Editing Frequency modulation (section)

==Applications==
=== Doppler effect===
When an echolocating [[bat]] approaches 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) [[Animal echolocation|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 is called the '''Doppler Shift Compensation''' (DSC), and was discovered by [[Hans Schnitzler]] in 1968.

===Magnetic tape storage===
FM is also used at [[Intermediate frequency|intermediate frequencies]] by analog [[Video cassette recorder|VCR]] systems (including [[VHS]]) to record the [[Luminance (video)|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 [[Tape bias|bias]]. FM is the only feasible method of recording 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 [[Equalization (audio)|equalizers]] to work with due to electronic noise below −60&nbsp;[[decibel|dB]]. FM also keeps the tape at saturation level, acting as a form of [[noise reduction]]; a [[audio level compression|limiter]] can mask variations in playback output, and 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 the ratio is around 10,000. Consider, for example, a 6-MHz carrier modulated at a 3.5-MHz rate; by [[Bessel function|Bessel]] analysis, the first sidebands are on 9.5 and 2.5&nbsp;MHz and the second sidebands are on 13&nbsp;MHz and −1&nbsp;MHz. The result is a reversed-phase sideband on +1&nbsp;MHz; on demodulation, this results in unwanted output at 6 – 1 = 5&nbsp;MHz. The system must be designed so that this unwanted output is reduced to an acceptable level.<ref>"FM Systems Of Exceptional Bandwidth" Proc. IEEE vol. 112, no. 9, p. 1664, September 1965</ref>

===Sound===
FM is also used at [[audio frequency|audio frequencies]] to synthesize sound. This technique, known as [[frequency modulation synthesis|FM synthesis]], was popularized by early digital [[synthesizer]]s and became a standard feature in several generations of [[personal computer]] [[sound card]]s.

===Radio===

{{Main|FM broadcasting}}
[[File:FM Broadcast Transmitter High Power.jpg|thumb|An American FM radio transmitter at [[WEDG]] in Buffalo, New York]]
[[Edwin Howard Armstrong]] (1890–1954) was an American electrical engineer who invented wideband frequency modulation (FM) radio.<ref>{{Cite book
 |title = Principles of modern communications technology
 |author = A. Michael Noll
 |publisher = Artech House
 |year = 2001
 |isbn = 978-1580532846
 |page = [https://archive.org/details/principlesofmode0000noll/page/104 104]
 |url = https://archive.org/details/principlesofmode0000noll
|url-access = registration
 }}</ref>
He patented the regenerative circuit in 1914, the superheterodyne receiver in 1918 and the super-regenerative circuit in 1922.<ref>{{patent|US|1342885}}</ref> 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.<ref>{{Cite journal
 |first = E. H.
 |last = Armstrong
 |title = A Method of Reducing Disturbances in Radio Signaling by a System of Frequency Modulation
 |journal = Proceedings of the IRE
 |volume = 24
 |issue = 5
 |pages = 689–740
 |publisher = IRE
 |date= May 1936
 |doi = 10.1109/JRPROC.1936.227383
|s2cid = 43628076
 }}</ref>

As the name implies, wideband FM (WFM) requires a wider [[signal bandwidth]] than [[amplitude modulation]] by an equivalent modulating signal; this also makes the signal more robust against [[Noise (radio)|noise]] and [[Interference (communication)|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 the [[BBC]] called it "VHF radio" because commercial FM broadcasting uses part of the [[VHF]] band{{snd}}the [[FM broadcast band]]). FM [[receiver (radio)|receivers]] employ a special [[Detector (radio)|detector]] for FM signals and exhibit a phenomenon known as the ''[[capture effect]]'', in which the [[Tuner (radio)|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 a lack of [[selectivity (radio)|selectivity]] may cause one station to be overtaken by another on an [[adjacent channel]]. Frequency [[drift (telecommunication)|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 [[stereophonic sound|stereo]] signal; this is done with [[multiplexing]] and demultiplexing before and after the FM process. The FM modulation and demodulation process is identical in stereo and monaural processes.

FM is commonly used at [[VHF]] [[radio frequencies]] for [[high-fidelity]] [[radio broadcasting|broadcasts]] of music and [[Speech communication|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) 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 envelope|constant-amplitude signals]]). For a given signal strength (measured at the receiver antenna), switching amplifiers use [[low-power electronics|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 [[Quadrature amplitude modulation|QAM]].

There are reports that on October 5, 1924, Professor [[Mikhail A. Bonch-Bruevich]], during 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.<ref>Ф. Лбов. [https://sergeyhry.narod.ru/rl/rl1924_06_09.htm Новая система радиофона] «Радиолюбитель».{{snd}}1924.{{snd}}№ 6.{{snd}}С. 86.</ref>

===Hearing assistive technology===
Frequency modulated systems are a widespread and commercially available [[assistive technology]] that make speech more understandable by improving 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.<ref>{{cite tech report |author=ASHA Ad Hoc Committee on FM Systems |date=2002 |orig-date=Original March 1994 |edition=Revised |title=Guidelines for Fitting and Monitoring FM Systems |institution=[[American Speech–Language–Hearing Association]] |url=https://www.asha.org/policy/gl2002-00010/ |doi=10.1044/policy.GL2002-00010}}</ref> 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]].<ref>{{Cite journal |last1=Schafer |first1=Erin C. |last2=Bryant |first2=Danielle |last3=Sanders |first3=Katie |last4=Baldus |first4=Nicole |last5=Algier |first5=Katherine |last6=Lewis |first6=Audrey |last7=Traber |first7=Jordan |last8=Layden |first8=Paige |last9=Amin |first9=Aneeqa |date=June 1, 2014 |title=Fitting and Verification of Frequency Modulation on Children with Normal Hearing |journal=Journal of the American Academy of Audiology |volume=25 |issue=6 |pages=529–540 |doi=10.3766/jaaa.25.6.3 |issn=1050-0545 |pmid=25313543 |id={{EBSCOhost|107832936}} |via=[[EBSCOhost]]}}</ref> 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 the user to alternate the setting.<ref>{{Cite journal |last1=Lewis |first1=M. Samantha |last2=Crandall |first2=Carl C. |last3=Valente |first3=Michael |last4=Enrietto Horn |first4=Jane |date=2004 |title=Speech perception in noise: directional microphones versus frequency modulation (FM) systems |url=https://digitalcommons.wustl.edu/audio_hapubs/5 |journal=Journal of the American Academy of Audiology |volume=15 |issue=6 |pages=426–439 |doi=10.3766/jaaa.15.6.4 |pmid=15341224 |doi-access=free|url-access=subscription }}</ref> 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.<ref>{{Cite journal |last=McArdle |first=Rachel |last2=Abrams |first2=Harvey B. |last3=Hnath Chisholm |first3=Theresa |date=2005 |title=When Hearing Aids Go Bad: An FM Success Story |journal=Journal of the American Academy of Audiology |volume=16 |issue=10 |pages=809–821 |doi=10.3766/jaaa.16.10.5 |id={{EBSCOhost|106441304}} |via=[[EBSCOhost]]}}</ref>