Abstract: Apparatus useful for communicating digital data using a steady stream of pulses which achieve very high ratios of bit rate per occupied bandwidth using digital signal synthesis techniques to produce a stream of constant phase tone pulses having exceptional spectral compactness. An optimal pulse is formed having either no sidelobe energy in the frequency spectrum and few to no sidelobes in the time domain, or no sidelobes in the time domain and minimal sidelobe energy in the frequency spectrum. Each optimal pulse has a specially shaped, non-constant amplitude envelope. The embodiment having no sidelobes in the time domain uses both a pulse envelope corresponding to a Dolph-Chebyshev function and more than one frequency of tones with offset timing of overlapping tone pulses so that their envelopes go to zero at different times. The invention is particularly well suited for single sideband radio communication at frequencies below 30 MHz.

Abstract: Apparatus useful for communicating digital data using a steady stream of pulses which achieve very high ratios of bit rate per occupied bandwidth using digital signal synthesis techniques to produce a stream of constant phase tone pulses having exceptional spectral compactness. An optimal pulse is formed having either no sidelobe energy in the frequency spectrum and few to no sidelobes in the time domain, or no sidelobes in the time domain and minimal sidelobe energy in the frequency spectrum. Each optimal pulse has a specially shaped, non-constant amplitude envelope. The embodiment having no sidelobes in the time domain uses both a pulse envelope corresponding to a Dolph-Chebychev function and more than one frequency of tones with offset timing of overlapping tone pulses so that their envelopes go to zero at different times. The invention is particularly well suited for single sideband radio communication at frequencies below 30 MHz.