  It is important to correctly subtract point sources from
radio-interferometric data in order to measure the power spectrum of diffuse
radiation like the Galactic synchrotron or the Epoch of Reionization 21-cm
signal. It is computationally very expensive and challenging to image a very
large area and accurately subtract all the point sources from the image. The
problem is particularly severe at the sidelobes and the outer parts of the main
lobe where the antenna response is highly frequency dependent and the
calibration also differs from that of the phase center. Here we show that it is
possible to overcome this problem by tapering the sky response. Using simulated
150 MHz observations, we demonstrate that it is possible to suppress the
contribution due to point sources from the outer parts by using the Tapered
Gridded Estimator to measure the angular power spectrum C_l of the sky signal.
We also show from the simulation that this method can self-consistently compute
the noise bias and accurately subtract it to provide an unbiased estimation of
C_l.
