Editing Frequency modulation (section)

{{Short description|Electronic method of transmitting information with a carrier wave}}
{{For|the application of frequency modulation to radio broadcasting|FM broadcasting}}
{{Redirect|NFM}}
{{Modulation techniques}}

[[File:Amfm3-en-de.gif|thumb|right|250px|A signal may be carried by an [[Amplitude modulation|AM]] or FM radio wave.|alt=Animation of audio, AM and FM signals]]
[[File:GE FM radio antistatic demonstration 1940.jpg|thumb|upright=1.5|FM has better noise ([[Radio Frequency Interference|RFI]]) rejection than AM, as shown in this dramatic New York publicity demonstration by [[General Electric]] in 1940. The radio has both AM and FM receivers. With a million-volt [[electric arc]] as a source of interference behind it, the AM receiver produced only a roar of [[Radio noise|static]], while the FM receiver clearly reproduced a music program from Armstrong's experimental FM transmitter [[W2XMN]] in New Jersey.]]

'''Frequency modulation''' ('''FM''') is a  [[signal modulation]] technique used in electronic communication, originally for transmitting messages with a [[radio wave]]. In frequency modulation a [[carrier wave]] is varied in its [[instantaneous frequency]] in proportion to a property, primarily the instantaneous amplitude, of a message signal, such as an [[audio signal]].<ref>{{Cite book|page=85|title=Machines and Inventions|first=Robert H.|last=Smith|publisher=Time Life|year=1993|location=Alexandria, VA|isbn=0-8094-9704-2}}</ref> The technology is used in [[telecommunications]], [[radio broadcasting]], [[signal processing]], and [[Run-length limited#FM: .280.2C1.29 RLL|computing]].

In [[Analog signal|analog]] frequency modulation, such as radio broadcasting of voice and music, the instantaneous [[frequency deviation]], i.e. the difference between the frequency of the carrier and its center frequency, has 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 [[modem]]s such as [[fax modem]]s, telephone [[caller ID]] systems, garage door openers, and other low-frequency transmissions.<ref>{{cite book |last=Gibilisco |first=Stan |title=Teach yourself electricity and electronics |url=https://archive.org/details/teachyourselfele00gibi |url-access=registration |quote=morse-code frequency-shift-keying sent-using-fsk. |publisher=McGraw-Hill Professional |year=2002 |page=[https://archive.org/details/teachyourselfele00gibi/page/477 477] |isbn=978-0-07-137730-0}}</ref> [[Radioteletype]] also uses FSK.<ref>{{cite book |last=Rutledge |first=David B. |title=The Electronics of Radio |url=https://books.google.com/books?id=ZvJYLhk4N64C&q=radio-teletype+fsk&pg=RA2-PA310 |publisher=Cambridge University Press |year=1999 |page=310 |isbn=978-0-521-64645-1}}</ref>

Frequency modulation is widely used for [[FM broadcasting|FM radio]] [[broadcasting]]. It is also used in [[telemetry]], [[radar]], seismic prospecting, and monitoring [[newborn]]s for seizures via [[EEG]],<ref>B. Boashash, editor, ''Time-Frequency Signal Analysis and Processing – A Comprehensive Reference'', Elsevier Science, Oxford, 2003; {{ISBN|0-08-044335-4}}</ref> [[two-way radio]] systems, [[Frequency modulation synthesis|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 [[AM broadcasting|amplitude modulation (AM)]] signal. For this reason, most music is broadcast over FM radio.

Frequency modulation and [[phase modulation]] are 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.