Very Homemade Radios

Discussion in 'General Electronics Chat' started by darenw5, Aug 19, 2009.

  1. darenw5

    Thread Starter Active Member

    Feb 2, 2008
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    What was the most extremely home-made radio you ever made?

    Not interested in Heathkit, Knight etc., or plans in a magazine article where you made your own PCB - I'm looking for radios where you made your own parts to the greatest extent possible. Capacitors out of aluminum foil, that kind of thing.

    Just one requirement: It had to drive a speaker, so that more than one person could hear it at one time. This eliminates simple crystal radios, which are fun and we've all made, and some other simpler designs. I'm interested i hearing about something more unusual and challenging, and how far you got with it.

    Of course, the speaker itself may be homemade, e.g. http://www.josepino.com/other_projects/index.php?homemade-hifi-speaker.jpc or http://www.instructables.com/id/Laterally-Driven-Speakers/

    Tell your story - what kind of radio, what parts you made yourself or tried to make, how well it worked? Could it have been even more homemade? If this was a long time ago, does it still work? (2nd hand stories are ok, too.)
     
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Alas...I don't have a photo. But in my early misspent childhood, I built a twin slider crystal radio. The coil was wound on 2x2' hunk of wood about a foot long, with a Gillette Blue Blade detector. :) No capacitor needed, as the design relied on the self resonance of the coil. (Didn't know that until MUCH later, after I became smart! :) ) I didn't build the headphones though, so I guess I sort of cheated. I did build some later, though.


    Eric
     
  3. davebee

    Well-Known Member

    Oct 22, 2008
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    This completely describes my garage radio.

    I built it just hacking around one weekend, but it has worked so well I've used it as is for many years.

    It has a wooden base with a two-foot by 2 foot wooden cross sticking up, with about 20 turns of wire in a diamond pattern pancake-wound on the cross. It's got a big three-gang metal-plate variable capacitor on the base.

    The loop antenna coil resonates with one of the capacitor gangs. A tap partway in the antenna loop feeds an mpf102 FET. The FET feeds two more tuned circuits that use the other two gangs of the varible cap.

    A simple diode detector feeds an LM386 amplifier that drives a little speaker.

    So it's basically a conventional tuned radio-frequency receiver, entirely built on an open wooden frame with dangling wires.

    The amazing part is that it works unbelievably well. It tunes about half of the local AM dial, and what it picks up comes in loud and clear and strong!

    It will run equally well on anything from about 3 volts to 12 volts. Usually I connect a spare gelcell to it, and its current draw is so little that I don't bother changing the battery for six months at a time. The little thing just works and works and works.

    About the only bad part is that its antenna is quite directional, but is so large, that not only does it take a lot of bench space, but for any given station, it only works well when its turned so the antenna is right in my way as I try to work at the bench...
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Hi Dave:

    A simple TRF receiver like yours is capable of incredibly high fidelity. Here's one more improvement that's really noticeable....it will sound just like FM if you do this.

    Use a FULL WAVE diode detector. This allows you to use less filter capacitance on the output side before diagonal clipping occurs. You can basically double your usable R.F. bandwidth this way!

    Eric
     
  5. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Built one of those old Quaker Oats crystal radios. Listened to Dr Demento on it.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Built my share of crystal units, using germanium diodes. Started hooking them up to audio amps for fun. My big problem was antenna's, I kept buying 100' of wire, using egg insulators and screen door springs to run them horizonally about 10' above ground between trees, and still kept finding them on the ground. Just occurred to me that maybe my neighbors weren't being to nice. Often as not my bedsprings made a better ground than the pipes. Of course, my antenna theory back then involved lots of length, which probably wasn't too far off given I was going for AM.

    What ever happened to Dr Demento? Used to like that show, when I could catch it.
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I also built my share of crystal sets, a 1-tube (1S5) regenerative receiver, a single transistor regen, etc.
    Our Op stipulated that the output needed to drive a speaker. No one has explicitly mentioned doing this, including me. I guess I felt that the most fascinating challenges were reception and selectivity. If someone wanted to actually listen to the radio, we had a couple of really nice ones, in pretty cabinets.
     
  8. darenw5

    Thread Starter Active Member

    Feb 2, 2008
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    Yes, I can understand that most attention would go to the antenna and tuning - absolutely essential. I am wondering if anyone was nuts enough to use a homemade transistor or vacuum tube, or something crazier. I guess there'd be some limits - I've never heard of anyone making homemade wire, but then there's a lot of creativity and cleverness among electronics hobbyists.

    Ah, Dr. Demento on a homemade radio sounds like a great time. Haven't heard that show in ages, but I did notice a website some months ago.
     
  9. flat5

    Active Member

    Nov 13, 2008
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