Sensitivity issues with the GMRT antennas
I have also been involved in regular tests of GMRT antennas
for its sensitivity. The sensitivity can be measured at the output of the
optical fibre using 30to1 recording programme or through lta file. 30to1
will tell us the health of signal before the correlator, where as lta
will tell us the health at the end of all the chain of systems, including
correlator. It is better to do a simple deflection expt, which require
hardly 20 min, using 30to1 just before or after taking point source
data (as lta). 30to1 data will primarily address the health of the feed and
Front End (FE) related components. Here is a typical
example of results from 30to1 recording. If we see that the antenna produces
the deflection at the expected amount at both 130 and 175 channels, this
part of the chain can be cleared. In the example, C08, E05 and W01 are
dead due to various reasons. Antennas C01 and C02, for example are
very healthy, S01, S02, S03 and W03 are not showing expected deflection.
The calibrator data such as on 3c48, 3c147
or 3c286 will tell us about whether the crosss power are OK.
Please wait for detailed write-up