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  • FM Stereo Transmitter

  • Created: Sep 17, 2014

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This project is a simple FM stereo transmitter used to send audio signals to a frequency band 88MHz to 108MHz. Some people want to create a small broadcasting network or simply a link between FM receivers (car stereo, cell phone with FM, MP3 player, MP4 player, iPod, and computers).

The design of this project is not so complicated, an IC is used to simplify the FM transmitter circuit. An audio signal is inputted into the input channels of the IC with proper configurations and outputted a signal through an antenna.

In this circuit, the input signal passes through the pre-emphasis network comprises of resistors and capacitors for matching the frequency response of the FM transmitter with the FM receiver, which then inputted to the right and left channels of the IC BA1404. An Inductor and capacitors are used to set the oscillator frequency connected to the OSC pins (10 and 11) of the BA1404. Another network of resistors and capacitors are connected to MPXOUT and PILOTOUT pins to improve the channel separation with a trimmer capacitor that is used to adjust the tuner of the FM transmitter.

A 38KHz crystal is connected between pins (5 and 6) designated for crystal input of the IC, the stereo modulator circuit using the 38KHz quartz controlled frequency creates a composite stereo signal. One important thing is that the IC BA1404 will be damaged if it operates on a voltage higher than 3.5 volts. The antenna can be a standard telescopic antenna or a 2-foot length of wire connected to the RFOUT pin of the IC BA1404.



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