  We report new results of a test of Lorentz invariance based on the comparison
of a cryogenic sapphire microwave resonator and a hydrogen maser. The
experimental results are shown together with an extensive analysis of
systematic effects. Previously, this experiment has set the most stringent
constraint on Kennedy-Thorndike type violations of Lorentz invariance. In this
work we present new data and interpret our results in the general Lorentz
violating extension of the standard model of particle physics (SME). Within the
photon sector of the SME, our experiment is sensitive to seven SME parameters.
We marginally improve present limits on four of these, and by a factor 7 to 10
on the other three.
