Early TV standards changed every few years as different interests put forth demand for frequencies and standards. After WWII, with the communication technology development that occurred during the war, higher frequencies became more usable, and with the technology came more commercial demands on the available bandwidth. During the 40's there were several services sharing the band used by television, and the TV stations themselves began to interfere with each other, as propogation of their signal was greater than expected. In 1948 the FCC realized that these other services needed a space of their own, and what used to be NTSC channel 1 became their home, and they were thus removed from the TV spectrum. Apparently it was decided that 12 clear channels were better than 13 shared channels.
