We’ve had some questions around our FM Transmitter and how exactly it works, especially for use for church services, a parking lot concert, or other events. Below we’re going to give you some ideas on how it might work for you.

A couple of things to keep in mind, FM is line of sight, if you have walls or obstructions, it will limit the reception. If you live in a populous area with a lot of FM stations, this solution may not work well for you because there are no vacant frequencies or too much interference.

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Our FM Transmitter 2 includes a 1/8″ stereo jack and an RCA to stereo female cable that allows you to plug into the line out or headphone jack of any device that you want to transmit audio from.

The transmitter doesn’t “care” what the source of the audio signal is, it just uses the FM frequency band to send that signal to other devices on that same frequency. It will accept a source of audio from about any line-out or headphone jack.

One of the greatest benefits of FM transmitters is the fact that the transmitted audio signal may be received by any and all FM radios within range. As far as the radios are concerned, they are receiving an FM signal just like a normal FM radio station.

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Locating a Vacant FM Freqency

Before we get to specifics there are a couple things you need to do.

First, find a vacant FM frequency in your area. On our FM Transmitter 2 page, we have a search tool to help you determine if there are any vacant frequencies in your area.

Enter your zip code and state. You’ll get results similar to below – you’re looking for great and good. If you only see poor and bad, it’s unlikely you will get the results you desire.

radiolocatorvacantfrequencies

Now tune the FM Transmitter to the open frequency you found. In our case, we’re using 107.6

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  • Church services – generally in this case someone is using a microphone. In this set up there are a couple of considerations. A powered (condenser type) mic is required to work with the FM Transmitter.
    • A powered wireless mic will work. You will plug the FM Transmitter Audio In, into the Line Out of the Wireless Mic.  Now everyone will tune their FM Radios to the frequency you selected above. In our case, it would be 107.6.2020-04-09 09_58_48-wirelessmicsetup1
    • If your church has one of the larger more traditional mics, you would plug into an amp or your audio mixer and the FM Transmitter would plug into the headphone jack or line out. Line out is preferable because the audio output is regulated differently than a headphone jack which results in better audio quality.
  • A cell phone
    • Any phone with a standard headphone jack, the FM Transmitter line in, will plug directly into the headphone jack and whatever audio is playing through your phone will now transmit over the frequency you have the FM Transmitter set to.
    • If you have one of the newer iPhones or other phones without a headphone jack, you will need a special adapter (often called a dongle) to make this work. Something like the one shown below with the correct connector for your phone. The one shown here is a lightning connector for the iPhone XR.lightningadapter
    • We have had some experiences with newer iPhones where the audio isn’t consistent from the microphone depending on how you’re broadcasting (such as Facebook Live or various apps). In that case you might need a special combination of adapters that look like the ones below. These are two separate pieces that you can purchase on Amazon or other similar place that sells connectors.
  •  A musical instrument
    • You would need an amp with a line out or headphone jack and the audio will now transmit over the frequency you have the FM Transmitter set to.
  •  A television or movie projector 
    • Again, you’d need a line out or a headphone jack and whatever audio is playing through the television or projector will now transmit over the frequency you have the FM Transmitter set to a nearby radio.
      • If the audio is digital as with some newer televisions, you might need a converter (available through a Google search).

Can I use the FM Transmitter 2 as a repeater?

As a matter of fact, yes, you can broadcast from one radio to another radio and then rebroadcast from that radio to another radio. At some point, there is likely to be loss, but it does work. Again, keep in mind it is still line of site. Also, it will require multiple open frequencies for this to work.

Can I use it with a 12V plug (cigarette lighter) in my car?

Yes, but you will need one that has the ability to stepdown to the correct voltage. We used to sell one similar to this one available here.

Is there any way to improve the range?

Yes, here are some things that impact the range:

  • The number of FM stations in the area
  • The quality of the FM receiver and the antenna – cars actually work quite well as receivers
  • The number of walls the signal needs to travel through, every wall presents a challenge to the line of site transmission so the more open the area with the fewer obstructions, the better
  • The types of walls (e.g. wood, metal, stucco, etc.

As a hobbyist, you can also search Google on ways to improve the range of the “FM Transmitter 2” to see what others have done.

The output power of the FM Transmitter 2 is set to the maximum limit specified by the FCC. Most of our customers achieve 40 – 60 feet depending on their situation. The signal will travel up to 70′ under good conditions. The FM Transmitter-2 will work better in a noise-free environment. In a noisy environment (such as one with lots of FM and computer noise) you can expect less range. We recommend extending the FM transmitter-2 input cable away from the computer (or any other RF noisy device) when connected.

In open environments with minimal radio noise, the range of an FM transmitter can be easily increased by attaching a length of wire to the telescoping whip antenna of the FM transmitter. In our experiment, we attached a 31-inch length of wire to the whip antenna of an FM transmitter using an alligator clip (Any wire will work. Any clip that secures the wire to the transmitter’s antenna will work). We highly recommend our FM Reflect 2 Antenna

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We attached the other end of the wire to a PVC pipe to keep the wire vertically oriented. We could have used a regular thumb tack, a stationery clip, or just about anything to pin the end of the wire up vertically.

Please keep in mind, that if you interfere with other FM broadcasts, you could get a visit from the FCC so please be smart and compliant about your broadcasts.

Here’s a video to provide a visual for all of this information.

If you have any additional questions or need help figuring out a specific setup, please contact us. If you have pictures of what you are trying to connect to/from, those are particularly helpful. We love seeing and hearing about how the FM Transmitter is being used, please share your uses in the comments below.