The antenna is mounted on the top of a 25 meter high tower. There are azimuth and elevation rotation axes on the tower. The vertical azimuth axis is made of massive 15 m tall pipe with 2.3 m diameter. On the top there is placed the elevation axis. The antenna system is of Cassagrain type. The supporting structure of the main mirror is made from steel pipes. This structure supports the mirrors' aluminium panels and surface have been adjusted with screws. At the centre of the main mirror there is a 4.4 m tall cone for receiving equipment. The main parameters of the antenna system are presented below.

PARAMETERS OF RT-32 CASSEGRAIN SYSTEM

• Diameter: 32.00 m
• Focal length: 11.45 m
• Effective focus length: 86.81 m
• F/D ratio: 0.36
• Subtended angle: 139.8°
• Diameter of the subreflector: 2.50 m
• Subtended angle of the subreflector: 21.06°
• Radiotelescope magnification: 7.58

There are radiometers and power density registration equipment installed in apparatus rooms (from the Solar observatory in Baldone). The measurements on frequency of 11 GHz let us to make assumption - there are no intended mechanical adjustments to destroy the antenna mirrors' system. The location of the focal plane was determined with 1mm tolerance.

The driving systems for each axis (in fact doubled) are very similar. They each have 2 motors to drive in awide dynamic range of velocities. There are differential gear-box systems to manage the total speed of each axis.

The resulting speed can be the difference of each motor's angular rotation speed. The maximum operational speed is 2 m/sec. The very complicated control system allows us to drive with 1, 2 or 3 motors together (including torsion brake motor). At the present only restoration of previous mechanical and electrical systems is completed allowing us to repair the system in cheep and simple way and let us start transit observations without the movement control. The parameters of operational speed are presented in table:

The control system for each axis consists of three parts:

• A n a l o g u e  s y s t e m   with 3 selsins, 2 rotating transformers and a tachogenerator. Visual accuracy is about 20". Fully operational.
• D i g i t a l  s y s t e m  of  PC-50 [reversive counter] with a 14 bit optical encoder for 90° angle sector and measurement accuracy about 20" connected to a separate computer to determine the coordinates. Fully operational.
• D i g i t a l  c o m p u t e r i z e d  s y s t e m  for azimuth and elevation axis is operational, but is installed for digital speed control only.

Perfomance parameters

• motion range around the elevation axis: -1° to 97°
• motion around the azimuth axis: ±330°
• max angular velocity around the altitude and the azimuth axis (2 direct-current, 60kw motors): 1'/sec to 2°/sec
• min angular velocity around the altitude and the azimuth axis (2 direct-current, 5.5 kW motors): 2"/sec to 5'/sec
• survival wind speed: 40 m/sec
• max observing wind speed: 15 m/sec

Accuracy characteristics

• manufacture of the surface: 0.25 mm
• rigging of the panels: 0.5 mm
• rigging of azimuth axis: 5'' to 10''
• azimuth-elevation axis orthogonality: 5'' to 10''
• angular incidence of focal axis when pointing at horizon: 2'9''
• deflection of focal point axis when pointing at horizon: 3.7 mm
• combined rms deviation of the reflecting surface of primary reflector (including action of dead weight and wind): 1.3 mm

Mass characteristics

• weight movable in altitude: 65t
• weight movable in azimuth: 600t

By G.Balodis and Z.Sika