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Overview of 45-m Telescope

Main Refrector
About 600 pieces of panels consist a paraboloid. Each panel has a surface accuracy of about 60 microns, and the deviation of the whole antenna from an ideal paraboloid is about 90 microns.
Sub Refrector
It refrects radio waves collected by the main refrector toward the lower cabin. The diameter is 4 m and the surface is a convex hyperboloid. The position is computer-controlled to follow the moving focal point because the main refrector deforms as the elevation angle changes.
Panel Adjustment System
Each panel can be adjusted using remote-controlled motors at its four corners. With holography method panels are adjusted to form an ideal paraboloid.
Framework of Main Refrector Panel
The main refrector deforms as the elevation angle changes due to its own weight. However, since the framework is designed to have homologous structure, deformed main refrector also forms another paraboloid.
Shading Panel
In order to prevent the main refrector from deforming due to sunlight, the framework is covered with heat insulator panels. The temperature in the framework is kept uniform within 0.4 degrees Celsium using 70 fans.
Collimator Tower
It is difficult to point the main refrector accurately toward celestial objects by itself. Instead, a collimator is settled on a collimator tower and the collimator is pointed at high accuracy. Then the main refrector is controlled to follow the collimator. In this way the antenna can be pointed to desired direction at an accuracy better than 1/1000 degrees.
Lower Cabin (and Mirros)
Radio wave collected by main- and sub-refrectors is guided to receivers by serveral mirrors in the lower cabin. By remote-controlling mirrors (made of alminum), the wave can be guided to any of receivers. Using wire-grids instead of mirros, two kind of polarized waves can be simultaneously observed using two receivers.
Azimuth Rotation Wheel
There are 6 wheels and 2 motors (CW and CCW) to rotate the telescope azimuthally.
Receivers
There are about 10 heterodyne receivers in the lower cabin. The radio wave from the sky is mixed with an artificial signal from local oscillator to down-convert the frequency, and then amplified. This principle (heterodyne detection) is the same one used in radios. However high-performance receivers are needed since the frequency is much higher than radio broadcasts. The receivers are cooled to 4 K (-269 degC) or 20 K (-253 degC) in order to reduce thermal noises.
2006-12-12 nro45mrt @ NRO

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