We present the preliminary results of a new survey of radio sources using the Ryle Telescope at 15.2 GHz .
This is the highest frequency at which a survey has been done that is relevant to the issue of radio source contamination in CMB experiments .
The differential source count of the 66 sources found in 63 deg ^ { 2 } is 80 ( S / Jy ) ^ { -2.0 } Jy ^ { -1 } sr ^ { -1 } , from \approx 20 mJy to \approx 500 mJy .
Extrapolating this to 34 GHz ( where many cm-wave CMB experiments operate ) gives an estimated temperature contribution of sources { \Delta } T _ { conf } = 9 \mu K in a CMB image , with a beam corresponding to multipole l \approx 500 .
A means of source subtraction is evidently necessary , otherwise the signal-to-noise ratio in CMB images will be limited to 4 or 5 , becoming worse at higher resolution .
We compare the population of sources observed in this new survey to that predicted by extrapolation from lower frequency surveys , finding that source fluxes , and indeed the existence of many sources , can not be determined by extrapolation .