White Noise Radio

overview: We created a simple crystal radio inspired by the following website http://www.crystalradio.net/cub_scouts/index.shtm... Materials: piece of wood/cardboard

Materials:

4 in piece of one inch diameter PVC pipe

large paper clip

alligator clip

30-100 ft of antenna wire

27 feet of copper wire, coated

sandpaper/knife

drill 1 N34A signal diode

47000 Ω carbon resistor

ceramic earphone

electrical tape

Diagram

Test results - We attempted to use this radio both inside and outside, outside worked better; it allowed more white noise and almost voices to come through. The voices get louder as you silence the people around you and create a web of wire to nest yourself in. We would suggest having closer to fifty feet of antenna wire to get stations more consistently.

Physics explanation

Radio waves alter the electric and magnetic fields around the antenna, moving electrons between it and the ground. The coil (whose length is effectively adjusted by the movement of the paper clip) acts as a capacitor which charges and discharges at a resonant frequency corresponding to the frequency to which the radio is tuned, enhancing the desired signal and discarding the others. The diode converts the signal to an intermittent direct current at the frequency of the radio waves whose average intensity over short periods of time affects the movement of the speakers, thus decoding an amplitude-modulated signal.

Step 1: 1. Drill a Hole a Half Inch From the End on Each End of the PVC Pipe.

Step 2: 2. Coil the Coated Copper Wire Around the PVC Pipe So That Coils Touch But Do Not Overlap, Leaving 2-3” of Uncoiled Wire Threaded Through the Holes at Each End.

Step 3: ​Using Sandpaper, Sand Away the Coating on the Copper Wire in a Roughly Inch-wide Strip on One Side.

Step 4: Tape the PVC Pipe and Coil to the Wooden Board

Step 5: Unwind the Large Paperclip and Bend It Into a Slight S Shape. Create a Hook at One End and a Loop at the Other.

Step 6: Cut One Three and Six Inch Piece of Wire From the Left Overs Piece From Step Four.

Step 7: Connect One End of the Three Inch Wire to One End of the Coil.

Step 8: Connect the Alligator Clip to the End of the Three Inch Wire.

Step 9: Connect the Loop of the Paper Clip to the Other End of the 3-inch Wire and to a 6-inch Piece of Wire. Tape the Wires Down Securely So That the End of the Paper Clip Can Move Freely Along the Coil of Copper Wire.

Step 10: Connect the Antenna Wire to the Other End of the Coil.

Step 11: Connect a Short Wire to Both the Antenna Wire and the End of the Coil. Connect the Other End of This Wire to the Diode.

Step 12: Use Additional Wire to Connect the Diode to One End of the Ceramic Earpiece- Note: There Is a Plastic Piece Partway Up the Earpiece, the Wire Needs to Attach to One Side of This.

Step 13: Connect the Wire From the Paperclip to the Other Side of the Plastic Piece, Putting a Plastic Sheet Between the Two.

Step 14: Connect the Resistor to the Ends of the Wires on Either Side of the Ceramic Earpiece.

Comments

[stechi]

Hey, I always thought you had to have a capacitor parallel with the coil to make a resonant R-C circuit, didn't know it would work this way. Would a capacitor give you a better result?

[TCSC47]

You are quite correct, In this case the capacitance will be the self capacitance of the coil, which is due to the coil wires lying alongside each other. Normally a coil designer tries to minimise self capacitance by careful design and winding of the coil, but in this case -- why not use it and save an extra component? Also the rest of the wiring may have enough self capacitance to be part of the L-C resonant circuit. The problem is that the exact layout of the coil and the wiring will have a big effect on the tuning, so different builders with different layouts may get quite different results.

You ask the question,"would a capacitor give a better result?". Well, you can try one if you build the circuit. Once you have got it working as per the original, then you could experiment with it. I would guess (complete guess!) at trying 100pF or less. You will need to move the coil wiper wire to a different point to bring the signal back.

Ps. It is an L-C resonant circuit not R-C. The symbol for an inductor (coil) is L. I suppose they couldn't use I for inductor because that is already used for current. Umm-m -- and C can't be used for current because it is used for capacitance!! Oh dear -- gets complicated!

[stechi]

Very interesting, thanks for that.

I did know it should be L-C, that was just a mistake, my brain is old and tired.

I did do some crystal sets many years ago, but always with a capacitor, usually a variable one for tuning. I got an audible signal from the power of the transmission, which was something. What I was always fascinated by was to use a piece of coke as a diode, but I never managed it.....

[TCSC47]

Well done. These radios can be difficult to get going so to anybody trying to make one - don't give up if you don't seem to get it working first time.

The earth connection is not mentioned or shown in the diagram. The bottom end of the coil , labelled "to alligator clip" should be connect to an "earth" such as a water pipe or metal radiator etc. It will improve the reception no end. (NB - don't use a mains earth. It is just amateurish! If you are going to be an electronic engineer then you need to learn respect for the mains early on.)

Also make sure you use a ceramic or crystal earpiece as shown here. Don't use a magnetic one which on the surface can look exactly the same as a ceramic one.

The main thing that worries me are the taped connections. The most successful versions of these radios that I have seen have been built on small bits of wood. Flat headed wood screws can be used to hold down and join the wires and components together firmly.

[TCSC47]

I've just enlarged the picture of the connections to the earpiece jack socket and to me, it looks as though one of the wires has slipped out of place. My advice would be to go the whole hog with the earpoece connection and buy a matching jack socket. It will be much easier to make reliable connections to

[wliu3]

Almost a 'breadboard' radio.

[peabody1929]

Google "oatmeal box radio".

[seamster]

Great project, thank you for sharing this. I need to make this with my kids!