ADF4355-3 spurs


We are using your evaluation board of synthesizer ADF4355-3.We are feeding externally 122.88MHz as reference,from a clean source without spurs.We locked 4355-3 and ensured 1KHz resolution.We are observing at every setting of output frequency the spurs at the offset of 80KHz either side @50dBc down.We need spur spec better than 60dBc.Can you please suggest how to reduce these spurs.Your immediate reply is appreciated.