Understanding the role of ocean swell, monitoring and modelling it is critical for a diverse range of oceanographic research, coastal management initiatives and for better weather forecasting and climate modelling. Currently, swell measurements are obtained through in-situ measurements, wave models, and satellite measurements. So far, swell wave parameters have been retrieved from orbit using optical instruments, imaging radars and wave spectrometers. The potential to retrieve swell wave spectra from radar altimeters was recently demonstrated using fully focused synthetic aperture radar (FFSAR) signal processing. Sentinel-6 (S6) would be a good candidate for investigating the potential of swell parameter retrieval, however, no study has been performed regarding the impact that the on- board data compression/ waveform truncation mode of S6 could have on the retrieval of swell parameters. Swell wave period estimates were thus derived from the raw and compressed S6 FFSAR waveforms collected over a study area in the Channel Islands of California during a 22 month- period. A performance analysis was carried out comparing the period estimate pairs from a given timestamp with the records obtained by a buoy in the study area at the same time. The study demonstrated the presence of differences in the performance of swell period retrieval for the different operating modes of S6. It was found that swell period estimates can be derived also from the compressed waveform signal, obtaining however a lower accuracy compared to raw waveforms.