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This is a Phased Array Feed (PAF) for the Green Bank Telescope. It is put at the prime focus of the GBT. Each of the flanges is a crossed dipole antenna. There are 19 of these crossed dipoles. Their signals are sent to a digital signal processor which combines the signals from the 19 elements to form a single radio beam.

The 110-meter dish of the Green Bank Telescope can be aimed all over the sky, thanks to its rotating base and a huge tilting gear. The GBT is the largest, fully-steerable telescope in the world and the largest moving object ever built on land.

Down the halls in the Green Bank Science Center, visitors can see the Green Bank Telescope framed between the walls. As one walks closer to the atrium, the GBT gets smaller, not larger!

At the Green Bank Telescope, astronomers can choose a variety of receivers to use to observe the radio skies. One of them can only fit up at the prime focus of the telescope. The cone at the left is the funnel entry into the feed of the receiver which is enclosed in a cage suspended on the end of the GBT’s 200-foot feed arms. It receives the radio waves bounced up here by the 100-meter dish of the telescope below.

The receivers of the Green Bank Telescope sit in a revolving cabin called the turret. The feed horns poke above the cabin, and their receivers hang beneath them in a suspended building that tilts with the telescope. When an astronomer wants to observe the longest wavelengths at the GBT, the telescope operator spins the largest horn into the beam of radio waves bouncing from the sub-reflector above the turret. The feeds are covered in a radio-clear fabric to keep debris and rain out, and blowers keep the fabric dry and free of obstructions.