CF210SP AM/FM Stereo Radio Kit DIY Electronic Assemble Set Kit For Learner July DropShip

1、 Working principle of "jc210sp FM and am radio"

1. Frequency modulation (FM) section

Cd9088 is a special single-chip FM radio chip. Its peripheral circuit is simple. A phase-locked loop system with an IF frequency of 70kHz is built in the circuit. The selectivity is realized by an active RC filter. The mute circuit can suppress non if signals and too weak if signals. Its features are as follows: it contains all functional circuits of mono radio from RF input to audio output, mute circuit, automatic frequency control system, which can be used for mechanical tuning, power polarity protection, and working power supply voltage can be as low as 1.8V.

The FM signal enters the 11 and 12 pin mixing circuit of IC1 through the input circuit of C8, C10 and L1 through the pull rod antenna

The circuit adopts variable capacitors Ca, L2 and other components, which can realize manual platform adjustment. FM broadcast signal and local oscillator circuit signal are mixed in IC1 to generate 70kHz IF signal. After internal if amplification, if limiter, it is sent to frequency discriminator to detect audio signal. After internal loop filtering, audio signal is output by pin 2. R2 and C2 in the circuit are squelch circuits, C4 connected at pin 3 is the audio loop filter capacitor, C13 connected between pins 6 and 8 is the if feedback capacitor, C14 connected at pin 7 is the low-pass capacitor, C17 connected between pins 8 and 9 is the if coupling capacitor, C12 connected at pin 10 is the low-pass capacitor of the limiting amplifier, and C6 connected at pin 13 is the offset voltage capacitor of the limiter. The audio signal output by pin 2 is coupled to pin 7 of the input terminal of the power amplification integrated circuit tda2822 through R6 and C18. After the internal power amplification of IC3 (tda2822), the amplified audio signal is output by pins 1 and 3 to drive the speaker. The potentiometer Vol with switch in the circuit is used to control the on and off of the power supply and the volume.

2. Amplitude modulation (AM) section