Sampling frequency to use with this signal to avoid aliasing

In summary: Essentially, the Nyquist frequency and rate are used to determine the minimum sampling frequency needed to accurately reconstruct a signal. In summary, the Nyquist frequency is the maximum frequency component of a signal and the Nyquist rate is the minimum sampling frequency needed to accurately reconstruct that signal. The Nyquist rate is calculated by multiplying the Nyquist frequency by two.
  • #1
Electgineer
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Homework Statement
The figure below shows the frequency spectrum of a CTS.
Relevant Equations
The sampling frequency without aliasing. I am posting this here because I don't even know how to approach the question. Is there a way to approach this kind of question. Thank you.
IMG_20210530_205602.jpg
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  • #2
Are you familiar with the Nyquist frequency and the Nyquist rate?
 
  • #3
FactChecker said:
Are you familiar with the Nyquist frequency and the Nyquist rate?
Yes. I am familiar till the part that the maximum angular frequency is 8 rad/s. So using the Nyquist rate, the sampling frequency should be twice the max frequency. But I don't understand how to systematically approach this kind of question. Thank you.
 
  • #4
Do you mean that you don't know how to systematically use the Nyquist rate or what?
You have answered the first question.
For the second question, assume point-by-point that anything below 1/2 the sampling frequency is not aliased and that everything above it is aliased to a lower frequency. What would the aliased spectrum graph look like?

PS. The simple Nyquist sample rate theorem (with perfect suppression of aliasing) assumes that the sample is taken for an infinite time. There is a more complicated version for a limited sample time, but it is rarely used and I can not find a reference for it.
 
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  • #5
Electgineer said:
Yes. I am familiar till the part that the maximum angular frequency is 8 rad/s. So using the Nyquist rate, the sampling frequency should be twice the max frequency. But I don't understand how to systematically approach this kind of question. Thank you.
Sort of. You have a triangle wave, so theoretically, your sampling frequency needs to be infinite since there are frequency components going out to infinity. The way to approach it is to do a Fourier decomposition of the triangle wave and decide how well you need the reconstruction to resemble the triangle wave. Sampling at twice the frequency of the triangle wave will result in reconstructing a sine wave with the frequency of the triangle wave (ignoring aliasing). You need to sample at twice the highest frequency in the Fourier series you want to use to reconstruct the reconstruction of the triangle wave with the precision you require. Since any "real" triangle wave will have a finite bandwidth and not be a perfect triangle wave, you might start there.
 
  • #6
bobob said:
Sort of. You have a triangle wave, so theoretically, your sampling frequency needs to be infinite since there are frequency components going out to infinity.
The figure shown is the frequency spectrum, not the wave. So it is much simpler.
 
  • #7
FactChecker said:
The figure shown is the frequency spectrum, not the wave. So it is much simpler.
Oops... My mistake for not looking at the figure more closely...
 

1. What is sampling frequency and why is it important in avoiding aliasing?

Sampling frequency refers to the rate at which a signal is sampled or measured. It is important in avoiding aliasing because if the sampling frequency is too low, it can result in the distortion of the original signal. This is because the sampled points may not accurately represent the original signal, leading to aliasing.

2. How do I determine the appropriate sampling frequency for a given signal?

The appropriate sampling frequency for a given signal can be determined by the Nyquist-Shannon sampling theorem. This theorem states that the sampling frequency should be at least twice the highest frequency component of the signal in order to avoid aliasing. In other words, the sampling frequency should be greater than the Nyquist frequency, which is half of the signal's maximum frequency.

3. Can using a higher sampling frequency than necessary cause any issues?

Yes, using a higher sampling frequency than necessary can result in unnecessary data and processing. This can lead to increased storage and computational requirements. However, it is generally recommended to use a sampling frequency that is slightly higher than the minimum required to ensure accuracy and avoid any potential issues.

4. What happens if the sampling frequency is too low?

If the sampling frequency is too low, it can result in aliasing, which is the distortion of the original signal. This can cause inaccuracies and errors in data analysis and processing. In some cases, it may also result in the loss of important information from the signal.

5. Are there any other factors to consider when choosing a sampling frequency?

Yes, there are other factors to consider when choosing a sampling frequency, such as the bandwidth of the signal, the type of signal (analog or digital), and the desired level of accuracy. It is also important to consider any potential noise or interference in the signal, as this may require a higher sampling frequency to accurately capture the signal's information.

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