Project Ultra is part of The Little Whippersnappers Crystal Radio project, which is part of the Tread-Stone-Pebble program. It is an ultra top-secret government project to get all the whippersnappers in the land to receive and decode spy radio signals in the Medium Wave (MW) and Long Wave (LW) bands. The radio consists of 8 bands to sweep a wide range of frequencies in the AM spectrum. Your assignment, should you choose to accept, is to make this multi-band receiver.

Typically, governments would pay millions (of taxpayers dollars) for a receiver such as this; however, The Little Whippersnappers Crystal Radio would be inexpensive. The materials list is very short and requires the rewiring of the ferrite antenna coil, and a selector switch, which costs two bucks! Remind me to write a letter to Ex President Obama. I just had an idea to cut the defence budget... Crystal Radios are the answer. They do not require many parts and are cheap to make. :-)

The Demands of the Whippersnapper's

After a few weeks, the whippersnappers became tired of the radio, and they realised that if you change the number of turns in the ferrite coil, you could detect other stations. Hence, they wanted to have more taps in the coil.

They tried changing the germanium diode for an LED, and even a Zener diode in the hope of increasing the signal strength, but in the end, they learned that those components do not work.

They wanted to add an amplifier stage to their crystal radio, and then submit the work for their science project, hence, the word was given, and the work began.

Ferrite Coil Assembly - Non-NSA Approved

In this project, you will need to make a new ferrite coil with seven taps. You will also need to find a cheap selector switch so that you can select from any one of the taps on the coil. A 1-pole to 12-way rotary switch that cost no more than two pounds was used for the selector circuit. There are some on eBay and one at Maplin, Code: FF73Q.

In this ferrite coil design, I made the taps after the following number of turns, 10, 30, 20, 20, 20, 20, 20, and 60.  I was thinking of using part of the Fibonacci sequence 13, 21, 34, 55, 89, 144, however, perhaps next time. The MW band is at around 45 turns of the coil, and the LW band is at around 100 turns of the coil.

Circuit Diagram

Please click on the image above to see the circuit diagram. Your task, should you choose to accept, is to make a new multi-band coil and test it using this crystal radio circuit diagram.

Wiring Diagram

Results

Once I connected the antenna and earth wire, I was able to test the circuit and was impressed with the reception. I managed to detect some strange sounding radio stations. I also heard some strange music, the type that would go well with a belly dancer...

Related Articles