Generation of waveforms at very low frequencies using the sampling technique

The purpose of this paper is to consider use of the sampling technique as an effective means of generating v.l.f. waveforms of good frequency stability and known harmonic content. The basic ideas of sampling are presented from the point of view of v.l.f. waveform generation, and two main types of sampling generator are discussed. A section is devoted to the harmonic content of a sampled sine wave, the results being deduced by a simple Fourier analysis; the paper concludes with a short section on the practical aspects of the two types of sampling generator. The potential frequency capability of a sampling-waveform generator is from 0 0001 c/s to 100 c/s with total harmonic distortion reducible to below 0.5%. Most distortion is due to frequency components much higher than the fundamental. Several simultaneous output channels may be provided with fixed or fully variable phase differences independent of output frequency. Nonsinusoidal waveforms may be generated.