Remembering the Crystal Radio (2020) | Hacker News Reader

Remembering the Crystal Radio (2020)

nutsvolts.com

75 points1970-01-0146 comments

Sometimes only in looking back you can see an event that was pivotal in your development. It was 1962 and John Glenn had just orbited the earth three times. My dad's brother paid his yearly visit to Detroit around the time of my tenth birthday and he brought me a present. It was a crystal radio in the shape of Glenn's capsule.

I remember eagerly hooking up the ground to the radiator and sitting on the bottom steps to the second floor. The joy I had in bringing signals out of the air. I kept a notebook on all the different stations and their call letters.

That led pretty directly to getting my amateur radio license four years later. A dozen years later I bought a HP programmable calculator and taught it how to do tasks at the business I then managed. Storage was a magnetic strip you fed into the machine.

Still later at another business I took my new business computer and taught myself to learn Lotus 123. That led in a straight line to dBase II and quickly a host of other languages. Another ten years it led to a new career as an entrepreneur leading to present day.

Most people if they look back there was a spark that led to a lifetime interest in something whether it be a hobby or a career. I told both my nieces before they headed off to university to take advantage of your time to try different things, if only a single time. I have a friend who tried scuba diving and that led to him owning his own diving shop. A buddy joined the bicycle club and met his wife.

Crazy how people's experiences can be so different.

I tried making crystal radios 5 or 6 times in my life (one of which from a kit) and never heard a thing.

I'm utterly useless but had a crystal set as a kid that worked, main thing was having a decent aerial. I got such a kick out of it even though I could only get one station.

For me, it was my first crystal radio led to an interest in electronics; electronics -> technology; technology -> science in general (hobby level interest) -> computers / computer sciences (starting with Apple ][ / Commodore / Atari days when 64K was a lot of memory, on through Windows, MacOS, Unix and Linux PCs). From there, the "sky's the limit" as computers can be a useful, educational, and entertaining tool for very nearly any career / hobby these days.

True. I think the spark for me getting into computing was that my parents took me to a thing at Cambridge University in the mid-1970s when I was a child. The thing was for bright children and you could choose whatever you wanted to do and who to talk to. I chose to ask someone (either a professor or a postgrad) how a computer worked. This kind person sat down with a piece of paper and described a Turing machine. After that I went home and started imagining "programs" on paper. I didn't see a real computer until around 1980.

For anyone wondering how you could pull enough energy out of thin air to get one of these to produce sound... my Dad and I just toured a 50kW clear channel AM radio transmitter site outside St. Louis[1], and it makes more sense when you see how much power is being pumped into that tower!

The coils that tune the tower vibrate enough from the RF they reproduce the sound too. Some people don't even need the coil to get sound if you're near enough to an AM tower—you can sometimes hear the signal in certain metal objects.

[1] https://www.jeffgeerling.com/blog/2023/mighty-mox-50kw-am-to...

> certain metal objects

If I remember correctly it isn't the metal object itself that receives the AM radio, there has to be a diode.

In practical terms, dissimilar material junctions - where one is a semiconductor and the other a conductor - form a crude diode.

Mercury-amalgam fillings in teeth (with the tooth being the semiconductor) are the apocryphal 'accidental AM radio receiver.'

My great grandfather (born 1900) related stories about receiving AM 700 in fence wire and a brass bed frame. I was too young to ask questions, but I bet he was talking about the 1930s when it was transmitting at 500,000 (!!!) watts. The family farm was about 40 miles from the transmitter.

There's a fascinating tour of WLW on YouTube, too...[1] back when radio was the cutting edge and all the young engineers would go balls to the wall with RF.

[1] https://www.youtube.com/watch?v=CbHjcwIoTiY

The power of AM radio is interesting. The best example I know of is this: https://www.youtube.com/watch?v=uo9nGzIzSPw

As always, crazy Russians. Listening to radio with grass detector: https://www.youtube.com/watch?v=b9UO9tn4MpI

Hah, that is such a late 2000s style video! I love it. That's genuinely interesting but also kind of frightening at the same time.

I'm not sure this effect makes total sense to me, though. Normally, a radio signal is a single (center) frequency that is modulated by either amplitude or frequency shift. How can the sound coming from the arcing between the antenna and the grass be that clear at certain points in the video? If it were FM, I'd expect to hear mostly arcing and some faint audio signal a side effect of constant arcing, so maybe it's using AM? Maybe I'm just trying to find a reason to not believe what I saw.

I watched that video... it was awesome! Thanks for putting it out there.

I enjoyed it a lot too: https://www.youtube.com/watch?v=Aax-ehkRTnQ

Coincidentally I didn't search for it, I was watching a video on how to use FFT on my oscilloscope and I noticed the name "Geerling" on one of the recommended videos on the right hand side and it was this one! And purely a coincidence too, I don't see how YT could have known I was reading this thread.

Reminds me of a kit I got as a kid in like 1999 that was just a diode, some enamel wire, and an earpiece. It had you wind a coil on a paper towel tube and make a capacitor out of aluminum foil and more paper towel tubes. I could only ever pick up a single station no matter how I tweaked thr "tuning capacitor".

After reading this, I bet it was just a local station swamping out everything else.

I'll have to find a similar kit for my nephew. He's real into engineering and I think he's old enough now for me to teach him about electronics

I recently recorded an interview with my father, who last year retired from his 50-year career as an electronics engineer.

He told me that the main reason he became interested in electronics as a kid in the 50s/60s was so he could build short wave crystal radios, to listen to radio content from around the world, particularly cricket and BBC programs. He grew up in a country town (now outer suburb) near Melbourne, Australia, so was a bit isolated and yearning to feel connected to the world. That led to a decade working for Australia's major telco (now Telstra, then PMG/Telecom) researching and building wireless networks, then 40 years running his own company that produced all kinds of different products using microprocessors for monitoring and control/automation.

I realised that this very much mirrored my own pathway into my career: I immediately dived into the web as soon as it was available in the mid 90s as a way of finding content and communities I was interested in, and for the thrill of being connected to the world, which then led to learning web development and software development and pursuing a career that's now been going for 25 years, doing all kinds of different things, but all of it on the web/internet (and to bring it full circle, for the past few years I worked with my father to make his devices internet-enabled and turn them into IoT products).

One of the Mattel toys in the Bionic Man line of toys had a crystal radio built into a backpack - a small earpiece and a little dial to tune it.

No batteries in it. Seemed like magic to 8 year old me.

Building a crystal radio was one of the first projects I did with my dad as a kid and it blew my mind. I was taking apart everything after that wondering what was inside the plastic shells of the phones and keyboards.

Indeed, that experience of hearing sounds suddenly materialise "from thin air" with no apparent power source is unforgettable.

I’m second grade I brought one in for show and tell that I had made.

The teacher was absolutely righteously confused, but seeing it didn’t plug into the wall or take batteries, allowed it. A team is kids held up the antenna so others could take a turn listening and tuning and it was a pretty big hit.

I used of the shelf transistors from radio shack and the design was out of a electrical engineering book I had read over the summer before. My dad is a geologist, but be helped me learn to solder and make it look nice. I wish i had pictures of all this.

I owe a huge amount of my success to my teacher and my dad for moments like this.

Every crystal radio I’ve tried to build has not made any sound. I’ve tried a Radio Shack kit (which should just work) and tried building it from scratch (making my own coils and so on) from online plans. Perhaps I’ll give it another shot though.

You need high impedance headphones, which are uncommon these days.

Try a high impedance portable speaker instead of headphones.

The "crystal" in the name actually refers to two components both of which are as you say of extraordinary high impedance, about 10M Ohms.

The harder part to get your hands on is the "Crystal ear-piece" These were popular in hearing aids circa 1960. They are piezo transducers with a diaphragm in a small housing. Perhaps , as you say, the next best modern component would be a piezo loudspeaker, but check its impedance is several M Ohms.

The second "crystal" in the set is a diode. Some designs just use a germanium diode like OA81 , but the authentic design that replicates the POW radios built in camps uses a coiled brass wire and a piece of "coke" (being a form of coal). The coke nugget contains silicon and similar elements. When the springy brass wire touches it just right it forms a semiconductor junction.

Getting that to work along with an improvised plate capacitor is pushing luck to the limit, so I am not surprised many kids never get this to work. If anything it's an exercise in tenacity, patience and faith it might be possible.

I did actually get this to work for about 10 minutes in 1975 when BBC World Service blasted out on "long wave".

Another problem is the disappearance of high power AM transmitters. So you need to be lucky and live in the right place for this to work nowadays.

> If anything it's an exercise in tenacity, patience and faith it might be possible.

The problem I realized last time was that I didn't have any way to troubleshoot it that I could figure out. I now have an oscilloscope but I'm not sure if that will help.

> Another problem is the disappearance of high power AM transmitters

I'm about 10 miles away from a 50,000 watt station (850 KOA[1]) so that should work.

[1] https://en.wikipedia.org/wiki/KOA_(AM) I used to listen to this station from other states at night.

I used the earpiece that came with the Radio Shack kit which is the type you mentioned. If I can't find one, I'll keep that in mind.

Well as a kid in the 80s I lived in a village whose link to the outside world was 15Km of wire over the hills hooking a device like this ( https://www.cristoiublog.ro/wp-content/uploads/2020/08/telef... ) to the manual telephone exchange. After picking up the phone from the handle I'd rotate the crank vigurously until the telephone lady looking like this ( https://pbs.twimg.com/media/DMMuSrLXkAAzvXA?format=jpg&name=... ) would pick up and ask where to connect me to.

So radio looked a bit miraculous to me, I tried to understand how it works on a deeper level, engineering level. There were kits to buy and solder but I never felt satisfied with that, it didn't "do it for me". OK, I hooked these things up but still have no idea how or why they work. In a "Lord of the Rings" analogy it's the difference between operating the ring (any idiot can do that) and building the ring (only a true wizard knows how). So this set me on a path where I made efforts to learn applied mathematics which can be used to explain these electronic circuits, eventually went to Techical University and finally fucking figured out the magic. I can now design a radio oscillator and modulator and amplifier and demodulator from the ground up, at differential equations level. Which ... after solving the issue of "understand radio", left me with the realization that I can't make a living out of that. So I pivoted to software development, taking advantage of my higher than usual level of knowledge in mathematics by eventually getting into finance as a quant developer.

So radio kinda got me into stock exchanges.

I made one of these in the 80s using the dick smith fun way to electronics kit, that are alas now defunct.

Same! What a great set of projects they were. Clever as well with the board where you would screw down wires over a paper template. You needed literally no tools other than a screw driver, perfect for the younger kid. Great memories!

I recently learned that the US Navy was installing crystal radios in ships as late as 1942. And why not? With one, the ship could still receive AM voice or Morse code even it it lost all electrical power.

https://californiahistoricalradio.com/wp-content/uploads/202...

https://en.wikipedia.org/wiki/Crystal_detector for more info :)

Fun fact: this is referenced in the book Children of Time! I thought it was a made-up device until I dug in a little and learned it was actually possible

I have made a similar one of these called a Foxhole radio. It needs only wire, pencil graphite, a razor blade, and a crystal earphone. Easy to make and fun to use. It requires no power because it uses the power of the radio signal itself. It only works with AM stations however.

The big thing about a crystal set is that it's independent of electricity supply and internet connectivity. We all had one, at some time or other, in the 1950s. The advent of the 'go anywhere' transistor radio was the thing that pushed the crystal set out of our collective consciousness. But even the transistor radio is being threatened by the ubiquitous internet.

However .....

The other day, our telecoms provider went down for six or seven hours. There was no smartphone, no texting, no internet. As my non-technical wife said, very sagely, at the time "That's the quickest way to bring down a country. Just blow up the 3 or 4 telecoms providers."

So there is still a place in our repertoires for the humble crystal set and/or a transistor radio.

I'm not that old, I'm in my 40s, but it astounds me how many people I know that cannot receive any kind of broadcast media. If their internet connection goes down, they have no TV, no radio, and often, no way of making or receiving a phone call.

This astounds me. I could not live with such a dependence on a single means of communication.

Most people these days have a smartphone which is essentially a broadcast receiver, and carriers give the government ways to sending emergency broadcasts. This isn't a substitute for a dynamo radio as a fallback in an emergency, but is just as effective as an emergency VHF broadcast for the TV or emergency broadcasts on AM/FM. In the '90s even though everyone was supposed to have a dynamo radio for emergencies, in practice I knew pretty much nobody who did.

If anything it's even better these days because they have their receiver with them at all times instead of in the living room or in the garage or in the car as used to be before smartphones. Most folks in the US have a different ISP at home than they do mobile carrier so there's redundancy that way as well. I do think it's a shame that there's no equivalent to something like the POTS which ran on separate power from the base power you get from the grid, but mobile networks also usually have layers of backup power that's independent of the grid so that's a good substitute.

I don’t recall the details but as I understand it there was a bit going around about how modern phones actually have a built in FM radio but none of them had them enabled or accessible through the software.

There was buzz of making that access mandatory but I haven’t heard anything about it for some time.

My understanding is that terrestrial radio is struggling against the streaming and satellite providers. Some of the large AM stations at one point had special civil defense status. KFI 640 in LA is one of those in that it’s very high power and no other station shares its frequency. I don’t know what the civil defense status of station are now.

Where I live was caught up in the SF bay area storms at the beginning of the year, and we had several extended multi-day power outages. It quickly became apparent that the battery backup in the local cell tower lasts about an hour, and then it's just gone. It was very worrying.

> If anything it's even better these days because they have their receiver with them at all times instead of in the living room or in the garage or in the car as used to be before smartphones.

It is not the receiver. It is only the transmiter.

They make emergency radios which do AM, FM, and weather radio. A lot of them have cranks for power. They are something worth having in emergency kit.

Also, lots of people have device that can receive radio, it’s their car. Many receivers have AM/FM, but many people have the antennas in the box.

Finally, mobile and home internet are separate. I have used phone as backup when home internet was down. Mobile is usually different provider and stays working longer when power is out.

There definitely is still a place for transistor radios. What your wife described is the exact reason why I and some other people own ham and GMRS handhelds. Even an off the shelf FRS radio from Wallmart or whatever is worth having around because they can receive signals from GMRS repeaters. And said repeaters by law are not supposed to be connected to the internet, so there's a good chance they'd continue working and relaying signals for tens of miles even if telecoms are down.

Battery power is so ubiquitous now that I think actually owning a crystal radio is mostly obsolete, but knowing how to build one is a valuable skill. Every part can be made from junk. Even a piezoelectric speaker can be made using Rochelle salt.

Not that long ago we had a 7-8 day regional power outage.

Many people got by just fine. Between wired connections and the cellular network (and a whole… two different companies providing both) there’s enough redundancy in place to cover the majority of people in the majority of situations. And it only takes one person in an area with information for it to be spread and distributed around.

I think many people should be more worried about having a few days of potable water available.

One birthday I was given a crystal radio kit because I was interested in electronics. I recall "Stuck in the Middle With You", "Rock On", and "D'yer Mak'er" were in heavy rotation at the time. I guess that pins it to be 1973, so I was 9. It was magic.

About five years ago I built an AM radio from a kit just for the fun of it. It worked but then I remembered there is nothing on AM radio I want to listen to these days (or the past 40 years).

I used the crystal radio that is one of the steps described in this [1] book a fair bit. My grandfather taught me how to make proper PCBs after this and built more complicated radios with him.

[1] https://www.worldradiohistory.com/BOOKSHELF-ARH/Technology/M...

Observation: Crystal Radios can be thought of as Radio Frequency (RF) to Direct Current (DC) "diodes"...

Also they can be thought of as RF to DC Transducers: https://en.wikipedia.org/wiki/Transducer

Wow, Nuts and Volts Magazine! I’m impressed they’re still around. When I was a teenager I won a subscription at a combat robotics event and it was my favorite thing to read every month. Highly recommend checking out their back issues for some good electronics projects!

I had a "rocket" crystal radio like this in the 60s: http://www.esnarf.com/7395k.htm

The Internet Utters Its First Word (https://www.youtube.com/watch?v=4u1twwqt4sw)

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