Pb-ions in harmonic number 4653 at SPS flat bottom

Pb-ion beams suer from strong beam degradation suchas transverse emittance growth and losses on the long flatbottom of the SPS cycles used for LHC filling. A possiblecontribution to the losses could come from RF noise, espe-cially due to the frequency and amplitude modulation duringeach revolution period of the fixed frequency accelerationmode required for the acceleration of these beams. A ma-chine development session in 2016 was devoted to a directcomparison of a cycle with fixed harmonic number at flatbottom and a cycle with the usually used fixed frequencymode. The main results are reported here.