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 Previous: The HAMsters Want You! | ![Next (later) Story](/images/sty-up.gif ""It Seems to Us . . ." No Complaint, No Interference"){kind=small} Next: "It Seems to Us . . ." No Complaint, No Interference |
By Chuck Counselman, W1HIS
December 31, 2004
A half-hour demonstration to an attentive group of seven year olds turns into a rewarding half-day.
When ARRL Eastern Massachusetts Section Manager Phil Temples, K9HI, recruited me to visit a first grade class, I agreed because I wanted to promote our hobby, not because I expected to have fun. However, it was more fun than I'd ever imagined.
(sm)-lrg.jpg) First-grade students watch as the author sticks clips into pieces of copper adhesive tape on a wooden fruit box--holding transmitter circuit components. [Photos by Donna LaRoche] |
With 21 six and seven year-old kids gathered around me on the floor, I built a CW transmitter starting with three resistors, two inductors, four capacitors, one 2N1613 (silicon NPN junction) transistor, a 9 volt battery, a few clip-leads, copper tape and a wooden fruit box for a chassis. In addition I had a Morse key mounted on a board. I assembled the transmitter as I talked about each part, trying to demystify everything. I also worked in some conversation about ham radio.
A Simple Oscillator Becomes a Transmitter
My transmitter circuit was the simple Colpitts LC oscillator shown in Figure 14.13(B) on page 14.14 of the 2000 edition of The ARRL Handbook. The inductor is a 3-inch diameter, 6-inch long, single-layer solenoid. The loaded Q of this inductor was so great that with the Morse-code key simply connected in series with the battery, both the keying and the long-term stability of the oscillator were excellent. Chirp and click were negligible and I never had to re-tune either the transmitter or receiver. The dc input power was 25 milliwatts. No antenna was connected to the transmitter nor should one be. The oscillator circuit, being unshielded and laid out quite openly, radiates well enough by itself.
My transmitter frequency was at the high end of the AM
broadcast band so the CW signal could be copied with an ordinary portable
radio. The carrier of a local AM broadcast station served as a BFO. The kids
found that they could hear the transmitter outside the classroom, even on the
playground outdoors. They also discovered that the unshielded transmitter made
a good metal detector and theremin.
-lrg.jpg) The author and first-grade students gathered around the finished transmitter, with the Morse code key. A crib sheet mounted on a board helped with coding and decoding. |
Kids Like Code
Each child took a turn at the key and transmitted one word
(usually his/her first name) in Morse code while the other children copied the
transmission. I coached the kids with their sending, but not too much; they
referred to crib sheets both for sending and for receiving. Their Morse sending
and receiving were surprisingly good. They copied about one-third of the
characters correctly, and they guessed well over half of the words correctly.
-lrg.jpg) One first-grade student sends CW while others coach him. |
(sm)-lrg.jpg) A close-up view of the fruit-box transmitter. The large coil is the resonating inductor of the single-transistor Colpitts oscillator. The ferrite bead wound with yellow wire is the RF choke in the transistor emitter lead. The capacitors are silver-mica and Mylar film, and the resistors are 1/2 watt carbon composition. The longer strips of copper adhesive tape stuck to the wooden box top serve as the B+ and ground (B--) busses, the short pieces as circuit nodes. Circuit components are held mechanically and connected electrically to the copper tape by clips. |
We also looked at DX QSL cards in relation to a map of the world and talked about the difference between sound and radio waves. I was pleasantly surprised by how much geography and physics the children already knew. One kid already knew that electricity is generated in a hydroelectric plant by water-driven turbines spinning big magnets within big coils of wire.
They Didn't Want to Stop
They were so fascinated by all this that they didn't want to stop. Their teacher, Ms LaRoche had planned for me to be there one hour. At the end of that hour was recess time, but the kids didn't want to go out for recess. Ms LaRoche told them they could stay in the classroom if they wanted. They did. After recess they still didn't want to stop, so I agreed to stay until lunchtime. But they didn't want to go to lunch, either! Ms LaRoche allowed them to go to the cafeteria and bring lunch back to the classroom, so they did; we just kept going. We continued for three and one-half hours, from 9:30 AM through 1 PM. They didn't want to stop at 1, but Ms LaRoche marched them off to their scheduled art class!
I expect more than one kid in this class to get a ham ticket. Not only ham radio but CW may have a future after all.
Chuck
Counselman, W1HIS, has been licensed since 1956. When he's not handling
emergency exercise traffic for the Air Force MARS TRANSCON digital network, he
plays a 1944 wireless-telegraphy operator in Headquarters Company, 1st Canadian
Parachute Battalion (Reenacted), and works to increase his CW DXCC total. He is
Professor of Planetary Science, Emeritus, at the Massachusetts Institute of
Technology, where he served as faculty advisor and Trustee of W1MX.
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