The problem of ad9364 transmitting spread spectrum code

We set the transmission bandwidth of AD9364 to the maximum, that is, RF BW = 40m, and then the baseband signal is a spread spectrum code with variable carrier frequency.

When the carrier frequency is 0, the RF signal quality observed by the spectrometer is very good, as shown in the figure below.

However, when the carrier frequency is 1.625M, the RF signal observed by the spectrometer seems to be the superposition effect of two peaks, as shown in the figure below.

In theory, when the carrier frequency of baseband spread spectrum signal is 1.625M, the RF spectrum should shift to the right compared the one when carrier frequency is 0, but the signal quality is poor.

We don't know why and how to solve this problem. I hope to get your valuable advice, thank you very much!

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