rfLib ACPR source usage

I'm attempting to use the ACPR_source block as an input to my circuit. I have baseband I and Q files for a modulated waveform, sampled at 30.72MHz. I'm encountering a problem that I believe is due to oversampling and interpolation, where unwanted images are appearing at multiples of the BB sampling frequency (see attached image). I see there is a filter option on the ACPR block, but when I tried using it it didn't seem to filter the images at all. How does one normally remove these?

Thanks,
Steve

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