Many still like to hear medium waves but live in places with difficult reception with many interference and low signal strength that require the use of external antennas. Reception at these locations can be improved by a pre-selector. The coil consists of 100 turns of wire 28 in a 1-inch cardboard or PVC tube with plugs every 20 turns. The variable is from an old medium wave radio. The circuit is connected between the antenna and the receiver's ground. The circuit is from Fun Projects for the Experimenter, a book by Newton C. Braga.
