Radio Shack Science Fair Crystal Radio Kit

The Radio Shack crystal radio kit from the 1980s and 1990s was popular with many people, providing an introduction to radio and electronics as an interest or career.

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Radio Shack Crystal Radio Kit    

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The Radio Shack crystal radio kit with the branding Science fair, was a popular kit sold by Radio Shack in the USA, although it was also sold in other countries under the branding of Tandy, Realistic, Micronta, etc.

The kit was available in the 1980s and 1990s and it obviously underwent a number of changes as the stock number changed: 28-219, 28-177 and a number of others.

This crystal radio set kit was very popular and gave many people their first introduction into the technology behind radio, and as a result many people can trace their interest or even career in radio and electronics electronics design back to building this vintage radio kit.

The radio is bound to hold many memories back to those who owned one many years ago and were able to make it work and receive radio stations without the need for any batteries or mains power.

Radio Shack crystal radio set kit box
Radio Shack crystal radio set kit box

Although the technology is now very old, and even this kit can be considered to be a vintage radio, it still has a place in teaching young people about technology. There are just a few crystal radio kits available, but this one was probably one of the best.

Crystal radio set kit

The kit contained everything needed to make a basic crystal set radio. The kit was well thought out and and provided everything that was needed.

The Radio Shack crystal radio kit was based around a purpose made baseboard that showed the wiring details as well as having springs placed at the relevant points so that wires could be clipped in position by the springs.

Radio Shack crystal radio set kit box
Radio Shack crystal radio set kit box internals

The baseboard not only provided a spacious base for the circuit and connecting up the various items of the crystal set, but it also showed the circuit elements and how they were connected - relating the circuit to the actual radio itself.

The kit also included the coil for medium wave reception as well as the tuning capacitor, detector diode, high impedance crystal earpiece and wire to make the connections and to provide a short wire antenna.

Crystal radio kit details summary

It is probably a bit much to call this a specification, but we have tabulated a summary of the highlight details of the vintage radio kit.

National HRO Performance Summary
Parameter Details
Difficulty level Easy
Tools required May be a pair of wire cutters for the wire
Frequency coverage 550 - 1600 kHz
Transducer High impedance crystal earpiece
Antenna requirements Wire provided for short antenna. Longer wire is definitely preferable and may be essential in many areas.

Radio Shack crystal set circuit

The circuit for the crystal set is very straightforward and consists of just four components: the coil, variable capacitor, germanium diode and crystal earpiece.

In the circuit, it will be seen that the circuit is based around a fixed coil and a variable capacitor. This gives coverage of approximately 550 - 1600 kHz enabling the medium wave broadcast band to be tuned.

Diagram showing how the tuning works within a crystal radio set.
Radio shack crystal radio circuit

The coil has a total of four connections. The outer connections are taken to the variable capacitor and the bottom connection is also taken to the earth line and the earth connection for the radio.

The coil tap nearer the top end of the coil is taken to the diode used for signal detection, as well as being used as the antenna connection for a short antenna.

The coil tap closest to the bottom of the coil, i.e. towards the ground connection, is used for a long antenna.

The combination of the coil and capacitor provides a tuned circuit and its resonant frequency, and hence the frequency where stations can be received can be changed by varying the variable capacitor.

Diagram showing how the tuning works within a crystal radio set.
How a crystal radio works: tuning

The diode is used as the rectifier to detect or demodulate the signals. A germanium diode is used in the Radio Shack kit as this has a much smaller turn on voltage than ordinary silicon diodes and therefore enables low levels signals to be detected.

By rectifying the incoming radio signal, it is converted to a direct current signal. Vintage radios used what was called a Cat's Whisker detector, but these days diode rectifiers are used.

Diagram showing how the detection process of a crystal radio works.
How crystal radio works: detection

The signal from diode is passed to the crystal earpiece. This has a high impedance and enables the very low levels signals to be heard.

Crystal set kit instructions

The instruction booklet that accompanies the kit is particularly well explained. As the kit is aimed at those with no electronics experience, it gives some basic and yet understandable explanations. It gives what is needed without over-complicating the topics.

Radio Shack crystal radio set kit instructions
Radio Shack crystal radio set kit instruction leaflet

After a brief introduction, the instructions detail how the set should be assembled, and it gives some really helpful diagrams and techniques for putting the crystal set kit together.

It shows how the spring terminals can be fitted to the board using a simple pencil, and it details how the components can be connected together using the terminal.

It is obvious that someone has used the instructions with a beginner and then revised them to add exactly what is needed. If only more instructions were like that today!

Details of suitable antennas and a ground connection are also provided. This is particularly important for those wanting to experiment.

Finally the booklet gives a brief description of how a crystal radio set works. It explains what radio signals are and how they can carry modulation (using amplitude modulation) for audio, etc.

It explains frequency, using the old cycles-per-second nomenclature as there is no need to complicate it further by introducing Hertz, Hz as the units.

Finally it gives a circuit diagram for the Radio Shack crystal set.

The Radio Shack crystal radio kit was a really good little kit. Using the Science Fair branding, it was one piece of electronics that gave very many people their introduction to radio and electronics design at a very young age. Being an easy entry point to radio and electronics, the Radio Shack crystal radio kit was very popular for many years.

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