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Friday, November 28, 2014

Bill's Dominican Mighty Mite (1993)

If you look closely, just in front of my keyboard you can see the Michigan Mighty Mite that I rebuilt this morning (scroll down to see the previous post).  Looks like I was using a polivaricon as the capacitor.  Other than the cap, all the parts used in this 2014 version were from the 1993 effort.  Here is how it is described in "SolderSmoke -- Global Adventures in Wirless Electronics"

    I decided to start off slow, with small projects that seemed likely to succeed.  The secretary in our office in the Embassy, Mady Bullen, had an interest in ham radio that had been sparked by service in far-off places where short-wave was the only way to talk to home.  She would pass me old issues of CQ magazine.  It was in the March 1992 issue that I found the Michigan Mighty Mite.
    It was originated by Ed Knoll, W3FQJ and developed by Tom Jurgens, KY8I. It is about as simple as you can get in a radio transmitter: just one stage, a crystal controlled oscillator.
    An oscillator is basically an amplifier in which some of the output signal is fed back into the input.  If you provide enough feedback in the right way, the amplifier will “take off” and begin generating a signal.  The howl you hear when the microphone of public address system gets too close to the speaker is this kind of signal.  The speaker (the output) is sending energy back to the input (the microphone) and what was an amplifier turns (annoyingly) into an oscillator.  In this case it is an audio frequency oscillator because all the filters and tuned circuits in the PA system are built for the audible frequencies.  But the same thing will happen at radio frequencies.  That’s what the Michigan Mighty Mite is all about. 
    I put the thing together using parts obtained from the Santo Domingo Radio Shack store. The resonant circuit used a coil that was just some wire wound around a discarded plastic 35mm film container.  Homebrew radio projects rarely work the first time you power them up.  I had to fidget with this thing quite a bit—obviously there wasn’t enough feedback.  I had my Drake 2-B on and tuned to the crystal’s frequency.  As I poked around on the little circuit board, I suddenly heard a little chirp from the 2-B.  There it was!  The little device that I had put together was producing radio frequency energy on the 40 meter band.  Hooray!  The joy of oscillation!  Now I felt like I was truly in league with Faraday and Marconi, with Shep, Stan and Bollis, and with Serge! Hilmar would have been proud of me (but he still would have been horrified by my sloppy wiring). 

    I never was able to talk to anyone with that little device—the power output was very low, and my antenna for the 40 meter band was very poor.  But it didn’t really matter.  I had had my first real success at homebrewing a piece of ham radio gear.


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

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