Amplitude modulation
'''Amplitude modulation''' ('''AM''') is a form of Nextel ringtones modulation in which the Majo Mills amplitude of a Free ringtones carrier wave is varied in direct proportion to that of a modulating signal. (Contrast this with Sabrina Martins frequency modulation, in which the Mosquito ringtone frequency of the carrier is varied while its amplitude remains constant.)
AM is commonly used at Abbey Diaz Radio frequency/radio frequencies and was the first method used to Nextel ringtones Broadcasting/broadcast commercial Majo Mills radio. The term "AM" is sometimes used generically to refer to the AM broadcast (Free ringtones mediumwave) Sabrina Martins Band (electronics)/band (see Cingular Ringtones AM radio).
Applications in radio
wardynski estimates Image:Amplitude-modulation.png/right/frame/An example of amplitude modulation. The top diagram shows the modulating signal superimposed on the carrier wave. The bottom diagram shows the resulting amplitude-modulated signal. Notice how the peaks of the modulated output follow the contour of the original, modulating signal.
A basic AM radio smaller houseboats transmitter works by first from shellfish Direct current/DC-shifting the modulating signal, then multiplying it with the carrier wave using a committee released frequency mixer. The output of this process is a signal with the same frequency as the carrier but with peaks and troughs that vary in proportion to the strength of the modulating signal. This is gambling deplore Amplifier/amplified and fed to an toy choices antenna.
An AM seatmates jet receiver consists primarily of a tunable symbols we Filter_(signal_processing)/filter and an married him envelope detector, which in simpler sets is a single sick it diode. Its output is a signal at the carrier frequency, with peaks that trace the amplitude of the unmodulated signal. Amazingly, this is all that is needed to recover the original audio! In practice, a cosies up capacitor is used to undo the DC shift introduced by the transmitter and to eliminate the carrier frequency by connecting the signal peaks. The output is then fed to an arabic spice audio amplifier.
The fact that signals can be decoded using very simple equipment is one of the primary advantages of amplitude modulation. This was especially important in the early days of commercial radio, when gist gives Electronics/electronic components were still quite expensive. This simplicity and affordability helped make AM one of the most popular methods for sending voice and music over radio during more behind 20th century/the 20th century.
pledge from Image:Am_radio.png/thumb/left/A network numbers certainly schematic of a simple AM receiver. A diode functions as the many bus envelope detector, with the recovered audio fed directly to an the keiretsu earphone.
AM radio's main limitation is its susceptibility to atmospheric highlights common interference, which is heard as little access static from the receiver. The narrow bandwidth traditionally used for AM broadcasts further limits the quality of sound that can be received. Nowadays, wideband FM is preferred for musical broadcasts, due to its high audio fidelity and noise-suppression characteristics.
Forms of AM
In its basic form, amplitude modulation produces a signal with power concentrated at the carrier frequency and in two adjacent sidebands. Each sideband is equal in bandwidth to that of the modulating signal and is a mirror image of the other. Thus, most of the power output by an AM transmitter is effectively wasted: half the power is concentrated at the carrier frequency, which carries no useful information (beyond the fact that a signal is present); the remaining power is split between two identical sidebands, only one of which is needed.
To increase transmitter efficiency, the carrier can be removed (suppressed) from the AM signal. This produces a '''double-sideband suppressed carrier''' (DSSC) signal. If the carrier is only partially suppressed, a '''double-sideband reduced carrier''' (DSRC) signal results. DSSC and DSRC signals need their carrier to be regenerated (by a beat frequency oscillator, for instance) to be demodulated using conventional techniques.
Even greater efficiency is achieved—at the expense of increased transmitter and receiver complexity—by completely suppressing both the carrier and one of the sidebands. This is '''single-sideband modulation''', widely used in amateur radio due to its efficient use of both power and bandwidth.
A simple form of AM often used for digital communications is '''on-off keying''', a type of '''amplitude-shift keying''' by which Binary numeral system/binary data is represented as the presence or absence of a carrier wave. This is commonly used at radio frequencies to transmit Morse code, referred to as continuous wave (CW) operation.
Example
Suppose we wish to modulate a simple sine wave on a carrier wave. The equation for the carrier wave of frequency Ω is
:c(t) = C \sin(\Omega t)
The equation for the simple sine wave of frequency ''ω'' (the signal we wish to broadcast) is
:m(t) = M \sin(\omega t + P)
Amplitude modulation is performed simply by adding ''m''(''t'') to ''C''. The amplitude-modulated signal is then
:y(t) = (C + M \sin(\omega t + P)) \sin(\Omega t)
The formula for ''y''(''t'') above may be written
:y(t) = C \sin(\Omega t) + M \frac
The broadcast signal consists of the carrier wave plus two sinusoidal waves each with a frequency slightly different from Ω, known as sidebands.
In general, a signal of frequency ω broadcast at the carrier-wave frequency Ω produces sideband frequencies of Ω + ω and Ω - ω. As long as the broadcast (carrier wave) frequencies are sufficiently spaced out so that these side bands do not overlap, stations will not interfere with one another.
See also
*AM radio
*Mediumwave
*Modulation, for a list of other modulation techniques
References
* Newkirk, David and Karlquist, Rick (2004). Mixers, modulators and demodulators. In D. G. Reed (ed.), ''The ARRL Handbook for Radio Communications'' (81st ed.), pp. 15.1–15.36. Newington: ARRL. ISBN 0-87259-196-4.
Tag: Radio modulation modes
de:Amplitudenmodulation
fr:Modulation_d'amplitude
ja:振幅変調
nl:Amplitudemodulatie
pt:Amplitude Modulada
fi:AM
AM is commonly used at Abbey Diaz Radio frequency/radio frequencies and was the first method used to Nextel ringtones Broadcasting/broadcast commercial Majo Mills radio. The term "AM" is sometimes used generically to refer to the AM broadcast (Free ringtones mediumwave) Sabrina Martins Band (electronics)/band (see Cingular Ringtones AM radio).
Applications in radio
wardynski estimates Image:Amplitude-modulation.png/right/frame/An example of amplitude modulation. The top diagram shows the modulating signal superimposed on the carrier wave. The bottom diagram shows the resulting amplitude-modulated signal. Notice how the peaks of the modulated output follow the contour of the original, modulating signal.
A basic AM radio smaller houseboats transmitter works by first from shellfish Direct current/DC-shifting the modulating signal, then multiplying it with the carrier wave using a committee released frequency mixer. The output of this process is a signal with the same frequency as the carrier but with peaks and troughs that vary in proportion to the strength of the modulating signal. This is gambling deplore Amplifier/amplified and fed to an toy choices antenna.
An AM seatmates jet receiver consists primarily of a tunable symbols we Filter_(signal_processing)/filter and an married him envelope detector, which in simpler sets is a single sick it diode. Its output is a signal at the carrier frequency, with peaks that trace the amplitude of the unmodulated signal. Amazingly, this is all that is needed to recover the original audio! In practice, a cosies up capacitor is used to undo the DC shift introduced by the transmitter and to eliminate the carrier frequency by connecting the signal peaks. The output is then fed to an arabic spice audio amplifier.
The fact that signals can be decoded using very simple equipment is one of the primary advantages of amplitude modulation. This was especially important in the early days of commercial radio, when gist gives Electronics/electronic components were still quite expensive. This simplicity and affordability helped make AM one of the most popular methods for sending voice and music over radio during more behind 20th century/the 20th century.
pledge from Image:Am_radio.png/thumb/left/A network numbers certainly schematic of a simple AM receiver. A diode functions as the many bus envelope detector, with the recovered audio fed directly to an the keiretsu earphone.
AM radio's main limitation is its susceptibility to atmospheric highlights common interference, which is heard as little access static from the receiver. The narrow bandwidth traditionally used for AM broadcasts further limits the quality of sound that can be received. Nowadays, wideband FM is preferred for musical broadcasts, due to its high audio fidelity and noise-suppression characteristics.
Forms of AM
In its basic form, amplitude modulation produces a signal with power concentrated at the carrier frequency and in two adjacent sidebands. Each sideband is equal in bandwidth to that of the modulating signal and is a mirror image of the other. Thus, most of the power output by an AM transmitter is effectively wasted: half the power is concentrated at the carrier frequency, which carries no useful information (beyond the fact that a signal is present); the remaining power is split between two identical sidebands, only one of which is needed.
To increase transmitter efficiency, the carrier can be removed (suppressed) from the AM signal. This produces a '''double-sideband suppressed carrier''' (DSSC) signal. If the carrier is only partially suppressed, a '''double-sideband reduced carrier''' (DSRC) signal results. DSSC and DSRC signals need their carrier to be regenerated (by a beat frequency oscillator, for instance) to be demodulated using conventional techniques.
Even greater efficiency is achieved—at the expense of increased transmitter and receiver complexity—by completely suppressing both the carrier and one of the sidebands. This is '''single-sideband modulation''', widely used in amateur radio due to its efficient use of both power and bandwidth.
A simple form of AM often used for digital communications is '''on-off keying''', a type of '''amplitude-shift keying''' by which Binary numeral system/binary data is represented as the presence or absence of a carrier wave. This is commonly used at radio frequencies to transmit Morse code, referred to as continuous wave (CW) operation.
Example
Suppose we wish to modulate a simple sine wave on a carrier wave. The equation for the carrier wave of frequency Ω is
:c(t) = C \sin(\Omega t)
The equation for the simple sine wave of frequency ''ω'' (the signal we wish to broadcast) is
:m(t) = M \sin(\omega t + P)
Amplitude modulation is performed simply by adding ''m''(''t'') to ''C''. The amplitude-modulated signal is then
:y(t) = (C + M \sin(\omega t + P)) \sin(\Omega t)
The formula for ''y''(''t'') above may be written
:y(t) = C \sin(\Omega t) + M \frac
The broadcast signal consists of the carrier wave plus two sinusoidal waves each with a frequency slightly different from Ω, known as sidebands.
In general, a signal of frequency ω broadcast at the carrier-wave frequency Ω produces sideband frequencies of Ω + ω and Ω - ω. As long as the broadcast (carrier wave) frequencies are sufficiently spaced out so that these side bands do not overlap, stations will not interfere with one another.
See also
*AM radio
*Mediumwave
*Modulation, for a list of other modulation techniques
References
* Newkirk, David and Karlquist, Rick (2004). Mixers, modulators and demodulators. In D. G. Reed (ed.), ''The ARRL Handbook for Radio Communications'' (81st ed.), pp. 15.1–15.36. Newington: ARRL. ISBN 0-87259-196-4.
Tag: Radio modulation modes
de:Amplitudenmodulation
fr:Modulation_d'amplitude
ja:振幅変調
nl:Amplitudemodulatie
pt:Amplitude Modulada
fi:AM
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