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
Posts
