I have been using a digital audio recorder to provide Hellschreiber test signals but this is clearly silly. So, thanks to Mark of the fabulous brainwagon blog I now generate test signals with an Arduino.
The Arduino sends port 13 (the one with the on-board LED) high and I use it to turn on a transistor to pull my final low. Off air locally it looks pretty good and the drift is quite mild.
I'm still running milliwatts with my big 2N2222a final transistor but Stephen, VK2BLQ can hear me 10km away fairly well over the noise. Here's how I look at his place:
On Sunday, November 25 2012, Stephen and I gave a little presentation about all this at the ARNSW Home Brew Group meeting at Dural NSW: