Upper and lower bounds on the average bit error probability are obtained for hybrid direct-sequence/slow-frequency-hopped Spread-Spectrum Multiple-Access (DS/SFH-SSMA), noncoherent digital systems employing predetection diversity (selection combining (SC) and equal gain combining (EGC)) operating through indoor radio channels. The bounds are valid for radio multipath channels in which the maximum delay spread does not exceed a data bit duration. The tightness of the bounds is examined in terms of the number of data bits per hop, N(b). For N(b) >>1 (which is the case of slow frequency hopping) the upper and lower bounds are very close to each other. We analyze the performance of hybrid systems employing diversity techniques, by using the above bounds as approximations.