FM Modulator Basics

FM Modulator Basics

Millions of people regularly play digital music on PCs, MP3 players, smartphones and other devices. These days, in fact, many music lovers no longer purchase CDs from the local music store but instead download their favorite songs from the Internet. With modern digital equipment, transferring music from your computer to an MP3 player, smartphone or other mobile device is relatively simple, and doing so allows you to listen to your music almost anywhere. Yet, the one place it is often difficult or impossible to use a mobile device is inside your car. Using your smartphone or laptop while driving is not only impractical but it’s also dangerous. With an FM modulator, however, you can listen to your favorite music from your portable devices over the radio already installed in your automobile.

Technology Options
When looking for devices that allow music to be played from a portable device over an FM radio, many people confuse FM transmitters and modulators. An FM transmitter typically connects to a portable music device and then plugs in to the cigarette lighter in your car. It then sends radio signals carrying the music from the portable player to the radio. This method tends to work intermittently at best because of interference from radio stations in the area through which the vehicle is traveling. FM modulators, on the other hand, connect directly to your car antenna and its stereo head unit. Because installers place an FM modulator device between the antenna and the head unit, the device is able to send radio wave signals to the stereo on a dedicated FM frequency while filtering out frequencies on the same channel from radio stations in the area.

Typical Designs
FM modulators come in two basic designs: in-dash units and external boxes meant to be mounted on the console or dash near the car stereo. Both designs perform the same essential functions, but in-dash models allow you to hide the device and cabling under the dash, while external FM modulator boxes reveal the wiring and may cause some interference while operating your vehicle if not properly placed. In-dash models are usually die-cast metal, silver and black in color; external boxes are usually more aesthetically pleasing and offer more frequency selection switches as well as more input types for connecting devices.

Cost and Features
In-dash FM modulators typically run about half the price of external units and sell for between $20 and $50. Most in-dash FM modulators offer one type of connection input, which is usually an auxiliary-type input port like the headphone jack on an iPod or laptop. External FM modulators usually offer two or more input ports, which commonly include a 3.5 mm headphone jack and a USB or dedicated iPhone data port. Some external FM modulator boxes in the $80 to $100 price range even provide advanced features such as device charging over the data cable and the ability to display text for artist and song title on car stereos equipped with Radio Data System, or RDS, capabilities. In-dash models usually only allow you to choose one or two dedicated FM frequencies in the 88 to 89 MHz range, while many external modulators let you choose virtually any FM frequency range you want.

Installation and Usage
Regardless of whether you select an in-dash or external modulator, installation and usage are essentially the same. In either case, you simply connect the cable from your car’s aerial antenna to the antenna input port on the back of the modulator. You then connect the antenna output cable from the modulator to the antenna input jack on the rear of the car stereo head unit. You complete the installation by connecting the appropriate cable from your portable device to the matching input on the modulator. In-dash units usually require that you screw or Velcro them underneath the dash, whereas you should place an external model in a location that’s easy-to-reach yet out-of-the-way. Once connected, tune the FM radio to the selected frequency and turn on your portable player. Music will stream from the portable device and play over the speakers connected to your car stereo.

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