Internews Center for Innovation & Learning

Internews Center for Innovation & Learning
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The English Video on how to create your own Radio Transmitter

We have finally tranlated the video on how to create your own Radio Transmitter by using common MP3 readers, for a total cost of now more than 15$.

FM transmitter is a portable device, which converts a specific audio output into an FM radio signal. It can be plugged into a CD player, satellite radio system, headphone jack, or a portable media player. One common use of an FM transmitter is to play music from an MP3 player through the speakers of a car. The majority of FM transmitters have a range of about 30 feet (about 9 meters). A good radio can increase that range to upwards of 75 feet (about 23 meters). Due to its low output, sometimes FM transmitters are not suitable for use in large urban areas, as the frequencies they use may become interrupted with other radio signals. This situation can be aggravated by strong FM signals that bleed into surrounding frequencies which the transmitter uses.

The FM transmitter has many helpful applications. It has, for example, made it possible to take any type of audio from a computer, including music or online debates, and transmit it to an FM radio. The FM radio, basically serves as alternative speakers. One benefit of this is that it removes the hassle of the listener from having to stay chained to a desktop PC to listen to Internet radio. There are several types of FM transmitters on the market. Besides the obvious price differences, they also differ in power source, transmission range, and the number of FM frequencies they can use.

A digital FM transmitter helps to connect an MP3 player with a car or a home stereo system through its radio receiver. It physically connects to the MP3 player and then broadcasts a short FM transmission of the songs playing on the MP3 player. Once it is plugged into the MP3 player, the transmission frequency on the FM transmitter is set to a FM station that is not used in that area. The FM receiver is then tuned to the FM transmission station and the music on the MP3 player can be heard via the car or home stereo speakers.

For those using an FM transmitter in a car, FM transmitters typically work within a 50 foot (about 15 meter) range. A car traveling behind one with a FM transmitter can have its radio set to the same station and listen to the same transmission.

Not all transmitters are compatible with all MP3 players. Before purchasing an FM transmitter you'll want to make sure that your MP3 player is compatible with that particular transmitter. Typically, the product packaging will provide this information. You'll also want to consider the power source before purchasing an FM transmitter. While most FM transmitters are battery driven, have a connector which allows it to be plugged into a car's cigarette lighter; this option is popular for those planning to use their FM transmitters in the car.

So how did we ended up building our DIY radio?

Today it is very popular to connect the  Ipod, MP3 or CD player to some kind of FM transmitter. The transmitting signal can then be picked up by any FM radio receiver, most often used in cars. The problem with most FM transmitter is that they have very weak signal and short transmitting range. Some units are so bad that even when they are placed really close to the receiver, you barely receive the signal.

The transmitting signal is just a few micro watts and that is no good, so on previous experiences with the mp3 car fm kits, the built in antennas in these kits are usually made to restrict the transmission capabilities to a very limited area 3m to max 10m distance. These antennas are either a dead end at the antenna output area or some of the  a very short wire which is soldered to the pcb circuit of the transmitter  which  by any mean not meeting the antenna theory ( length of antenna should ½  the wave length of the transmitted frequency which is for the FM signals varies between 100 cm and 180 cm ) for best transmission and coverage .

The antenna development and change can be achieved by wiring a wire to the RF output and make it of the kit and connect it to any cupper wire or any antenna which is a dipole antenna with Omni directional propagation.   

First - Find out the effect of adding external antenna to the unit:

1-      Check the built in antennas of the kit and what type of  antenna used in the fm kit

2-     Find out if there is any attenuators at the RF output which some of the kits also have to reduce the coverage of the unit

3-     If there is any resistance on the output of the RF stage – it will work as an attenuator to the transmitted  signal and reduce the voltage on the output , so check the possibility of adding the antenna before the attenuator component

4-     If there is no attenuator (resistor) at the output before the built in antenna, connect the antenna wire which will be extended out of the circuit to be connected to the external antenna .

5-     Build a dipole antenna for receiver side similar to the transmitting side for better reception.


 We hope this video can help you to create your own radio antenna, and if it does, please let us know how it went and what did you use it for!

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