We present experimental results demonstrating enhanced current modulation of an antireflection-coated edge-emitting laser diode placed in an external cavity. By eliminating the internal cavity of the laser diode and matching the external cavity free spectral range to the modulation frequency we have increased the modulation response up to nearly complete carrier suppression. We demonstrate the tunability of this enhanced modulation over a range of more than 3 GHz. The power of the modulated beam has been measured to be 10 mW. We have recorded a beat note between the first two optical sidebands of width 1 Hz at 6.834 GHz (corresponding to the hyperfine splitting of the ⁸⁷Rb ground state). This technique enables the generation of two high-power phase-locked beams for coherent manipulation of atomic states.