Specifically dimethylates two adjacent adenosines (A1518 and A1519) in the loop of a conserved hairpin near the 3'-end of 16S rRNA in the 30S particle. May play a critical role in biogenesis of 30S subunits. adenosine(1518)/adenosine(1519) in 16S rRNA + 4 S-adenosyl-L-methionine = 4 H(+) + N(6)-dimethyladenosine(1518)/N(6)-dimethyladenosine(1519) in 16S rRNA + 4 S-adenosyl-L-homocysteine Belongs to the class I-like SAM-binding methyltransferase superfamily. rRNA adenine N(6)-methyltransferase family. RsmA subfamily.