The bands mentioned in this article are in the very high frequency (VHF) range, which extends from 30 to 300 MHz. While all countries use FM channel center frequencies ending in 0.1, 0.3, 0.5, 0.7, and 0.9 MHz, some countries also use center frequencies ending in 0.0, 0.2, 0.4, 0.6, and 0.8 MHz. A few others also use 0.05, 0.15, 0.25, 0.35, 0.45, 0.55, 0.65, 0.75, 0.85, and 0.95 MHz. An ITU conference in Geneva , Switzerland , on December 7, 1984, resolved to discontinue

4116-476: The bandwidth currently occupied by analog television channels 5 and 6 (76–88 MHz) over to extending the FM broadcast band when the digital television transition was to be completed in February 2009 (ultimately delayed to June 2009). This proposed allocation would have effectively assigned frequencies corresponding to the existing Japanese FM radio service (which begins at 76 MHz) for use as an extension to

4200-402: The basis for a mathematical understanding of frequency modulation in the frequency domain. As in other modulation systems, the modulation index indicates by how much the modulated variable varies around its unmodulated level. It relates to variations in the carrier frequency : where f m {\displaystyle f_{m}\,} is the highest frequency component present in

4284-405: The binary state 0 or 1 of the modulation signal. If h ≫ 1 {\displaystyle h\gg 1} , the modulation is called wideband FM and its bandwidth is approximately 2 f Δ {\displaystyle 2f_{\Delta }\,} . While wideband FM uses more bandwidth, it can improve the signal-to-noise ratio significantly; for example, doubling

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4368-515: The car's antenna may perform poorly on the higher FM band. Some converters simply down-convert the FM band by 12 MHz, leading to logical frequencies (e.g. 78.9 for 90.9, 82.3 for 94.3, etc.), but leaving off the 102–108 MHz band. Also, RDS is not used in Japan, whereas most modern car radios available in Europe have this system. Also the converter may not allow pass-through of the MW band , which

4452-575: The carrier frequency which would result in a modulated signal that has spurious local minima and maxima that do not correspond to those of the carrier. While most of the energy of the signal is contained within f c ± f Δ , it can be shown by Fourier analysis that a wider range of frequencies is required to precisely represent an FM signal. The frequency spectrum of an actual FM signal has components extending infinitely, although their amplitude decreases and higher-order components are often neglected in practical design problems. Mathematically,

4536-482: The change in the carrier frequency is about the same as the signal frequency, or as wideband if the change in the carrier frequency is much higher (modulation index > 1) than the signal frequency. For example, narrowband FM (NFM) is used for two-way radio systems such as Family Radio Service , in which the carrier is allowed to deviate only 2.5 kHz above and below the center frequency with speech signals of no more than 3.5 kHz bandwidth. Wideband FM

4620-482: The conventional band of 87.5 to 108 MHz that was previously used. The reclaimed spectrum was previously used to broadcast analog television channels 5 and 6 before the country's digital television transition . The first eFM stations began broadcasting on May 7, 2021, and the spectrum is being used as part of a plan to migrate AM stations to the FM band. The idea of converting the former channels 5 and 6 for sound broadcasting use had been first floated in Brazil in 2013, as

4704-470: The demodulation may be carried out by using the Hilbert transform (implemented as a filter) to recover the instantaneous phase, and thereafter differentiating this phase (using another filter) to recover the instantaneous frequency. Alternatively, a complex mixer followed by a bandpass filter may be used to translate the signal to baseband, and then proceeding as before. When an echolocating bat approaches

4788-515: The end of 1999. Hungary closed down its remaining broadcast transmitters in 2007, and for thirty days in July of that year, several Hungarian amateur radio operators received a temporary experimental permit to perform propagation and interference experiments in the 70–70.5 MHz band. In Belarus, only government-run public radio stations are still active on OIRT. All stations on OIRT in Belarus are

4872-421: The existing North American FM broadcast band. Several low-power television stations colloquially known as " Franken-FMs " operated primarily as radio stations on channel 6, using the 87.7 MHz audio carrier of that channel as a radio station receivable on most FM receivers configured to cover the whole of Band II , from 2009 to 2021; since then, a reduced number have received special temporary authority to carry

4956-579: The fields of radio engineering and government. The center frequencies of the FM channels are spaced in increments of 200 kHz. The frequency of 87.9 MHz, while technically part of TV channel 6 (82 to 88 MHz), is used by just two FM class-D stations in the United States. Portable radio tuners often tune down to 87.5 MHz, so that the same radios can be made and sold worldwide. Automobiles usually have FM radios that can tune down to 87.7 MHz, so that TV channel 6's audio at 87.75 MHz (±10 kHz) could be received while driving. This

5040-423: The first 20 channels reserved for educational stations. A period of allowing existing FM stations to broadcast on both the original "low" and new "high" FM bands followed, which ended at midnight on January 8, 1949, at which time all low band transmissions had to end. In 1978 one additional frequency reserved for educational stations, 87.9 MHz, was allocated. In March 2008, the FCC requested public comment on turning

5124-457: The first extended-band stations to begin broadcasts on May 7, 2021. In 2023, Chile announced the expansion of the FM band to 76-108 MHz as part of the analog TV shutdown, scheduled for April 2024. Normally each channel is 200  kHz (0.2 MHz) wide, and can pass audio and subcarrier frequencies up to 100 kHz. Deviation is typically limited to 150 kHz total (±75 kHz) in order to prevent adjacent-channel interference on

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5208-511: The frequency coverage may be selectable by the user, or during assembly the radio may be set to operate on one band by means of a specially placed diode or other internal component. Conventional analog-tuned (dial & pointer) radios were formerly marked with "TV Sound" in the 76–88 section. If these radios were sold in the US, for example, the 76–88 section would be marked TV sound for VHF channels 5 and 6 (as two 6 MHz-wide NTSC TV channels), with

5292-579: The information signal is through a Foster–Seeley discriminator or ratio detector . A phase-locked loop can be used as an FM demodulator. Slope detection demodulates an FM signal by using a tuned circuit which has its resonant frequency slightly offset from the carrier. As the frequency rises and falls the tuned circuit provides a changing amplitude of response, converting FM to AM. AM receivers may detect some FM transmissions by this means, although it does not provide an efficient means of detection for FM broadcasts. In Software-Defined Radio implementations

5376-491: The location and class conform to the rules in the FCC separation table. The rules for second-adjacent-channel spacing do not apply for stations licensed before 1964. In 2017, Brazil laid the groundwork to reclaim channels 5 and 6 (76.1–87.5 MHz) for sound broadcasting use and required new radio receivers to be able to tune into the new extended band ( Portuguese : faixa estendida , abbreviated eFM). Five transmitters of public broadcaster Brazil Communication Company were

5460-444: The luminance ("black-and-white") component of video to (and retrieving video from) magnetic tape without distortion; video signals have a large range of frequency components – from a few hertz to several megahertz , too wide for equalizers to work with due to electronic noise below −60  dB . FM also keeps the tape at saturation level, acting as a form of noise reduction ; a limiter can mask variations in playback output, and

5544-402: The modulating signal x m ( t ), and Δ f {\displaystyle \Delta {}f\,} is the peak frequency-deviation – i.e. the maximum deviation of the instantaneous frequency from the carrier frequency. For a sine wave modulation, the modulation index is seen to be the ratio of the peak frequency deviation of the carrier wave to the frequency of

5628-536: The modulating sine wave. If h ≪ 1 {\displaystyle h\ll 1} , the modulation is called narrowband FM (NFM), and its bandwidth is approximately 2 f m {\displaystyle 2f_{m}\,} . Sometimes modulation index h < 0.3 {\displaystyle h<0.3}  is considered NFM and other modulation indices are considered wideband FM (WFM or FM). For digital modulation systems, for example, binary frequency shift keying (BFSK), where

5712-448: The modulation index. The carrier and sideband amplitudes are illustrated for different modulation indices of FM signals. For particular values of the modulation index, the carrier amplitude becomes zero and all the signal power is in the sidebands. Since the sidebands are on both sides of the carrier, their count is doubled, and then multiplied by the modulating frequency to find the bandwidth. For example, 3 kHz deviation modulated by

5796-480: The new service. Following the end of the war, the FCC moved to standardize its frequency allocations. One area of concern was the effects of tropospheric and Sporadic E propagation , which at times reflected station signals over great distances, causing mutual interference. A particularly controversial proposal, spearheaded by the Radio Corporation of America (RCA), which was headed by David Sarnoff ,

5880-541: The other Warsaw Pact member countries of the International Radio and Television Organisation in Eastern Europe (OIRT), with the exception of East Germany , which always used the 87.5 to 100 (later 104) MHz broadcast band—in line with Western Europe. The lower portion of the VHF band behaves a bit like shortwave radio in that it has a longer reach than the upper portion of the VHF band. It

5964-505: The power of a frequency-modulated signal lies within a bandwidth B T {\displaystyle B_{T}\,} of: where Δ f {\displaystyle \Delta f\,} , as defined above, is the peak deviation of the instantaneous frequency f ( t ) {\displaystyle f(t)\,} from the center carrier frequency f c {\displaystyle f_{c}} , β {\displaystyle \beta }

6048-411: The ratio is around 10,000. Consider, for example, a 6-MHz carrier modulated at a 3.5-MHz rate; by Bessel analysis, the first sidebands are on 9.5 and 2.5 MHz and the second sidebands are on 13 MHz and −1 MHz. The result is a reversed-phase sideband on +1 MHz; on demodulation, this results in unwanted output at 6 – 1 = 5 MHz. The system must be designed so that this unwanted output

6132-619: The regenerative circuit in 1914, the superheterodyne receiver in 1918 and the super-regenerative circuit in 1922. Armstrong presented his paper, "A Method of Reducing Disturbances in Radio Signaling by a System of Frequency Modulation", (which first described FM radio) before the New York section of the Institute of Radio Engineers on November 6, 1935. The paper was published in 1936. As the name implies, wideband FM (WFM) requires

6216-463: The result of Armstrong's efforts, the FCC decided to eliminate the Apex band, and authorized an FM band effective January 1, 1941, operating on 40 channels spanning 42–50 MHz, with the first five channels reserved for educational stations. There was significant interest in the new FM band by station owners, however, construction restrictions that went into place during World War II limited the growth of

6300-404: The sensitivity of the frequency modulator and A m {\displaystyle A_{m}} being the amplitude of the modulating signal or baseband signal. In this equation, f ( τ ) {\displaystyle f(\tau )\,} is the instantaneous frequency of the oscillator and f Δ {\displaystyle f_{\Delta }\,}

6384-575: The signal-to-noise ratio in the user's ear. They are also called auditory trainers , a term which refers to any sound amplification system not classified as a hearing aid . They intensify signal levels from the source by 15 to 20 decibels. FM systems are used by hearing-impaired people as well as children whose listening is affected by disorders such as auditory processing disorder or ADHD . For people with sensorineural hearing loss , FM systems result in better speech perception than hearing aids. They can be coupled with behind-the-ear hearing aids to allow

6468-459: The two complementary principal methods of angle modulation ; phase modulation is often used as an intermediate step to achieve frequency modulation. These methods contrast with amplitude modulation , in which the amplitude of the carrier wave varies, while the frequency and phase remain constant. If the information to be transmitted (i.e., the baseband signal ) is x m ( t ) {\displaystyle x_{m}(t)} and

6552-609: The use of 50 kHz channel spacings throughout Europe . The original frequency allocation in North America used by Edwin Armstrong used the frequency band from 42 through 50 MHz, but this allocation was changed to a higher band beginning in 1945. In Canada , the United States , Mexico , the Bahamas , etc., there are 101 FM channels numbered from 200 (center frequency 87.9 MHz) to 300 (center frequency 107.9 MHz), though these numbers are rarely used outside

6636-515: The user to alternate the setting. FM systems are more convenient and cost-effective than alternatives such as cochlear implants , but many users use FM systems infrequently due to their conspicuousness and need for recharging. FM extended band in Brazil In Brazil, the FM extended band ( Portuguese : faixa estendida ), abbreviated eFM , refers to the extension of the FM broadcast band between 76.1 and 87.3 MHz , beyond

6720-434: The value of Δ f {\displaystyle \Delta {}f\,} , while keeping f m {\displaystyle f_{m}} constant, results in an eight-fold improvement in the signal-to-noise ratio. (Compare this with chirp spread spectrum , which uses extremely wide frequency deviations to achieve processing gains comparable to traditional, better-known spread-spectrum modes). With

6804-479: Was also prompted by the lack of equipment for the OIRT band and the modernisation of existing transmission networks. Many countries have completely ceased broadcasting on the OIRT FM band, although use continues in others, mainly the former republics of the USSR. The future of broadcasting on the OIRT FM band is limited, due to the lack of new consumer receivers for this band outside of Russia. Countries which still use

6888-460: Was ideally suited for reaching vast and remote areas that would otherwise lack FM radio reception. In a way, FM suited this band because the capture effect of FM could mitigate interference from skywaves . Transition to the 87.5 to 108 MHz band started as early as the 1980s in some East European countries. Following the collapse of the communist governments, that transition was remarkably accelerated as private stations have been established. This

6972-400: Was in. In the late 1980s, the FCC switched to a bandplan based on a distance separation table using currently operating stations, and subdivided the class table to create extra classes and change antenna height limits to meters. Class A power was doubled to six kilowatts, and the frequency restrictions noted above were removed. As of late 2004, a station can be "squeezed in" anywhere as long as

7056-411: Was that the FM band needed to be shifted to higher frequencies in order to avoid this potential problem. Armstrong charged that this reassignment had the covert goal of disrupting FM radio development, however RCA's proposal prevailed, and on June 27, 1945 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, with

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