erp I was editing my response because I realized I think I didn't exactly answer the "one radical per character". Pasting it here also:

only one radical per character:: examples 明：日 is the radical，月is not the radical；安 ：宀 is the radical, 女 is not the radical. (I specifically used these because 月 and 女 are also common radicals, ex 朋 in 朋友friend ; 好good 姐older sister)

Oh, also, it's a lot less common (since a bulk of chinese characters are constructed/typed via phonetic loaning 形声) but the nonradical portion sometimes also confers semantic information, hooray for compound logograph （会意）characters. Easily my favorite category. 好good -> 女woman + 子child; 尘dust -> 小small + 土earth/dirt; 歪askew,crooked -> 不not + 正complete/orderly