Studies for the Skylab PCM links reveal that for a binary PCM/FM communication receiving system with a rectangular predetection bandpass filter, an ideal limiter discriminator and an ideal integrate-and-dump postdetection filter, suboptimal system performance can be achieved by choosing the largest possible value of deviation index which lies approximately at0.7 + 2n, wheren = 0,1,.. ,k. The upper limitkofnis partially determined by the reconstructability of the PCM signal after passing through the bandpass filter. Experimental data support favorably the theoretical result.