Crystal Radio Project

Introduction

In the first half of the 20^th century, radio was the dominate method of getting news and entertainment.  Early radios used crystals to rectify the radio signals, and many people built their own radios from materials they found around their homes.  The Boys Scouts required their boys to learn Morse Code for the First Class Rank through the late 1960’s, and many of these boys learn to build their own radio sets.  In fact, when I was a Cub Scout in 1979 my Bear Book had instructions on how to build a set.

Crystal Radio Project from “Bear Cub Scout Book” circa 1978.  Elective 3- Radio.

This build is defiantly more challenging, but is a lot of fun as you are building your own capacitor (aka condenser) and using a Galena crystal and safety pin (cat whisker) for the diode.  The build that we will discuss in this forum will use conventional electrical components to keep it easy.

One item to point out is that the crystal radio does not require batteries, as it derives it’s current from the radio waves resonating with the antennae.

Cub Scout Achievements

Ultimately, this type of project really no longer a actual requirement for scouting.  However, it can meet the following requirements:

		Webelos Elective Adventure: Engineer Requirement 4 (one of two projects). Pick and do two projects using the engineering skills you have learned. Share your projects with your den, and also exhibit them at a pack meeting.
		Science is Every Where NOVA Award: Requirement 3 Act like a scientist! Explore EACH of the following: A. With your counselor, choose a question you would like to investigate. B. With your counselor, use the scientific method/process to investigate your question. Keep records of your question, the information you found, how you investigate C. Discuss your investigation and findings with your counselor.
		Dr. Luis W Alvarez SUPERNOVA Award: Requirement 6 Participate in a science project or experiment in your classroom or school OR do a special science project approved by your teacher. Discuss this activity with your mentor.
		Dr. Charles H Townes SUPERNOVA Award: Requirement 8 Under the direct supervision of your mentor, do an experiment that shows how the scientific method (or scientific process) is used. Prepare a short report on the results of your experiment for your mentor. OR Requirement 9 Participate in a Nova- or other STEM-related activity in your Webelos Scout den or pack meeting that is conducted by a Boy Scout or Venturer who is working on his or her Supernova award. If this is not possible, participate in another Nova- or STEM-related activity in your den or pack meeting.

Required Parts (for one radio)

Item	Quantity	Best Source
6x6x3/4-inch pine wood plank	1	Hardware Store
felt footpads	4	Hardware Store
2-inch diameter x 3.5 inch long Schedule 40 PVC pipe	1	Hardware Store
22 AWG enamel coated magnet wire	150 feet	Electronic Store
120 picofarad ceramic disc capacitor (or 100 and 22 picofarad in parallel)	1	Electronic Store
1N34A germanium diode	1	Electronic Store
82 kΩ, 5% ¼-watt carbon resistor (bands: violet, red, orange, gold)	1	Electronic Store
Brass rod, ⅛ inch diameter, 7 inch long	1	Hardware Store
⅛ inch inner diameter black plastic knob		Hardware Store
#6 nickel-plated Fahnestock clips	4	Electronic Store
#6 x ½ inch screws	7	Hardware Store
#6 washer	1	Hardware Store
#8 x ¾ screw	1	Hardware Store
#8 washer	1	Hardware Store
Fine-grit sandpaper (2 inch square)	1	Hardware Store
Mini-audio Amplifier	1	Radio Shack
Speaker Wire	55 feet	Hardware or Electronic Store
Grounding Rod	3 feet	Hardware Store
OPTIONAL: 1/8-inch mono audio jack	1	Electronic Store
OPTIONAL: High Impedance Ear Phone	1	http://www.amazon.com/Crystal-Radio-Earphone-Impedance-3-5mm/dp/B0052EE0AU

You will obviously need enough parts for all the radio sets for your group.  If buying in bulk a lot of the electrical components are best purchased from Amazon.

Instructions

SAFETY WARNING: DO NOT OPERATE THIS RADIO OR HAVE THE ANTENNA CONNECTED DURING THUNDERSTORMS OR OTHER SEVERE WEATHER.

I used the following website as the basis for my project:

Radio Instructions

Go ahead and follow those instructions, and see below for some of the alteration I made.

Here is my finished product:

The following alterations were made:

1-      I used the PVC pipe instead of the Cardboard Tube.  My reason is that the PVC seems more durable during the wrapping process.

1-      I couldn't find a 120 picofarad capacitor so I used 100 and 22 picofarad capacitors in parallel.

2-      I used a 1/8-inch mono phono jack.  Both the amplified (RadioShack) and high impedance earphone comes with a 1/8-inch jack, so to use them, rather than cut the jack off and strip the wires, I added this component.

3-      I bought a 3 foot ¼-inch diameter steel rod from Home Depot, and push it 2 feet into the ground for the grounding.  I created a connection from the radio and the grounding rod with 5 feet of speaker wire and an alligator clip.

Advice:

1-      Pre-wrap the coils to avoid complications in the construction of the devices.  This takes times, and if you get some parents to help you all the better.

2-      Make sure the black band on the diode is orientated properly (towards the earphone/speaker connector).

3-      Use this document to send home with parents.  It has important safety information regarding the antennae and hazardous weather.

4-      For the antenna I bought spools of 300 feet of speaker wire, cut into 50 foot lengths, and split the wire (there are 2 wires side by side, you just need to use a razor to cut between them and then pull apart).  This gives you 12 sets of antenna.  I also soldered one end of the wire to prevent it from fraying when connected to the radio.

5-      Do not provide them with a ground rod, as they may be able to connect to their own (usually the gas meter at their house) or provide their own.  This will keep the costs down on materials.

6-      The same thing for the amplified speakers, this component is $25 at radio shack (though less expensive ones can be found for less than $10 for battery powered speakers).  I provided the boys with an earphone and if they want speakers they can get their own.  Computer (plug in the wall) speakers also work well.

7-      When demonstrating have an adult hold the far end of the antennae so they can move around to get the best signal.