My G0UPL QRSS beacon is working pretty well, but is only putting out about 40mw of power, when it probably should be putting out 100mw. I was pondering oscillators in general, and (as I do often) surf for information and inspiration. I found both on Steve “Melt Solder” Weber’s website, in the form of a ATtiny based Wireless Morse thermometer. It was just a cool little circuit, so I tossed it together on a corner of my breadboard.

Works pretty well! I simulated the circuit using LTSpice before I built it, and found that it takes about 2ms for the oscillator to stabilize after powering down. At 12 wpm, each dit lasts 100ms, so it’s pretty clear that you can do a reasonable job of sending morse at pretty much any speed that most humans can use. To test the oscillator, I hooked up a pair of new D cells which were measured at 3.42 volts, and the current draw was a miserly 0.461 milliamperes for a maximum input power of around 1.5mw. The Arduino can supply 20ma, so it’s pretty obvious that you can drive this oscillator directly from an output pin. So, I used the Morse code sketch that I wrote a couple of years ago and voila! Instant beacon.

Regarding the legality, without any antenna, the effective radiated power of this antenna is incredibly low. I haven’t done any analysis of the circuit to state categorically that it falls inside the restrictions of Part 15 wireless devices, but I’d be shocked if it didn’t.