BA1404 Stereo FM Transmitter with Amplifier

This is a classic, low-cost stereo FM transmitter that sends a signal to an FM receiver within a 500-meter range. The transmitter uses the well-known BA1404 all-in-one chip and operates at 5V. Stereo channel separation is excellent. You can even use this as the front-end stereo RF signal generator for a large FM transmitter setup; simply add RF amplifiers incrementally. A few inches of copper wire can be soldered onto the PCB as an antenna. A variable capacitor can be used to adjust the frequency output. You can use this with an iPod or other audio sources at home, in your car, at an outdoor garden party, or anywhere you prefer.

The transmit radio frequency can be set by adjusting the coil. This 7-turn coil is paired with an adjustable 47 pF capacitor to provide a frequency range from 87 MHz to 106 MHz.

Tuning

Turn on the radio and adjust the tuning knob to a position (frequency) where no radio station is using it.

Connect a 5V DC power supply and insert the transmitter's input plug into the MP3 player's headphone jack. Adjust the player's volume control to approximately 30% to 40% of its maximum volume.

Slowly adjust the coil until the radio receives a clear sound from the transmitter.

Make fine adjustments on the radio's tuning knob to achieve the best sound quality.

Next, adjust the MP3 player's volume to a suitable level to avoid overloading the BA1404's inputs. Distortion will occur if the signal level at each input of the BA1404 is too high. Acceptable signal levels are 20~200mV.