Digital Up-Converter block converts a complex digital baseband signal to a real passband signal. Since the output of DUC block is real you are getting such constellation. You will get the expected QPSK contellation when you down convert the output of DUC.
Constellation not visisble after DUC?
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I am trying to simulate a system in Simulink, where i am trying to generate a QPSK modulated waveform (As you can see in the image below)
![Screenshot from 2019-12-25 20-50-07.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/257134/Screenshot%20from%202019-12-25%2020-50-07.png)
I am getting a proper constellation after the Fiilter block (as you can see in the image below)
![Screenshot from 2019-12-25 20-53-08.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/257135/Screenshot%20from%202019-12-25%2020-53-08.png)
But after the DUC unit, i am getting something
![Screenshot from 2019-12-25 21-00-25.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/257136/Screenshot%20from%202019-12-25%2021-00-25.png)
The spectrum i am getting afetr both the stages are shown below
After Root Cosine
![Screenshot from 2019-12-25 21-05-20.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/257137/Screenshot%20from%202019-12-25%2021-05-20.png)
After DUC unit
![Screenshot from 2019-12-25 21-06-08.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/257138/Screenshot%20from%202019-12-25%2021-06-08.png)
In the image below, we can see the DUC block setting
![Screenshot from 2019-12-25 21-10-34.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/257139/Screenshot%20from%202019-12-25%2021-10-34.png)
Please help me to resolve this issue.
Regards
Amol
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