1. In a frequency modulation transmitter for transmitting a first signal or a second data signal, a data preemption circuit characterized by a data modulator and control circuit (312, 302, 307) for generating a modulated data signal (J) and a control signal (K) indicating the presence of data, a signal muting switch (405), responsive to the control signal of the data modulator and control circuit, for muting the first signal, and a gain switch (406), responsive to the control signal of the data modulator and control circuit, for attenuating the level of the modulated data signal.