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: <math>f_s > 2F_{Max}</math>
 
: <math>f_s > 2F_{Max}</math>
  
For a HIFI audio signal, the maximum audio frequency <math>F_{Max Audio}</math> is close to 20 kHz, so the sampling rate must be higher than 40 kHz (44.8 kHz is often used in computer sound cards, 8 kHz is used for mobile phones since voice has a lower frequency range than HIFI audio).  
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For a HIFI audio signal, the maximum audio frequency <math>F_{Max Audio}</math> is close to 20 kHz, so the sampling rate must be higher then 40 kHz (44.8 kHz is often used in computer sound cards, 8 kHz is used for mobile phones since voice has a lower frequency range than HIFI audio).  
  
For an AM signal modulated by an audio signal, the maximum frequency of the modulated spectrum is <math>F_{Max}=F_0+F_{Max Audio}</math>. Direct sampling of such a signal is not possible with conventional hardware such as a low cost SDR dongle. If the carrier frequency is close to 1 GHz, the sampling rate should be at least 2 GHz. This is obviously too much for the computer to handle (higher than some CPU clocks).
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For an AM signal modulated by an audio signal, the maximum frequency of the modulated spectrum is <math>F_{Max}=F_0+F_{Max Audio}</math>. Direct sampling of such a signal is not possible with conventional hardware such as a low cost SDR dongle. If the carrier frequency is close to 1 GHz, the sampling rate should be at least 2 GHz. This is obviously too much for the computer can handle (higher than some CPU clocks).
  
 
Flowgraph [[Media:IQ_tutorial_AM_TX_real.grc|IQ_tutorial_AM_TX_real.grc]] illustrates amplitude modulation using only real blocks (excepted for bits source). As a consequence, the maximum carrier frequency is limited to several tens of kHz.  
 
Flowgraph [[Media:IQ_tutorial_AM_TX_real.grc|IQ_tutorial_AM_TX_real.grc]] illustrates amplitude modulation using only real blocks (excepted for bits source). As a consequence, the maximum carrier frequency is limited to several tens of kHz.  

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