The FCC called for technical demonstrations of color systems in 1948, and the Joint Technical Advisory Committee (JTAC) was formed to study them. CBS displayed improved versions of its original design, now using a single 6 MHz channel (like the existing black-and-white signals) at 144 fields per second and 405 lines of resolution. Color Television Inc. (CTI) demonstrated its line-sequential system, while Philco demonstrated a dot-sequential system based on its beam-index tube-based "Apple" tube technology. Of the entrants, the CBS system was by far the best-developed, and won head-to-head testing every time.