I know hardware and this is NOT A MODULATOR. Contains no signal modulating equipment. Its just a cheap line splitter (connected metal). You could make one. But it is not a modulator. I would think that if the title says modulator it would contain some modulating hardware. Do not buy if you want to modulate a analog signal (like from and mp3) before passing it to a fm receiver. Those of use who would assume something titled a modulator would be a modulator, would mistakenly buy.