Instead of blaring our music for all the neighbors to loath, we are employing an FM transmitter. With that, people who come to see our show can simply tune their car radio to a certain frequency and hear the music that the lights are sequenced to.
With the help of this website that tells you vacant FM radio stations in your area, we chose 87.9 MHz FM.
Once that was chosen, our “Tune To” sign was ordered:
The sign itself is 18″ x 54″ which is plenty big to be seen and read as people drive by. I made a PVC/bungee structure to hold the sign during the display as well as a custom tuned dipole antenna for 87.9 FM that our Vast Electronics FM02 .5mW modulator will hook up to. I have done minor testing of the modulator and antenna and the signal is great for just a few house radius, which is perfect so we don’t anger the FCC! As licensed Hams, neither Tiffany nor I want that!
This is a picture of the unregulated wall-wart I’m using for power attached to the voltage regulator to make sure I don’t overdrive the FM02. There wasn’t any noticeable hum coming form my power source. Since the voltage regulator is based on an LM317 which is a linear voltage regulator I wouldn’t expect that to introduce any hum, but with cheap wall warts, often the rectifying circuit introduces 60Hz hum. If I ever notice any, I will likely try a snap on ferrite core before going crazy with other solutions.
Here is a picture of the FM02 itself. It consists of 2 PCBs connected with a 6-pin ribbon cable, a typical 2.5mm audio jack for audio in, an SMA jack for the antenna, and a 2-pin power connection. I don’t yet have an enclosure and I’m not sure how I’m going to mount the modulator yet. “Stay tuned” for updates for an enclosure. (Sorry, I couldn’t help myself).
Finally, the dipole antenna I made enclosed in PVC. I used 1″ PVC and somewhat followed this guide to make my dipole. To attach the common copper cable, my soldering iron couldn’t get the SO-259 connector hot enough, so I used a propane torch just long enough to solder the wire without (completely) melting the coax insulator.
Tags: antenna, fm, music, radio