Non-Polar Mode

In this mode of observation the visibility for only one of the two polarizations can be measured in each of 256 spectral channels for all baselines (including self correlations). The maximum bandwidth possible is 2 $\times$ 16 MHz. Thus the observation will have half the total sensitivity of the GMRT.

Figure 25.6: The signal flow in the GMRT correlator for the Non-Polar mode. Signal names preceding with a $T$ indicate time series and angular brackets denote time average. Numeric subscripts indicate the sample number for time series data and the frequency channel number for spectral data.

In the non-polar mode the required sampling frequency is selected in the delay-DPC system. The multiplexer in the delay-DPC is configured such that the data flow is as shown in Fig 25.6. $TR_{Ui}, TR_{Li}, TL_{Ui}$ and $TL_{Li}$ are the time series of the four baseband signals for a given antenna. The FFTs of these time series are $R_{Ui}, R_{Li}, L_{Ui}$ and $L_{Li}$ respectively (for $i=1~{\rm to}~256$). $R_{Ui}^{'}$, $L_{Ui}^{'}$ are the corresponding signals from a second antenna. The MAC mode is selected such that the 256 channels in one of the sidebands of one of the polarizations (in this case $R_{Ui}$) is integrated in its 256 accumulators. A second set of MACs integrate the signals from the second sideband of the same polarization (in this case $R_{Li}$).