I first heard of them about 10-15 years ago and was fascinated by it. Only a couple pieces of scrap material is all needed to build a radio receiver that requires no electricity or other power source to operate... amazing.
Still haven't built one. Chalk it in as another intention not followed through (yet). But what a great project. The only problem is the earphone/speaker aspect. The soldiers just used a headset borrowed from one of their comrade, but If you were on a deserted island what would you do for a speaker??
Fox Hole Transmitter
Step 1 -- Dig hole.
What does burning the blade to make it blue have to do with it?
Bluing the blade along with a carbon pencil lead makes it a diode.
Dig hole, burn blade to create diode.. How do you create it's speaker from similar junk?
Don't know. Maybe you'll be lucky enough to already have a set of headphones when you get stranded on that deserted island. Found a couple interesting things on the internet. This guy built a crystal radio which, despite no power was enough to power a speaker on it's own...
"It derives its power from an outside antenna strung across the roof of my house. It is quite sensitive, and it's efficient enough to drive a speaker directly from the earphone jack (that's right, no amplifier), which never fails to astound me. With Walkman-style headphones, the fidelity is awesome, rivaling FM. Who would think AM could sound so good! - Crystal Radio for Casual Listening
It's a beautiful radio he built. Another guy made one with a big speaker horn like the old Victors had. It's pretty sharp looking too:
"I’m here again this time with an original design for a crystal radio loudspeaker.. ...The amplifier is a standard little amplifier made using an LM386 chip and the clever bit an 8ohm transistor output transformer used in reverse, giving approximately 2Kohm impedance to drive a standard Piezo tweeter driver for the speaker." - DIY Horn Speaker
Those are both crystal radios which I guess is just an upgraded foxhole, and they're both cool. But still don't know how to make a makeshift speaker out of nothing.
Makeshift Speaker
Parts List --
- Empty oatmeal box open at one end
- string
On another note... Wonder how far away a foxhole or crystal radio could still pick up a part 15 signal?
Carl, I know your making a joke, but could something along that same line work? Thin wire instead of string, and a can instead of an oatmeal box? If so, how would you connect it to the radio?
Following that Thought
I think we used tin-cans in the early days and they resonate very well.
Thin wire would probably carry the base-band audio vibrations.
This is a guess, but maybe you could use the same thin wire to make a matching transformer by using a big iron nail as the core. Probably could make a step-up transformer.
Sounds interesting. You seem to think it feasible and it sounds to be junk construct, so it might be an answer.
I was just still looking around: hears another horn speaker built with a funnel, two plastic megaphones, a styrofoam cup, a dynamic headset, 2 crystal earphones, straight pins and epoxy. And he used a microphone mount to connect the horn speaker to the wooden cabinet....
"I live about 25 miles from the nearest station. I've constructed a fairly elaborate antenna system in the tops of the trees around my home. This speaker can, and does clearly fill my whole living room and behond with sound! The cost for parts to build it will be around $40.00 or less." - Styrophone Crystal Loud Speaker
Possibly at a greater distance as crystal radios when using a proper diode are quite sensitive. A better alternative might be a simple regenerative receiver.