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Crystal Radio

Discussion in 'Home Brew' started by C2, Mar 12, 2011.

  1. C2

    C2 Sr. Member

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    Hopefully, somewhat of an inspirational post. While searching the parts bin for something to tack together, I came across a couple large air variable caps. What to make of them?

    Well, a crystal radio, of course!

    A 2-inch plastic tube with about 40 turns of high gauge insulated wire

    Coupled to an old-school crystal earpiece with a germanium diode

    ...and the air variable capacitor...

    you have a rather crude, but quite functional AM receiver.

    The earpiece sits at my elbow and a couple of stations can be heard when things are just right, a couple more when everything else comes into place and I lean into the cone.

    [​IMG]



    Hmmm...not more, nore less than I was expecting; entertaining nonetheless...

    This is actually the poorest design, but will pursue significant improvements in the coils, their coupling, detector, and finally class of the set, perhaps finished in a deep oak slab free of clutter while presenting luxurious controls; presuming that I do not again fall victim to function over form...
     

  2. wcsd106

    wcsd106 Active Member

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    I haven't made one of those in years... I fondly remember the first time I built one and how exciting it was to hear the local AM station on it.
     
  3. KE3W

    KE3W Active Member

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    [​IMG]Outstanding C2 This sure looks like a 2011 Spring Contest submission!
     
  4. Beetle

    Beetle Sr. Member

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    You should get some Monster Cables to connect to your speaker, though! :D
     
  5. C2

    C2 Sr. Member

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    Went out and got some new diodes today - going to build a push pull design. The BAT85 schottky diode that I got was not better than the standard Germanium 1N34A. Wondering about that old HP?
     
  6. Moleculo

    Moleculo Administrator
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    Can we get an audio clip of what it sounds like? (y) Also a simple schematic for those new to the concept would be helpful :)
     
  7. RatsoW8

    RatsoW8 Supporting Member, W9WDX ARC Member - WD8T

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    Great post..haven't built one since my teens. (y)
     
  8. C2

    C2 Sr. Member

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    I messed around with a bifilar-wound, tightly coupled inductor. It workes great! Best of all, you get to choose between a broad bandwidth or more selective...I like more selective as I was able to distinguish up to 6 stations. I also added a microammeter I found rolling around the shop...

    The schematics are abundant. wikipedia has the basic 'bad' design, which is more or less a classic design:

    (scroll down to the "simple version")

    [​IMG]


    The second is the mystery crystal radio set. I do not have the original plans I was looking at for the build, but this is the same set, the first one:

    Consruct the Mystery Crystal Set

    I'll work on audio, but it sounds just like AM!
     
  9. C2

    C2 Sr. Member

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    The radio is evolving. What's left here is to add the diode, .001 cap, and a phone jack to the front panel.

    I plan to put the diode between the coil and air cap on a couple of brass screws with thumbnuts, and I'll run all the wiring hidden under the base.

    Using an RF generator, I measured the tuning range from about 400 kHz to 1.9 MHz.

    [​IMG]
     
  10. C2

    C2 Sr. Member

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    Sneak peak at my second attempt, using a basket wound bifilar coil with a loosely, inductively coupled wave trap shown. This one is just a wee bit better than the first - a bit more selective and the wave trap works great! Sensitivity is about the same though... I tried measureing the Q, but could not do it...


    I need some more dual gang air caps...


    [​IMG]
     
  11. xPosTech

    xPosTech Gimpy Gadgeteer

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    I remember making one from a toilet paper roll, a Gillette Blue Blade and a safety pin and some scrounged wire when I was in the Cub Scouts. Tuning was a slider on the coil wound on the TP roll. The razor blade served as the crystal.

    You can find lots of different designs with Google. Search for "Foxhole Radio". Lots of GIs kludged them together in WWII with whatever materials they could find.

    Memories. Thanks.

    Ted
     

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