Upgraded Arecibo radio observatory. Aerial view of the Arecibo radio telescope, with its gregorian subreflector system newly installed in 1997. This largest radio telescope in the world is situated in a natural crater in the mountains of Puerto Rico. The new subreflector system with two mirrors is housed in a 90-tonne dome receiver seen suspended 130 metres above the fixed dish. It can send and receive signals to examine planets and asteroids & also analyse Earth's upper atmosphere. To scan the sky the dome is steered above the 305m dish. The upgrade includes a 16m high buffer screen around the dish and a new radar transmitter that increases Arecibo's power by 20 times.