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This paper focuses on the measurement of the main reflector gravity deformation and sub-reflector position change on Tianma 65 m (TM65 m) radio telescope. Firstly the paper summarizes the methods of principal measurement. Microwave holography and cross scan pattern are disscussed. Then the gravity deformation of the main reflector over the entire elevation measured by VLBI method is discribed. The measurement accuracy is also estimated. At last, the gravity model is constructed and compared with the simulation. They agree with each other. The formulas along with the simulation give a description between the offsets of feed, sub-reflector and the aperture phase. The sub-reflector position ofTM65 m is obtained by the least square method that applied on the aperutre phase and the formulas. The sub-reflector positions measured are consistent with that of the traditional amplitude method in X , Y and Z directions. This method provides a different way to measure the position model of the sub-reflector.

In the paper, the main factors influencing pointing precision of large radio telescopes are discussed. Then the TianMa radio telescope (TM65 m) is selected for demonstration. The methods of detecting and separating the pointing errors which produce in all the segments from the subreflector to the track rail of the telescope are introduced. They includes: (1) half power point tracking to evaluate the overall antenna pointing error; (2) detecting the pointing error due to position changing of the subreflector support; (3) detecting the deviation of the antenna mount due to temperature changing; (4) detecting the asynchronization of the mechanical axis and the encode axis; (5) high precision pointing modeling based on the uneveness of track rail. A few measurement methods and their respective results are discussed.

Microwave holography is a valuable technique used in the diagnostics and adjustment of large antennas. A brief outline of the technique is given first. Then detail simulations for surface deviation and sub-reflectorr offsets solving method that applied on the TianMa 65 m are described. After several rounds of adjustments, a reflector surface accuracy 0.28 mm and repeated measurement error 0.13 mm were achieved for the TM65 antenna. At last the antenna efficiency on Ka band was measured at elevations between 45 and 60 degrees. The efficiency improved from 37% to 56% when the active surface model is loaded that is consistent with the theoretical predictions.