Frequency domain measurements and models in the S-parameter format are now used virtually exclusively in high-speed system design and characterization. Common practice dictates that S-parameter data have a frequency content of three times the fundamental frequency of the data rate of interest. However, the investigations conducted during the development of Optical Internetworking Forum's StatEye v 4.2 channel compliance tool revealed such frequency content to be possibly insufficient. The results were further confirmed with other simulation techniques. In this article, the frequency content issue is introduced and explained, and the results using full, truncated, and padded S-parameter data are compared. The results are of particular importance for the emerging 10+ Gbps backplane designs and evaluations.