(a) Design a square wave signal generator by means of which the pulse duty factor and the frequency of the periodic rectangular signal can be set as desired. If necessary use the enclosed Illustration to help you.

(b) Interconnect (as above) your square wave signal generator with our standard circuit for the analysis and visualisation of signals in the time and frequency domain. (c) Examine the amplitude spectrum by keeping the frequency of the square wave signal constant and making the pulse duration τ smaller and smaller. Observe particularly the development of the "zero positions" of the spectrum as shown in Illustration 33 ff.

(d) In the amplitude spectrum usually additional small peaks appear between the expected spectral lines. Experiment on ways of optically avoiding these, for instance by the selection of suitable scanning rates and block lengths (A/D setting in the upper control bar) and signal frequencies and pulse lengths. You will discover their cause in Chapter 10 (Digitalisation).

(e) Try to develop a circuit such as that used for the representation of signals in Illustration 38 - transition from a line spectrum to a continuous spectrum. Only the frequency, not the pulse length should be variable.