An iterative method for modifying an initial time signal to form a created signal having a prescribed envelope, and frequency notches at prescribed frequency values, wherein the created signal closely resembles the initial time signal, the envelope of the created time signal is the prescribed envelope, and the Fourier magnitude of the created time signal at the prescribed frequency values is nearly zero. The created time signal may be a real-valued signal as well as a complex-valued time signal which closely resembles an arbitrary initial time signal, including initial time signals which are standard transmit signals for radar systems, and which have Fourier transform magnitudes with notches and stop-bands at prescribed frequency values. These notches and stop bands are created by enforcing nulls of prescribed order at the prescribed frequency values within the modified time signal.