  Sun's gravitation potential at earth varies during a year due to varying
Earth-Sun distance. Comparing the results of very accurate measurements of
atomic clock transitions performed at different time in the year allows us to
study the dependence of the atomic frequencies on the gravitational potential.
We examine the measurement data for the ratio of the frequencies in Hg$^+$ and
Al$^+$ clock transitions and absolute frequency measurements (with respect to
caesium frequency standard) for Dy, Sr, H, hyperfine transitions in Rb and H,
and obtain significantly improved limits on the values of the gravity related
parameter of the Einstein Equivalence Principle violating term in the Standard
Model Extension Hamiltonian $c_{00} = (3.0 \pm 5.7) \times 10^{-7}$ and the
parameter for the gravity-related variation of the fine structure constant
$\kappa_{\alpha} = (-5.3 \pm 10) \times 10^{-8}$.
