For the demonstration of ESASE as the soft X-ray beamline Athos at SwissFEL at the Paul Scherrer Institute, spectral measurements have been taken for normal SASE operation and ESASE operation, where the electron beam is modulated in energy by an external laser and then transformed into a series of current spikes. The effect on the electron beam has been measured with a transverse deflecting cavity projecting the longitudinal phase space onto a screen in the dispersive region. These measurements have been done for various degrees of compressor settings, laser power and configuration of the laser heater.