Making a Foxhole radio Very primitive

I made my own Foxhole Radio, the most primitive radio receiver. You can hear AM radio sound even without power.
Foxhole Radio wiki ↓

★ Equipment used (including amazon associate link)
Timber
Copper wire (enamel wire) 0.5mm, about 20m Obtained at home centers
Obtained at home centers, etc., about 20 cm of solid copper wire
pencil
Cutter blade
Wood screw

★ Playlist

music: Kevin MacLeod, The Big Beat 80's.

■Business inquiries

[jackx]

A tip - if you can find one of the old-fashioned blue razor blades, they work even better. The blueing on them is a microscopically thin film of oxide, and this works very well as a semiconductor. HTH

[terryhayward]

The only thing that you did not mention is that this only works with AM radio, not FM. I built many of these years ago in the 1950/60s. This was what got me into amateur radio, and electronic repairs years later.

[certuv]

Thank you for posting, Very interesting more basic than a crystal set.

[johnnywad]

I built one of these many years ago as a kid. I used the cardboard tube from TP for my coil. Also if done properly the safety pin is let in it's original wedge shape with pencil lead attached with a dozen wraps of fine copper wire. Then just pushing down on safety pin it travels across the old school razor blade, and they is your tuner. I liked it so much that I bought a radio shack kit that used a germanium diode and a regular potentiometer for a tuner. With a wire about 100 feet long from my bedroom to the peak of the shed, I could pick up just about any AM radio station east of Mississippi from our home in Pennsylvania. And in the winter and night it was unreal how far stations would come in.

[tonyv]

When I was a kid in cub scouts (back in the 50's) we made project crystal diode radios. Amazing that they worked so well. Thank you for sharing this video.

[capnchip]

Neato! As a kid I had something like this, using a razor blade. That was about 75 years ago. Thanks for a super reminder of times gone past in the hills of Tennessee!

[MLampner]

A couple of suggestions and a correction, the design actually dates back to WWI not WWII, this the correction though I am sure GI's in WWII still used them. Another point this type of radio will only receive an AM signal as you note and these are increasingly rare.

I think your use of the pencil end will work well, but if so it becomes the "crystal" as graphite the "lead" in a pencil is crystalline in structure. If so the cutter blade could be anything metallic to act as the contact. It acts as a rectifier separating the DC audio from the AC carrier.

In a more conventional trench/foxhole radio the crystal would have been a double or single edge razor blade. Preferable one where the manufactures name was carved rather than printed on blade and a double edged blade had still more surface. Any place the blade had been ground you'd expose a crystal. To made the needed junction you'd just need a fine piece of wire to serve as the cat's whisker. The trick is to find either with your setup the edge of the crystal. I think a classic cat's whisker works better but will try your approach.

One last thing, you didn't mention but I am sure you did. The point of the safety pin if you use your design needs to be in the graphite and not the wood of the pencil.

I'd also make two other points, in most modern American homes, plumbing is plastic at least in part as such water pipes no longer function as a ground, secondarily when using an electric outlet the best place to ground is to the screw holding the face place on.

Still it was a great video and there is much to like about your design!

[jwc]

Built one as a child, only got one station, seems I lived too close to the transmitter. In the ground plane .... but it worked and the station was good, rock n roll. AM stations are becoming harder to tune in too many other signals . Fun project for kids none the less ....thanks for a trip down memory lane that kid is 70 years older now and had almost forgotten.

[Dwigt_Rortugal]

Thanks for taking the time to translate and dub this. 😊 We appreciate the kind gesture

[rich]

As a kid I had an electronics kit that had instructions for a trench radio, and it blew my mind. It was like magic hearing a radio station without any power being used, simply using the power of the transmission itself. I could only pick up one station, and the ear piece was garbage and sounded really rattly and distorted, but it still amazed me regardless.

あなたのビデオをとても楽しんだ。ありがとうございました。

[marcderiveau]

When I was young, my father was still using the radio he built in early 20’s, based on this principle.

[j.campbell]

if you drop a variable capacitor in parallel with the coil you will have much greater control of tuning also the height of your antennae isn't nearly as important as the length the longer the better with frequency's this low and the best ground is still a couple of feet of copper rod driven into damp soil. Thanks for the video it brought back a lot of memories.

[kimchee]

My dad was into electronics (all tubes) had his little bench with oscilloscope, signal generator, signal tracers, and so on. When I was little he put together a crystal set for me and place a headphone on my ears. Wow didn't expect that, it was magic for a little boy, put an unforgettable smile on the face. The AM station came in was so clean like true HiFi, better than any radio at the time and even with today's components, pretty loud as well connected to a raw speaker. Free energy!

[eventhisidistaken]

I suppose the blade is a crude diode. Might as well just buy a diode. I made crystal radios as a kid that I stuffed into ball point pens. The pen still worked, but the clicker mechanism didn't (need that space for the diode). I wrapped the ink tube with fine wire I scavenged from transformers for the coil. It was not tunable - it just picked up whatever the most powerful AM station was, but it worked. I sold them to classmates who were amazed at the idea of a pen radio that didn't even need a battery. ...and yes, I became an engineer obviously.

[christianlingurar]

lived close to a main am station some 50 y ago. an old-school telephone ear piece connected by a diode to a metal mass like a tap was all you needed. used to listen to that "radio" in the bathtub. btw, a greenspan corroded cent works as a semiconductor, as well!.

[harrymartin]

Thats great, no "power" needed...
I had done those more than 40 years ago.

Please more.

[lucdrouin]

Thank you! I have been waiting so many decades to find crystal earphone! These devices were brilliant!

[tikisailor]

Wonderful video. I liked the fact that you let us see both the things that worked and the shortcomings of this radio. Thanks for sharing!

[paulmoffat]

The oxide layer and a point contact works, but a better one is a lead-sulphide crystal that is easily made by mixing lead filings with sulfur, and melting together in a test tube, and cooling slowly. The crystal made, is usually surrounded with leftover lead, making that one contact, then a wire 'whisker' is used to find the 'sweet' spot, where reception is greatest. I made one some 60 years ago.

[francoisplaniol]

Wonderful! And I learned: you can make a diode with a cutter blade and a pencil. Thanks.