China set up military jamming equipment on Spratly Islands, U.S. says

The video discusses the installation of equipment on two Spratly island outposts by China, which can disrupt communications and radar systems. Satellite imagery from Digital Globe reveals suspected jamming systems on Mischief Reef, one of China's seven artificial islands. US intelligence reports that new jamming equipment was installed within the last 90 days on Fiery Cross and Mischief Reef. These outposts now feature extensive infrastructure, including runways, hangars, ammunition depots, barracks, and deep-water piers.

What is the purpose of the jamming equipment mentioned in the text?

When was the new jamming equipment installed according to US intelligence?