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We first discuss the sensitivity of the WMAP CMB power spectrum to systematicerrors by calculating the raw CMB power spectrum from WMAP data. We find thatthe power spectrum is surprisingly sensitive to the WMAP radiometer beamprofile even at the position of the first acoustic peak on ~1 degree scales.Although the WMAP beam profile core is only 12.6arcmin FWHM at W, there is along power-law tail to the beam due to side-lobes and this causes significanteffects even at the first peak position. We then test the form of thebeam-profile used by the WMAP team which is based on observations of Jupiter.We stacked radio source beam profiles as observed in each WMAP band and foundthat they showed a wider profile in Q, V, W than the Jupiter profile. We havenow checked that this is not due to any Eddington or other bias in our sampleby showing that the same results are obtained when radio sources are selectedat 1.4GHz and that our methods retrieve the Jupiter beam when it is employed insimulations. Finally, we show that the uncertainty in the WMAP beam profileallows the position as well as the amplitude of the first peak to be changedand how this could allow simpler cosmologies than standard Lambda-CDM to fitthe CMB data.

Lambda-CDM and the WMAP power spectrum beam profile sensitivity