Complex sentence: The mountain was the longtime site for the transmitter tower of San Jose television station KNTV (from 1955 to 2005), which moved its transmitter to San Bruno Mountain in September 2005, after it became the Bay Area's NBC affiliate.
Split into simpler sentences: The mountain was the longtime site for the transmitter tower of San Jose television station KNTV (from 1955 to 2005). It moved its transmitter to San Bruno Mountain in September 2005, after it became the Bay Area's NBC affiliate.