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FM transmitter for MP3

Discussion in 'Radio and Wireless' started by Don6558, Jul 26, 2018.

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  1. Don6558


    Jul 26, 2018
    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.
  2. dimwit_flathead


    Jul 26, 2018
    How about using the audio cassette? You really have an antenna jack on your truck's stereo? I've never seen that before, but then I drive a bicycle. :)
  3. kellys_eye


    Jun 25, 2010
    Your understanding of the adapter is basically correct. The only thing missing is that it will have an internal change-over switch (either electronic or a simple relay) that feeds the antenna signal to the radio or cuts it off when you use it for MP3s

    The standard MP3-FM transmitters will work if you place the sender closer to your vehicles antenna where it 'should' swamp any stations anyway.

    You could get an antenna splitter for the radio and feed a wire from one of the split inputs straight to the MP3/FM device and achieve the same result.
  4. Don6558


    Jul 26, 2018
    Consider this, I may have delivered your bicycle to the warehouse that supplies your bicycle store. At the very least some tractor trailer did deliver it.

    All auto stereos that consist of an AM and/or FM radio must have an antenna jack so that you can connect it to the vehicles antenna.

    I should have mentioned that this stereo does not have a tape player. It does have a CD player that no longer works. I've also been considering adding a Blue Tooth curcuit to the cd input circuit but want to try a simple solution 1st.
    davenn likes this.
  5. Don6558


    Jul 26, 2018
    Thank you for your confirmation and suggestions. I will try the splitter closer to the transmitter 1st. I do prefer the kiss principal.
    Thanks again.
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