A high frequency pulse-time modulation signal generator employs first and second microwave or laser oscillators which are mutually locked uniquely either in a symmetric mode or an antisymmetric mode by means of an electronic phase shifter. The output signals from the oscillators are combined to generate pulse-time modulated output pulses through application of a control voltage to the electronic phase shifter which switches the mutual locking of the oscillators back and forth between the symmetric and antisymmetric modes. In a microwave embodiment, a hybrid-tee, such as a magic-tee, is employed to combine the oscillator output signals, while in the optical or laser embodiment, a half-silvered mirror is employed to combine the oscillator output signals. When the oscillators are locked in the symmetric mode, the hybrid-tee generates an output pulse, and when the oscillators are locked in the antisymmetric mode, the hybrid-tee generates a zero level output. The signal generator is particularly adapted for use in microwave communication systems having an operating frequency from between 50 and 200 GHz, as well as in laser based optical communication systems.