How to Find the Best FM Frequencies for Your Car Transmitter

Unless you live in a rural area, you may need help finding a clear frequency

FM transmitters are one of the easiest and most affordable ways to listen to your iPhone's music on your car stereo, but they have one big drawback: FM interference. To use them properly, you have to find a frequency free of interference. This process is simple if you live in a rural area where there isn't much competition for radio frequencies. But if you live in a city, finding a clear frequency is harder.

FM Interference and How FM Tuners Work

FM transmitters work like tiny radios, broadcasting audio from your iPhone or mobile music player over a standard FM frequency that you tune in on your car stereo. Set the transmitter to broadcast on 89.9 FM, tune your radio to that frequency, and you should hear your music.

Radio transmitter tower against a partially cloudy blue sky
Francesco Marino / Getty Images

The transmitters are weak and can only broadcast a few feet. This is both good and bad. It's good because you don't want a transmitter in the car next to you on the highway to override your signal. But it's bad because weak signals are vulnerable to interference. If there's a radio station broadcasting on the frequency you choose, it will likely prevent you from hearing your music. The interference can even happen at nearby frequencies. For example, a radio station on 89.9 can make 89.7 and 90.1 unusable for transmitter audio, too.

Finding interference-free frequencies isn't that hard when you're stationary, but in a moving car, the frequencies that work well with FM transmitters constantly change as you drive.

Tools to Find Open FM Frequencies

The three tools listed below can help you find open FM frequencies to use with your FM transmitter wherever you are, based on your location and their databases of open channels. Use them when traveling to find a frequency for your music.

  • ClearFM: This free iOS app uses the GPS features on your iPhone to determine your location and give you the best open frequencies in your current area. The simplicity of one-touch searching and the performance of an app, combined with not needing to visit a website, make this an appealing option.
  • Radio-Locator: The Radio-Locator website can help you find open signals by city, state, and ZIP code. If you visit it on your smartphone, it can use your smartphone's GPS to determine your exact location and suggest stations based on where you are.
  • SiriusXM Channel Finder: SiriusXM satellite radio maintains the FM Channel Finder website for owners of the company's portable and otherwise not-in-dash radios. You don't have to have a satellite radio to use it, though. Just enter your ZIP code, and the site offers five suggestions for clear frequencies near you.