The energy dependence of the amplitude of synchrotron oscillations due to radiation fluctuations is investigated. A simple stationary solution for the phase equation is obtained; this equation can be applied, with accuracy sufficient for practical purposes, to all large synchrotrons. It is shown that in accelerating electrons to energies to several millions of electron volts the value of the maximum allowable frequency multiplication is sharply limited and is determined by the limiting amplitude of the accelerating voltage.