Frequency modulation: Difference between revisions
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'''Frequency |
'''Frequency modulation''' ('''FM''') is an analog [[modulation scheme]] where the signal modulates the frequency of the carrier signal by a tiny fraction. It is used in FM radio. |
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The digital equivalent is [[frequency shift keying]] (FSK). |
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A variation of Frequency Modulation is sometimes also used for digital Transmissions, this is then called ''Frequency Shift Keying'' or FSK-Modulation. |
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== Mathematical setting == |
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== Visualisation == |
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== Acquired bandwidth == |
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''it would be nice to have a gnuplot picture here, is it possible to upload the gnuplot script for toying, too?'' |
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Noise immunity is higher than [[amplitude modulation]] because noise does not shift the frequency of a signal, but adds to it with the superposition principle. |
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== External links == |
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* [[Wikipedia:History of radio|History of radio]] at Wikipedia |
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[[Category:Technology]] |
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== Aquired Bandwidth == |
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is higher than the one of Amplitude Modulation Schemes since athmospheric disturbances and noise usually don't shift the frequency of a signal but add their contribution to the amplitude of the transmitted signal. Amplitude variations don't affect FM much. |
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== Links == |
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* [[Wikipedia:History_of_radio|A nice introduction to the History of Radio on Wikipedia]] |
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Latest revision as of 07:07, 26 December 2016
Frequency modulation (FM) is an analog modulation scheme where the signal modulates the frequency of the carrier signal by a tiny fraction. It is used in FM radio.
The digital equivalent is frequency shift keying (FSK).
Mathematical setting
The output voltage of a FM modulator with input voltage <math>u_{in}</math> is described by:
- <math>u_{out} = sin(2 \pi (f_{carrier} + u_{in} \cdot \Delta f))</math>
where <math>\Delta f</math> is the frequency deviation from the center frequency at <math>u_{in} = 1V</math>.
Acquired bandwidth
Acquired bandwidth can be determined using Carson's bandwidth rule: two times the sum of the peak deviation <math>\Delta f</math> from the highest frequency occurring in the spectrum of the modulating signal <math>(f_m)</math>:
- <math>bandwidth = 2 \ (\Delta f + f_{m})</math>
Noise immunity
Noise immunity is higher than amplitude modulation because noise does not shift the frequency of a signal, but adds to it with the superposition principle.
External links
- History of radio at Wikipedia
- Frequency modulation at Wikipedia