The present invention relates to a method and arrangements in a radio base station for turning off the output power for a frequency carrier of a cell. The radio base station is configured to use at least two different modulation schemes. Each of the modulation schemes requires a different output power spectrum density for the frequency carrier. The method in the radio base station comprises reducing (410) the available output power spectrum density for the frequency carrier gradually, and disabling (420) the modulation scheme with the highest required output power spectrum density, before the available output power spectrum density falls below said highest required output power spectrum density. It also comprises turning off (430) the output power for the frequency carrier before the available output power spectrum density falls below the highest required output power spectrum density of the at least one remaining non-disabled modulation scheme.