Handcraft AM radio using toilet paper cores

JH5ESM, Cosy MUTO
Released on 29 April, 2007

This material is a brief translation of my article: “Introduction to a simple IC radio,” Eleki-Jack, no.2, pp.164-169, May 2007 Issue, published by CQ Publishing, Co., Ltd, Tokyo.

The radio is designed for “Handcraft Radio Workshop for Kids,” which is supported by the local foundation for science and technology. The most important feature of this workshop is: “Reuse materials such as toilet paper cores and an empty tissue paper box and find a wonder world of electronics and science.”

The schematic in PDF format is shown left. It uses a three-terminal radio IC LMF501T (equiv. to MK-484) and a general purpose NPN transistor. It drives a 32[Ω] magnetic earphone.  The switch S2 changes both AGC and transistor gain to control audio output level in two stages.

The resonator inductor (antenna coil) is made of a toilet paper core. Use 0.32[mm] UEW for winding. It requires 100 turns in 37[mm] width for 45[mm] diameter core.  For D=40[mm], N=120 in 45[mm] width.

After winded up, glue the inductor to fix wound wire.

Inner core of the variable capacitor. At first, cut-off a toilet paper core.

Then, overlap the edges by 5 to 7[mm] and tape to make a slim core. For the outer core, use another toilet paper core without any preforming.

Glue aluminum foil on both inner and outer core.

Insert the inner core to the outer core to complete the variable capacitor.

The rest of the circuit is placed on a small solder-less breadboard.

The PDF file on the left is a copy from the workshop textbook.  It is very easy to build the circuit. At the last, put items into an empty tissue paper box to make your own radio!