Generation of signals with prescribed spectral characteristics

The main causes of undesirable changes in signal frequency-amplitude characteristics at the output of modern generators are stated in the paper. A functional scheme of the waveform generator is presented. The generator is constructed with the use of home-produced hardware components. A simplified scheme of the on-board transmitting device for the small spacecraft «Aist-2» is taken as an example. The operation and interaction of units of the scheme, as well as the principle of generation of signals with various types of modulation are described. The device developed is analyzed. The units that make the most undesirable changes in the frequency-amplitude characteristic of the output signal are identified. A method of combatting bandpass flatness of frequency-amplitude characteristics is described. The spectra of the output signal prior to and after frequency correction are presented. The process of origination of parasitic amplitude modulation in a digital computation synthesizer in the case of generating signals with frequencies close to the Nyquist rate is explained. A method of combatting parasitic amplitude modulation caused by the use of a digital attenuator in the digital computation synthesizer is also discussed. It is shown that the application of the methods proposed makes it possible to develop a special waveform generator that can ensure the required spectral characteristics of the signals.