Many people like to listen to the radio - at home, in the car, at work, doing what they love, because broadcasting at the frequencies of VHF (88-108 MHz) is carried out in every large settlement. However, few people know that you can build a high-quality radio receiver on a chip yourself, it does not contain scarce or expensive components. Its basis is the TDA7021 chip, which is available both in the DIP package and in the package for surface mounting. Its full domestic counterpart is the K174XA34 chip. The output of the radio is connected to the input of the amplifier on the well-known TDA2003 chip, which can work with either a speaker or headphones.
Potentiometer R2 is responsible for tuning to the desired radio station, it changes the voltage on the varicap. You can take any with a nominal value of 50-100 kOhm. Potentiometer R6 controls the volume of the sound, any resistance of 470 Ohm - 1 kOhm will do. Transistor T1 is a low-power NPN structure, suitable for KT315, BC547, 2N3904 and other similar ones. It should be borne in mind that they have a different arrangement of conclusions, the board in the article is designed for KT315. Varicap KV109 with any letter, I used KV109B.
- Coil L1: 8 turns of wire with a diameter of 0.5 mm.
- Coil L2: 13 turns of wire with a diameter of 0.5 mm.
Coils are wound with enameled copper wire, coil to coil, on a mandrel with a diameter of 3 mm. It is most convenient to wind on a drill of a given diameter, in our case 3 mm. Then the wound coil is removed from the drill and soldered into the board. It is not necessary to strictly observe the diameter of the wire for winding - but it is worth choosing the closest to 0.5 mm.
The receiver is assembled on a printed circuit board, the file of which is attached to the article.
radiopriemnik-na-tda7021.zip [182.47 Kb] (downloads: 283)
The board is made by laser-iron technology.
First we solder small parts - resistors, capacitors, varicaps, transistors, microcircuits. Then large electrolytic capacitors and wound coils. When sealing the coil, strip the lacquer insulation at its ends. The simplest, but nonetheless effective antenna is a piece of wire about 70 cm long, located vertically, is soldered directly to the board. After sealing all the parts, we connect the controls - potentiometers, wires for power supply, wires for connecting the speaker / headphones. We check the correctness of the installation, wash off the flux residues from the board, and the assembly is completed.
First start-up and setup
When you first turn on the volume control should be in the minimum position, pulling the input of the amplifier to the ground. We give power, then gradually increase the volume - a characteristic noise should immediately appear in the speaker. Then slowly rotate the potentiometer until the noise changes to a signal from a radio station. Now it remains to adjust the frequency adjustment boundaries so that by rotating the potentiometer it is possible to catch all the stations in the range 88-108 MHz. This can be done by stretching / compressing the turns of the coil L1, as well as by changing the capacitance of the capacitor C8. When the capacity changes, the total width of the receiver adjustment range will also change, it should be about 20 MHz (“distance” between 88 and 108 MHz). Have a nice build!