Improve the FM reception from the FM transmitter in your satellite radio by building your own antenna and connecting it to the FM output jack (Sirius Starmate ST1 and similar products with a built in FM transmitter usually have an FM out jack).


The Sirius Starmate ST1 radio has a built in FM transmitter which will allow you to hear satellite stations on your existing FM radios. However, the built in FM transmitters I've tested have a very small coverage area. I had trouble getting good FM stereo reception even 12 feet away from my satellite receiver. However, adding a simple FM antenna easily extends the coverage to 100+ feet or more.

I expect that the 2.5 mm FM transmitter antenna construction project detailed below will help improve your local reception with any product with a 2.5mm FM out jack. I have tested this project on the Sirius Starmate ST1 with excellent results ( I love satellite radio and now I can listen to it every where in the house or yard.)

Parts List :

  1. 2.5mm phone plug: part# 2740289 at the Source (also know as Radio Shack where the part number is probably 274-289). Click here to view the 2.5mm plug online. I paid $2.99 (March 2006) for a package of two. Jan 2007 update: In Canada, you can find the 2.5mm phone plug at this link or go to and search for part number 2740289.
  2. Approximately 3 feet of insulated fine gauge copper wire (i.e. 22 or 24 gauge but not 12 or 14 gauge power cord). A good choice of wire would be a twisted pair from inside of a surplus telephone cable or or computer cable. Or you can buy some 22 or 24 gauge hook-up wire at your local hobby shop or Radio Shack.
  3. A half inch of heat shrink tubing that is a bit wider in diameter than the wire you select in 2 above, or you can use a piece of tape or some hot glue to prevent shorting the 2.5 mm plug inner and outer connectors when you connect the wire and replace the connector insulator.

If you have experience with small construction projects, you probably don't know need anymore instructions to finish up the project. But if not, please read the assembly insturctions below.

Assembly Instructions:

  1. Take a 2.5mm phone plug ( part# 274-289 ) and unscrew the black plastic insulator to reveal the inner solder terminals.

    You will be connecting your copper wire to the inner terminal (smaller terminal with the wire hole showing below). Please note that you do NOT connect any wires to the outer terminal (the larger and longer terminal at the top right hand corner of the photo below) and you need to ensure the wire you connect to the inner terminal does NOT make contact with the outer terminal.
  2. Remove the insulation from one end of the insulated copper wire (or wires if you have a twisted pair like I do in the photo), push the black plastic insulator onto the stripped end of the wire, push the heat shrink tubing onto the stripped end of the wire, and connect the stripped end of wire to the smaller (inner) terminal. Twist the wires to make a firm connection. If you have a soldering iron, you should solder the connection to ensure good long term operation (but twisting the wire in place without soldering will work OK).
  3. Slide the heat shrink tubing down over the inner connector

    This is a critical step to ensure that neither the inner connector or wire is touching the outer plug connector. If the inner and outer connector do touch, your radio's FM transmitter will be shorted and stop working (see troubleshooting below).
  4. Replace the black plastic insulator and connect your antenna to the 2.5mm FM transmitter on your satellite radio (or any radio with a 2.5mm FM out plug).


  1. Always ensure that the FM transmitter is turned on in your Sirius radio and set to an FM frequency that is clear of other stations. You can find the FM transmitter options in the setup menu of your radio -- check your user's manual.
  2. If your FM transmitter stops working (i.e., your FM radio signal disappears) when you plug in your antenna, you most likely have a short in the 2.5mm plug assembly. Unplug the antenna, and check to see if inner terminal is shorted to the outer terminal on the FM plug. If you have an ohm meter then then you should measure the resistance between the plug center pin and the threads / other metal parts of the assembly below (outer terminal) -- the resistance should be infinite if everything is ok.
  3. The type of wire you use is not critical. I used a twisted pair but a single wire wire would work just as well. The key is to make sure the wire is small enough to allow you to connect it to the inner terminal on the 2.5mm plug. And be sure NOT to short the inner terminal with the outer terminal. See Troubleshooting step 1 above.
  4. The length of the wire is not critical although you might find a very slight distance improvement if you made the wire a 1/4 wavelength of your local FM transmit frequency. If you are having poor FM reception quality then check to ensure the wire is securely connected to the center connector of the 2.5mm plug.

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Good luck and enjoy your satellite radio!!

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