Alright.. This is really cool, a video presenting how to build a AM radio with no tools and minimal materials. It is based on the methods used by creative soldiers during WW2 so they could enjoy listing to music while confined in their foxholes.. Thus the name “Foxhole Radio”
It’s probably already common knowledge to many of you, but then again, so is about every other topic posted here.
As for myself, it looks so basic and simple, that it impressed me!
Ken Norris says
10 years old
Thanks for the memories …
At the age of 10, I was only 11 years from the end of WWII. The circuit was shown in magazines like MI and EI from time-to-time for years, and my grandad and I made one, too. I was amazed that it worked. Later I built a crystal set that worked really well … I’m pretty sure I used the same toilet roll core, but I think I used my mom’s nail polish to shellac it.
RichPowers says
Re-using old rolls
…I’m pretty sure I used the same toilet roll core, but I think I used my mom’s nail polish to shellac it.
Wow, really? The same one?.. How did the guy in the video manage to get your old toilet paper roll?
mram1500 says
Memories….
I thumb tacked a Gillette Blue Blade to the window sill along with a safety pin with a piece of pencil lead wired to it for the detector.
I used the earphone from my Cub Scout crystal radio.
No coil but I had a long wire antenna. We had one local AM close by that came in real loud.
This was in 1960.
RichPowers says
the earphone.
A few hours ago, I suddenly began pondering about about the earphone. The radio seemed simple enough, but let’s say you were stranded on a deserted island and you managed to construct the receiver.. what would you make an earphone out of?
(google wouldn’t tell me)
If I recall correctly, on Gilligan’s island they used coconut shell headphones, but that I suppose only works on tv reruns!
So, if you didn’t have a earphone handy, what would you do?
Just curious, in case I ever get stranded on a deserted island..
mram1500 says
How Would The Egyptians Do It?
Depends upon how you got there.
If you crashed a plane or beached a boat, you could salvage parts from the comm equipment that was on the craft.
If you had enough fine magnet wire, a magnet and a small, thin metal disc you could fashion an earphone.
Or, maybe if there was a piezo sounder, like the beeper in your PC, that might work like a piezo speaker.
The 1929 Sparton Radio I have uses a speaker that works like an earphone. There is a horseshoe magnet with coils wound on it. The coils are a couple thousand ohms and are the plate load for the final audio amp. Then, a fragile mechanical link to a paper cone causes the cone to vibrate producing the audio.
This is not an “electromagnet” type of speaker where the coil is part of the power supply as a choke coil. Rather, the audio from the final amp causes a fluctuating magnetic field to vibrate the mechanical linkage to the paper cone.
scwis says
Not quite sure how to apply this, but…
When I lived quite close to an AM tower farm the station transmitting on 1520 used to play on the cheap metal tubing headboard on my bed. I figured it had something to do with the tiny gaps in the tubing where one tube had a hole drilled in the side and another smaller tube was slid into the hole – it was cheap, so the tubing wasn’t fit that well and there were all kinds of little gaps around the tubes and the fittings.
I called the station on a whim and asked to talk to the engineer – the DJ told me the engineer would be by that station on such-and-such date and time so I called back then and got right through to him. When I told him about my “receiver” he chuckled and asked me if it was a brass bed – I told him no, it was just a cheap metal tubing headboard. The engineer told me that he had received several vehement complaints from owners of ornate brass beds and that for them the volume was loud enough to be annoying.
Either way, the cure was to ground the headboard to a nearby outlet using a three prong plug adapter ground lead.
All that to say that apparently a speaker could be made with poorly fitting metal tubes 🙂 I’m guessing something to start the gap vibrating and a small tube punched into the side of a big tube, the big tube being the “amplifier” and resonating with enough energy to make the sound audible – but I’m only guessing.
Basically, there is a low energy analog wave available at the fox hole receiver and the task is to translate that into physical movement to move air so your ear can pick it up.
Carl Blare says
What About the Reverse
SCWIS I love stories like that, because it hints at the possibility there may be as yet undiscovered technologies. Your example described conversion of RF into audio, but what about the reverse?
Is there a way to convert audio directly into RF waves?
I’m getting some junk metal right now.
RichPowers says
I keep visualizing somehow
Scwis, the vibrating tube in a hole sounds promising.
I keep visualizing somehow using the old taught-string-and-can method..
Ken Norris says
Window mullions
We once had an apartment with aluminum windows with aluminum mullions between panes. One day, I could faintly hear a radio station, kind of dream-like, tended to go in and out. Could the mullions have picked up enough signal to vibrate the glass without a magnet?
mram1500 says
Farmers Fence Scares Cows-Local Radio Station To Blame
In both cases, the most likely cause enabling you to hear the radio broadcast on the head board and the window was a non-linear contact point formed by corrosion or dissimilar metals.
The non-linear contact point forms a diode rectifier which is what recovers the audio from an AM signal. The very strong signal inturn caused the audio vibrations in the metal.
A favorite story is about the farmer whose cows produced sour milk. He blamed the local radio station which could be heard on his wire fencing.
Carl Blare says
Metal Magic
Tiny Radio I love your use of the world “mullions.” In my sheltered world I’ve never heard that word before. It is worth “mullions.”
Otherwise, I’ve heard of people hearing radio stations in their teeth fillings.
RichPowers says
Tune in on your tooth
..Otherwise, I’ve heard of people hearing radio stations in their teeth fillings.
I actually had put that on my reception tips page!
(about half way down)under “Listen on your tooth”
http://end80radio.com/tune-in.htm
Ken Norris says
Mullions
http://www.google.com/search?q=pictures+of+window+mullions&hl=en&prmd=ivns&tbm=isch&tbo=u&source=univ&sa=X&ei=VeOsTf-PHc_PiALphfXYDA&ved=0CC0QsAQ&biw=1024&bih=475
Carl Blare says
Maybe An Antenna
There’s an antenna hiding in those mullions.
MICRO1700 says
Crystal Radios and also Gilligan’s Island
I have two pretty good crystal radios. With a 150 foot wire
antenna my best DX has been Cuba and Toronto from
here in Connecticut. I also had a really crude shortwave
circuit that used to get Radio Canada International on
5960 kHz years ago.
I have always wanted to make a high performance crystal
set. Maybe someday.
if I went back to Gilligan’s Island in 1965 maybe the professor
could show me how to make a good crystal radio out of parts
from the radio. After all, almost everything they made was
from parts from the radio. Its a real blessing that my eyesight
isn’t good. Otherwise, I would be too distracted by Ginger and
Maryanne. (sp?) I guess that’s really outside of the scope of
Part15.US.
Best Wishes,
Bruce, MICRO1690/1700
MICRO1700 says
WLW in the 1930s
Oh yeah, I forgot. WLW on 700 kHz ran
500,000 watts for a short time in the
1930s.
Farmers would complain that they couldn’t
sleep because their metal fences were making too
much noise playing the station audio.
Best Wishes,
Bruce, MICRO1690/1700
Carl Blare says
Dazzling Website
Yes, I see the tooth reception guide on your website. Good.
Your End80 Tybee Island website deserves an award for being a holiday carnival vacation experience in itself.
Attention Part15.us Main Office. Please consider the idea of Best Website Awards for member stations.
Some members could be on the judge panel, and if there’s a category called “nominators,” that’s the panel I’d like to be on.
Also, please have the first event out on Tybee Island!
Carl Blare says
Inside the Scope
Ginger and Maryanne from Gilligin’s Island are definitely within the scope of part 15. With our clever transmitters, antennas and studios we hope to be admired by the Gingers and Maryannes of the world.