FM-AM two-band radio circuit composed of ULN2204

FM and AM two-band radio circuit composed of ULN2204 integrated circuit .
    This machine is an FM/AM two -band pocket radio, and its basic circuit form is consistent with the third method introduced above. In addition to the common part,
the FM part also has dedicated antennas, input circuits, high-frequency amplification, frequency conversion, frequency discrimination and other circuits.
    It can be seen from the circle that the radio waves in the sky are induced from the FM antenna (usually a whip antenna) and become an FM signal current, which
is coupled to the resonant circuit composed of Ll and C2 through C1. The resonant frequency of the resonant circuit composed of Ll and C2 is selected within the FM frequency
band . When an FM signal current enters the circuit through Cl, there is a large voltage at both ends of Ll and C2. This voltage passes through C3 Coupled to
the emitter of the high-frequency amplification stage Vl, the high-frequency amplified FM signal is coupled by C5 to the emitter of the frequency conversion stage V2; then through frequency conversion, the intermediate frequency
(10.7 MHz:) signal is obtained, and the frequency selection signal is obtained by the The resonant output of the intermediate frequency transformers T3 and T4 and the resonant capacitors C15 and C20 enters
the ② pin of the integrated circuit ULN2204; the other five-level intermediate frequency amplified intermediate frequency signal is output from the @ pin, and is frequency discriminated by the circuits between @ and @1.
Take out the audio signal; the signal is output from the @ pin, and enters the @ pin through the de-emphasis network, etc.; after the audio signal is amplified by the low frequency, it is output from the @ pin and sent
to speaker B.