Introduction

Giant Metrewavelength Radio Telescope(GMRT)

What is GMRT ?
The GMRT ,an aperture synthesis array, has been set up about 80 Km. north of Pune .It consists of an array of 30 fully steerable parabolic dishes,each of 45m in diameter,located over a region of about 25 Kms.(Fig. 2).Six dishes are installed in each of the three arms of the Y shaped array and the remaining 12 antennas are installed in and around Central Electronics Building(CEB).

A simplified block diagram of the GMRT receiver system is shown in Fig(GMRT SYSTEM).The antennas have dual polarised feeds at all the six frequencies.The feeds are mounted on the four faces of a micro-processer controlled rotating turret near the prime focus.The receiver system consists of RF,LO,IF electronics and is required to have a very low system temperature and good phase stability.The linearly polarised signals received from the sky are converted to circularly polarised signals,amplified and brought thro' two low-loss cables to the base of the antenna.Then the RF signals are converted to 130 and 175 MHz band using the regenerated LO signals locked to a central frequency standard and transmitted to the CEB thro' the Single mode 1310 nm Optical Fibre cable and converted to the video signal of 16 MHz bandwidth by the baseband system.The back end consists of a correlator system which digitizes the analog signals at 32 MHz clock rate,introduces proper path delays to compensate for the time difference in the signal path to maximise the received signal from all the 30 antennas and helps in producing high quality image maps.

Control and Monitor (C & M)System for GMRT
What is the purpose of C & M ?
The Control and Monitor System of a Radio Telescope is required to provide the necessary co-ordination between the various building blocks of the receiver system.This system is used for Controlling the activities of the various building blocks of GMRT like FE,LO,IF,BB,SERVO and FPS etc and Monitor the healthiness of the same in each of the antenna shells and CEB.It provides the human interface to persons like Telescope Observers,Scientists and maintenance personnel for operating all the antennas from CEB.It has to monitor all parts of the telescope system for correct operation and alert the operator in case of any anomalous behaviour.And in the case of severe fault conditions,safety procedures have to be initiated locally.It has also to prevent human error from placing the telescope in a dangerous situation.This Control and Monitor System for GMRT tries to meet all the points mentioned above.

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Contact :www@gmrt.ncra.tifr.res.in