Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

78 FREQUENCY MODULATION, Volume I» 90 90 KX> 900 900 BOO 1000 203090X9000 10000M00ULATI0H INOEX m SFig.12—Variation of bandwidth with modulation index.If the maximum deviation is for one-fourth the time, x = 0.25,the curves of Figure 12 show the corresponding limits of the bandwidth.Other sets of curves, for other values of x, can be computedfrom (18).Itwill be noted that the band does not end as abruptly with rectangularmodulation as it did with sinusoidal modulation. The curvesof Figures 11 and 12 are much farther apart than the correspondingcurves of Figure 5.The Spectrum of a Carrier Wave which is Frequency-Modulatedwith a Triangular SignalWhen a uniformly spaced series of parallel bars, each one unitwide, is scanned at a uniform rate with a rectangular aperture ofunit width, as shown by Figure 13, the resulting signal is proportionalto the area of the bar covered by the aperture. The signal willhave a triangular wave form, as shown by Figure 14. During thetime the aperture is between the bars, the output will be constant. Asthe aperture starts to cover a bar, the output increases linearly until.PictureElement-fcH±1Fig. 13—Scanning of picture element.Fig. 14—Modulating signal.