1K meter small stereo FM transmitter circuit diagram

However, to get the best performance from the BA1404, there are several important considerations to keep in mind:

1. To ensure that the transmitter’s frequency response matches that of an FM broadcast receiver, a pre-emphasis circuit with a 50 μs time constant should be connected in series with the left and right audio input channels. This helps maintain signal clarity and compatibility. In radio remote control applications, the left and right inputs can be combined using a 0.1 to 1 μF capacitor, simplifying the setup while maintaining good audio quality.

2. The external resistors and capacitors connected to pins 12 through 14 play a crucial role in combining the stereo modulator output with the pilot tone into a composite signal. These components help maintain phase alignment between the signals, ensuring good channel separation. It's generally recommended not to alter these values unless you have tested them thoroughly, as changing them could affect performance.

3. When using stereo modulation, the maximum audio frequency should not exceed 19 kHz. If the input signal contains any pulsed or noise-like components, a low-pass filter should be added at the input stage to prevent interference, which could lead to issues like buzzing or reduced channel separation.

4. Pins 16 and 17 are used for adjusting the balance between the left and right channels. Even if they are not connected, the circuit can still provide acceptable results. However, for optimal performance, a 50kΩ potentiometer is usually connected, allowing for fine-tuning of the DC balance to improve overall resolution and sound quality.

5. Pin 11 provides a fixed DC output voltage of 0.7V relative to VDD, which is internally set and does not require external adjustment.