TA31136 Radio Receiver Circuit Diagram

As shown, the circuit Vcc of 5 V supply. After the first single-conversion, the received signal becomes 21.7 MHz, and then after two 21.7 MHz crystal filter to enhance the selectivity of the input signal. T10 for the resonant frequency of 21.7 MHz in the week, and form selective frequency amplifier transistor Q2. VCC2 for 5 V bias voltage to the transistor. U3 (TA31136) 16-pin input signal of 21.7 MHz and 21.245 MHz, a foot of the vibration signal carried mixer to form two intermediate frequency 455 kHz. IF amplifier, the demodulation signal from the 455 kHz frequency discriminator low-pass filter composed of internal resistor R64 and an external capacitor C116, filtered intermediate frequency and high-order harmonic into the low amp circuit.

Before the Kam-frequency part of this program in 10 feet and 11 feet out in the week, the results found in weeks coil is difficult to debug, and later switched to Murata Seisakusho Ceramic Discriminators Frequency CDB450C24. Because the simple structure CDB450C24, easy to implement, the frequency accuracy of plus or minus 1%, about 10 kHz bandwidth, and do not need to load capacitance.