QRP transmitter powered by a CW key
by OH6DC
Inspiration to this project came when I read about Mike AA1TJ's astonishing transmitter, called the New England Code Talker. It is a voice-powered CW transmitter, meaning that the operator shouts loud the CW signals to a speaker, and the resulting voltage is used as transmitter power supply. (Take a look at Mike AA1TJ transmitting on air in this Youtube-video.)
I built a same sort of QRPp transmitter circuit as Mike did, but decided to power it by hand muscles, using a special CW key.
I bought five small torches with built-in recharging generator. When the hand lever is pressed, the generator starts to rotate producing electricity. I discarded the batteries and LEDs but kept the bridge rectifiers and added small electrolytic capacitors.
I then connected those five generators in series and glued them side by side. A piece of plywood was screwed to the generator levers to combine them mechanically and a wooden knob was added for hand keying.
The key gives about 9 volts maximum to this tiny one-transistor xtal-controlled 80m CW transmitter. I measured up to 50 milliwatts of RF output power. The harder the key is pressed, the more power is produced.
Because the generator voltage rises and falls relatively slowly, the CW signal is very soft, reminding a sick cat meowing. My test QSOs failed: the 50mw signal was strong enough in good band conditions, but only some peculiar carrier whining was reported.
I solved the problem by adding this keying switch. The transmiter now gets supply voltage only when the key is pressed all the way down.
Now the CW signals are readable. Some QSOs have already been made successfully. (Antenna in use: a horizontal-plane full wave loop at 8-10 m above ground.)
station RST received distance
OH1CM 559-579 71 km
OH1NDW 579 138 km
SM4PBL 529 287 km
SM6KNL 519 626 km
Schematic diagram, click to enlarge:
A video clip of the key & transmitter on air: