Frequency modulation

"FM" redirects here. For other uses, see FM (disambiguation).

See also: Amplitude modulation

Modulation techniques
Analog modulation
AM · SSB · FM · PM · QAM · SM
Digital modulation
OOK · FSK · ASK · PSK · QAM MSK · CPM · PPM · TCM · OFDM
Spread spectrum
v • d • e FHSS · DSSS

In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its frequency (contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant). Amplitude modulation ( AM) is a technique used in electronic communication most commonly for transmitting information via a Radio Carrier wave In Telecommunications, modulation is the process of varying a periodic Waveform, i In Telecommunications, modulation is the process of varying a periodic Waveform, i Amplitude modulation ( AM) is a technique used in electronic communication most commonly for transmitting information via a Radio Carrier wave Single-sideband modulation ( SSB) is a refinement of Amplitude modulation that more efficiently uses electrical power and bandwidth. Phase modulation (PM is a form of Modulation that represents information as variations in the instantaneous phase of a Carrier wave. Space modulation is a radio Amplitude Modulation technique used in Instrument Landing Systems that incorporates the use of multiple antennas fed with various radio In Telecommunications, modulation is the process of varying a periodic Waveform, i On-off keying ( OOK) is a type of Modulation that represents Digital Data as the presence or absence of a Carrier wave. Frequency-shift keying (FSK is a Frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a Carrier wave Amplitude-shift keying ( ASK) is a form of Modulation that represents Digital Data as variations in the Amplitude of a Carrier Phase-shift keying (PSK is a Digital Modulation scheme that conveys data by changing or modulating the phase of a reference signal In Digital modulation, Minimum-shift keying (MSK is a type of continuous phase Frequency-shift keying that was developed in the late 1960s Continuous phase modulation ( CPM) is a method for modulation of data commonly used in Wireless modems In contrast to other coherent digital Phase Pulse-position modulation is a form of signal Modulation in which M message bits are encoded by transmitting asingle pulse in one of 2^M possible time-shifts In Telecommunication, trellis modulation (also known as trellis coded modulation, or simply TCM) is a modulation scheme which allows highly efficient Orthogonal frequency-division multiplexing ( OFDM) — essentially identical to Coded OFDM ( COFDM) and Discrete multi-tone modulation ( Spread-spectrum techniques are methods by which Energy generated in a particular bandwidth is deliberately spread in the Frequency domain, resulting Frequency-hopping spread spectrum ( FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using In Telecommunications direct-sequence spread spectrum ( DSSS) is a Modulation technique Information as a concept has a diversity of meanings from everyday usage to technical settings In Telecommunications, a carrier wave, or carrier is a Waveform (usually Sinusoidal) that is modulated (modified with an input signal Frequency is a measure of the number of occurrences of a repeating event per unit Time. Amplitude modulation ( AM) is a technique used in electronic communication most commonly for transmitting information via a Radio Carrier wave Amplitude is the magnitude of change in the oscillating variable with each Oscillation, within an oscillating system In analog applications, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. An analog or analogue signal is any continuous signal for which the time varying feature (variable of the signal is a representation of some other Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying. A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for Debt AIDS Trade in Africa (or DATA) is a Multinational non-government organization founded in January 2002 in London by U2 's Frequency-shift keying (FSK is a Frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a Carrier wave

FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech (see FM broadcasting). Very high frequency (VHF is the Radio frequency range from 30 MHz to 300 MHz. Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz High fidelity or hi-fi reproduction is a term used by home stereo listeners and home audio enthusiasts ( Audiophiles to refer to high-quality reproduction This article is about radio broadcasting for other uses see Radio (disambiguation. Music is an Art form in which the medium is Sound organized in Time. Speech refers to the processes associated with the production and perception of Sounds used in Spoken language. See also Frequency modulation, FM band FM broadcasting is a broadcast Technology invented by Edwin Howard Armstrong that Normal (analog) TV sound is also broadcast using FM. A narrowband form is used for voice communications in commercial and amateur radio settings. Narrowband refers to a situation in radio communications where the bandwidth of the message does not significantly exceed the channel's Coherence bandwidth. Amateur radio, often called ham radio, is both a Hobby and a service in which participants called "hams" use various types of Radio communications 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.

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. PLEASE BEAR IN MIND THAT THIS IS A GENERAL ARTICLE ABOUT VCRs/VIDEOCASSETTE RECORDERS As applied to video signals luma represents the brightness in an image (the "black and white" or achromatic portion of the image 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. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. The decibel ( dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity relative to FM also keeps the tape at saturation level, and therefore acts as a form of audio noise reduction, and a simple limiter can mask variations in the playback output, and the FM capture effect removes print-through and pre-echo. Noise reduction is the process of removing Noise from a signal. Dynamic range compression, also called DRC (often seen in DVD player settings or simply compression, is a process that reduces the Dynamic range of 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 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 Pre-echo is an audio Compression artifact where a sound is heard before it occurs (hence the name 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. Note This article is about the format sometimes known as 'VCC' or 'Video Compact Cassette' Time base correction is a technique to reduce or eliminate errors caused by mechanical instability present in Analog recordings on mechanical media

FM is also used at audio frequencies to synthesize sound. An audio frequency (abbreviation AF) or audible frequency is characterized as a periodic vibration whose Frequency is audible to the average human 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. A 220 Hz carrier tone modulated by a 440 Hz modulating tone with A personal computer ( PC) is any Computer whose original sales price size and capabilities make it useful for individuals and which is intended to be operated A sound card (also known as an audio card is a Computer Expansion card that facilitates the input and output of audio signals to/from a computer under

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

1 Applications in radio
2 Theory
3 Implementation
4 Miscellaneous
5 See also
6 External links
7 References

Applications in radio

An example of frequency modulation. This diagram shows the modulating, or message, signal, x_m(t), superimposed on the carrier wave, x_c(t)

The modulated signal, y(t), produced from frequency-modulating x_c(t) with x_m(t).

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. Edwin Howard Armstrong ( December 18, 1890 &ndash January 31, 1954) was an American Electrical engineer and Inventor New York ( is a state in the Mid-Atlantic and Northeastern regions of the United States and is the nation's third most populous 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 Events 355 - Roman Emperor Constantius II promotes his cousin Julian to the rank of Caesar, entrusting him with Year 1935 ( MCMXXXV) was a Common year starting on Tuesday (link will display full calendar of the Gregorian calendar. The paper was published in 1936. ^[1]

As the name implies, wideband FM (W-FM) requires a wider signal bandwidth than amplitude modulation by an equivalent modulating signal, but this also makes the signal more robust against noise and interference. Bandwidth is the difference between the upper and lower Cutoff frequencies of for example a filter, a Communication channel, or a Signal spectrum Amplitude modulation ( AM) is a technique used in electronic communication most commonly for transmitting information via a Radio Carrier wave Radio noise in radio reception is the superposition of White noise (also called "static" and other disturbing influences on the signal caused either by Thermal In physics interference is the addition ( superposition) of two or more Waves that result in a new wave pattern 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 called 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). Standardization (or standardisation) is the process of developing and agreeing upon technical standards. High fidelity or hi-fi reproduction is a term used by home stereo listeners and home audio enthusiasts ( Audiophiles to refer to high-quality reproduction Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. See also Frequency modulation, FM band FM broadcasting is a broadcast Technology invented by Edwin Howard Armstrong that 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 effect, where the tuner is able to clearly receive the stronger of two stations being broadcast on the same frequency. This article is about a radio receiver for other uses see Radio (disambiguation. A detector is a device that recovers Information of interest contained in a Modulated wave A phenomenon (from Greek φαινόμενoν, pl φαινόμενα - phenomena) is any observable occurrence 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 A tuner is an adjustable device which passes one Radio Frequency, or band of frequencies and excludes others by using electrical Resonance. Problematically however, frequency drift or lack of selectivity may cause one station or signal to be suddenly overtaken by another on an adjacent channel. In Electrical engineering, and particularly in Telecommunications, frequency drift is an unintended and generally Arbitrary Offset of an Selectivity is a measure of the Performance of a Radio receiver to respond only to the tuned transmission (such as a Radio station In broadcasting an adjacent channel is an AM, FM, or TV channel that is next to another channel. Frequency drift typically constituted a problem on very old or inexpensive receivers, while inadequate selectivity may plague any tuner. In Telecommunication, a drift is a comparatively long-term change in an attribute value or operational parameter of a System or equipment

An FM signal can also be used to carry a stereo signal: see FM stereo. Stereophonic sound, commonly called stereo, is the reproduction of Sound, using two or more independent audio channels through a Symmetrical See also Frequency modulation, FM band FM broadcasting is a broadcast Technology invented by Edwin Howard Armstrong that However, this is done by using multiplexing and demultiplexing before and after the FM process, and is not part of FM proper. For multiplexing in electronics and signal processing see Multiplexer. 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.

A high-efficiency radio-frequency switching amplifier can be used to transmit FM signals (and other constant-amplitude signals). A switching amplifier or class-D amplifier is an Electronic amplifier which in contrast to the active resistance used in linear mode AB-class amplifiers For a given signal strength (measured at the receiver antenna), switching amplifiers use less battery power and typically cost less than a linear amplifier. A linear amplifier is an electronic circuit whose output is proportional to its input but capable of delivering more power into a Load. This gives FM another advantage over other modulation schemes that require linear amplifiers, such as AM and QAM.

Theory

Suppose the baseband data signal to be transmitted is

$x_m(t)\,$

and is restricted in amplitude to be

$\left| x_m(t) \right| \le 1, \,$

and the sinusoidal carrier is

$x_c(t) = A \cos (2 \pi f_c t)\,$

where f_c is the carrier's base frequency and A is an arbitrary amplitude. The modulator combines the carrier with the baseband data signal to get the transmitted signal,

$y(t) = A \cos \left( 2 \pi \int_{0}^{t} f(\tau)\, d \tau \right) = A \cos \left( 2 \pi \int_{0}^{t} \left[ f_c + f_\Delta x_m(\tau) \right] \, d \tau \right)$

where $f(\tau) = f_c + f_\Delta x_m(\tau). \,$

In this equation, $f(\tau)\,$ is the instantaneous frequency of the oscillator and $f_{\Delta}\,$ 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, the instantaneous phase (or "local phase" or simply "phase" of a complex-valued function x(t\ is the real-valued Frequency deviation (Δf is used in FM radio to describe the maximum instantaneous difference between an FM modulated frequency and the nominal carrier 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 In Mathematics, Bessel functions, first defined by the Mathematician Daniel Bernoulli and generalized by Friedrich Bessel, are Canonical

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:

$h = \frac{\Delta{}f}{f_m} = \frac{f_\Delta |x_m(t)|}{f_m} \$

where f_m is the highest modulating frequency of x_m(t). If $h \ll 1$ , the modulation is called narrowband FM, and its bandwidth is approximately $2 f m$ . If $h \gg 1$ , the modulation is called wideband FM and its bandwidth is approximately $2 f Δ$ . 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 also used in other fields (such as scientific Measurements

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; 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.

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

$\ B_T = 2(f_\Delta +f_m)\,$

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). A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation In Telecommunication, Carson 's bandwidth rule defines the approximate bandwidth requirements of Communications system components for a carrier

Bessel functions

The carrier and sideband amplitudes are illustrated for different modulation indices of FM signals. Based on the Bessel functions. In Mathematics, Bessel functions, first defined by the Mathematician Daniel Bernoulli and generalized by Friedrich Bessel, are Canonical

Modulation index	Carrier	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16
0. 00	1. 00
0. 25	0. 98	0. 12
0. 5	0. 94	0. 24	0. 03
1. 0	0. 77	0. 44	0. 11	0. 02
1. 5	0. 51	0. 56	0. 23	0. 06	0. 01
2. 0	0. 22	0. 58	0. 35	0. 13	0. 03
2. 41	0	0. 52	0. 43	0. 20	0. 06	0. 02
2. 5	−. 05	0. 50	0. 45	0. 22	0. 07	0. 02	0. 01
3. 0	−. 26	0. 34	0. 49	0. 31	0. 13	0. 04	0. 01
4. 0	−. 40	−. 07	0. 36	0. 43	0. 28	0. 13	0. 05	0. 02
5. 0	−. 18	−. 33	0. 05	0. 36	0. 39	0. 26	0. 13	0. 05	0. 02
5. 53	0	−. 34	−. 13	0. 25	0. 40	0. 32	0. 19	0. 09	0. 03	0. 01
6. 0	0. 15	−. 28	−. 24	0. 11	0. 36	0. 36	0. 25	0. 13	0. 06	0. 02
7. 0	0. 30	0. 00	−. 30	−. 17	0. 16	0. 35	0. 34	0. 23	0. 13	0. 06	0. 02
8. 0	0. 17	0. 23	−. 11	−. 29	−. 10	0. 19	0. 34	0. 32	0. 22	0. 13	0. 06	0. 03
8. 65	0	0. 27	0. 06	−. 24	−. 23	0. 03	0. 26	0. 34	0. 28	0. 18	0. 10	0. 05	0. 02
9. 0	−. 09	0. 25	0. 14	−. 18	−. 27	−. 06	0. 20	0. 33	0. 31	0. 21	0. 12	0. 06	0. 03	0. 01
10. 0	−. 25	0. 04	0. 25	0. 06	−. 22	−. 23	−. 01	0. 22	0. 32	0. 29	0. 21	0. 12	0. 06	0. 03	0. 01
12. 0	0. 05	−. 22	−. 08	0. 20	0. 18	−. 07	−. 24	−. 17	0. 05	0. 23	0. 30	0. 27	0. 20	0. 12	0. 07	0. 03	0. 01

Implementation

FM signals can be generated using either direct or indirect frequency modulation.
Direct FM can be achieved by directly feeding the message into the input of a VCO.
For indirect FM, the message signal is integrated to generate a phase modulated signal. Phase modulation (PM is a form of Modulation that represents information as variations in the instantaneous phase of a Carrier wave. This is used to modulate a crystal controlled oscillator, and the result is passed through a frequency multiplier to give an FM signal. A crystal oscillator is an Electronic circuit that uses the mechanical Resonance of a vibrating Crystal of piezoelectric material to create an ^[2]

A common method for recovering the information signal is through a Foster-Seeley discriminator. The Foster-Seeley discriminator is a common type of FM detector circuit, invented in 1936 by Dudley E

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. Phase modulation (PM is a form of Modulation that represents information as variations in the instantaneous phase of a Carrier wave.

Frequency-shift keying is the simple case of frequency modulation of a signal by using only discrete states, such as in Morse code^[3], most early telephone-line modems, and radioteletype applications. Frequency-shift keying (FSK is a Frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a Carrier wave Morse code is a Character encoding for transmitting telegraphic information using standardized sequences of short and long elements to represent the letters numerals Radioteletype ( RTTY) is a Telecommunications system consisting of two or more Teleprinters using Radio as the Transmission medium.

When used in supervisory signaling in telephony, the term frequency-change signaling has been used to describe frequency modulation. In Telecommunication, frequency-change signaling is a Telegraph signaling method in which one or more particular frequencies correspond to each

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. A detector is a device that recovers Information of interest contained in a Modulated wave

External links

References

^ Armstrong, E. Amplitude modulation ( AM) is a technique used in electronic communication most commonly for transmitting information via a Radio Carrier wave In Telecommunication, Carson 's bandwidth rule defines the approximate bandwidth requirements of Communications system components for a carrier A 220 Hz carrier tone modulated by a 440 Hz modulating tone with 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 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 radio instruments that use Radio waves Within the Timeline of Phase modulation (PM is a form of Modulation that represents information as variations in the instantaneous phase of a Carrier wave. See also Frequency modulation, FM band FM broadcasting is a broadcast Technology invented by Edwin Howard Armstrong that In most of the world the FM broadcast band, used for Broadcasting FM Radio stations goes from 87 H. (May 1936). "A Method of Reducing Disturbances in Radio Signaling by a System of Frequency Modulation". Proceedings of the IRE 24 (5): 689-740. IRE.
^ "Communication Systems" 4th Ed, Simon Haykin, 2001
^ frequency-shift keying.

A. Bruce Carlson: "Communication systems, 2nd edition", McGraw-Hill, Inc, 1981, ISBN 0-07-085082-2

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