Dipole Antenna

A fact of Christmas Light Show life is being able to transmit good quality sound over FM radio.

Instructions
If you’re eager to get started here is the Easy Guide to Build a Dipole Antenna or watch the build video on the FPP Shorts channel.

.
TIP:  Download the guide to your computer and open in Adobe Acrobat Reader and choose “Enable All Features” if prompted. This allows the automated lookup of Wire & PVC lengths when you enter your FM Channel in the box.

Find Your Frequency
Once you have an FM transmitter you will want to find an open radio station using the Radio Locator site https://radio-locator.com/ to help you find an unused FM frequency in the area of your Light Show. Put in your zip code, run a search, and look for an FM frequency that is not in use.  Confirm your choice by listening to that station with an FM radio during your show hours.  Ideally you won’t hear any music or talk, just static or nothing at all.  This will help keep you out of trouble with the FCC. 

The Good, The Bad, and The FCC
The Federal Communications Commission regulates interstate and international communications by radio, television, wire, satellite and cable for the United States.  You don’t want your neighbors complaining to the FCC they can’t listen to their favorite radio station due to you broadcasting on the same FM channel.  If you use an unused or weak frequency you should be ok.

How-to Improve Sound Quality
There is a long, but in-depth video TLDR Perfect Sound, Perfect Show: Audio & FM Transmission by Jason Rasmussen who has presented for several years on the topic of making better sound for your light show. 

This presentation does a great job going into detail how to improve sound quality end-to-end from the audio file, optimizing level/volume settings, sound cards, through FM transmission. This is definitely worth a watch; however, you do not need to watch in order to build a dipole antenna.

Optimizing Gains

Here’s the 100hz Test Tone to use when optimizing gains (watch at 4:16 in the video above). This is a lower “bass” tone so you may not hear it on small speakers.

  1. Download this to your computer and copy it onto your show player (FPP or Computer).
  2. Set FPP volume = 70, if running show from a Computer then volume = 100
  3. Tune a quality radio with larger speakers, or you can use your car radio, to listen to the Test Tone.
  4. Play the Test Tone on a loop while you adjust the gain(s) on your FM Transmitter appropriately.
  5. Set your FM transmitter gain just below where you hear any distortion from the Test Tone.

Why build a Dipole Antenna?
Because its so much fun?  No, but at least its not difficult.
So why do I need a dipole antenna? 

  1. Eliminate the buzz & hum from stock antennas
  2. Increases range
  3. Reduce static & drops
  4. FM Transmitter can be mounted separately from the antenna
  5. Antenna can be mounted in more locations (inside, outside, roof, chimney, attic, etc.)

Building the Dipole Antenna
Materials cost around $75 and the build takes about 30 minutes making this one of the fastest light show improvements ever! 

If you use the Easy Guide to Build a Dipole Antenna there is no cutting/splicing of coax cable, no soldering, and heck I’ve even done the math for you so its a breeze to build – just enter your FM Frequency into the box and press enter!

My Results
I had my transmitter in a spare bedroom above the garage and transmission went from 150 feet to nearly 1/2 mile or more, but more importantly the sound quality improved dramatically.  What I mean is the static, crackling, and drop outs disappeared  from the transmission.  The dipole doesn’t improve fidelity, get a Soundblaster for that. 

See the other pages in the Build menu to learn more details about each display element or click here to see the Build Overview.