Spurious sidelobes with WBX

Hello,

I am using the USRP1 + WBX to create a DAB OFDM signal (1.5MHz
bandwidth) in VHF
band.
The sampling rate used is 3.2MHz (interpolation 40)

However, there’s something I don’t understand. On the picture attached,
you can
see 2 spurious sidelobs that appear at about 2.5MHz from the center (red
arrow).

They are not present when monitoring the spectrum of the baseband IQ
signal
before going to USRP.

They also don’t appear when sending a tone signal.

Is there any explanation for this ? and any hint to avoid or reduce it ?

Thank you for your help.

Mathias C.
opendigitalradio.org

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