This small experimental radio, very simple, captures well the local stations of the medium wave band. Playback is on a small speaker and power can be supplied by two or four small batteries.
Although medium-wave transmissions are expected to close soon, there are still many stations operating in this range, especially in small towns.
The receiver we describe has both didactic and recreational purposes, and can use scrap components.
The receiver uses only an excellent gain integrated circuit capable of providing good power on a small speaker powered by 4 small batteries.
This is the ideal assembly for a course of initiation to electronics.
In figure 1 we have the complete diagram of the receiver for the medium wave band.
The printed circuit board for assembly is shown in Figure 2, although the circuit may also be mounted in a protboard.
The coil is wrapped in a ferrite stick that can be harnessed from an old out-of-use transistor radio.
L1 consists of 20 turns of enamelled wire 28 to 30 and L2 of 30 + 70 turns of the same wire, as shown in the figure.
The variable capacitor can be harnessed from an out-of-use radio, as well as the small speaker and even some other components.
Capacitors conform to BOM specifications.
To test, connect an antenna (piece of wire from 2 to 5 meters) and ground connection, adjusting CV and P1 for best reception.
List of materials
CI-1 - TDA7052 - integrated circuit
D1 - 1N34 or equivalent - germanium diode
L1, L2 - Coils - see text
CV - variable capacitor - see text
S1 – On-Off switch
B1 - 3 or 6 V - 2 or 4 small batteries
FTE - 4 or 8 ohms - small speaker
P1 - 47 k ohms - potentiometer
C1 - 100 nF - ceramic capacitor
C2-470 pF - ceramic capacitor
C3 - 100 uF x 6 V or more - electrolytic capacitor
Several:
Printed circuit board, mounting box, battery holder, wires, solder, etc.
