A method of and apparatus for digitally generating a broadband signal comprising a plurality of CW or quadrature modulated signals having incrementally related frequencies wherein said plurality of signals are centered about a center RF frequency is disclosed. The invention provides for generating a first and second composite baseband signal each comprising a linear combination of N sinusoids, or N modulated signals each modulated in quadrature so as to achieve a desired instantaneous phasor value for each of the RF signals. The invention further provides for modulating in quadrature the first and second composite baseband signals on a local oscillator signal having a frequency equal to the center RF frequency. The invention further provides for the generation of the composite baseband signals by means of D/A converters that are clocked at a sampling rate that is half of that which would have been required for the generation of the same number of RF signals using single sideband frequency conversion methods, while permitting further savings in computational complexity by the use of a common stored digital filter impulse response waveforms for the quadrature components of all the RF signals.