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Topic: Frequency modulation

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In the News (Sat 25 May 19)

  Frequency modulation - Wikipedia, the free encyclopedia
Frequency modulation (FM) is a form of modulation which represents information as variations in the instantaneous frequency of a carrier wave.
Problematically, however, frequency drift or lack of selectivity may cause one station or signal to be suddenly overtaken by another on an adjacent channel.
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.
en.wikipedia.org /wiki/Frequency_modulation   (1060 words)

 Frequency modulation - Wikipedia, the free encyclopedia
(Contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant.) In analog applications, the carrier frequency is varied in direct proportion to changes in the amplitude of an input signal.
In this equation, f(t) is the instantaneous frequency of the oscillator and f
Manchester encoding may be regarded as a simple version of frequency shift keying, where the high and low frequencies are respectively double and the same as the bit rate, and the bit transitions are synchronous with carrier transitions.
en.wikipedia.org /wiki/Frequency_modulated   (1060 words)

 Frequency modulation
Frequency modulation (FM) is the encoding of information in either analog or digital form into a carrier wave by variation of its instantaneous frequency in accordance with an input signal.
Frequency modulation requires a wider bandwidth than amplitude modulation by an equivalent modulating signal, but this also makes the signal more robust against interference.
Frequency shift keying (FSK) refers to the simple case of frequency modulation by a simple signal with only two states, such as in Morse code or radio-teletype applications.
www.ebroadcast.com.au /lookup/encyclopedia/fm/FM.html   (292 words)

Frequency modulation is a single-photon absorption technique used to increase the sensitivity in absorption spectroscopy by shifting the measurement into a frequency regime where little or no background signal is present.
is the absorption at the frequency corresponding to the ith sideband and
The absorption is defined by the difference between absorption at the frequencies corresponding to the lower and upper sidebands, and the dispersion is related to the difference between the phases of the sideband waveforms relative to the carrier phase.
www.chem.tamu.edu /rgroup/north/FM.html   (672 words)

The modulated carrier consists mainly of three frequency components: the original r-f signal at 500 kc, the sum of the a-f and r-f signals at 501 kc, and the difference between the a-f and r-f signals at 499 kc.
The modulating signal is shown in A. The dashed-line waveforem, in B, is the curve of the reference vector and the solid-line waveform is the carrier.
The percentage of modulation of an a-m wave is the percentage ratio of the peak-to-peak amplitude of the modulating voltage to the peak-to-peak amplitude of the carrier.
www.geocities.com /SoHo/Study/8903/fmod1.html   (4685 words)

Time-dependent spectra may be produced by varying the modulation index during the course of the sound.
Three examples of frequency modulated signals, where (A) the carrier frequency is higher than the modulating frequency (c:m = 10:1), (B) both frequencies are equal, and (C), the modulating frequency is higher than the carrier (c:m = 1:10).
Negative frequencies as shown may be considered as equivalent to positive frequencies with a phase shift of 180°.
www2.sfu.ca /sonic-studio/handbook/Frequency_Modulation.html   (452 words)

 Modulation   (Site not responding. Last check: 2007-10-22)
Modulation is the process where a Radio Frequency or Light Wave's amplitude, frequency, or phase is changed in order to transmit intelligence.
Frequency Modulation occurs when a carrier's CENTER frequency is changed based upon the input signal's amplitude.
In Pulse Amplitude Modulation, a pulse is generated with an amplitude corresponding to that of the modulating waveform.
telecom.tbi.net /mod1.html   (797 words)

 Frequency Modulation
A Frequency Modulated wave is a sine wave with a periodically varying instantaneous frequency and a constant amplitude.
The average frequency is called the carrier frequency and the instantaneous frequency changes at the modulation frequency.
If this were an FM radio transmission, the carrier frequency would be the station you tune to, and you would hear a pure audio tone at the modulation frequency, with a loudness derived from the modulation depth.
www.chemistry.bnl.gov /gpmd/old-pages/FM.HTML   (574 words)

 Privateline.com: Digital Wireless Basics: Modulation
Frequency modulation, such as analog cell phones use, provides better sound but it needs more bandwidth to achieve that quality and is technically more complex to produce.
Amplitude modulation means a carrier wave is modulated in proportion to the strength of a signal.
The word frequency in FM relates, instead, to the rate at which this method varies a carrier wave, not to any particular radio frequency it is used on.
www.privateline.com /PCS/modulation.htm   (2492 words)

 Frequency Modulation
In frequency modulation, the instantaneous frequency of the radio-frequency wave varies with the modulation signal.
The amount by which the frequency departs from the average is controlled by the amplitude of the modulating signal.
The amount of amplitude modulation determines the increase in the number of sidebands within the applied pulse spectrum; an increase in frequency modulation increases the amplitude of the side-lobe frequencies.
www.tpub.com /neets/book21/90d.htm   (1152 words)

 Frequency Modulation
In frequency modulation, the instantaneous frequency of the radio-frequency wave is varied in accordance with the modulating signal, as shown in view (A) of figure 2-5.
Both the frequency and the amplitude of the modulating signal are translated into variations in the frequency of the rf carrier.
This indicates an increase in frequency of the modulating signal to 2,000 hertz.
www.tpub.com /neets/book12/49b.htm   (1094 words)

Chowning found that when the frequency of the modulating signal increased beyond a certain point, the vibrato effect disappeared from the modulated tone, and a complex new tone replaced the original.
Suppose that the Carrier is a sine wave of frequency 500Hz and the Modulator is a sine wave of frequency 300Hz.
Frequency Modulation is a powerful method of synthesis that is as relevant to analogue synthesizers as it is to digital ones, and which is capable of generating sounds unobtainable by any other method.
www.soundonsound.com /sos/apr00/articles/synthsecrets.htm   (3055 words)

 FM Tutorial
Frequency Modulation (or FM) synthesis is a simple and powerful method for creating and controlling complex spectra, introduced by John Chowning of Stanford University around 1973.
When the frequency of the modulator (which we'll call M) is in the sub-audio range (1-20 Hz), we can hear siren-like changes in pitch of the carrier.
To determine which sidebands are present, we have to control the ratio between the carrier frequency (C) and the modulating frequency (M).
www.sfu.ca /~truax/fmtut.html   (2588 words)

 Reference.com/Encyclopedia/Frequency modulation synthesis
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.
For synthesizing harmonic sounds, the modulating signal must have a harmonic relationship to the original carrier signal.
Through the use of modulators with frequencies that are non-integer multiples of the carrier signal (i.e., non harmonic), bell-like dissonant and percussive sounds can easily be created.
www.reference.com /browse/wiki/Frequency_modulation_synthesis   (389 words)

 Frequency Modulation
FM is a so called angle modulation scheme, it was inspired by phase modulation but has proved to be more useful partly for its ease of generation and decoding.
is called the frequency deviation of the modulation scheme.
Your FM dial goes from 88 MHz to 108 MHz (this range is in between the frequency ranges for the TV channels 1-6, and 7-12.
robotics.eecs.berkeley.edu /~sastry/ee20/modulation/node4.html   (327 words)

 FM   (Site not responding. Last check: 2007-10-22)
--> In frequency modulation the amplitude is kept constant and the frequency is modulated by the amplitude of the modulating signal.
The frequency spectrum can be found by rewriting the above expression as a sum of components of constant frequency using the properties of the Bessel Functions.
Applet below shows a modulating signal in orange, the FM signal in red, the frequency spectrum in fl and how they vary with the modulation index and modulating frequency.
cnyack.homestead.com /files/modulation/modfm.htm   (101 words)

 Sinusoidal Frequency Modulation (FM)   (Site not responding. Last check: 2007-10-22)
Frequency Modulation (FM) is well known as the broadcast signal format for FM radio.
Note that, strictly speaking, it is not the frequency of the carrier that is modulated sinusoidally, but rather the instantaneous phase of the carrier.
Potential confusion aside, any modulation of phase implies a modulation of frequency, and vice versa, since the instantaneous frequency is always defined as the time-derivative of the instantaneous phase.
ccrma-www.stanford.edu /~jos/mdft/Sinusoidal_Frequency_Modulation_FM.html   (239 words)

 RF Cafe - Frequency Modulation Equations Formulas Bessel
Frequency modulation uses the instantaneous frequency of a modulating signal (voice, music, data, etc.) to directly vary the frequency of a carrier signal.
, is used to describe the ratio of maximum frequency deviation of the carrier to the maximum frequency deviation of the modulating signal.
Depending on the modulation index chosen, the carrier and certain sideband frequencies may actually be suppressed.
www.rfcafe.com /references/electrical/frequency_modulation.htm   (246 words)

 [No title]   (Site not responding. Last check: 2007-10-22)
In this, some base signal (e.g., a sinusoidal carrier wave) has one of its properties altered: amplitude modulation involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation changes the frequency....
Amplitude modulation (AM) is a form of modulation in which the amplitude of a carrier wave is varied in direct proportion to that of a modulating signal.
These amplifiers use pulse width modulation, pulse density modulation (sometimes referred to as pulse frequency modulation) or some combination of the two.
www.worldhistory.com /wiki/F/Frequency-modulation.htm   (881 words)

 Define frequency modulation - a definition from Whatis.com - see also: FM
Frequency modulation (FM) is a method of impressing data onto an alternating-current (AC)
When the instantaneous input wave has positive polarity, the carrier frequency shifts in one direction; when the instantaneous input wave has negative polarity, the carrier frequency shifts in the opposite direcetion.
Frequency modulation is similar in practice to phase modulation (PM).
whatis.techtarget.com /definition/0,289893,sid9_gci213999,00.html   (425 words)

 Information Headquarters: Frequency modulation
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").
Technology The harmonic distribution of a simple sine wave signal modulated by another sine wave signal can be represented with Bessel functions - this provides a basis for a mathematical understanding of frequency modulation in the frequency domain.
A rule of thumb, Carson's rule states that nearly all the power of a frequency modulated signal lies within a bandwidth of 2(Δf + fm) where Δf is the peak instantaneous deviation of the carrier from the centre frequency and fm is the highest modulating frequency.
www.informationheadquarters.com /Radio/Frequency_modulation.shtml   (540 words)

 Definition: frequency modulation   (Site not responding. Last check: 2007-10-22)
frequency modulation (FM): Modulation in which the instantaneous frequency of a sine wave carrier is caused to depart from the center frequency by an amount proportional to the instantaneous value of the modulating signal.
Note 2: FM is a form of angle modulation.
The lightwave is varied in intensity at an instantaneous rate corresponding to the instantaneous frequency of the electrical FM carrier.
www.its.bldrdoc.gov /fs-1037/dir-016/_2377.htm   (147 words)

 The PC Technology Guide
The first widespread technology to be used in sound cards was Frequency Modulation, or FM, which was developed in the early 1970s by Dr John Chowning of Stanford University.
FM synthesisers produce sound by generating a pure sine wave, known as a carrier, and mix it with a second waveform, known as a modulator.
Their OPL3 synthesiser hardware is the de facto standard for games cards, and uses parameters downloaded from the driver software to control cascaded FM oscillators to generate a crude analogue of acoustic and electronic musical instruments.
www.pctechguide.com /44SoundCards_Frequency_Modulation.htm   (304 words)

 Radio Modes and Modulation RTTY
In amplitude modulation, the strength (amplitude) of the carrier from a transmitter is varied according to how a modulating signal varies.
However, it is possible to modulate a signal by changing its frequency in accordance with a modulating signal.
The frequency space occupied is directly proportional to the speed at which messages are transmitted, and radio digital modes are very slow compared to their Internet equivalents.
www.dxing.com /modesand.htm   (1929 words)

 audio-rate frequency modulation
This article explains the phenomenon of audio-rate frequency modulation of sound, which was explored and used compositionally by John Chowning of Stanford University around 1970.
The rate of the vibrato is determined by the modulator's frequency, the depth of the vibrato (or how far above and below its center frequency the carrier will be pushed) is determined by the modulator's amplitude and the shape of the vibrato is determined by the modulator's waveform.
The greater the amplitudes of the modulating wave are at its peaks, the greater the maximum distance the carrier is pushed off its center frequency.
www.indiana.edu /~emusic/fm/fm.htm   (2969 words)

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