The EM base-emitting frequency was an engineering term for measuring a phaser beam's component electromagnetic wavelengths. In 2366, while preparing for a battle against a Borg cube, Geordi La Forge retuned the phases of the USS Enterprise-D to higher EM base-emitting frequencies. La Forge hoped this adjustment would disrupt the enemy ship's subspace field. In the battle, the new phaser frequencies had no impact on the field. (TNG: "The Best of Both Worlds" )