Okay I know this sounds like a crazy idea, but has anyone ever tried this? Would it be possible to modulate the output signal of a spectrum analyzer say with 400hz for AM receiver alignments? I have a Rigol DSA815TG which has no external MOD capabilities in fact I've never even seen an SA with this ability myself. I have a audio generator just need a way to injected audio onto the tracking generator output somehow, or I could just scrap the whole idea and purchase a real RF sig gen and be done with it. Anyway crazy thought.