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.


top photoThe 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.”
schematic
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.

photo 3The 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.
photo 4After winded up, glue the inductor to fix wound wire.

photo 5Inner core of the variable capacitor.
At first, cut-off a toilet paper core.
photo 6Then, 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.

photo 7Glue aluminum foil on both inner and outer core.
photo 8Insert the inner core to the outer core to complete the variable capacitor.

photo 9The rest of the circuit is placed on a small solder-less breadboard.
Fig 4The 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!

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