Step 4: Prepare the Induction Coil

Picture of Prepare the Induction Coil
There is an option with the Induction coil to run it direct with an antenna connection, or to wrap the Induction Coil with about 10 wraps of 22 gauge wire that runs from the antenna to ground. The first method gives a better chance of a station signal being loud enough with a short antenna. The second wrapped inductor method is best for using a long (20 foot plus) antenna. See schematic for clarification.

I like the inductive method even with a short antenna, because it gives a clearer signal with less 60 cycle hum. The amplitude of sound will be less in AM tuning unless a long antenna is used however. The amplitude can be partially made up by using the human body as an antenna by touching the jam jar ring, which has a connecting wire that goes to the antenna + wire when the lid is twisted on.

The other advantage of wrapping the inductor is that it gets supported inside the jar by the heavier wires.
Thax2 years ago
I'm having real problems with my radio and I'm trying to understand the options you describe. I've built my radio as you've pictured yours, but I'm getting no signal or noise. I've checked all my parts and connections. "Run it direct with an antenna connection" doesn't help me understand. Can you clarify this? Thank you!
mrfixitrick (author)  Thax2 years ago
"Run it direct with an antenna connection" means when the induction coil does not have a 10-coil wire wrapped around it, and uses just the tiny wires of the induction coil in the circuit, as seen in inductor L1 and antenna Ant1 in the circuit diagram. The antenna Ant 2 and Ant 3 are auxiliary, and in some circumstances may work better.

For diagnosis, let's go back to basics first...
1.) Are you using a Mac with Audio Hijack, or what is your way of hearing the radio? Test: Do you get a very strong hum when you touch the end of the audio stereo plug on the wire that connects to the computer? If you don't, then the audio software or other adjustments must be made, as the radio needs tons of gain to be heard.
So, touching the end of the plug that goes into the radio, should sound very loud.

2.) If above test is ok, plug in the radio. Is there any sound at all? Turn up the volume if necessary. Touching the antenna should increase the sound.

Let me know, and we'll go from there!
I loaded Audio Hijack onto my Mac, but couldn't see how to make it open the windows you present. Then I loaded AudioMulch, which appeared much closer to 'right', but I still couldn't get anything out.
Better option, I thought, was to apply an Oscope to it and see if there was anything there. I found nothing but what I believe was that 60 cycle hum you mention. Phoey.
I hard wired the funny little 1970's earpiece that came with the crystal radio kit so I could more easily monitor if I made any change from further tweeks. In fact, your suggestion of removing the 10 coil seems to have some change. When I poke the variable cap a tiny burst of noise comes through the earpiece.
Still, this kit was supposed to be for kids, and it mocks me. I feel dumb.
mrfixitrick (author)  Thax2 years ago
Ok, what you likely need is lots more gain (assuming the radio is wired correctly and the diode was not overheated durting soldering ;)

Here's what to do: You need to set up Audio Hijack with my Spooky Tesla Spirit Radio Patch, which I just stored on Google Drive at this web address;

Go to the above address, and download the patch file there to your desktop. Then, open Audio Hijack, look at the top row and click on "Control" then select, "Import Effects Patch". In the window, find the patch on your desktop and open it. It should make Audio Hijack ready to go except for minor tweaking.

Note: You may need to set "Source Type" to "Audio Device". There should be 6 modules set up, AUBandpass, 10-Band EQ, 3 of AUPitch, and Reverb.  Be careful, as it could be very loud, turn down gain if necessary. 

The other thing that makes a huge difference in sound level is to attach a 20 or 22 foot long piece of wire to the antenna circuit and stretch it across the room. 
You should hear a sound increase by touching the antenna.

As a kid I spent hours messing with a chunk of germanium and a needle-like gizmo probe to finally get a station...and it would disappear the next day!  The crystal radio pros have big tuned coils and proper antennas. It becomes all about the tuning, selectivity and sensitivity at that level. 

Good luck, and let me know re: Audio Hijack. 
first, thank you for taking the time to work with me here. It is really a big help. I found a few mistakes I've made that have made a big help.
1: the output port I have has three leads. One ground, and two that appeared to be connected. I realized today that when the plug is in they disconnect and I had the circuit to the wrong lead. Fixed!
2: Audio Hijack is not the program I needed. Audio Hijack PRO provided what you've been describing that I couldn't find. Hallelujah! (on a side note, I used Pro for only a matter of minutes before it started piping in noise to get me to buy. grumble.)

So now I can hear a very deep low throbbing hum. Actually I get it even with just the patch cabe. Touching the antenna gets more static, better than nothing. I'm ready to attach a long antenna. Where in the circuit do i wire it to? Ground as the other seems to be? Or a separate floating 10 loop coil around the loopstick as it appears in the diagram? Or, as I find in another crystal radio circuit, on this unused third thread into the main antenna coil?
mrfixitrick (author)  Thax2 years ago
Glad to hear you are getting some results. That is the hum you are looking for, and the hum should be less with the patch cable connected to radio and computer. The free version of Audio Hijack PRO (hehe) will run for 10 minutes without static being added. Then just re-start the program. I liked Audio Hijack so much I gladly bought it.

As for antenna, I would wrap a 10-coil copper wire around the induction coil, and attach one end to "ground" or negative, and the other end to the long antenna. You may be wish to attach the antenna directly to that "third thread" wire instead of the 10-coil. Try each technique and see what sounds louder.

Especially with the antenna, if you are close to an AM radio station, you should be able to hear something when adjusting the variable cap. You might need to centre the "AUPitch" pitch controls to make sense of it.

Keep in mind, for the kind of fun I have with the radio, it's often best to tune outside of the main stations instead of on them. The AUPitch and other modules are used for "tuning". The idea is to crank it up with gain, so it becomes super-sensitive to whatever you are listening to, and adjust pitch and reverb, etc. for best sounds.

Have fun...it's a perfect Halloween activity!