The transmitter is just 2 transistors, (not counting the mic pre-amp and audio power amplifier), here's how it looks:
Whistling into the microphone looks like this on the cro:
I'm certainly not getting 100% modulation.
I've just had a contact with Sam, VK2BVS, who reported that with his pre-amp in I'm 10dB over S9, with excellent quality audio "like the BBC".
Next step is to box all this up and make it a bit easier to switch from receive to transmit. (Currently I have to clip a clip lead on to power it and switch a co-ax switch).
The circuit is closely based on the beacon by Alan VK2ZAY. My construction is huge compared to his.
For the audio amplifier to drive this I used a Jaycar "Short Circuits 3" #13 High Power 12V amp which seems to do the trick quite nicely.