I'm using a FM transmitter, in my commercial truck, to connect my mp3 player to the trucks stereo. Traveling through many cities in the course of a day I must find an empty fm frequency and retune both the transmitter and the stereo to the new frequency many times a day. Talk about distracted driving. SiriusXm has a device called "FM Direct Adapter". This device plugs into the stereo antenna jack and the antenna plugs into the device. A SiriusXm specific jack is used to connect the adapter to the SiriusXm receiver. Reading the blurb on Amazon for the adapter says it's connected to the receivers FM transmitter output. I cannot find this type of adapter for mp3. I'm thinking what this adapter does, is basically directly feed the transmitting signal directly to the antenna thereby over powering all other FM signal to the antenna. The adapter requires power so it must have some sort of amplifier circuitry inside. Does this sound resonable? I'm just a electronics hobbyist who would like to understand how this FM Direct Adapter works so I can make one for my own use. I've thought about winding the fm transmitter antenna wire around a short length of unshielded antenna wire (like a transformer) but run into problems with adding the proper plugs to the ends of the cable for pluging one end into the stereo and the other end into the truck antenna. This assembly would be shielded by a metal box enclosure. Do you think this would work? Any ideas, including links to a comercial version if one exists, would be greatly appeciated.