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What if Carrier Frequency is greater than Sampling Frequency?


In general, we consider that the sampling frequency should be greater than the carrier frequency. No straightforward rule tells us how many times the sampling frequency should be compared to the carrier signal's frequency. 

However, Nyquist Criteria tells us the sampling frequency must be at least twice the highest available frequency components in the message signal.

If the baseband message signal is 3 KHz, the sampling frequency must be 6 KHz or above. However, in the practical scenario, we can keep it ten times more than the message signal. 

Similarly, we can set the sampling frequency ten times more than the carrier frequency. Some simulation examples show what happens if the carrier signal is less, equal, or greater than the sampling frequency.

1. If the Sampling Frequency is Greater than the Carrier frequency 




2. If the Sampling Frequency is Equal to the Carrier frequency

 

 
 
 

3. If the Sampling Frequency is less than the Carrier frequency

 

 

Conclusion

Sampling frequency indicates the total number of samples or data points available in a signal of the duration of 1 second. If the sampling frequency is greater than the carrier frequency, then it is okay to represent a signal completely. But if the sampling frequency is less than the carrier frequency, you will lose the information in the carrier signal. 

 

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[1] What should be the relationship among the message, carrier, and sampling frequencies?

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