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Worlds Simplest Radio Redux
radio : by Tommy - December 5th 2006, 08:41PM
radio
After the success of my last post about my simple razor-blade radio (link here), I began work on making a slinky dipole. I tried to use 2 Slinky Jr. toys which I bought at Walmart for $.88 each. It didn't work as well as I had hoped. After quite a while of the coils sitting on my desk and playing with them, it dawned on me that I could easily use the small Slinkys as the tuning coil for a simple radio. I started to do the math to find the inductance of the coils. I measured 1.5" in diameter, which gave me 4.7" in circumference. I started to count the coils to calculate the open-air coil formula that I had used before. I stopped and thought, why bother? Just try it out!

I stretched the slinky to the length of the board I used on the old razor-blade radio and tacked it down. I made the proper connections, using a diode first. (Ground went to the 3rd prong on a power outlet, the antenna wire and clip was hooked to my 20m ham radio antenna, on my roof) I started with the diode because it is far more efficient than the razor blade, which equates to louder audio in the earpiece.

Right off the bat I was able to hear shortwave broadcast stations! Wilder still was my ability to receive the signal without having the antenna clip attached! I tried various points along the coil, finding I was able to hear certain stations better at different points on the coil. As before, I was able to hear local AM broadcast stations just fine, and various strong shortwave stations with a "shorter tap".
After listening with the diode for a few minutes, once again amazed at the simplicity of the setup, I switched to the razor blade setup I had used in the past and was just able to pull out the same local broadcast signal from before. The key to using the razor blade/saftey pin is using a pencil lead wrapped soldered to the pin. Then ever-so-lightly "fishing" for the sweet spot on the razor that allows the signal to pass. It's also important to note you'll need to be in a fairly quiet environment to hear the signal, but if you listen - it's there.

So now you have no excuse but to find a crystal set earpiece, the coil has been made for you and it'll cost you under a dollar to buy. Alligator clips help, but as you can see, are not 100% necessary. Also note at the top of the picture is the old coil from my last setup.
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tags: radio kit


+ anonymous
  Dec 17, 2006 01:09
  
#971
wow this is great your idea for simple dipole works.

reply

+ Tommy G.
  Feb 08, 2007 16:50
  
#984
Here's another radio I found, it uses a cut up old metal pot as the capacitor. Neat, in a redneck/hillbilly kind of way.

reply

+ Tommy G.
  May 02, 2007 14:43
  
#1026
I want to try a OA47 diode. It supposed to be more sensative.

reply

+ Tommy G.
  May 02, 2007 15:26
  
#1027
Comparison of diodes

reply

+ anonymous
  Aug 22, 2007 13:50
  
#1149
Now, if you were simply to use a very long wire, run it out your window to a nearby tree, or the next balcony in an apartment, or a convenient piece of lawn furniture or something, it will also work very well. You can increase the volume very significantly. You're going to of course want a mechanism to tune the inductance of the antenna itself, but even without, it will work quite well.

Zorb

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