This work is a study of the effects of frequency selectivity on multi-carrier wideband signals in three different environments; indoors, outdoor to indoor and outdoors. The investigation was made using measurements carried out with a sounder with a 300 MHz bandwidth. The main part of this work is related to evaluate the contribution of several parameters; frequency selective fading, coherence bandwidth and delay spread on the frequency selectivity of the channel. A description of the sounder parameters and the sounded environments are given. The 300 MHz bandwidth is divided in segments of 60 kHz to perform the evaluation of frequency selective fading. Sub channels of 20 MHz for OFDM systems and 5 MHz for WCDMA were evaluated. Figures are provided for a number of bands, parameters and locations in the three environments. It is also shown the variation of the signal level due to frequency selective fading. The practical assumptions about the coherence bandwidth and delay spread are reviewed and a comparison is made with actual measurements. Statistical analysis was performed over some of the results.