Beijing, Nov 22 (IANS): The construction of the world's largest ever radio telescope in China's Guizhou province has entered the final stage as scientists tested the installation of the "retina", the media reported on Sunday.

The scientists on Saturday lifted a 30-tonne feed cabin of the Five hundred-metre Aperture Spherical Telescope - or FAST - above a half-finished dish-like reflector measuring 500 metres in diameter and 1.6 km in perimeter, China.org reported.

Once completed by September 2016, the cabin, home to a feed source which collects signals from the universe, will be suspended 140 to 160 metres above the reflector made up of 4,450 panels.

Each panel is an equilateral triangle with a side length of 11 metres, and has cables fixed to the back of it so that it could adjust angles and positions in synchronisation with the source cabin, which is driven by cables, servomechanisms in addition to a parallel robot as a secondary adjustable system.

"If you compare the FAST to an eye, then the feed source is its retina," said Sun Caihong, a chief engineer with the FAST programme, adding, "All signals we collect eventually come here."

Sun said control of high-precision and long-distance movements of the source cabin using steel cables was a serious challenge for experts, but they managed to narrow down maximum error to less than 10 mm.

"This is one of our greatest innovations," he said.

Construction of the FAST began in March 2011 with an investment of 1.2 billion yuan.

Technicians are still continuing the work that started months ago to assemble the reflector, which is hung over the ground supported by thousands of steel pillars and cables in a valley in the mountainous Guizhou province.

The Karst formation in the local landscape is good for draining rainwater underground and protecting the reflector, Sun said.

The surrounding area has "radio silence" as there are no towns and cities within a sphere of five km and only one county centre within a sphere of 25 km.

Upon completion, the telescope will be the world's largest of its kind, overtaking Puerto Rico's Arecibo Observatory, which is 300 metres in diameter.

It will also be 10 times more sensitive than the steerable 100-metre telescope near Bonn, Germany, according to Zheng Xiaonian, deputy head of the National Astronomical Observatories under the Chinese Academy of Sciences.

"FAST will be the top level facility in the world for at least 20 to 30 years," Zheng added.