What FM Transmitter Do I Need for My Christmas Light Show?

If you’re going to have a Christmas light display, one of the best parts is having friends, family, and strangers pull up and turn the dial in their cars to hear your display.

Okay, maybe they aren’t “turning the dial” quite like the old days, but if you want your display to be heard, you need an FM transmitter.

Even though setting up some large PA speakers might seem like a good idea, you’ll quickly lose the friendship of your neighbors!

An FM transmitter for Christmas lighting is pretty simple, but if you’re like me, you’ve looked online and noticed that every model available has both great and terrible reviews if you look hard enough – making it extremely difficult to figure out what’s good!

For that reason, this article is going to have 3 parts – first, I’m going to share some background about FM transmitters in general, and then share with you the model I purchased and why.

Then, we’ll work on getting your transmitter set up. This is actually the most crucial part of the process, and is often the difference between frustration and a great, clear signal!

How to Legally Use an FM Transmitter

FM radio is an interesting animal because on one side, we’ve got the FCC who regulates professional, high-powered radio, and on the other side, we have hobbyist and personal FM transmitters.

And both of these can work with the same frequencies, at the same time, in the same place.

When you’re using an FM transmitter for your home’s Christmas lights, you are falling under “personal use”, and need to stay under .01 microwatts of power at 3 meters. Any transmitter labeled as “FCC Part 15 Compliant” with an FCC ID number will stay within these limits.

One question that I often get is “Will the FCC come after me if I use an unlicensed/overpowered FM transmitter”?

While it’s not likely that they’ll come after you, they can, and if they do, the fines for running unlicensed radio are $10,000-$75,000.

The “big loophole” here is that the FCC rules are all about how much power you run the transmitter at, which can be a combination of antenna design and power settings. If a transmitter is NOT Part 15 licensed, you run the risk of running an over-powered FM station.

What FM Transmitter Should You Use?

My point in the section above is that it truly is important to be compliant with the FCC’s regulations, and the cost of buying a compliant transmitter can be less than $150.

And with a compliant transmitter, you literally can’t set it up to be overpowered. So just do it!

When I was looking for a transmitter, I saw a few popular options online:

Out of all of these, the “Whole House FM Transmitter” seemed the simplest for a first-timer, and is FCC compliant with the proper, included antenna.

I write that last part, as the transmitter does indeed come with a second antenna that is sealed and labeled “Not for use in the United States”. It’s probably great, but I’m going to pass on using it!

Other transmitters, like the Ebay/EDM transmitters may also require additional setup, possibly including soldering the components together. Again, this is all fine if you want to go through that trouble, and I was considering it.

But, at the end of the day, the Whole House FM Transmitter was not overly expensive and gets me clear signal all the way to the end of my street (further than you can see the display from!).

Advanced: What is RDS?

If you begin looking at more advanced FM transmitters, you’ll see that they may include “RDS” or “Radio Data System”. This is the protocol that sends the text from an FM transmitter to share the station name, song titles, or whatever else you desire!

Most people do not use RDS for their displays, but some find it to be helpful. Like any upgrade, it does cost more and take more configuration, but it may be worth it for you.

Where Should You Place Your FM Transmitter?

The biggest mistake that I see people making with FM transmitters is placement.

Think about it for a moment – “real”, commercial FM stations that you may listen to in your car seek out the highest points of land to place their tall towers. This is because the extra height allows them the get the maximum distance possible with a clear signal.

Shouldn’t you do the same for your FM transmitter?

The answer, of course, is “Yes”. When you are looking for a place to locate your transmitter, get it as high as possible. For example, I located my transmitter at the top of the interior wall for my first year. After that, I moved it to the attic for even better coverage.

It’s also worth noting that any building materials such as insulation and drywall will dampen the signal. For that reason, it is best to get your transmitter on the wall closest to your display.

Any metal sheets or wire mesh will completely block your signal, so you want to keep your transmitter away from those!

In my testing, I found that the inside wall of the attic was the best place for my display – it gave me exactly the coverage I needed and more. But, you might find that you need more coverage, in which case it’s probably time to locate it outside!

How Do You Get Good Quality Sound Out Of Your FM Transmitter?

Getting your FM transmitter in the right place is a really, really good first step to getting the sound to be loud and clear!

But we also need to get things right with the actual audio and our cabling to ensure a great broadcast!

Step 1: Quality, Shielded Cabling

Don’t buy cheap cables. Actually, just don’t buy un-shielded cables.

When the audio leaves your computer or Rasberry Pi to head to your FM transmitter, it needs to get there without interference.

Some cables that you can buy are NOT shielded, and interference from power supplies and LED’s can get in and mess with your signal.

A cable like this is great. (See, it doesn’t have to be expensive!)

Step 2: Normalize Your Audio

Normalizing is the simple step of taking each audio track (music and spoken) that you are using for your display and making sure it’s at the same audio level.

No matter what type of music you’re doing – new, old, or a mix, you need to do this, and you can do it with a simple program like Audacity.

This will ensure that no tracks are too loud or too soft – a topic that we’re about to dive in to!

Step 3: Set the Right Frequency

RadioLocator.com

While your FM transmitter can be set to a wide variety of frequencies, it’s usually defaulted to the bottom of the frequency band…which isn’t guaranteed to be the best place!

Finding the right frequencies to test is simple. Just head to Radio-Locator.com, and enter your location. The site will then give you a report of the best radio frequencies to use.

Step 4: Set the Right Level

The last thing that you need to do is to set the volume of your computer to what your FM transmitter wants to see.

This is really going to vary by computer and transmitter, but it’s rare to run your computer at full volume.

Some people use an audio mixer to set the volume level, but that really isn’t necessary, and it just makes your system more complex.

To experiment, bring down the volume to about 70% and tune in on a radio. Listen to the music, and bring the volume up until you start to hear pops, static or other noise excessively.

Then, back the volume down until it’s quiet and give it a little space. You’ve found the perfect level! The key here is to make it as loud as possible to the transmitter before distortion occurs.

This keep noise from coming in and annoying your listeners!

How Can You Test Your FM Transmitter?

As you set up your FM transmitter, you may quickly get tired of running to your car to see if it’s working!

I bought this simple, battery-powered radio, and it is perfect.

Not only is it a time-saver for testing, but we also use it when we have friends over and people want to watch the display from the sidewalk.

Once you’ve got that perfect volume dialed in, be sure to test it on a few different radios, just to be sure it’s good!

How Do People Know to Tune To Your Station?

Last, but not least, we’ve got to get people listening to your display while you play the music.

This might seem simple, but I don’t want to gloss over it! Having some kind of “tune-to” sign that instructs viewers to listen in on radio is key.

You can make a simple “tune to” sign out of pretty much anything – some people buy printed coroplast, or use a pixel matrix or panel.

Whatever you do, the most important thing is that you make sure that your sign is large enough to be seen, and that it is lit up (if it is not made up of lights itself!).

That way, we can ensure that your guests can hear all of the hard work you’ve put in to getting the radio right!

About the author

David Henry

David first began using pixels in stage lighting, and then decided to try it out on his house. The result? An urge to create useful and helpful information to help non-technical folks create great Christmas lighting with pixels on their homes!


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