1000m small stereo FM transmitter circuit
BA1404 is used to make FM stereo transmitting circuit. BA1404 is a FM stereo transmitting dedicated integrated circuit. Due to its excellent performance, it is also commonly used in radio remote control. The working power supply voltage required by BA1404 is 1.5V ~ 3V, power consumption is small, and the circuit structure is perfect. There are few external components, and the work is stable and reliable. However, if you want to use the BA1404 well, you should pay attention to the following items: (1) In order to make the frequency characteristics of the transmitter and the frequency characteristics of the FM broadcast receiver consistent, you need to connect the left and right input channels in series A pre-emphasis circuit with a time constant of 50 μs is shown in the figure. When used in radio remote control transmission circuits, the left and right input terminals can be combined and connected to the signal input terminal with a 0.1 to 1 μF capacitor. (2) The 12 to 14 pins are connected with R and C components to ensure that when the output signal of the stereo modulator and the pilot signal are combined into a composite signal, the phase characteristics of the two are the same, and the channel separation is not deteriorated. In general, it cannot be changed. . If changes are needed, they should be determined after actual testing. (3) During stereo modulation, the upper limit of the audio frequency of the modulated signal is 19kHz. If the input signal is accompanied by a pulse signal, in order to prevent the buzz and channel separation from deteriorating, a low-pass filter should be connected in series at the input. (4) Pins 16 to 17 are pins used to adjust the balance. Even if these two pins are not connected at all, satisfactory separation can be obtained. In normal use, a 50kΩ potentiometer is always connected, and the degree of separation is further improved by adjusting the DC balance. (5) The DC output voltage of pin 11 is fixed to VDD ~ 0.7V by the internal circuit.
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