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Crystal Radio Set

Posted on 2006-07-14
Last Modified: 2008-01-09
Crystal Radio Set:

1) What is it, describe how to build, what is needed

2) Explain it, what makes it work, what is it that is working

Use? Useage?

Links discouraged as sole contibution, they may be broken, but copying something from them is ok, where link is given for anyone wanting more.

This should be a couple easy questions, we'll see. I've an idea from experience, I just do not want to devote time to remember well or to look it up myself. The objective centers around a device that does not plug into wall for power source, or to use batteries either.
Question by:SunBow
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Assisted Solution

JR2003 earned 25 total points
ID: 17113627
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Assisted Solution

moorhouselondon earned 25 total points
ID: 17114630
>The objective centers around a device that does not plug into wall for power source, or to use batteries either.

Have you considered a clockwork radio?

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Assisted Solution

d-glitch earned 100 total points
ID: 17114671
I made a lot of crystal sets as a kid.
They are great, but with limitations.

JR2003's link is alive and well, and it certainly covers the basics.

All you need are five simple components: a long wire antenna,  a variable capacitor (365 MMF was the old standard),
a coil (you can wind your own or get one from a transistor radio), a diode (you don't want to use a crystal and cat's whisker but you can), and a high-impedance earphone (8 ohms won't work -- it should be something like 20K).

With this basic design, all you are apt to get is the biggest AM station in your region.  There used to be a few 50 kW stations spread over the US, like WBZ and KDKA.  Maybe there still are.

I remember a fascinating column in Popular Electronics back in the 60's where somebody built a state-of-the-art crystal set with more and better coils and capacitors (for better tuning selectivity), and the best full-wave diodes you could get (for at least 4x better sensitivity).  They also had a lot about how to configure your antenna for optimum performance.  They did not break the passive components/no power rule.

I may even hit the library myself to find that issue, now that you've reminded me of it.

But don't wait for me, I'm off to the ocean for a week, and I'm not going to be online.

You think links are bad?  How about vague references to disintergrating pulp magazines.
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Assisted Solution

aburr earned 100 total points
ID: 17115163
D-glitch as answered most of your question along with good references. (and the previous link).Here are some short direct comments

1) What is it, describe how to build, what is needed

a radio, d-glitch areticle will give complete details. he has listed the compontnts. Very simple to build.
antenna to an inductance (coil) in parallet with a capacitor tuned to the frequency which you wish to receive, connected to a headphone in series wih a diode. (Doide a one end of capacitor, other lead from headpnone to other side of capacitor (and groung).  d-glitch circuit diagran reference will have all the detail necessary.

2) Explain it, what makes it work, what is it that is working

antenna to pick up the radio frequency energy, coil and capacitor to select the desired frequency, diode to rectify the signal. Headphones to hear it.

Use? Useage?

a simple easy to build radio receiver requiring no external power.
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Author Comment

ID: 17151165
>   How about vague references to disintergrating pulp magazines

I've relatives have suggested I visit to review attics and other areas I thought I'd cleaned out in some past.                                                [130/220]
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Accepted Solution

WaterStreet earned 230 total points
ID: 17156751

“Explain it, what makes it work, what is it that is working”

I built a lot of crystal radios too.  Moved to diode radios then vacuum tubes.  My father got me started by telling me how he would wind wire around an ice cream carton to make the inductor coil used with a capacitor for the resonant circuit that would pick up the radio frequencies he wanted for his crystal set.  When I was a kid, my room was full of wires – some going out the window to the roof.  My dream was to build a radio that I could listen to on my bike [heh! last week, I upgraded my MP3 player to 2Gb]

The heart, so to speak, of the crystal radio is its crystal.  Although all the parts mentioned are required to make it function (the inductor/coil, the capacitor, the high impedance headphones and the antenna – an actual ground connection is not always needed), the combination of the crystal/cat’s whisker is what makes this radio unique.

The combination of the metal spring-like “cat’s whisker” in contact with the right sweet-spot on the quartz crystal, would make a non-linear conductor that would “split” the audio signal from the broadcasted radio waves (that were modulated by the audio signal).   AM radio sends out programming via radio frequencies at around 1mhz (for one example).  These radio waves, by themselves are useless to the public, but when then are modulated at the radio transmitter with sound-wave frequencies (like music, or news for example) they can carry the sound wave information across a city - and around the world under the right conditions.  In this way the radio frequency waves are the carrier for the human usable sounds that are being broadcast by AM radio (FM is a slightly different case).  The audio signal is broadcasted with a (let’s say a 1 MHz) radio wave carrier, because the radio station transmitter modulates the radio signal’s strength in accordance with the audible sound of the radio programming.  That’s what AM means – Amplitude Modulation.  In other words the radio frequency signal is modulated at an audible rate.  The useful information is the audio, but the radio wave is required to “carry” it, the carrier signal, until it can be made available after being passed through the detector component of a radio.

AM radios have to be able to take the audio signal off of the radio frequency that carries it.  The component of an AM radio that does this is called the detector.  The first detector was a crystal (and cat’s whisker), it was replaced with a vacuum tube, then a diode (a simple semiconductor).

Here is what makes it work.  Aside from the other essential components, the detector, because it does not process bi-directional currents (like radio waves signals) linearly, causes the audio component of the modulated radio wave frequency to be detected and made available to other components in a radio (like headphones or an amplifier).

The crystal (and later innovation of the diode) are different than the vacuum tube because they require no extra power source when using the proper headphones.  This is because radio waves are being broadcasted with enough power of their own, in order to drive sensitive headphones connected to a crystal (or diode) radio.

Most of us who have built crystal radios could probably build a working one in about 10 minutes if we had the right parts with connecting wires on them (I'll take a diode and a ferrite coil, please).  The wire connections could be all hand twisted together.   A good part of that time would be hanging the antenna wire.


Assisted Solution

David_Ward earned 20 total points
ID: 17191640
ahhhh, memories of simple childhood days :)
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Expert Comment

ID: 17194096
I still haven't been to the library, but I have been hunting on line:

Here is a 1960 article from Popular Electronics about a crystal set that can power a small speaker:

Of course, I was still learning how to read in 1960.  So this can't be the state-of-the-art design I mentioned earlier.  That probably came out between 1964 and 1968.  My college library has PE on microfiche but only back to 1971.  
I will keep looking.  I couldn't stop if I wanted to.

Here is a guy who has written a lot of Crystal Set articles and has kits, plans, and parts.
He also mnaged to stake out a cool URL:

But this is probably the best Crystal Set website I've found so far:
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Expert Comment

ID: 17194762

Very nice links.
Had I seen the original Popular Electronics article in 1960, I would have built it. That’s the kind of thing I was always looking for.
Same for the DX article link.

I got hooked on electronics by a friend eight years earlier.  Back then there were all kinds of fun ads in Popular Mechanics.  Like build a 100 power telescope for $2.95 or make all kinds of money by drilling water wells or sharpening saws in your spare time.  My friend had something called an “Audio-Vox” that he bought for $4.95 through Popular Mechanics.  It was a low power AM radio transmitter that had a range of up to 75 feet.  The ad said that you could use it make your own broadcasts through your radio.  The ad showed a picture of somebody broadcasting into a neighbor’s radio and pretending to be the announcer.  We kids thought that we could do that too, but whenever we tried to do that we realized that we didn’t sound like the radio announcer.

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Author Comment

ID: 17197320
:-))                                          [220/400]
I think kids can still do that announcer thing without the electrical plug, given something like a ball and enough room. At first they seem to be meandering about and talking to themselves, but when you get closer, the word choices are more second hand - the announcer describing their play-by-play performance. They may kick the ball, then catch up to it and kick again, or throw the ball (hopefully to a friend who can throw it back), or bat it, probably with bases loaded and the game on the line for another Casey. While they broadcast, I do not think their intent is for their real neighbours to overhear.

I still do not remember the crystal well, but it is starting to sound familiar, and all that talk on coils reminds me of being more weakling, where I'd read something, and got at some old TV set, removed a transformer, then wound copper around it until it could run a car radio, or rather, with a little money for a few parts it was able to apply a recharge to the car's battery. It was very heavy, compared to crystal or transistor. That part I remember well. Not somethiing I wanted to lift more than once. Although parts were cheap, I also don't remember getting the money for that. That might have been the period of finding a road hardly anyone used (during day), and finding some bottles that had recycle value.
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Author Comment

ID: 17276128
Posting Counts
2      d-glitch
2      SunBow
2      WaterStreet
1      JR2003
1      moorhouselondon
1      aburr
1      David_Ward
10      Total Postings
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Author Comment

ID: 17276187
230     WaterStreet
100     aburr
100     d-glitch
 25     JR2003
 25     moorhouselondon
 20     David_Ward

that's about easy 100 ea, severe penalty for links I'd not seen yet (all), but a little something since others said something nice about links, a small reprieve and 30 for general best to all questions
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Expert Comment

ID: 17276450
Thank you SunBow.


Forgot to say 365 and MMF in my mind will forever go to together like a horse and carriage. It could be one word AFAIC.   Had forgotten all about that.

By the way, I just googled "superheterdyne" and discovered that somehow during the last few decades, a radio listener is now called a user.   http://en.wikipedia.org/wiki/Superheterodyne_receiver

"Good morning all you wonderful users out there in radio land"

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Author Comment

ID: 17283740
I guess I now be a user wannabe
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Expert Comment

ID: 17283878
I've still got a crystal, in its original 'tin' tin box. I believe the whisker is lost, sadly. My father gave it to me along with a whole bunch of other old toys of his. :-)

Thanks WaterStreet for an enlightening description.

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Author Comment

ID: 17284712
;-0)                                    [and thanks for belated comment]              

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