Some effects of bandwidth limitation on p.s.m., p.l.m., and p.p.m. signals

A comparative study has been made of the effects of bandwidth reduction on such important parameters as sideband and harmonic distortions, crosstalk attenuation and message/noise ratios, in pulseslope modulation, pulse-length modulation and pulse-position modulation systems. It is shown that the harmonic distortions in p.s.m. and p.l.m. are similar, whereas p.p.m. has no harmonic distortion; but the sideband distortion for large modulation indices is considerable in both p.p.m. and p.l.m. The crosstalk attenuation is generally the maximum in p.p.m., and for very narrow bandwidths, p.s.m. shows improvement over p.l.m. The message/noise ratios are also the maximum in p.p.m. for average bandwidths, but the p.s.m. ratios are better when the bandwidth is very much restricted. Owing to the absence of sideband distortion in p.s.m., the overall message grade in this system is found to be higher, for narrow-band working, than those in p.p.m. and p.l.m. For large bandwidths, however, p.p.m. gives the best quality of service.