Looking at a PSK modulated signal, my spectrum analyzer reveals a spectral line in the middle of the main lobe, right at the carrier frequency. What is causing this and how can I correct it?
If the sequence you are using is non-maximal (i.e. not an m-sequence), the code may be highly imbalanced (a lot more ones than zeros, or vice-versa), which can cause a significant carrier component to appear. This is normal. But if the sequence is an m-sequence, you may have a defective mixer. Or you may be connecting the generator to the mixer incorrectly. Refer to the FAQ on mixer connections for instructions on driving a double-balanced mixer. If you still have a problem after confirming correct mixer setup, and you’re sure you are generating an m-sequence, the problem may be due to carrier imbalance. Refer to the FAQ on carrier imbalance for more information.
Related Questions
- Looking at a PSK modulated signal, my spectrum analyzer reveals a low carrier spectral line, much lower in magnitude than what theory would suggest. What is causing this and how can I correct it?
- Looking at a PSK modulated signal, my spectrum analyzer reveals a spectral line in the middle of the main lobe, right at the carrier frequency. What is causing this and how can I correct it?
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