Methods and systems for modulating a signal are described. A phase-modulated signal that includes a sequence of contiguous one-cycle sinusoidal waveforms having a frequency above 50 MHz is generated. The phases of the one-cycle sinusoidal waveforms correspond to symbols of a message signal. A bandwidth of the phase-modulated signal is reduced using a bandpass filter centered at the frequency of the contiguous one-cycle sinusoidal waveforms. The phase-modulated signal is wirelessly transmitted.