I’ve run a quick test using an RSP1A and get results similar to those you have posted. Reducing the signal input level to the RSP caused the spur levels to reduce. At an input level of around -20 to -25dBm the spurs had gone. If you still have problems, please post a full screen-shot of the analyser as this lets me see any other settings that could be causing problems. A reference level of 0dBm is OK – Check front of manual for information about gains and what the reference level setting is actually doing.