OK, so I have replaced the Sundtek USB DVB-C stick with an Hauppauge 292e one 
and I get HDTV. I also get a lot more channels, so there was a hardware 
problem.
Kaffeine tends to freeze and sometimes crash however (sorry to say that it 
works far better on Windows).

There is something I'd like to try: on starting DVB, Keffeine 
says "Deinterlace on" - it takes some time after that to get a picture, 
sometimes frozen, then most of the time it does work.

There seems to be a way to turn deintelace off, but I haven't found it yet. 
There is nothing about it in kaffeinerc, maybe I should add a line? Does 
anyone know?

Thierry