  We first discuss the sensitivity of the WMAP CMB power spectrum to systematic
errors by calculating the raw CMB power spectrum from WMAP data. We find that
the power spectrum is surprisingly sensitive to the WMAP radiometer beam
profile 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 a
long power-law tail to the beam due to side-lobes and this causes significant
effects even at the first peak position. We then test the form of the
beam-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 found
that they showed a wider profile in Q, V, W than the Jupiter profile. We have
now checked that this is not due to any Eddington or other bias in our sample
by showing that the same results are obtained when radio sources are selected
at 1.4GHz and that our methods retrieve the Jupiter beam when it is employed in
simulations. Finally, we show that the uncertainty in the WMAP beam profile
allows the position as well as the amplitude of the first peak to be changed
and how this could allow simpler cosmologies than standard Lambda-CDM to fit
the CMB data.
