Relativity Theory and a Real Pioneer Effect
  Keeping the relativistic laws of motion a non-conventional Pioneer effect would prove an increase of the scale rate of atomic clocks in comparison with planetary ones. Together with a slowly decreasing amount of about 60% due to anisotropic radiation this would be a thinkable explanation for an apparent anomalous acceleration of the Pioneer 10/11 probes. Such a difference between atomic time and ephemeris time, however, (coincidentally corresponding to that of atomic time and cosmic time as derived from any cosmological model of general relativity, where the cosmic 'coordinate' speed of light is fixed to be c* = c) is ruled out by solar system's observational facts. Thus a non-conventional Pioneer effect would inevitably contradict relativity theory. 
Peter Ostermann