----------------------

To understand the MWA data, we calculate the APS using different 5 data sets. The 5 data sets are: i) the visibility with no source peeling, ii) visibility with peeling of 1000 sources, iii) image with peeling of 1000 sources, iv) image with the polynomial foreground removal and peeling of 1000 sources and v) visibility of the thermal noise. Fig. \[fig:APSimage\] compares the resulting APS at $\nu=$ 167MHz, 176MHz, 186MHz and 194MHz.

The APS using visibilities without peeling increases with $l$ and overwhelms the APS with peeling of 1000 sources at all scales. Thus, the apparent 1000 point sources dominate the signal. Meanwhile, the APS calculated from visibility with peeling shows a flat slope at large scales and rises at small scales. This different index can be understood as that the point source foregrounds dominate at small scales and the diffuse Galactic emission is powerful at large scales. Typically, the expected 21cm APS is less than $10^{-4}\rm [K^2]$ at $\ell = 100$ [@2007MNRAS.378..119D], and therefore we have to reduce the foregrounds by at least 6 orders of magnitude in $\rm K^2$ to measure the 21cm-line signal.

The noise APS of the MWA observation is sufficiently smaller than the measured 