The radio presented was found in a 1980 documentation. It consists of 3 stages: the tuning circuit whose basic element is a coil where the frequency variation is obtained by changing the position of the nucleus that must be mobile, the detector circuit formed by a diode and finally the output element which is a high impedance phone (crystal preferably). The antenna used must be long to allow a higher level of signal in the headphones and there must be a good ground connection. The reader suggests the neutral pole of the socket as an efficient earthing for this receiver. The coil is made as shown in the figure, being formed by 80 turns of enameled wire in a hollow cardboard cylinder in such a way that the ferrite core of approximately 1 cm in diameter and 15 cm in length can be moved inside to tune the seasons.
