Integrated AM and FM radio circuits for household appliances

Integrated AM, FM, and stereo radios are composed of integrated components and have multiple functions of AM, FM, and stereo. They have
the characteristics of good and clear sound quality. This section describes the frequency conversion circuit shown in Figure 1-15 as follows:
    This radio can receive four bands: 87-108MHz FM, medium wave AM and two shortwave AM.
  After the FM signal enters from the whip antenna, it is sent to the ① pin (FM high amplifier input terminal) of TA7335P through the ceramic bandpass filter 10P. Pin ③
is connected to an external high-amplification load tuning circuit L, etc., and pin ④ is sent back to the mixing stage. ⑦Pin is externally connected to the local oscillator tuning circuit b, etc. The @ and ◎ pins are connected to the fixed negative
bias and AF to control the voltage and local oscillator varactor diode. The intermediate frequency signal after frequency conversion is output from pin ⑥.
    In order to prevent the limiting sensitivity from decreasing, an additional transistor can be added to prevent attenuation. The FM IF signal is filtered by 14 and then sent to
the @ pin of ULN2204A. The stereo composite signal (or mono audio signal) after frequency discrimination is output from the ⑧, @ pin. If the signal sent is a mono signal, since
there is no 19kHz pilot, ULN2204A automatically enters the mono state, causing pins ⑧ and ⑨ to output the same signal.
  T4 and T5 externally connected to the @ pin are local oscillator tuning circuits.
  Figure 1-15 is using TA7335P and UI. AM, FM and stereo combination radio made of four integrated circuits: N2204A, ULN3809A and ULN2283B .     Although only a single low amplifier ULN2283B is used for the low amplifier here, the other low amplifier is played by one of the ULN2204A low amplifiers, so the two-way stereo sound is still maintained. The performance of ULN2283B is basically the same as the low amplifier part in ULN2204A, and it can maintain the symmetry of the characteristics of the left and right channels.