Retro mediumwave detector-radio

Old school detector radio technology meets 21st century 3d-printing. This is a simple to build and use detector radio for the mediumwave band. And yes - it runs without batteries (by only using the transmitted radio energy).

We developed this project for a kids day at our ham radio club. It is fun to build and to use - no matter if you're 9 or 99 years of age!

For most of the most popular stations in Europe you'll need about 28 turns which gives an impedance of 50 - 180 uH. Frequency range is about between 550kHz and 1100kHz.

Instructions

Things you'll need

• 1x the set of printed parts (coil housing, chassis, slider and cap)

1x ferrite rod (standard type with two flat sides), length: 4 cm (1.57inch)

1x diode (germanium type) AA 112 or similar

1x ceramic capacitor 470 pF

1x crystal earpiece (very high impedance of about 2000 ohms)

30 m / 98 feet of 0.4 mm / AWG 26 laqued copper wire for the antenna and ground connection.

Construction manual

• Plug the ferrite rod into the slider (usually no glue is needed, but putting the slider into hot water can help when it's too tight.
• Try to put the ferrite into the coil housing and make sure it slides smooth. Use a file to broaden it.
• Put the cap on to prevent loss or damage of ferrite rod.
• Wind 28 turns of 0,4 mm lacqued copper wire on the coil housing and leave about 10 cm loose to connect the coil.
• Add diode (black ring directs away from the coil) and condensator to the chassis (like on the photos)
• Add the coil to the chassis, strip the two wires and connect (wind or solder) them with diode and condensator.
• Strip the ends of the two earplug wires and connect them with the free end of the diode (the side with the black ring) and condensator
• Turn about 20 m of lacqued copper wire on the chassis (side close to the coil) as antenna wire. You can use the two small holes to create a pull relief. Strip the end on the chassis and connect it to the diode / condensator corner.
• Turn about 10 m of lacqued copper wire on the chassis (side away from the coil) as ground connection. You can use the two small holes to create a pull relief. Strip both ends and connect the chassis side to the condensator.
• If you like glue a sticker or piece of paper into the pit and use it as scale.

That's it!

First Contact

• Stretch out the antenna and connect the ground wire to an earthed device like central heating radiator, water tap or tent peg when you're outside. !NEVER ever to a power socket!

Use the slider to find a station. Listen and mark the frequency on the scale.

Have fun building and using your own detector-radio