Fourier Series of 2 Segment Function. 
The diagram opposite shows a periodic function consisting of 2 segments
ab and cd. The height and slope of the segments can be changed by a,b,c,d
and the width of each segment can be changed by e and f. For a flat symmetric pulse, the spectrum falls within a sinc envelope. The frequency of the first zero of the sinc increases as the width of the pulse reduces. The Fourier spectrum of the pulse can be investigated by the applet below. 
