In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its frequency. In analog applications, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying. (Contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant.) Telecommunication involves the transmission of signals over a distance for the purpose of communication. ... The ASCII codes for the word Wikipedia represented in binary, the numeral system most commonly used for encoding computer information. ... This article or section does not adequately cite its references or sources. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ... An analog or analogue signal is an allergy continuous in both time and amplitude. ... A digital system is one that uses discrete values (often electrical voltages), especially those representable as binary numbers, or non-numeric symbols such as letters or icons, for input, processing, transmission, storage, or display, rather than a continuous spectrum of values (ie, as in an analog system). ... For other uses, see Data (disambiguation). ... It has been suggested that this article or section be merged with audio frequency-shift keying. ... Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. ... It has been suggested that pulse amplitude be merged into this article or section. ...

FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech (see FM broadcasting). Normal (analog) TV sound is also broadcast using FM. A narrowband form is used for voice communications in commercial and amateur radio settings. The type of FM used in broadcast is generally called wide-FM, or W-FM. In two-way radio, narrowband narrow-fm (N-FM) is used to conserve bandwidth. In addition, it is used to send signals into space. Very high frequency (VHF) is the radio frequency range from 30 MHz to 300 MHz. ... It has been suggested that this article or section be merged with Radio waves. ... high fidelity, or hi-fi, generally means high audio quality. ... Radio broadcasting can be done via cable FM, local wire networks, satellite and the Internet. ... // Music is an art form consisting of sound and silence expressed through time. ... Speech communication is the aural form of transferring ideas, thoughts, instructions and/or directives utilizing the speakers vocal chords and mouth to stimulate the air, thus causing waves of sound to strike the audible receptors of the hearer, resulting in a transformation back into mental images and/or symbols... FM broadcasting is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation (FM) to provide high-fidelity sound over broadcast radio. ... Narrowband (narrow bandwidth) refers to a signal which occupies only a small amount of space on the radio spectrum -- the opposite of broadband or wideband. ... The human voice consists of sound made by a human using the vocal folds for talking, singing, laughing, crying and screaming. ... Amateur radio station with modern solid-state transceiver featuring LCD display and DSP capabilities Amateur radio, often called ham radio, is a hobby that uses various types of radio broadcasting equipment to communicate with other radio amateurs for public service, recreation and self-training. ...

FM is also used at intermediate frequencies by most analog VCR systems, including VHS, to record the luminance (black and white) portion of the video signal. FM is the only feasible method of recording video to and retrieving video from magnetic tape without extreme distortion, as video signals have a very large range of frequency components — from a few hertz to several megahertz, too wide for equalisers to work with due to electronic noise below -60 dB. FM also keeps the tape at saturation level, and therefore acts as a form of noise reduction, and a simple limiter can mask variations in the 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. The video cassette recorder (or VCR, less popularly video tape recorder) is a type of video tape recorder that uses removable cassettes containing magnetic tape to record audio and video from a television broadcast so it can be played back later. ... Bottom view of VHS cassette with magnetic tape exposed Top view of VHS cassette with front casing removed The Video Home System, better known by its abbreviation VHS is a recording and playing standard for analog video cassette recorders (VCRs), developed by Victor Company of Japan, Limited (JVC) and launched... As applied to analog television signals, two different words are used, luminance and luma, meaning two different things. ... MHZ redirects here. ... MegaHertz (MHz) is the name given to one million (106) Hertz, a measure of frequency. ... This article is about equalisers in mathematics. ... The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power) relative to a specified or implied reference level. ... Noise reduction is the process of removing noise from a signal. ... Audio level compression, also called dynamic range compression, volume compression, compression, limiting, or DRC (often seen in DVD player settings) is a process that manipulates the dynamic range of an audio signal. ... In telecommunication, the capture effect, or FM capture effect, is a phenomenon, associated with FM reception, in which only the stronger of two signals at or near the same frequency will be demodulated. ... Print-through (sometimes referred to as bleed-through) is a generally undesirable effect that arises in the use of magnetic tape for storing analogue information, in particular music. ... Pre-echo is a psychoacoustic phenomenon where an unusually noticeable artifact is heard in a sound recording from the energy of time domain transients smeared backwards in time after processing in the frequency domain due to the Gibbs phenomenon. ... Video 2000 (or V2000; also known as Video Compact Cassette, or VCC) was a consumer VCR system and videotape standard developed by Philips and Grundig to compete with JVCs VHS and Sonys Betamax video technologies. ... Timebase correction is a technique to reduce or eliminate errors present in all analog recordings on mechanical media, including video tape recorders and videocassette recorders, caused by mechanical instability. ...

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 for several generations of personal computer sound cards. An audio frequency (abbreviation: AF) is any frequency from about 20 hertz to about 20 kilohertz, which is the approximate range of sound frequencies that is audible to humans. ... Frequency modulation synthesis (or FM synthesis) is a form of audio synthesis where the timbre of a simple waveform is changed by frequency modulating it with a modulating frequency that is also in the audio range, resulting in a more complex waveform and a different-sounding tone. ... Synthesizer as used in music, is a term derived from a Greek word syntithetai < synthesis (συντίθεται < σύνθεσις) and is used to describe a device capable of generating and/or manipulating electronic signals for use in music creation, recording and performance. ... A sound card (also known as an audio card) is a computer expansion card that can input and output sound under control of computer programs. ...

An audio signal (top) may be carried by an AM or FM radio wave.

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

Applications in radio

Edwin 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. ^[1] Diagram of frequency modulation, made by User:Stw using gnuplot and GIMP. See also: Image:Amplitude-modulation. ... Edwin Howard Armstrong (December 18, 1890 – January 31, 1954) was an American electrical engineer and inventor. ... “NY” redirects here. ... Following several attempts to form a technical organization of wireless practitioners in 1908-1912, the Institute of Radio Engineers (IRE) was finally established in 1912 in New York. ... is the 310th day of the year (311th in leap years) in the Gregorian calendar. ... 1935 (MCMXXXV) was a common year starting on Tuesday (link will display full calendar). ...

Wideband FM (W-FM) requires a wider bandwidth than amplitude modulation by an equivalent modulating signal, but this also makes the signal more robust against noise and interference. Frequency modulation is also more robust against simple 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 insisted on calling it "VHF radio", because commercial FM broadcasting uses a well-known part of the VHF band; in certain countries, expressions referencing the more familiar wavelength notion are still used in place of the more abstract modulation technique name). This article does not cite any references or sources. ... Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. ... Radio noise If there was no noise picked up with radio signals, then tiny transmitters could be received at any distance just by making a radio receiver that was sensitive enough. ... Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ... Standardization, in the context related to technologies and industries, is the process of establishing a technical standard among competing entities in a market, where this will bring benefits without hurting competition. ... High Fidelity is also the title of a book by Nick Hornby and a film directed by Stephen Frears, based upon Hornbys book. ... FM radio is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation to provide high-fidelity sound over broadcast radio. ... The British Broadcasting Corporation, which is usually known as the BBC, is the largest broadcasting corporation in the world in terms of audience numbers, employing 26,000 staff in the United Kingdom alone and with a budget of more than GB£4 billion. ... Very high frequency (VHF) is the radio frequency range from 30 MHz to 300 MHz. ...

FM receivers employ a special detector for FM signals and exhibit a phenomenon called capture, where the tuner is able to clearly receive the stronger of two stations being broadcast on the same frequency. Problematically however, frequency drift or lack of selectivity may cause one station or signal to be suddenly overtaken by another on an adjacent channel. Frequency drift typically constituted a problem on very old or inexpensive receivers, while inadequate selectivity may plague any tuner. In radio terminology, a receiver is an electronic circuit that receives a radio signal from an antenna and decodes the signal for use as sound, pictures, navigational-position information, etc. ... A detector is a device that recovers information of interest contained in a modulated wave. ... A phenomenon (Greek: , pl. ... A Sansui TU-X1 stereo FM tuner. ... In electrical engineering, and particularly in telecommunications, frequency drift is an unintended and generally arbitrary offset of an oscillator from its nominal frequency. ... Selectivity is a measure of the performance of a radio receiver to respond only to the tuned transmission (such as a radio station) and reject other signals nearby, such as another broadcast on an adjacent channel. ... In broadcasting an adjacent channel is an AM, FM, or TV channel that is next to another channel. ... In telecommunication, a drift is a comparatively long-term change in an attribute or value of a system or equipment operational parameter. ...

An FM signal can also be used to carry a stereo signal: see FM stereo. However, this is done by using multiplexing and demultiplexing before and after the FM process, and is not part of FM proper. The rest of this article ignores the stereo multiplexing and demultiplexing process used in "stereo FM", and concentrates on the FM modulation and demodulation process, which is identical in stereo and mono processes. Label for 2. ... FM radio is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation to provide high-fidelity broadcast radio sound. ... In telecommunications, multiplexing (also muxing or MUXing) is the combining of two or more information channels onto a common transmission medium using hardware called a multiplexer or (MUX). ...

Theory

Suppose the signal to be transmitted is

and is restricted in amplitude to be

and the sinusoidal carrier is A sine wave or sinusoid is a waveform whose graph is identical to the generalized sine function y = Asin[ω(x − α)] + C where A is the amplitude, ω is the angular frequency (2π/P where P is the wavelength), α is the phase shift, and C is the vertical offset. ...

where f_c is the carrier's base frequency and A is an arbitrary amplitude. Then the carrier will be modulated by the signal as in

where

In this equation, is the instantaneous frequency of the oscillator and 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. In signal processing, a general sinusoidal signal with constant amplitude can be defined as: where is the amplitude, and is the instantaneous phase (or local phase or simply phase) . The simplest useful form is: which is effectively the same as the cyclical form: , where mod is the Modulo_operation. ... In telecommunication, the term frequency deviation has the following meanings: The amount by which a frequency differs from a prescribed value, such as the amount an oscillator frequency drifts from its nominal frequency. ...

Although it may seem that this limits the frequencies in use to f_c ± f_Δ, this neglects the distinction between instantaneous frequency and spectral frequency. The frequency spectrum of an actual FM signal has components extending out to infinite frequency, although they become negligibly small beyond a point. Familiar concepts associated with a frequency are colors, musical notes, radio/TV channels, and even the regular rotation of the earth. ...

The harmonic distribution of a sine wave carrier modulated by a sine wave signal can be represented with Bessel functions - this provides a basis for a mathematical understanding of frequency modulation in the frequency domain. In acoustics and telecommunication, the harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency. ... In trigonometry, an ideal sine wave is a waveform whose graph is identical to the generalized sine function y = Asin[&#969;(x &#8722; &#945;)] + C, where A is the amplitude, &#969; is the angular frequency (2&#960;/P where P is the wavelength), &#945; is the phase shift, and C... In mathematics, Bessel functions, first defined by the mathematician Daniel Bernoulli and generalized by Friedrich Bessel, are canonical solutions y(x) of Bessels differential equation: for an arbitrary real or complex number α. The most common and important special case is where α is an integer n, then α is referred to...

Modulation index

As with other modulation indices, in FM this quantity indicates by how much the modulated variable varies around its unmodulated level. For FM, it relates to the variations in the frequency of the carrier signal: The modulation index (mf) is defined as the ratio of the frequency deviation &#963; to the modulating signal frequency fi, i. ...

If , the modulation is called narrowband FM, and its bandwidth is approximately 2f_m. If , the modulation is called wideband FM and its bandwidth is approximately 2f_Δ. While wideband FM uses more bandwidth, it can improve signal-to-noise ratio significantly. Signal-to-noise ratio (often abbreviated SNR or S/N) is an electrical engineering concept defined as the ratio of a signal power to the noise power corrupting the signal. ...

With 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 stays the same. If the frequency deviation is held constant and the modulation index increased, the bandwidth stays roughly the same, but the spacing between spectra decreases.

Carson's rule

A rule of thumb, Carson's rule states that nearly all (~98%) of the power of a frequency-modulated signal lies within a bandwidth B_T of A rule of thumb is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination. ... In telecommunication, Carsons bandwidth rule defines the approximate bandwidth requirements of communications system components for a carrier signal that is frequency modulated by a continuous or broad spectrum of frequencies rather than a single frequency. ... This article does not cite any references or sources. ...

where f_Δ is the peak deviation of the instantaneous frequency f(t) from the center carrier frequency f_c (assuming x_m(t) is in the range ±1) and f_m is the highest modulating frequency of x_m(t).

Bessel Functions

The carrier and sideband amplitudes are illustrated for different modulation indexes of FM signals. Based on the Bessel Functions. In mathematics, Bessel functions, first defined by the Swiss mathematician Daniel Bernoulli and named after Friedrich Bessel, are canonical solutions y(x) of Bessels differential equation: for an arbitrary real number &#945; (the order). ...

Implementation

One common method of generating the FM signal is to feed the information signal into the input of a VCO. A common method for recovering the information signal is through a Foster-Seeley discriminator. A voltage-controlled oscillator or VCO is an electronic circuit that uses amplification, feedback and a resonant circuit to generate a repeating voltage waveform. ... The Foster-Seeley discriminator is an FM detector circuit that works on the same principle as most commonly used FM detectors, which is through variations in frequency. ...

Miscellaneous

• Note that frequency modulation can be regarded as a special case of phase modulation where the carrier phase modulation is the time integral of the FM modulating signal.

• Frequency-shift keying is the simple case of frequency modulation by a signal with only discrete states, such as in Morse code or radioteletype applications.

• When used in supervisory signaling in telephony, the term frequency-change signaling has been used to describe frequency modulation.

• By the phenomenon of slope detection whereby FM is converted to AM in a frequency-selective circuit tuned slightly away from the nominal signal frequency, AM receivers may detect some FM transmissions, though this does not provide an efficient method of detection for FM broadcasts.

Phase modulation (PM) is a form of modulation which represents information as variations in the instantaneous phase of a carrier wave. ... It has been suggested that this article or section be merged with audio frequency-shift keying. ... 1922 Chart of the Morse Code Letters and Numerals Morse code is a method for transmitting telegraphic information, using standardized sequences of short and long elements to represent the letters, numerals, punctuation and special characters of a message. ... RadioTeleType (RTTY) is a telecommunications system consisting of two teleprinters linked by a radio link. ... In telecommunication, frequency-change signaling is a signaling method in which one or more discrete frequencies correspond to each desired significant condition of a code. ... A detector is a device that recovers information of interest contained in a modulated wave. ...

See also

• Amplitude modulation
• Carson bandwidth rule (Estimate of RF bandwidth required for an FM signal)
• Frequency modulation synthesis (FM as an audio synthesis method)
• FM-UWB (FM and Ultra Wideband)
• Modulation, for a list of other modulation techniques
• History of radio
• Phase modulation

Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. ... In telecommunication, Carsons bandwidth rule defines the approximate bandwidth requirements of communications system components for a carrier signal that is frequency modulated by a continuous or broad spectrum of frequencies rather than a single frequency. ... Frequency modulation synthesis (or FM synthesis) is a form of audio synthesis where the timbre of a simple waveform is changed by frequency modulating it with a modulating frequency that is also in the audio range, resulting in a more complex waveform and a different-sounding tone. ... FM-UWB is a modulation scheme using double FM: a low-modulation index digital FSK followed by a high-modulation index analog FM to create a constant-envelope UWB signal. ... In telecommunications, modulation is the process of varying a periodic waveform, i. ... The pre-history and early history of radio is the history of technology that produced instruments that use radio waves. ... Phase modulation (PM) is a form of modulation which represents information as variations in the instantaneous phase of a carrier wave. ...

External links

• Frequency Modulation
• Frequency Modulation
• FM receiving antennas
• Ratio Detector with schematics

References