[jgrahamc]

If my memory serves, the German High Command were using teleprinters and were sending the teleprinter signals via radio. This did sound totally different from Morse (which was used for other signals, such as those encrypted with Engima), but I don't think this was very new.

The transmission technology was RTTY (http://en.wikipedia.org/wiki/RTTY) which was active well before the Second World War. It would have sounded odd to Morse operators, but would have been recognizable and easily decoded as it is just FSK.

[antimagic]

It's been a while since I read the book, but I thought the modulation scheme was a form of QAM, which was new at the time. The book certainly emphasizes that it took the interceptors quite some time to realise what they were seeing. Still, my memory of the details is a bit fuzzy, and I know that you have researched this area quite extensively, so I defer to greater knowledge ;)