Turning a radio into an FM transmitter is useful when you want to transmit audio from one radio to another. For example, if you have an older boom box that plays cassette tapes, but you car radio doesn't have a tape player, you can connect an FM transmitter to the boom box and tune your car radio to the station selected on the transmitter. FM transmitters are inexpensive devices that can be purchased at a local electronics store, such as Radio Shack or Best Buy. You can also purchase the device online.
Make sure that your radio has an "auxiliary" out or a headphone port. The port is required to connect a FM transmitting device.
Obtain an FM transmitter from your local electronics store. The transmitter has a headphone plug that you need to plug in to your device's aux port or headphone jack.
Power on the transmitter and select an FM station that your transmitter will broadcast to. You should choose a lower FM station number as there tends to be a fewer stations in those numbers. The more stations you have near your chosen signal, the more likely it is that you will receive signal interference.
Tune the FM radio to the station you selected. You will be able to hear the audio from the device containing the transmitter on the radio that's tuned to the transmitter's station. For example,