Wireless active subwoofer 02

This speaker uses the stereo transmitter integrated circuit
BA1404 to
transmit the left and right channel mixed signals with a carrier wave of 76~100MHz, which is received by the FM receiving
circuit and sent to the power amplifier input terminal through the low-pass loop
to drive the speaker to produce sound. Using wireless transmission method can save
the trouble of connecting signal lines, and the speakers can be placed more
casually.
    The peripheral circuit of BA14 04 is simple and can be installed in one go. When debugging, you only need to adjust the inductance of L so that the transmitting frequency is
the same as the frequency of the receiving circuit. L in the circuit is wound 3 times around the cylinder of 5. It is connected in parallel with the 47pF capacitor, so that the transmitting
frequency is within Select D between 76 and 100MHz. The transmitting circuit is shown in Figure 9-43; the receiving circuit is shown in Figure 9-44. The radio can use a finished FM radio board, such as the pocket FM
radio board     produced by Dahua Electronics Factory in Zhongshan City, Guangdong, which is very suitable. The core component of this board is TDA7021. Its second pin is grounded through the iOkfl resistor, which has a squelch function.