News from India.
PPD Update
Cluster Antenna
Research Articles

Preloaded Parabolic Dish (PPD) project update

Activities related to this project are progressing on various fronts. While the receiver system and control systems are being assembled and tested in the Raman Research Institute campus in Bangalore, the mount for the dish and the mechanical drive system is being fabricated by M/s. V.M. Jog Constructions, in Pune. Civil work has also picked up at the installation site in Gauribidanur. Meanwhile, various tests are being carried out on the dish at RRI in collaboration with the Central Power Research Institute (CPRI), Bangalore.

Fig. 1 shows a single polarization 4 to 8 GHz front-end receiver presently characterized in the lab. The testing of the control system has been completed. To provide redundancy and flexibility we have investigated two approaches, one using a Programmable Multi Axis Controller (PMAC) and the other using a LINUX-based PC.

Modal analysis of the 12m PPD to determine its dynamical characteristics like resonant frequencies, damping values and patterns of deformation, has been carried out in collaboration with engineers at the Central Power Research Institute (CPRI), Bangalore. Based on analysis using NASTRAN FEM software and measurements on the assembled dish, it was decided to install stiffeners between the central hub and the alternate spokes (see fig. 2), which increased the resonant frequencies of the various modes from 1.4Hz to 2.2Hz approximately. Further studies were done in which the dish is set into vibration by a mechanical shaker (modal shaker of 50 pounds capacity. See fig. 2) and the system response to a driving force input was acquired using a special purpose data acquisition system. The average damping measured during the above modal testing is 0.978. Detailed analysis of the data to determine different mode shapes is under progress.