I have a question about the dvb api architecture and hardware that has been puzzling me for some time.

I had thought the idea of a phase locked loop was that it locked onto and tracked a frequency compensating for drift in the sending and receiving apparatus. I had also assumed that most frontends would use PLL technology. So why do we need to have a in kernel thread to keep the frontend tuned. I ask this out of curiosity only. I assume that it is something to do with the nature of the dvb signal (is it spread spectrum?).

Roger