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Galactic foreground emission is a limiting factor for precise cosmicmicrowave background (CMB) anisotropy measurements. We perform an angular powerspectrum analysis (APS) of all-sky total intensity maps at 408 MHz and 1420MHz, which are dominated by synchrotron emission out of the Galactic plane. Wesubtract the brighter sources from the maps. We study the APS as a function ofGalactic latitude by considering various cuts and as a function of sky positionby dividing the sky into patches of about 15 deg x 15 deg in size. The APS ofthe Galactic radio diffuse synchrotron emission is best fitted by a power law,$C_{\ell} \sim k \ell^{\alpha}$, with $\alpha \in [-3.0,-2.6]$, where the lowervalues of $\alpha$ typically correspond to the higher latitudes. Nevertheless,the analysis of the patches reveals that strong local variations exist. Themean APS for $\ell \in [20,40]$ is used to determine the mean spectral indexbetween 408 MHz and 1420 MHz, which is then adopted to extrapolate thesynchrotron APS results to the microwave range. A simple extrapolation to 23GHz of the synchrotron emission APS found at 408 and 1420 MHz does not explainall the power in the WMAP synchrotron component even at middle/high Galacticlatitudes. This suggests a significant microwave contribution (of about 50% ofthe signal) by other components such as free-free or spinning dust emission.The comparison between the extrapolated synchrotron APS and the CMB APS showsthat a mask excluding the regions with $|b_{gal}| \lesssim 5^{\circ}$ wouldreduce the foreground fluctuations to about half of the cosmological ones at 70GHz even at the lowest multipoles. We discuss the main implications of ouranalysis for the cosmological exploitation of microwave temperature anisotropymaps.

The impact of Galactic synchrotron emission on CMB anisotropy measurements. I. Angular power spectrum analysis of total intensity all-sky surveys