  We present the results of the flux density measurements at 4.85 GHz and 10.45
GHz of a sample of 5998 NVSS radio sources with the Effelsberg 100 m telescope.
The initial motivation was the need to identify the NVSS radio sources that
could potentially contribute significant contaminating flux in the frequency
range at which the Cosmic Background Imager experiment operated. An efficient
way to achieve this challenging goal has been to compute the high frequency
flux density of those sources by extrapolating their radio spectrum. This is
determined by the three-point spectral index measured on the basis of the NVSS
entry at 1.4 GHz and the measurements at 4.85 GHz and 10.45 GHz carried out
with the 100 m Effelsberg telescope. These measurements are important since the
targeted sample probes the weak part of the flux density distribution, hence
the decision to make the data available. We present the table with flux density
measurements of 3434 sources that showed no confusion allowing reliable
measurements, their detection rates, their spectral index distribution and an
interpretation which explains satisfactorily the observed uncertainties.
